Staff Publications

Staff Publications

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    'Staff publications' is the digital repository of Wageningen University & Research

    'Staff publications' contains references to publications authored by Wageningen University staff from 1976 onward.

    Publications authored by the staff of the Research Institutes are available from 1995 onwards.

    Full text documents are added when available. The database is updated daily and currently holds about 240,000 items, of which 72,000 in open access.

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    CD-MUSIC-EDL modeling of Pb2+ adsorption on birnessites : Role of vacant and edge sites
    Zhao, Wei ; Tan, Wenfeng ; Wang, Mingxia ; Xiong, Juan ; Liu, Fan ; Weng, Liping ; Koopal, Luuk K. - \ 2018
    Environmental Science and Technology 52 (2018)18. - ISSN 0013-936X - p. 10522 - 10531.
    adsorption - Birnessite - CD-MUSIC Modeling - Electrical double layer model - External surface - Interlayer space - Manganese oxide - Mn average oxidation state - Pb - Rietveld refinement

    The surface complexation modeling of metal adsorption to birnessites is in its infancy compared to the charge-distribution multi-site ion complexation (CD-MUSIC) models for iron/aluminum (hydr)oxides. Therefore, using X-ray diffraction with Rietveld refinement to obtain the reactive sites and their densities, a CD-MUSIC model combined with a Stern-Gouy-Chapman electrical double layer (EDL) model for the external surface and a Donnan model for the interlayer surface is developed for birnessites with different Mn average oxidation state (MnAOS). Proton affinity constants and the charge distributions of Pb surface complexes were calculated a priory. By fitting Pb adsorption data to the model the obtained equilibrium constants (logKPb) of Pb complexes were 6.9-10.9 for the double-corner-sharing and double-edge-sharing Pb2+ complexes on the edge sites and 2.2-6.5 for the triple-corner-sharing Pb2+ complex on the vacancies. The larger logKPb value was obtained for higher MnAOS. Speciation calculations showed that with increasing MnAOS from 3.67 to 3.92 the interlayer surface contribution to the total Pb2+ adsorption increased from 43.2% to 48.6%, and the vacancy contribution increased from 43.9% to 54.7%. The vacancy contribution from interlayer surface was predominant. The present CD-MUSIC-EDL model contributes to understand better the difference in metal adsorption mechanism between birnessite and iron/aluminum (hydr)oxides.

    Microfluidic methods to study emulsion formation
    Muijlwijk, Kelly - \ 2017
    Wageningen University. Promotor(en): C.G.P.H. Schroën, co-promotor(en): C.C. Berton-Carabin. - Wageningen : Wageningen University - ISBN 9789463430715 - 169
    emulsions - microfluidics - food emulsions - droplets - adsorption - colloidal properties - emulsies - microfluidics - voedselemulsies - druppels - adsorptie - colloïdale eigenschappen

    Emulsions are dispersions of one liquid in another that are commonly used in various products, and methods such as high-pressure homogenisers and colloid mills are used to form emulsions. The size and size distribution of emulsion droplets are important for the final product properties and thus need to be controlled. Rapid coalescence of droplets during emulsification increases droplet size and widens the size distribution, and therefore needs to be prevented.

    To increase stability of emulsions, emulsifiers are added to adsorb at the oil-water interface before droplets collide. The time allowed for emulsifier adsorption is typically in the range of sub-milliseconds to seconds and to optimise emulsification processes, emulsifier adsorption and coalescence stability need to be measured in this time-scale, for which the microfluidic methods described in this thesis were developed.

    Chapter 2 provides an overview of existing literature on cross-flow microfluidic emulsification. The effects of various parameters such as microfluidic design, shear forces, and interfacial tension forces on droplet formation and the resulting droplet size are discussed, as well as the use of microfluidics to produce food-grade emulsions. Based on this evaluation, the methods to elucidate interfacial tension and coalescence stability are chosen, and these are presented in the next chapters.

    To measure emulsifier adsorption in the sub-millisecond time-scale, a tensiometric method was developed using a cross-flow microfluidic Y-junction, which is described in Chapter 3. This method is based on the relation between droplet size and interfacial tension at the moment of droplet formation, which is referred to as the acting interfacial tension. The acting interfacial tension of a system with hexadecane as the dispersed phase and sodium dodecylsulfate (SDS, a model surfactant) solutions as the continuous phase was successfully measured for droplet formation times ranging from 0.4 to 9.4 milliseconds and with high expansion rates (100-2000 s-1). Comparison of these results with data from a drop tensiometer (a conventional, static, and supra-second time-scale method) indicates that mass transport in the microfluidic Y-junction is fast and probably not limited by diffusion.

    Emulsifier mass transport conditions were further investigated in Chapter 4. The continuous phase viscosity and velocity were systematically varied and the effect on the acting interfacial tension in presence of water-soluble SDS was measured. We found that the acting interfacial tension was independent of the continuous phase viscosity, but was inversely dependent on continuous phase velocity. Both aspects led us to conclude that convective emulsifier transport in the continuous phase determines the acting interfacial tension in the Y-junction. When using oil-soluble surfactant Span 20 (dissolved in hexadecane), the acting interfacial tension also decreased with increasing continuous phase velocity, and we therefore concluded that convection also dominated mass transport of emulsifiers dissolved in the to-be-dispersed phase.

    The Y-junction method was used in Chapter 5 to elucidate the effect of the dispersed phase viscosity on adsorption of the food-grade emulsifiers Tween 20 (dissolved in the continuous water phase) and Span 20 (dissolved in the dispersed oil phase). A reduction in dispersed phase viscosity sped up adsorption of Tween 20, probably because the shorter hydrocarbon made intercalation of the hydrophobic surfactant tail at the interface easier. Dispersed phase viscosity had an even greater effect on adsorption of Span 20 because convective transport towards the interface was increased.

    Next to interfacial tension, also coalescence can be measured with microfluidics and a microfluidic collision channel was used in Chapter 6 to measure emulsion coalescence stability shortly after droplet formation under flow. Coalescence of emulsions stabilised with proteins was measured at various concentrations, pH values, and adsorption times. We found that protein concentrations just below the concentration needed for monolayer surface coverage may be used effectively. β-lactoglobulin-stabilised emulsions were most stable. Emulsions stabilised with whey protein isolate (with as main component β-lactoglobulin), were less stable and when these proteins were oxidised, this led to reduced stability, therewith indicating that also the oxidative state of proteins needs to be considered in emulsion formulation.

    The relevance of our work for microfluidic research and industrial emulsification processes is discussed in Chapter 7. Microfluidic devices can be used to study emulsion formation and stability under conditions relevant to industrial emulsification processes; at short time-scales and with convective mass transport. In this thesis we used various food-grade ingredients, and with that application in that field has come closer. We expect that the findings on emulsions can also be applied on foams. With the discussed microfluidic devices different aspects that are important for emulsion formation can be decoupled: for example interfacial tension during droplet formation and emulsion coalescence stability. Furthermore, microfluidic methods are available to for example gain insight in emulsion interface mobility and emulsion storage stability, and we envision that all these microfluidic methods will lead to faster ingredient screening, lower ingredient usage, and more energy efficient emulsion production.

    Core-shell particles at fluid interfaces : performance as interfacial stabilizers
    Buchcic, C. - \ 2016
    Wageningen University. Promotor(en): Martien Cohen Stuart, co-promotor(en): R.H. Tromp; Marcel Meinders. - Wageningen : Wageningen University - ISBN 9789462578968 - 140
    stabilization - stabilizers - particles - colloidal properties - adsorption - interface - fluids - stabilisatie - stabiliseermiddelen - deeltjes - colloïdale eigenschappen - adsorptie - grensvlak - vloeistoffen (fluids)

    There is a growing interest in the use of particles as stabilizers for foams and emulsions. Applying hard particles for stabilization of fluid interface is referred to as Pickering stabilization. By using hard particles instead of surfactants and polymers, fluid interfaces can be effectively stabilized against Ostwald ripening and coalescence. A drawback of the use of hard particles as interfacial stabilizers is that they often experience a pronounced energy barrier for interfacial adsorption and that hard particles are very specific with regard to the type of fluid interface they can adsorb to. Soft particles, on the other hand, are known as good stabilizers against coalescence and they spontaneously adsorb to a variety of different fluid interfaces.

    The aim of this thesis was to investigate core-shell particles comprising a hard core and soft shell with regard to their interfacial behaviour and their ability to act as sole stabilizers for foams and emulsions. We hypothesised that the presence of the soft shell allows for easier interfacial adsorption of core-shell particles compared to the hard core particles only. To test this hypothesis, we prepared core-shell particles comprising a solid polystyrene (PS) core and a soft poly-N-isopropylacrylamide (PNIPAM) shell. To ascertain the effect of shell thickness, we prepared a range of core-shell particles with different shell thicknesses, containing identical core particles. We found that core-shell particles are intrinsically surface active and can generate high surface pressures at the air-water interface and oil-water interfaces, whereas core particles seemed to experience a large energy barrier for interfacial adsorption and did not lower the surface tension. We also confirmed by microscopy that core-shell particles are actually adsorbing to the fluid interface and form densely packed interfacial layers. Further, we found that a certain critical thickness of the soft shell is necessary in order to ensure facile interfacial adsorption. If the PNIPAM shell on top of the core particles is well above 100nm thick, particle adsorption at the air-water interface was found to be diffusion limited.

    By gentle hand-shaking we were able to produce dispersion of air bubbles and emulsion droplets solely stabilized by core-shell particles. The resulting bubbles still underwent Ostwald ripening, albeit slowly. For oil-in-water emulsions of hexane and toluene, both of which have a relatively high solubility in the continuous phase, we found that core-shell particles can stop Ostwald ripening. The resulting emulsion droplets adopted pronounced non-spherical shapes, indicating a high elasticity of the interface. The high stability and the remarkable non-spherical shape of the emulsion droplets stabilized by core-shell particles were features we also observed for fluid dispersion stabilized by hard particles. This shows that in terms of emulsion stability core-shell particles behave similar to hard particles as interfacial stabilizer.

    As to why the differences between the stability of bubble and oil dispersions arise could not be finally answered. Yet, microscopic analysis of the interfacial configuration of core-shell particles at the air-water interface reveals some peculiar insights which may suggest that core-shell particles adsorb in a polymer-like fashion with the soft PNIPAM shells adsorbing to the air-water interface only, while the hard PS cores reside in the continuous phase.

    In summary, we showed that core-shell particles with a hard core and a soft shell can indeed combine the advantageous properties of hard and soft particles. The soft shell enables spontaneous adsorption to a variety of fluid interfaces. Despite their spontaneous adsorption, core-shell particles strongly anchor and do not spontaneously desorb from the fluid interface again. Further, the hard core provides enough rigidity to the core-shell particles to allow the establishment of a stress bearing interfacial particle network. This network eventually stops Ostwald ripening in oil-in-water emulsions. Our results therefore show that in the case of oil-water interfaces, core-shell particles can perform better than solely hard particles as interfacial stabilizers.

    Assembly of jammed colloidal shells onto micron-sized bubbles by ultrasound
    Buchcic, C. ; Tromp, R.H. ; Meinders, M.B.J. ; Cohen Stuart, M.A. - \ 2015
    Soft Matter 11 (2015)7. - ISSN 1744-683X - p. 1326 - 1334.
    interfacial rheological properties - aqueous foams - stabilized emulsions - contact-angle - particles - water - surfactants - polymerization - nanoparticles - adsorption
    Stabilization of gas bubbles in water by applying solid particles is a promising technique to ensure long-term stability of the dispersion against coarsening. However, the production of large quantities of particle stabilized bubbles is challenging. The delivery of particles to the interface must occur rapidly compared to the typical time scale of coarsening during production. Furthermore, the production route must be able to overcome the energy barriers for interfacial adsorption of particles. Here we demonstrate that ultrasound can be applied to agitate a colloidal dispersion and supply sufficient energy to ensure particle adsorption onto the air–water interface. With this technique we are able to produce micron-sized bubbles, solely stabilized by particles. The interface of these bubbles is characterized by a colloidal shell, a monolayer of particles which adopt a hexagonal packing. The particles are anchored to the interface owing to partial wetting and experience lateral compression due to bubble shrinkage. The combination of both effects stops coarsening once the interface is jammed with particles. As a result, stable bubbles are formed. Individual particles can desorb from the interface upon surfactant addition, though. The latter fact confirms that the particle shell is not covalently linked due to thermal sintering, but is solely held together by capillary interaction. In summary, we show that our ultrasound approach allows for the straightforward creation of micron-sized particle stabilized bubbles with high stability towards coarsening.
    Comparing foam and interfacial properties of similarly charged protein–surfactant mixtures
    Lech, F.J. ; Meinders, M.B.J. ; Wierenga, P.A. ; Gruppen, H. - \ 2015
    Colloids and Surfaces. A: Physicochemical and Engineering Aspects 473 (2015). - ISSN 0927-7757 - p. 18 - 23.
    sodium dodecyl-sulfate - bovine serum-albumin - air-water interfaces - beta-lactoglobulin - titration calorimetry - binding - sds - adsorption - rheology - layers
    The foam stability of protein–surfactant mixtures strongly depends on the charge of the protein and the surfactant, as well as on their mixing ratio. Depending on the conditions, the mixtures will contain free proteins, free surfactants and/or protein–surfactant complexes. To be able to compare different protein–surfactant mixtures, generic knowledge about the occurrence of each of these states and their relative contribution to foam stability is essential. In this work, the foam stability and interfacial properties of bovine serum albumin (BSA) mixed with sodium dodecyl sulphate (SDS) as well the binding of SDS to BSA as are studied at different molar ratios (MR). A comparison is made with ß-lactoglobulin (BLG) mixed with SDS. Both proteins and SDS are negatively charged at pH 7. The foam stability in the presence of small amounts (up to MR 1) of SDS is half the value of the pure protein solutions. The foam stability for both protein surfactant mixtures reaches a minimum at MR 20. A further increase of the MR leads to an increase of foam stability. The foam stability of BLG–SDS at MR >20 follows the foam stability of pure SDS solutions at equivalent concentrations, while BSA–SDS mixtures have an offset and begin to increase from MR >50. This behaviour was also reflected in the surface pressure and complex dilatational elastic moduli, and could be linked to the binding of the surfactant to the proteins. Both proteins bind SDS at high and low affinity binding sites. BSA's high affinity binding sites have a binding stoichiometry of 5.5 molSDS/molprotein, and BLG's high affinity binding site has a stoichiometry of 0.8 molSDS/molprotein (determined by isothermal titration calorimetry). Binding to the low affinity binding sites, occurs with a binding ratio, leading to an accumulation of free surfactants. While the basic mechanisms underlying the foam properties of mixed systems are not explained in detail by this approach, the foam stability plots of both protein surfactant mixtures could be superimposed using the concentration of free SDS.
    Transformation by photolysis in water in the pesticide model TOXSWA : implementation report
    Beltman, W.H.J. ; Mulder, H.M. ; Horst, M.M.S. ter; Wipfler, E.L. - \ 2015
    Wageningen : Alterra (Alterra report 2649) - 47
    waterverontreiniging - pesticiden - fotolyse - biochemische omzettingen - waterbodems - adsorptie - ecotoxicologie - modellen - water pollution - pesticides - photolysis - biochemical pathways - water bottoms - adsorption - ecotoxicology - models
    The TOXSWA model has been extended with the functionality to simulate photolysis in water. TOXSWA simulates the fate of substances in water bodies to calculate exposure concentrations for aquatic organisms or sediment-dwelling organisms as part of the risk assessment of plant protection products (PPP). Photolysis is modelled as a first-order process, where transformation occurs in the water phase only. The transformation rate is considered to be linearly proportional to global radiation. Studies in outdoor surface water systems can in principle be used to derive the PPP transformation rates due to photolysis.
    Phosphorus leaching from soils: process description, risk assessment and mitigation
    Schoumans, O.F. - \ 2015
    Wageningen : Alterra, Wageningen-UR (Alterra scientific contributions 46) - ISBN 9789462573666 - 261
    nutrient leaching - leaching - soil chemistry - adsorption - phosphorus - phosphate leaching - risk assessment - water quality - eutrophication - nutriëntenuitspoeling - uitspoelen - bodemchemie - adsorptie - fosfor - fosfaatuitspoeling - risicoschatting - waterkwaliteit - eutrofiëring
    Theory of brushes formed by psi-shaped macromolecules at solid-liquid interfaces
    Zhulina, E.B. ; Leermakers, F.A.M. ; Borisov, O.V. - \ 2015
    Langmuir 31 (2015)23. - ISSN 0743-7463 - p. 6514 - 6522.
    starlike polymer brushes - dendronized polymers - gold nanoparticles - good solvent - surface - polysaccharides - adsorption - dendrimers - coatings
    We present a theoretical analysis targeted to describe the structural properties of brushes formed by ¿-shaped macromolecules tethered by terminal segment of stem to planar surface while exposing multiple free branches to the surrounding solution. We use an analytical self-consistent field approach based on the strong stretching approximation, and the assumption of Gaussian elasticity for linear chain fragments of the tethered macromolecules. The effect of weak and strong polydispersity of branches is analyzed. In the case of weakly polydisperse macromolecules, variations in length of branches lead to a more uniform polymer density distribution with slight increase in the brush thickness compared to the case of monodisperse chains with the same degree of polymerization. We demonstrate that in contrast to linear chains, strong polydispersity of ¿-shaped macromolecules does not necessarily lead to strong perturbations in polymer density distribution. In particular, mixed brushes of the so-called “mirror” dendrons (in which number of stem monomers in one component coincides with number of monomers in a branch of the other component, and vice versa) give rise to a unified polymer density distribution with shape independent of the brush composition. The predictions of analytical theory are systematically compared to the results of numerical self-consistent field modeling based on the Scheutjens–Fleer approach
    Interactions between nodes in a physical gel network of telechelic polymers; self-consistent field calculations beyond the cell model
    Bergsma, J.P. ; Leermakers, F.A.M. ; Gucht, J. van der - \ 2015
    Physical Chemistry Chemical Physics 17 (2015)14. - ISSN 1463-9076 - p. 9001 - 9014.
    aqueous-solutions - statistical thermodynamics - chain molecules - adsorption - micelles - formulation - copolymers - scattering - neutron - layer
    Triblock copolymers, with associative end-groups and a soluble middle block, form flower-like micelles in dilute solutions and a physical gel at higher concentrations. In a gel the middle blocks form bridges between domains/nodes that contain the ends. We combine the self-consistent field theory with a simple molecular model to evaluate the pair potential between the nodes. In this model the end-groups are forced to remain in nodes and the soluble middle blocks are in solution. When the distance between the centres of the nodes is approximately the corona diameter, loops can transform into bridges, and the pair potential is attractive. Due to steric hindrance, the interaction is repulsive at smaller distances. Till now a cell-model has been used wherein a central node interacts through reflecting boundary conditions with its images in a spherical geometry. This artificial approach to estimate pair potentials is here complemented by more realistic three-gradient SCF models. We consider the pair interactions for (i) two isolated nodes, (ii) nodes positioned on a line (iii) a central node surrounded by its neighbours in simple cubic ordering, and (iv) a central node in a face centred cubic configuration of its neighbours. Qualitatively, the cell model is in line with the more refined models, but quantitative differences are significant. We also notice qualitative differences for the pair potentials in the specified geometries, which we interpret as a breakdown of the pairwise additivity of the pair potential. This implies that for course grained Monte Carlo or molecular dynamics simulations the best choice for the pair potentials depends on the expected node density.
    Leaching of plant protection products and their transformation products : proposals for improving the assessment of leaching to groundwater in the Netherlands : version 2
    Boesten, J.J.T.I. ; Linden, A.M.A. van der; Beltman, W.H.J. ; Pol, J.W. - \ 2015
    Wageningen : Alterra, Wageningen-UR (Alterra report 2630) - 105
    bodemchemie - adsorptie - pesticiden - uitspoelen - chemische afbraak - schatting - modellen - soil chemistry - adsorption - pesticides - leaching - chemical degradation - estimation - models
    Assessment of leaching of plant protection products to groundwater is an important aspect of the environmental risk assessment of these substances. Analysis of available Dutch groundwater monitoring data for these substances triggered a critical review of the current Dutch leaching assessment. As a result, proposals were developed for improving this assessment. These include: (i) a procedure for correcting systematic errors in measured sorption coefficients, (ii) a preliminary procedure for a quality check of Freundlich exponents, (iii) a flow chart for obtaining parameters describing the relationship between the organic-matter/water distribution coefficient, Kom, and the pH for weak acids, (iv) a procedure for obtaining a Kom endpoint from a population of Kom values including lower and upper limits, (v) a procedure for estimating the total amount of substance in soil from a concentration profile (needed for assessment of degradation half-lives from field experiments). This report is an update of the proposals reported in 2011 by the same authors based on testing the feasibility of the proposals to a few dossiers
    A process synthesis approach for isolation of isoflavones from okara
    Jankowiak, L. ; Mendez Sevillano, D. ; Boom, R.M. ; Ottens, M. ; Zondervan, E. ; Goot, A.J. van der - \ 2015
    Industrial & Engineering Chemistry Research 54 (2015)2. - ISSN 0888-5885 - p. 691 - 699.
    driven process synthesis - antioxidant activity - food - adsorption - extraction - separation - products - recovery - integration - components
    Owing to the complexity of food matrices, process synthesis methodologies have not been as widely applied in the food industry as in the chemical industry. Here, we describe the application of a process synthesis methodology to design a system to separate valuable components from a byproduct of the soymilk production. The method yielded a number of potential processing pathways and relevant mechanistic questions, which required experimental input. The combination of considering the overall system on the level of general transformations, heuristics, and additional insights through experiments resulted in a simplified conceptual process design for the separation of isoflavones from okara with a globally more sustainable choice. The holistic approach within process design as an implication of the methodology is discussed.
    Phosphorus leaching from soils: process description, risk assessment and mitigation
    Schoumans, O.F. - \ 2015
    Wageningen University. Promotor(en): Sjoerd van der Zee, co-promotor(en): Wim Chardon. - Wageningen : Wageningen University - ISBN 9789462572997 - 261
    nutriëntenuitspoeling - uitspoelen - bodemchemie - adsorptie - fosfor - fosfaatuitspoeling - risicoschatting - waterkwaliteit - eutrofiëring - nutrient leaching - leaching - soil chemistry - adsorption - phosphorus - phosphate leaching - risk assessment - water quality - eutrophication
    Er zijn succesvolle management strategieën voor P nodig om de waterkwaliteit te verbeteren en daarvoor is allereerst kwantitatieve informatieve nodig over de ruimtelijke verdeling van de fosfaatbelasting van het oppervlaktewater vanuit landbouwgronden. In Nederland is een protocol fosfaatverzadigde gronden ontwikkeld om het potentiële risico van verhoogde fosfaatconcentraties in het bovenste grondwater (op termijn) te voorspellen voor kalkarme zandgronden, omdat in deze gebieden veel intensieve veehouderij voorkomt. Voor deze grondsoort zijn de parameters voor het protocol vastgesteld. Echter, voor de overige grondsoorten is geen informatie verzameld, waardoor er voor Nederland als geheel geen ruimtelijke beeld bestaat van de mate van fosfaatverzadiging en van het potentiële risico van verhoogde fosfaatconcentraties in het bovenste grondwater. Daarnaast is er behoefte aan eenvoudige methoden om het (huidige) actuele risico van de fosfaatbelasting van het oppervlaktewater in kaart te brengen, zodat inzichtelijk gemaakt kan worden welke gebieden nu al substantieel de oppervlaktewaterkwaliteit en de eutrofiestatus beïnvloeden.
    On the edge energy of lipid membranes and the thermodynamic stability of pores
    Pera, H. ; Kleijn, J.M. ; Leermakers, F.A.M. - \ 2015
    Journal of Chemical Physics 142 (2015). - ISSN 0021-9606 - 14 p.
    molecular-dynamics simulations - interacting chain molecules - statistical thermodynamics - bilayer-membranes - phase-transition - cell-membranes - adsorption - model - size - vesicles
    To perform its barrier function, the lipid bilayer membrane requires a robust resistance against pore formation. Using a self-consistent field (SCF) theory and a molecularly detailed model for membranes composed of charged or zwitterionic lipids, it is possible to predict structural, mechanical, and thermodynamical parameters for relevant lipid bilayer membranes. We argue that the edge energy in membranes is a function of the spontaneous lipid monolayer curvature, the mean bending modulus, and the membrane thickness. An analytical Helfrich-like model suggests that most bilayers should have a positive edge energy. This means that there is a natural resistance against pore formation. Edge energies evaluated explicitly in a two-gradient SCF model are consistent with this. Remarkably, the edge energy can become negative for phosphatidylglycerol (e.g., dioleoylphosphoglycerol) bilayers at a sufficiently low ionic strength. Such bilayers become unstable against the formation of pores or the formation of lipid disks. In the weakly curved limit, we study the curvature dependence of the edge energy and evaluate the preferred edge curvature and the edge bending modulus. The latter is always positive, and the former increases with increasing ionic strength. These results point to a small window of ionic strengths for which stable pores can form as too low ionic strengths give rise to lipid disks. Higher order curvature terms are necessary to accurately predict relevant pore sizes in bilayers. The electric double layer overlap across a small pore widens the window of ionic strengths for which pores are stable.
    Partitioning of humic acids between aqueous solution and hydrogel. 3. Microelectrodic dynamic speciation analysis of free and bound humic metal complexes in the gel phase
    Yasadi, K. ; Pinheiro, J.P. ; Zielinska, K. ; Town, R.M. ; Leeuwen, H.P. van - \ 2015
    Langmuir 31 (2015)5. - ISSN 0743-7463 - p. 1737 - 1745.
    dissolved organic-matter - stability-constants - alginate gel - thin-films - adsorption - ions - fluorescence - substances - cells - soil
    The hydrogel/water partitioning of the various species in the cadmium(II)/soil humic acid (HA) system is studied for two types of gel, using in situ microelectrodic voltammetry. Under the conditions of this work, with HA particles of ca. 25 and 125 nm radius, the CdHA complex is shown to be close to nonlabile toward a 12.5 µm radius microelectrode. This implies that its kinetic contribution to Cd2+ reduction at the medium/microelectrode interface is practically negligible. The polyacrylamide (PAAm) gels equilibrate with the aqueous medium under significant sorption of HA at the gel backbone/gel medium interface, which in turn leads to induced sorption of Cd(II) in the form of immobilized gel-bound CdHA. The rather high total Cd content of the PAAm gel suggests that the binding of Cd2+ by the hydrophobically gel-bound HA is stronger than that for dispersed HA particles. Still, the intraparticulate speciation of Cd(II) over Cd2+ and CdHA corresponds to an intrinsic stability constant similar to that for simple monocarboxylate ligands such as acetate. Alginate gels are negatively charged, and their free [Cdaq2+] is higher than that in the medium by the corresponding Donnan coefficient. On top of that, Cd2+ is specifically sorbed by the gel backbone/gel medium interface to reach accumulation factors as high as a few tens. HA and CdHA accumulate in the outer 20 µm film of gel at the gel/water interface of both gels, but they do not penetrate into the bulk of the alginate gel. Overall, the gel/water interface dictates drastic changes in the speciation of Cd/HA as compared to the aqueous medium, with distinct features for each individual type of gel. The results have broad significance, for example, for predictions of reactivity and bioavailability of metal species which inherently involve partitioning and diffusion into diverse gel layers such as biointerfacial cell walls, biofilm matrices, and mucous membranes.
    Afvangen van fosfaat uit bloembollensector met ijzerzand : Test van maatregelen die fosforemissie verminderen
    Chardon, W.J. ; Groenenberg, J.E. ; Jansen, S. ; Buijert, A. ; Talens, R. ; Krol, A.F. - \ 2014
    Bodem 24 (2014)6. - ISSN 0925-1650 - p. 20 - 22.
    vollegrondsteelt - bloembollen - bodemchemie - emissiereductie - fosfaten - adsorptie - ijzer - bollenstreek - outdoor cropping - ornamental bulbs - soil chemistry - emission reduction - phosphates - adsorption - iron - bollenstreek
    In het oppervlaktewater van de Bollenstreek is de fosfaatconcentratie veel hoger dan de norm van de Europese Kaderrichtlijn Water. Met ijzerzand, een nevenproduct van drinkwaterproductie, kan fosfaat worden afgevangen. Het hoogheemraadschap van Rijnland heeft drie maatregelen op basis van ijzerzand laten onderzoeken op hun effectiviteit. Welke was de beste?
    One-step synthesis of delta-MnO2 nanoparticles using ascorbic acid and their scavenging properties to Pb(II), Zn(II) and methylene blue
    Wang, M.X. ; Pang, P. ; Koopal, L.K. ; Qiu, G.H. ; Wang, Y. ; Liu, F. - \ 2014
    Materials Chemistry and Physics 148 (2014)3. - ISSN 0254-0584 - p. 1149 - 1156.
    high-temperature decomposition - manganese oxide - structural evolution - oxidation-state - layered mno2 - birnessite - adsorption - mechanism - nanobelts - dissolution
    To obtain delta-MnO2 particles with a large specific surface area, MnO2 was synthesized in an ice-water bath using ascorbic acid (AA) to reduce KMnO4. At pH 3 and 5 and KMnO4/AA molar ratios of 8/1 and 10/1, nanoparticles of delta-MnO2 were produced. The specific surface areas (SSAs) of the samples ranged from 163 to 207 m(2)/g. The Mn average oxidation state of the samples ranged from 3.88 to 3.98 and increased with the KMnO4/AA ratio and pH. The adsorption of the samples with respect to metal ion revealed pseudo adsorption capacities of 3425 mmol Pb2+/kg and 1789 mmol Zn2+/kg. The decolorization behaviors of sample S10-5 (produced at pH 5 and KMnO4/AA molar ratios of 10/1) to methylene blue (MB) were compared at different pH values and temperatures. After 120 min at room temperature, 97% of the MB was adsorbed, and approximately 68% was oxidized. The adsorbed amount and the level of oxidation increased with increasing temperature and decreased with increasing pH. (C) 2014 Elsevier B.V. All rights reserved.
    Direct observation of ionic structure at solid-liquid interfaces: A deep look into the Stern layer
    Siretanu, I. ; Ebeling, D. ; Andersson, M.P. ; Stipp, S.L.S. ; Philipse, A. ; Cohen Stuart, M.A. ; Ende, D. van den; Mugele, F. - \ 2014
    Scientific Reports 4 (2014). - ISSN 2045-2322 - 7 p.
    molecular-dynamics - charging behavior - atomic-resolution - surface-charge - gibbsite - adsorption - water - (hydr)oxides - force - kaolinite
    The distribution of ions and charge at solid-water interfaces plays an essential role in a wide range of processes in biology, geology and technology. While theoretical models of the solid-electrolyte interface date back to the early 20th century, a detailed picture of the structure of the electric double layer has remained elusive, largely because of experimental techniques have not allowed direct observation of the behaviour of ions, i.e. with subnanometer resolution. We have made use of recent advances in high-resolution Atomic Force Microscopy to reveal, with atomic level precision, the ordered adsorption of the mono- and divalent ions that are common in natural environments to heterogeneous gibbsite/silica surfaces in contact with aqueous electrolytes. Complemented by density functional theory, our experiments produce a detailed picture of the formation of surface phases by templated adsorption of cations, anions and water, stabilized by hydrogen bonding.
    Mesoscale models of dispersions stabilized by surfactants and colloids
    Sman, R.G.M. van der; Meinders, M.B.J. - \ 2014
    Advances in Colloid and Interface Science 211 (2014). - ISSN 0001-8686 - p. 63 - 76.
    dissipative particle dynamics - fluid-fluid interfaces - lattice-boltzmann simulations - phase-separation dynamics - pickering emulsions - soluble surfactants - amphiphilic fluids - binary fluids - adsorption - flows
    In this paper we discuss and give an outlook on numerical models describing dispersions, stabilized by surfactants and colloidal particles. Examples of these dispersions are foams and emulsions. In particular, we focus on the potential of the diffuse interface models based on a free energy approach, which describe dispersions with the surface-active agent soluble in one of the bulk phases. The free energy approach renders thermodynamic consistent models with realistic sorption isotherms and adsorption kinetics. The free energy approach is attractive because of its ability to describe highly complex dispersions, such as emulsions stabilized by ionic surfactants, or surfactant mixtures and dispersions with surfactant micelles. We have classified existing numerical methods into classes, using either a Eulerian or a Lagrangian representation for fluid and for the surfactant/colloid. A Eulerian representation gives a more coarse-grained, mean field description of the surface-active agent, while a Lagrangian representation can deal with steric effects and larger complexity concerning geometry and (amphiphilic) wetting properties of colloids and surfactants. However, the similarity between the description of wetting properties of both Eulerian and Lagrangian models allows for the development of hybrid Eulerian/Lagrangian models having advantages of both representations.
    Influence of the relative humidity on the morphology of inkjet printed spots of IgG on a non-porous substrate.
    Mujawar, L.H. ; Kuerten, J.G.M. ; Siregar, D.P. ; Amerongen, A. van; Norde, W. - \ 2014
    RSC Advances : An international journal to further the chemical sciences 4 (2014)37. - ISSN 2046-2069 - p. 19380 - 19388.
    experimental-verification - protein microarrays - dna microarrays - contact-angle - evaporation - surfaces - drops - performance - fabrication - adsorption
    During the drying of inkjet printed droplets, the solute particles (IgG-Alexa-635 molecules) in the drop may distribute unevenly on the substrate, resulting in a “coffee-stain” spot morphology. In our study, we investigated the influence of the relative humidity on the distribution of inkjet printed fluorophore labeled IgG molecules on a polystyrene substrate. A theoretical model for an evaporating droplet was developed in order to predict the changes in the spot diameter, height and volume of a drying droplet. An experiment was performed where a sessile droplet was monitored using a CCD camera installed on a goniometer and good agreement was found between the experimental results and simulation data. We also compared the predicted morphology for an inkjet-printed microarray spot with the experimental results where IgG molecules were printed for various relative humidities. The spot morphology of the dried spots was analyzed by a confocal laser microscopy. At a lower relative humidity (i.e.,
    Catalytic Deoxygenation of Fatty Acids: Elucidation of the Inhibition Process
    Hollak, S.A.W. ; Jong, K.P. de; Es, D.S. van - \ 2014
    ChemCatChem 6 (2014)9. - ISSN 1867-3880 - p. 2648 - 2655.
    stearic-acid - mesoporous carbon - vegetable-oils - diesel fuel - continuous decarboxylation - palladium catalysts - reaction pathways - supported nickel - hydrocarbons - adsorption
    Catalytic deoxygenation of unsaturated fatty acids in the absence of H2 is known to suffer from significant catalyst inhibition. Thus far, no conclusive results have been reported on the cause of deactivation. Here we show that CC double bonds present in the feed or the products dramatically reduce the deoxygenation activity of supported palladium catalysts. In the case of stearic acid deoxygenation the addition of 0.1 equivalents of a mono-unsaturated fatty acid or olefin already reduces the catalytic deoxygenation activity by 60¿%. This effect becomes more pronounced with an increasing number of double bonds. The inhibition is shown to be reversible in H2 atmosphere, indicating no significant contribution from irreversibly deposited hard coke. Furthermore, the type of support material has no apparent effect on catalyst inhibition. Hence we propose that initial catalyst inhibition proceeds through reversible adsorption of CC double bonds on the palladium active sites.
    Improved emulsion stability by succinylation of patatin is caused by partial unfolding rather than charge effects
    Delahaije, R.J.B.M. ; Wierenga, P.A. ; Giuseppin, M.L.F. ; Gruppen, H. - \ 2014
    Journal of Colloid and Interface Science 430 (2014). - ISSN 0021-9797 - p. 69 - 77.
    in-water emulsions - protein-exposed hydrophobicity - beta-lactoglobulin - drop size - adsorption - flocculation - interface - stabilization - ph - dependence
    This study investigates the influence of succinylation on the molecular properties (i.e. charge, structure and hydrophobicity) and the flocculation behavior of patatin-stabilized oil-in-water emulsions. Patatin was succinylated to five degrees (0% (R0) to 57% (R2.5)). Succinylation not only resulted in a change of the protein charge but also in (partial) unfolding of the secondary structure, and consequently in an increased initial adsorption rate of the protein to the oil–water interface. The stability against salt-induced flocculation showed two distinct regimes, instead of a gradual shift in stability as expected by the DLVO theory. While flocculation was observed at ionic strengths > 30 mM for the emulsions stabilized by the variants with the lowest degrees of modification (R0–R1), the other variants (R1.5–R2.5) were stable against flocculation ¿ 200 mM. This was related to the increased initial adsorption rate, and the consequent transition from a protein-poor to a protein-rich regime. This was confirmed by the addition of excess protein to the emulsions stabilized by R0–R1 which resulted in stability against salt-induced flocculation. Therefore, succinylation of patatin indirectly results in stability against salt-induced flocculation, by increasing the initial adsorption rate of the protein to the oil–water interface, leading to a shift to the protein-rich regime.
    Partitioning of humic acids between aqueous solution and hydrogel: Concentration profiling of humic acids in hydrogel phases.
    Zielinska, K. ; Town, R.M. ; Yasadi, K. ; Leeuwen, H.P. van - \ 2014
    Langmuir 30 (2014)8. - ISSN 0743-7463 - p. 2084 - 2092.
    natural organic-matter - fluorescence correlation spectroscopy - diffusion-coefficients - mineral particles - ionic-strength - alginate gel - fulvic-acid - substances - adsorption - soil
    The partitioning of the natural polyelectrolyte humic acid (HA) from an aqueous dispersion into a model biomimetic gel (alginate) and a synthetic polyacrylamide gel (PAAm) is explored. In both gels, the spatial distribution of HA in the gel body, as measured by confocal laser scanning microscopy, is markedly nonhomogeneous. A striking feature is the enhanced accumulation of HA in a thin film of thickness ca. 15 µm at the surface of the gel body, resulting in average local concentrations that are, for PAAm and alginate respectively, a factor of 10 and 4 greater than that in the bulk solution. The time dependence of accumulation in the surface film is predominantly controlled by the diffusive supply of HA from the aqueous medium, with a time constant on the order of 103 s for both gels. The concentration of HA within the bulk gel body differs significantly from that in the bulk aqueous medium: substantially higher for PAAm but much lower for alginate. The results are significant for understanding the nature and rate of sink/source functioning at permeable phases in contact with aqueous media, e.g., biofilms and gel-like layers at biological interfaces or employed in chemical speciation sensors.
    Solid phase microextraction speciation analysis of triclosan in aqueous mediacontaining sorbing nanoparticles
    Zielinska, K. - \ 2014
    Environmental Chemistry 11 (2014)1. - ISSN 1448-2517 - p. 72 - 76.
    nd-spme - samples - water - adsorption - products - binding - surface
    Solid phase microextraction (SPME) is applied in the speciation analysis of the hydrophobic compound triclosan in an aqueous medium containing sorbing SiO2 nanoparticles (NPs). It is found that these NPs, as well as their complexes with triclosan, partition between the bulk medium and the solid phase poly(dimethylsiloxane) (PDMS). Furthermore, they appear to aggregate at the PDMS–water interface. The total triclosan concentration in the solid phase thus includes both the free and the NP-bound forms. Proper computation of the analyte concentration in the sample medium requires (i) consideration of the speciation of triclosan inside the solid phase and (ii) elimination of the effects of aggregation of NP complexes at the solid phase–bulk medium interface. Possible solutions include application of a protective membrane with pore size smaller than the NP diameter. This allows measurement of the free triclosan concentration, albeit at the cost of longer accumulation times and loss of kinetic information on the triclosan–NP complex.
    Linking lipid architecture to bilayer structure and mechanics using self-consistent field modelling
    Pera, H. ; Kleijn, J.M. ; Leermakers, F.A.M. - \ 2014
    Journal of Chemical Physics 140 (2014). - ISSN 0021-9606 - 23 p.
    interacting chain molecules - statistical thermodynamics - spontaneous curvature - bending moduli - association colloids - membranes - elasticity - adsorption - monolayers - vesicles
    To understand how lipid architecture determines the lipid bilayer structure and its mechanics, we implement a molecularly detailed model that uses the self-consistent field theory. This numerical model accurately predicts parameters such as Helfrichs mean and Gaussian bending modulus k c and k ¯ and the preferred monolayer curvature J m 0 , and also delivers structural membrane properties like the core thickness, and head group position and orientation. We studied how these mechanical parameters vary with system variations, such as lipid tail length, membrane composition, and those parameters that control the lipid tail and head group solvent quality. For the membrane composition, negatively charged phosphatidylglycerol (PG) or zwitterionic, phosphatidylcholine (PC), and -ethanolamine (PE) lipids were used. In line with experimental findings, we find that the values of k c and the area compression modulus k A are always positive. They respond similarly to parameters that affect the core thickness, but differently to parameters that affect the head group properties. We found that the trends for k ¯ and J m 0 can be rationalised by the concept of Israelachivili's surfactant packing parameter, and that both k ¯ and J m 0 change sign with relevant parameter changes. Although typically k ¯
    Terrestrial selenium distribution in China is potentially linked to monsoonal climate
    Blazina, T. ; Sun, Y. ; Voegelin, A. ; Lenz, M. ; Berg, M. ; Winkel, L.H.E. - \ 2014
    Nature Communications 5 (2014). - ISSN 2041-1723
    red clay formation - loess plateau - atmospheric selenium - trace-metals - adsorption - speciation - pliocene - records - water - soil
    The prevalence of terrestrial environments low in the essential trace element selenium (Se) results in large-scale Se deficiency worldwide. However, the underlying processes leading to Se-depleted environments have remained elusive. Here we show that over the last 6.8 million years (Ma) climatic factors have played a key role in the Se distribution in loess–paleosol sequences in the Chinese Loess Plateau (CLP), which lies in a severely Se-depleted region with a history of Se deficiency-related diseases. We use a combination of geochemical and paleoclimate data to demonstrate that during interglacial periods between 2.30 and 0.16¿Ma, variations in the Se concentration in the CLP are potentially related to variability in Se input via East Asian monsoon-derived precipitation. Our results identify precipitation as an important controlling factor of Se distribution in monsoonal China. We suggest that atmospheric Se inputs via precipitation could also play an important role in other regions worldwide.
    Technologieën voor verwijdering gewasbeschermingsmiddelen
    Beerling, E.A.M. - \ 2014
    gewasbescherming - chemische bestrijding - milieueffect - cost effective analysis - afvalverwerking - oxidatie - scheidingsapparaten - bioremediëring - adsorptie - plant protection - chemical control - environmental impact - cost effectiveness analysis - waste treatment - oxidation - separators - bioremediation - adsorption
    Mogelijk geschikte technieken om chemische gewasbeschermingsmiddelen te verwijderen zodat ze niet het milieu verontreiningen worden geïnventariseerd met behulp van onafhankelijke experts uit de watersector (o.a. KWR, Wetsus, Mannen van de Wit en Stowa)
    Gedrag van chloorprofam en 3-chlooraniline in de bodem : bepaling van adsorptie, omzetting en uitloging met tarragrond van aardappelen
    Beltman, W.H.J. ; Matser, A.M. ; Linden, A.M.A. van der; Brand, E. - \ 2014
    Wageningen : Alterra, Wageningen-UR (Alterra-rapport 2523) - 65
    aardappelopslagplaatsen - aardappelen - opslag - kiemremmers - adsorptie - uitspoelen - grondwaterverontreiniging - potato stores - potatoes - storage - germination inhibitors - adsorption - leaching - groundwater pollution
    Bij de bewaring van aardappelen wordt als kiemremmer de werkzame stof chloorprofam gebruikt. Na verwerking van de aardappelen in de fabriek blijft chloorprofam en haar omzettingsprodukt 3-chlooraniline in de resterende tarragrond aanwezig. De tarragrond wordt hergebruikt in grootschalige bodemtoepassingen. Omzetting, adsorptie en uitloging van chloorprofam en haar metaboliet 3-chlooraniline zijn onderzocht met tarragrond van aardappelen (onbelast en belast met chloorprofam) en met bouwvoorgrond. De omzettingssnelheid van chloorprofam en 3-chlooraniline is bepaald in bouwvoorgrond, in onverzadigde onbelaste tarragrond en in waterverzadigde onbelaste tarragrond. De adsorptieparameters van de Freundlich sorptie isotherm zijn bepaald voor 3-chlooraniline in onbelaste tarragrond en in bouwvoorgrond. De uitloogproeven zijn gedaan met onverzadigde belaste tarragrond en met waterverzadigde belaste tarragrond. De omzettingssnelheden en adsorptieparameters uit deze studie worden gebruikt voor het bepalen van het risico van uitspoeling van chloorprofam en 3-chlooraniline uit grote bodemtoepassingen naar het grondwater.
    Implications of nanoparticles in the aquatic environment
    Velzeboer, I. - \ 2014
    Wageningen University. Promotor(en): Bart Koelmans. - Wageningen : Wageningen University - ISBN 9789461739506 - 253
    microplastics - polychloorbifenylen - nanotechnologie - adsorptie - ecotoxicologie - aquatisch milieu - verontreinigde sedimenten - aquatische ecologie - microplastics - polychlorinated biphenyls - nanotechnology - adsorption - ecotoxicology - aquatic environment - contaminated sediments - aquatic ecology
    De productie en het gebruik van synthetische nanodeeltjes (ENPs) nemen toe en veroorzaken toenemende emissies naar het milieu. Dit proefschrift richt zich op de implicaties van ENPs in het aquatisch milieu, met de nadruk op het sediment, omdat er wordt verwacht dat ENPs hoofdzakelijk in het aquatisch sediment terecht zullen komen. ENPs kunnen directe effecten veroorzaken op organismen in het aquatisch milieu, indirecte effecten op het levensgemeenschap niveau en/of voedselweb en kunnen effecten op het gedrag en de risico’s van andere contaminanten hebben. Om de risico’s van ENPs vast te stellen, is niet alleen informatie nodig over het gevaar, oftewel de kans op een effect, maar ook over de kans op blootstelling.
    Multi-face modeling to predict free zinc ion concentrations in low-zinc soils
    Duffner, A. ; Weng, L. ; Hoffland, E. ; Zee, S.E.A.T.M. van der - \ 2014
    Environmental Science and Technology 48 (2014)10. - ISSN 0013-936X - p. 5700 - 5708.
    donnan membrane technique - organic-matter - heavy-metals - contaminated soils - isotopic exchange - humic substances - trace-metals - sandy soil - adsorption - speciation
    Multi-surface models are widely used to assess the potential ecotoxicological risk in metal-contaminated soils. Their accuracy in predicting metal speciation in soils with low metal levels was not yet tested. Now highly sensitive analytical techniques are available to experimentally validate such models at low concentration levels. The objective of this study was to test the accuracy of a multi-surface model to predict the Zn2+ concentration and to improve our understanding of Zn bioavailability in low-Zn soils. High-Zn soils were included as controls. Model parameters were determined independently on the basis of earlier peer-reviewed publications. Model output was validated against free Zn2+ concentrations determined with the soil column Donnan membrane technique in a range of soils varying in potentially available Zn, organic matter, clay silicate, and iron (hydr)oxide contents and pH. Deviations between predicted Zn2+ concentrations and experimentally determined values over the whole Zn concentration range were less or equal to the experimental standard error, except for one low-Zn soil. The Zn2+ concentration was mainly controlled by adsorption, where organic matter was predicted to be the dominant soil sorbent. The predicted Zn2+ concentration depends more sensitively upon changes of the reactive Zn pool (application of 0.6, 1.2, 2.4, and 3.6 mg of Zn kg–1 of soil) and organic matter content (±0.2 and 0.4%) than pH changes (±0.5 and 1 pH unit).
    Stability of (Bio)Functionalized Porous Aluminum Oxide
    Debrassi, A. ; Ribbera, A. ; Vos, W.M. de; Wennekes, T. ; Zuilhof, H. - \ 2014
    Langmuir 30 (2014). - ISSN 0743-7463 - p. 1311 - 1320.
    self-assembled monolayers - lactic-acid bacteria - lactobacillus-plantarum - nanoporous alumina - click chemistry - anodic alumina - surfaces - adsorption - membrane - carbohydrate
    Porous aluminum oxide (PAO), a nanostructured support for, among others, culturing microorganisms, was chemically modified in order to attach biomolecules that can selectively interact with target bacteria. We present the first comprehensive study of monolayer-modified PAO using conditions that are relevant to microbial growth with a range of functional groups (carboxylic acid, a-hydroxycarboxylic acid, alkyne, alkene, phosphonic acid, and silane). Their stability was initially assessed in phosphate-buffered saline (pH 7.0) at room temperature. The most stable combination (PAO with phosphonic acids) was further studied over a range of physiological pHs (4–8) and temperatures (up to 80 °C). Varying the pH had no significant effect on the stability, but it gradually decreased with increasing temperature. The stability of phosphonic acid-modified PAO surfaces was shown to depend strongly on the other terminal group of the monolayer structure: in general, hydrophilic monolayers were less stable than hydrophobic monolayers. Finally, an alkyne-terminated PAO surface was reacted with an azide-linked mannose derivative. The resulting mannose-presenting PAO surface showed the clearly increased adherence of a mannose-binding bacterium, Lactobacillus plantarum, and also allowed for bacterial outgrowth.
    Strong Sorption of PCBs to Nanoplastics, Microplastics, Carbon Nanotubes, and Fullerenes
    Velzeboer, I. ; Kwadijk, C.J.A.F. ; Koelmans, A.A. - \ 2014
    Environmental Science and Technology 48 (2014)9. - ISSN 0013-936X - p. 4869 - 4876.
    polycyclic aromatic-hydrocarbons - hydrophobic organic-chemicals - polychlorinated biphenyl sorption - mytilus-edulis l. - aquatic sediments - activated carbon - marine-environment - passive samplers - humic acids - adsorption
    The presence of microplastic and carbon-based nanoparticles in the environment may have implications for the fate and effects of traditional hydrophobic chemicals. Here we present parameters for the sorption of 17 CB congeners to 10–180 µm sized polyethylene (micro-PE), 70 nm polystyrene (nano-PS), multiwalled carbon nanotubes (MWCNT), fullerene (C60), and a natural sediment in the environmentally relevant 10–5–10–1 µg L–1 concentration range. Effects of salinity and sediment organic matter fouling were assessed by measuring the isotherms in fresh- and seawater, with and without sediment present. Sorption to the “bulk” sorbents sediment organic matter (OM) and micro-PE occurred through linear hydrophobic partitioning with OM and micro-PE having similar sorption affinity. Sorption to MWCNT and nano-PS was nonlinear. PCB sorption to MWCNT and C60 was 3–4 orders of magnitude stronger than to OM and micro-PE. Sorption to nano-PS was 1–2 orders of magnitude stronger than to micro-PE, which was attributed to the higher aromaticity and surface–volume ratio of nano-PS. Organic matter effects varied among sorbents, with the largest OM fouling effect observed for the high surface sorbents MWCNT and nano-PS. Salinity decreased sorption for sediment and MWCNT but increased sorption for the polymers nano-PS and micro-PE. The exceptionally strong sorption of (planar) PCBs to C60, MWCNT, and nano-PS may imply increased hazards upon membrane transfer of these particles.
    Bifunctional immobilization of a hyperthermostable endo ß 1,3 glucanase
    Przybysz, A. ; Volmer, A.A. ; Westphal, A.H. ; Berkel, W.J.H. van - \ 2014
    Applied Microbiology and Biotechnology 98 (2014)3. - ISSN 0175-7598 - p. 1155 - 1163.
    pyrococcus-furiosus - enzyme immobilization - epoxy supports - proteins - stabilization - adsorption - reagent - acid
    Laminarinase A (LamA) from Pyrococcus furiosus is a hyperthermostable endo-ß-1,3-glucanase (EC 3.2.1.39) belonging to the glycosyl hydrolase family GH16. Here, we report the two-step immobilization of LamA on macroporous acrylic epoxy beads, extra-functionalized with disulfide groups. To facilitate initial immobilization via thiol–disulfide exchange, we introduced, by site-directed mutagenesis, a superficial cysteine residue near the protein C-terminal end. The thus-obtained S296C variant showed similar catalytic properties as native LamA. The activity of immobilized S296C displayed an inverse relationship with particle size. Use of conventional beads (150–300 µm in diameter) obstructed the catalytic efficiency due to pore diffusion limitation of the polysaccharide substrate. Bifunctional attachment to milled beads (20–40 µm) resulted in high enzyme load and outstanding catalytic features. Bifunctional immobilized S296C showed extreme pH stability and could be repeatedly used at 60 °C without significant activity loss.
    Effect of charged polysaccharides on the techno-functional properties of fractions obtained from algae soluble protein isolate
    Schwenzfeier, A. ; Wierenga, P.A. ; Eppink, M.H.M. ; Gruppen, H. - \ 2014
    Food Hydrocolloids 35 (2014). - ISSN 0268-005X - p. 9 - 18.
    in-water emulsions - diffusing wave spectroscopy - tetraselmis sp - adsorption - microalgae - dissociation - hydrolysis - stability
    It has been suggested previously that charged polysaccharides present in algae soluble protein isolate (ASPI) contribute to its foaming and emulsifying properties. In this study ASPI was fractioned into one fraction enriched in uronic acids (the building blocks of charged polysaccharides, [ASPI-UA]), one enriched in protein (ASPI-P) and one containing small, dissociated (glyco-)proteins (ASPI-S). Emulsions prepared using ASPI-UA were stable against flocculation between pH 3e7, while ASPI-P and ASPI-S showed decreased emulsion stabilities around pH 5. This indicates the importance of the charged polysaccharides present in ASPI for emulsion stability at pH 5. For the foaming properties of ASPI no effect of charged polysaccharides was observed. Instead, ASPI-S showed considerably higher foam stabilities at pH 5e7 than the other fractions. These results suggest that dependent on the application charged polysaccharides or dissociated (glyco-) proteins can contribute to ASPI’s techno-functional properties. Its further fractionation yields a fraction with improved emulsion stability and a fraction with improved foaming properties.
    Sulphate reduction and calcite precipitation in relation to internal eutrophication of groundwater fed alkaline fens
    Cirkel, D.G. ; Beek, C.G.E.M. van; Witte, J.P.M. ; Zee, S.E.A.T.M. van der - \ 2014
    Biogeochemistry 117 (2014)2-3. - ISSN 0168-2563 - p. 375 - 393.
    organic-matter - calcareous fens - phosphate - sulfur - soils - water - netherlands - sediments - adsorption - peatland
    Although in Europe atmospheric deposition of sulphur has decreased considerably over the last decades, groundwater pollution by sulphate may still continue due to pyrite oxidation in the soil as a result of excessive fertilisation. Inflowing groundwater rich in sulphate can change biogeochemical cycling in nutrient-poor wetland ecosystems. Incoming sulphate loads may induce internal eutrophication as well as the accumulation of dissolved sulphide, which is phytotoxic. We, however, argue that upwelling sulphate rich groundwater may also promote the conservation of rare and threatened alkaline fens, since excessive fertilisation and pyrite oxidation also produces acidity, which invokes calcite dissolution, and increased alkalinity and hardness (Ca2+ + Mg2+) of the inflowing groundwater. Our observations in a very species-rich wetland nature reserve show that sulphate is reduced and effectively precipitates as iron sulphides when this calcareous and sulphate rich groundwater flows upward through the organic soil of the investigated nature reserve. Furthermore, we show that sulphate reduction coincides with an increase in alkalinity production, which in our case results in active calcite precipitation in the soil. In spite of the occurring sulphate reduction we found no evidence for internal eutrophication. Extremely low phosphorous concentration in the pore water could be attributed to a high C:P ratio of soil organic matter and co-precipitation with calcite. Our study shows that seepage dependent alkaline fen ecosystems can be remarkably resilient to fertilisation and pyrite oxidation induced groundwater quality changes.
    Surface Pressure and Elasticity of Hydrophobin HFBII Layers on the Air-Water Interface: Rheology Versus Structure Detected by AFM Imaging
    Stanimirova, R.D. ; Gurkov, T.D. ; Kralchevsky, P.A. ; Balashev, K.T. ; Stoyanov, S.D. ; Pelan, E.G. - \ 2013
    Langmuir 29 (2013)20. - ISSN 0743-7463 - p. 6053 - 6067.
    class-ii hydrophobins - air/water interface - langmuir monolayers - trichoderma-reesei - proteins - films - adsorption - stability - emulsions - mechanisms
    Here, we combine experiments with Langmuir trough and atomic force microscopy (AFM) to investigate the reasons for the special properties of layers from the protein HFBII hydrophobin spread on the airwater interface. The hydrophobin interfacial layers possess the highest surface dilatational and shear elastic moduli among all investigated proteins. The AFM images show that the spread HFBII layers are rather inhomogeneous, (i.e., they contain voids, monolayer and multilayer domains). A continuous compression of the layer leads to filling the voids and transformation of a part of the monolayer into a trilayer. The trilayer appears in the form of large surface domains, which can be formed by folding and subduction of parts from the initial monolayer. The trilayer appears also in the form of numerous submicrometer spots, which can be obtained by forcing protein molecules out of the monolayer and their self-assembly into adjacent pimples. Such structures are formed because not only the hydrophobic parts, but also the hydrophilic parts of the HFBII molecules can adhere to each other in the water medium. If a hydrophobin layer is subjected to oscillations, its elasticity considerably increases, up to 500 mN/m, which can be explained with compaction. The relaxation of the layers tension after expansion or compression follows the same relatively simple law, which refers to two-dimensional diffusion of protein aggregates within the layer. The characteristic diffusion time after compression is longer than after expansion, which can be explained with the impedence of diffusion in the more compact interfacial layer. The results shed light on the relation between the mesoscopic structure of hydrophobin interfacial layers and their unique mechanical properties that find applications for the production of foams and emulsions of extraordinary stability; for the immobilization of functional molecules at surfaces, and as coating agents for surface modification.
    Sterke vermindering van fosfaatuitspoeling uit landbouwgronden met de fosfaatbindende drain
    Groenenberg, J.E. ; Chardon, W.J. ; Koopmans, G.F. - \ 2013
    draineerbuizen - drainagewater - ijzer - adsorptie - waterkwaliteit - fosfaten - veldproeven - drain pipes - drainage water - iron - adsorption - water quality - phosphates - field tests
    Voor gedraineerde landbouwgronden (meer dan 50% in Nederland) heeft Alterra de fosfaatbindende drain ontwikkeld. Dit is een normale buisdrain die is ingebed in ijzerzand. De omhulling met ijzerzand bindt het fosfaat uit het fosfaatrijke water voor het de drainbuis instroomt. Het schone water wordt afgevoerd naar het oppervlaktewater.
    Surface and mineral structure of ferrihydrite
    Hiemstra, T. - \ 2013
    Geochimica et Cosmochimica Acta 105 (2013). - ISSN 0016-7037 - p. 316 - 325.
    oxide-water interface - x-ray-absorption - nanocrystalline material - synthetic ferrihydrite - mossbauer-spectroscopy - 6-line ferrihydrite - iron oxyhydroxide - model - adsorption - nanoparticles
    Ferrihydrite (Fh) is an yet enigmatic nano Fe(III)-oxide material, omnipresent in nature that can bind ions in large quantities, regulating bioavailability and ion mobility. Although extensively studied, to date no proper view exists on the surface structure and composition, while it is of vital importance to our understanding of ion complexation in terrestrial and aquatic systems. Here, the surface structure of Fh is elucidated in relation to that of the mineral core, showing a unique surface composition differing from the mineral core. The mineral core is basically defect-free for all Fh particles. Key for understanding Fh is the very large contribution of the surface as an “inter-phase”. The surface of Fh is depleted by two specific types of polyhedra (Fe2,Fe3). Surface depletion (SD) explains the observed particle size dependency of the (a) Pair Distribution Function (PDF) derived from High Energy X-ray total Scattering (HEXS), (b) thermogravimetric water content, and (c) mass density. It also explains the isotopic 57Fe exchange ratio. Due to surface groups, two-line Fh particles are water rich but its mineral core is hydrogen poor. The SD model elucidates the surface structure of crystal faces of idealized Fh such as the 1 -1 0 and 1 -1 1 type of faces that may strongly contribute (e.g. ~75 ± 10%) to the total surface area. These faces are terminated by protruding Fe1 octahedra, creating the singly-coordinated FeOH(H) groups at the Fh surface. Alternating rows of Fe1 octahedra with singly-coordinated surface groups enable the formation of either double corner (2C) or edge (1E) surface complexes. For Fh, the site densities derived are much higher than for goethite. In combination with the high surface area, it makes Fh to an extremely reactive natural phase.
    Influence of soil humic and fulvic acid on the activity and stability of lysozyme and urease
    Li, Y. ; Tan, W. ; Koopal, L.K. ; Wang, M. ; Liu, Fan ; Norde, W. - \ 2013
    Environmental Science and Technology 47 (2013). - ISSN 0013-936X - p. 5050 - 5056.
    isothermal titration calorimetry - insecticidal cry1ab protein - ionic-strength - prion protein - ph - adsorption - complexes - binding - substances - fractions
    Humic substances (HS), including humic acids (HA) and fulvic acids (FA), are important components of soil systems. HS form strong complexes with oppositely charged proteins, which will lead to changes in the enzyme activity. The effect of soil HS on the activity and stability of two enzymes was investigated as a function of pH, ionic strength, and mass ratio HS/enzyme. Humic acid (JGHA) and fulvic acid (JGFA) are negatively charged, lysozyme is net positive at pH values below 10.4, and urease is net positive below pH 5.2 or net negative above pH 5.2. The enzyme activities in the HS-enzyme complexes were suppressed when the enzymes were oppositely charged to the HS. The largest activity suppression was observed around the mass ratio HS/enzyme where the HS-protein complex was at its isoelectric point (IEP). At the IEP strong aggregation of the complexes led to encapsulation of the enzyme. The ionic strength was important; an increase decreased complex formation, but increased aggregation. Due to the larger hydrophobicity of JGHA than JGFA, the reduction in enzyme activity was stronger for JGHA. The enzyme stability also decreased maximally at mass ratio around the IEP of the complex when HS and protein were oppositely charged. When urease and HS were both negatively charged no complexes were formed, but the presence of JGHA or JGFA improved the activity and stability of the enzyme.
    Proton binding to soil humic and fulvic acids: Experiments and NICA-Donnan modelling
    Tan, W. ; Xiong, J. ; Li, Y. ; Wang, M. ; Weng, L. ; Koopal, L.K. - \ 2013
    Colloids and Surfaces. A: Physicochemical and Engineering Aspects 436 (2013). - ISSN 0927-7757 - p. 1152 - 1158.
    natural organic-matter - metal-ion binding - potentiometric titrations - affinity distributions - base properties - substances - heterogeneity - parameters - adsorption
    Proton binding to one soil fulvic acid (JGFA), two soil humic acids (JGHA, JLHA) and a lignite-based humic acid (PAHA) was investigated. The results were fitted to NICA-Donnan model and compared directly with the predictions using the generic parameters. NICA-Donnan model can describe proton binding satisfactorily when parameter fitting is allowed for humic substance (HS). However, predictions based on the generic parameter sets deviate for soil samples in a non-systematic way from the measured results. Replacing Qmax,H1 in generic parameter sets with material-specific values improves the predictions for soil HA significantly. For JGFA, the agreement between the model prediction and data is still not satisfactory after substitution. This is due to a very different pattern of site distribution of JGFA from that of generic FA. For two other soil FAs (FH-14, FH-22 of Milne's database) the generic predictions can be improved significantly with material-specific Qmax,H1. Adjusting also Qmax,H2 to HS material-specific value improves the prediction only slightly further. In practice, Qmax,H1 and Qmax,H2 of HS can be obtained in a relatively simple way by performing one acid–base titration at a given ionic strength and applying the procedure of Lenoir et al. to fit data to NICA equation. Introduction of thus obtained Qmax,H1 and Qmax,H2 into generic parameter sets improves the generic predictions significantly. The functional group contents as obtained by SG-method are not adequate for this purpose.
    Carbon Nanofiber-Supported K2CO3 as an Efficient Low-Temperature Regenerable CO2 Sorbent for Post-Combustion Capture
    Meis, N.N.A.H. ; Frey, A.M. ; Bitter, J.H. ; Jong, K.P. de - \ 2013
    Industrial & Engineering Chemistry Research 52 (2013)36. - ISSN 0888-5885 - p. 12812 - 12818.
    metal-organic frameworks - fixed-bed operations - solid base catalysts - flue-gas - dioxide - adsorption - recovery - adsorbents - sorption - k2co3-on-carbon
    This study focuses on regenerable sorbents for post-combustion CO2 capture at low temperature (373 K). K2CO3 loaded on three different supports, carbon nanofibers (CNF), alumina (¿-Al2O3), and activated carbon (AC), was investigated. K2CO3–CNF revealed excellent properties as CO2 sorbent, displaying capacities of 1.2–1.6 mmol g–1 and fast desorption kinetics at low temperatures (423 K). This temperature was too low to completely regenerate K2CO3–Al2O3 and K2CO3–AC, and consequently, these sorbents lost 8% and 50%, respectively, of their capacity after the first absorption–desorption cycle. K2CO3–CNF could be regenerated to restore 80% of its capacity with a low energy input, estimated at 2–3 GJ/ton CO2, which is competitive to currently used amines.
    Comparison of Tungsten and Molybdenum Carbide Catalysts for the Hydrodeoxygenation of Oleic Acid
    Hollak, S.A.W. ; Gosselink, R.J.A. ; Es, D.S. van; Bitter, J.H. - \ 2013
    ACS Catalysis 3 (2013)12. - ISSN 2155-5435 - p. 2837 - 2844.
    stearic-acid - fatty-acids - ruthenium catalysts - diesel production - reaction pathways - deoxygenation - biodiesel - hydrocarbons - adsorption - oils
    Group 6 (W, Mo) metal carbide catalysts are promising alternatives to hydrodesulfurization (NiMo, CoMo) catalysts and group 10 (Pd) type catalysts in the deoxygenation of vegetable fats/oils. Herein, we report a comparison of carbon nanofiber-supported W2C and Mo2C catalysts on activity, selectivity, and stability for the hydrodeoxygenation of oleic acid to evaluate the catalytic potential for the upgrading of fat/oil feeds. W2C/CNF was more selective toward olefins, whereas Mo2C/CNF was more selective toward paraffins. This was related to the hydrogenation activities of the respective metal carbides. Mo2C/CNF showed higher activity and stability compared with W2C/CNF.
    On the collapse transition of a polymer brush: the case of lateral mobility
    Leermakers, F.A.M. ; Egorov, S.A. - \ 2013
    Soft Matter 9 (2013)12. - ISSN 1744-683X - p. 3341 - 3348.
    terminally attached chains - consistent field-theory - poor solvents - molecular-dynamics - tethered polymers - model - adsorption - interface - surfaces - layers
    We consider a polymer brush composed of end-grafted polymer chains. Classical theory advocates that a worsening of the solvent quality results in a smooth decrease of the brush height from a swollen to a dense brush. We report that a homogeneous brush under poor solvent conditions can have a negative surface pressure, indicating an instability in favour of lateral segregation. Also by using a two-gradient version of the self-consistent field (SCF) theory we show that, in contradiction to the classical result, but in line with the negative pressure, the collapse transition for laterally mobile chains has a first-order character, exemplified by the presence of a compact brush that coexists with a dilute gas of end-grafted chains. The dense brush assumes a pancake shape wherein the chains balance the stretching entropy against surface energies. The height of the pancake scales sub-linearly with the chain length because the local grafting density decreases with increasing chain length. In analogy with wetting studies we discuss how the spreading parameter has an influence on the pancake structure. Accordingly, the height increases with worsening of the solvent quality and decreases with increased affinity for the substrate. The two-phase state is expected in many practical situations
    Self-consistent field predictions for quenched spherical biocompatible triblock copolymer micelle
    Lebouille, J.G.J.L. ; Tuinier, R. ; Vleugels, L.F.W. ; Cohen Stuart, M.A. ; Leermakers, F.A.M. - \ 2013
    Soft Matter 9 (2013)31. - ISSN 1744-683X - p. 7515 - 7525.
    interacting chain molecules - angle neutron-scattering - aqueous-solution - statistical-theory - block-copolymers - micellization - adsorption - biodegradation - microspheres - degradation
    We have used the Scheutjens–Fleer self-consistent field (SF-SCF) method to predict the self-assembly of triblock copolymers with a solvophilic middle block and sufficiently long solvophobic outer blocks. We model copolymers consisting of polyethylene oxide (PEO) as the solvophilic block and poly(lactic-co-glycolic) acid (PLGA) or poly(e-caprolactone) (PCL) as the solvophobic block. These copolymers form structurally quenched spherical micelles provided the solvophilic block is long enough. Predictions are calibrated on experimental data for micelles composed of PCL-PEO-PCL and PLGA-PEO-PLGA triblock copolymers prepared via the nanoprecipitation method. We establish effective interaction parameters that enable us to predict various micelle properties such as the hydrodynamic size, the aggregation number and the loading capacity of the micelles for hydrophobic species that are consistent with experimental findings
    Bending rigidities of surfactant bilayers using self-consistent field theory
    Leermakers, F.A.M. - \ 2013
    Journal of Chemical Physics 138 (2013). - ISSN 0021-9606 - 11 p.
    interacting chain molecules - lipid-bilayers - curvature elasticity - statistical-theory - adsorption - membranes - size - thermodynamics - interface - relevance
    Self-consistent field (SCF) theory is used to find bending moduli of surfactant and lipid bilayers. Recently, we successfully applied low-memory search methods to solve the SCF equations. Using these we are now able to directly evaluate the Gaussian bending modulus for molecularly detailed models of bilayers by evaluating the excess Helmholtz energy of tensionless bilayers in a (part of the) Im3m cubic phase. The result prompted us to reconsider the protocol that has been used thus far to find the mean bending modulus k c and Gaussian bending modulus k¯. With respect to previous predictions, the value of k c is reduced by a factor of two and the Gaussian bending modulus is less negative and much closer to zero. In line with experimental data we now find that k¯can also become positive. In this paper we use the non-ionic surfactants series of the type C n E m for illustration.
    Equivalence of chain conformations in the surface region of a polymer melt and a single Gaussian chain nder critical conditions
    Skvortsov, A.M. ; Leermakers, F.A.M. ; Fleer, G.J. - \ 2013
    Journal of Chemical Physics 139 (2013). - ISSN 0021-9606 - 10 p.
    monte-carlo simulations - linear flexible macromolecules - molecular-dynamics simulations - variable-density model - atomistic simulation - solid interfaces - adsorption - tension - graphite - ends
    In the melt polymer conformations are nearly ideal according to Flory's ideality hypothesis. Silberberg generalized this statement for chains in the interfacial region. We check the Silberberg argument by analyzing the conformations of a probe chain end-grafted at a solid surface in a sea of floating free chains of concentration f by the self-consistent field (SCF) method. Apart from the grafting, probe chain and floating chains are identical. Most of the results were obtained for a standard SCF model with freely jointed chains on a six-choice lattice, where immediate step reversals are allowed. A few data were generated for a five-choice lattice, where such step reversals are forbidden. These coarse-grained models describe the equilibrium properties of flexible atactic polymer chains at the scale of the segment length. The concentration was varied over the whole range from f = 0 (single grafted chain) to f = 1 (probe chain in the melt). The number of contacts with the surface, average height of the free end and its dispersion, average loop and train length, tail size distribution, end-point and overall segment distributions were calculated for a grafted probe chain as a function of f, for several chain lengths and substrate/polymer interactions, which were varied from strong repulsion to strong adsorption. The computations show that the conformations of the probe chain in the melt do not depend on substrate/polymer interactions and are very similar to the conformations of a single end-grafted chain under critical conditions, and can thus be described analytically. When the substrate/polymer interaction is fixed at the value corresponding to critical conditions, all equilibrium properties of a probe chain are independent of f, over the whole range from a dilute solution to the melt. We believe that the conformations of all flexible chains in the surface region of the melt are close to those of an appropriate single chain in critical conditions, provided that one end of the single chain is fixed at the same point as a chain in the melt.
    Pearl-necklace complexes of flexible polyanions with neutral-cationic diblock copolymers
    Golinska, M.D. ; Wolf, F.A. de; Cohen Stuart, M.A. ; Hernandez Garcia, A. ; Vries, R.J. de - \ 2013
    Soft Matter 9 (2013)28. - ISSN 1744-683X - p. 6406 - 6411.
    polyelectrolyte complexes - core micelles - poor solvent - adsorption - stability - brushes - films
    We study the complexation of very asymmetric diblock copolymers (consisting of a cationic block of 12 lysines connected to a 400 amino acid long hydrophilic polypeptide block with a net charge that is nearly zero) with oppositely charged sodium poly(acrylic acid) (NaPAA) with a range of molar masses between 2 and 1300 kg mol-1. For shorter Na-PAA chains, spherical complex coacervate micelles are formed, but for long Na-PAA chains, with molar masses in excess of 250 kg mol-1, atomic force microscopy indicates the presence of pearl-necklace structures. Complexes most likely consist of only a single NaPAA chain, complexed to multiple diblocks. Hence, the size of the complexes can be fully controlled via the NaPAA molar mass. The occurrence of pearl-necklace complexes at higher NaPAA molar masses is attributed to the packing frustration that arises due to the small size of the cationic block of the diblock copolymers
    Goede waterkwaliteit en meer kansen voor natuur : met immobilisatie van fosfaat door restmaterialen
    Chardon, W.J. ; Groenenberg, J.E. - \ 2013
    landbouwgrond - fosfaatuitspoeling - adsorptie - kaderrichtlijn water - natuurgebieden - agricultural land - phosphate leaching - adsorption - water framework directive - natural areas
    Hoge fosfaatgehalten in landbouwgronden kunnen eutrofiëring van het oppervlaktewater veroorzaken, waardoor overmatige groei van waterplanten en algen optreedt. Met alleen het mestbeleid lukt het niet om de doelstellingen van de Kaderrichtlijn Water (KRW) te bereiken, onder andere als gevolg van de voorraden fosfaat die in de bodem aanwezig zijn. Daarom zijn aanvullende maatregelen noodzakelijk.. Een mogelijke oplossing is de verwijdering van fosfaat in het naar het oppervlaktewater uitstromende water.
    Non-linear surface dilatational rheology as a tool for understanding microstructures of air/water interfaces stabilized by oligofructose fatty acid esters
    Kempen, S.E.H.J. van; Schols, H.A. ; Linden, E. van der; Sagis, L.M.C. - \ 2013
    Soft Matter 9 (2013)40. - ISSN 1744-683X - p. 9579 - 9592.
    air-water-interface - monolayers - layers - shear - viscoelasticity - adsorption - systems - foams
    In this paper, the rheological response of air/water interfaces, stabilized by various oligofructose fatty acid esters, to oscillatory dilatational deformations was studied and compared to the response of interfaces stabilized by sucrose esters. We have followed a traditional approach to surface rheology, where the development of the modulus as a function of time is studied as well as the frequency dependence of the modulus. We also adopted a different approach where we investigate in detail the amplitude dependence of the modulus. Finally, we studied the temperature dependence. We show that for an accurate characterization of the dilatational rheology of fluid-fluid interfaces with a complex microstructure, a protocol should be used that not only involves variations of surface pressure, frequency, and temperature, but also establishes amplitude dependence. We show that Lissajous plots of surface pressure versus deformation can be useful tools to help interpret surface dilatational behavior in terms of interfacial microstructure. The rheological response of interfaces stabilized by oligofructose esters differed significantly from the response of those stabilized by sucrose esters. Sucrose esters behaved like typical low molecular weight surfactants, and gave interfaces with relatively low moduli, a frequency scaling of the dilatational modulus with an exponent close to 0.5, and displayed no asymmetries in Lissajous plots. In contrast, the oligofructose esters gave, depending on the fatty acid tail, relatively high moduli, almost independent of frequency. Significant asymmetries were observed in the Lissajous plots, with strain hardening during compression and strain softening during extension. Our results suggest that the unusual rheological properties of interfaces stabilized by oligofructose esters may be the result of the formation of a two-dimensional soft glass phase by the oligofructose part of the ester.
    Protein Concentration and Protein-Exposed Hydrophobicity as Dominant Parameters Determining the Flocculation of Protein-Stabilized Oil-in-Water Emulsions
    Delahaije, R.J.B.M. ; Wierenga, P.A. ; Nieuwenhuijzen, N.H. van; Giuseppin, M.L.F. ; Gruppen, H. - \ 2013
    Langmuir 29 (2013)37. - ISSN 0743-7463 - p. 11567 - 11574.
    diffusing wave spectroscopy - beta-lactoglobulin - coalescence stability - disjoining pressure - drop size - adsorption - films - ph - interfaces - ovalbumin
    DLVO theory is often considered to be applicable to the description of flocculation of protein-stabilized oil-in-water emulsions. To test this, emulsions made with different globular proteins (ß-lactoglobulin, ovalbumin, patatin, and two variants of ovalbumin) were compared under different conditions (pH and electrolyte concentration). As expected, flocculation was observed under conditions in which the zeta potential is decreased (around the isoelectric point and at high ionic strength). However, the extent of flocculation at higher ionic strength (>50 mM NaCl) decreased with increasing protein-exposed hydrophobicity. A higher exposed hydrophobicity resulted in a higher zeta potential of the emulsion droplets and consequently increased stability against flocculation. Furthermore, the addition of excess protein strongly increased the stability against salt-induced flocculation, which is not described by DLVO theory. In the protein-poor regime, emulsions showed flocculation at high ionic strength (>100 mM NaCl), whereas emulsions were stable against flocculation if excess protein was present. This research shows that the exposed hydrophobicity of the proteins and the presence of excess protein affect the flocculation behavior.
    Protein transfer to membranes upon shape deformation
    Sagis, L.M.C. ; Bijl, E. ; Antono, L. ; Ruijter, N.C.A. de; Valenberg, H.J.F. van - \ 2013
    The European Physical Journal. Special Topics 222 (2013)1. - ISSN 1951-6355 - p. 61 - 71.
    blood-cell deformability - in-water emulsions - fat globule size - interfacial permeability - flow - drops - milk - dissolution - infections - adsorption
    Red blood cells, milk fat droplets, or liposomes all have interfaces consisting of lipid membranes. These particles show significant shape deformations as a result of flow. Here we show that these shape deformations can induce adsorption of proteins to the membrane. Red blood cell deformability is an important factor in several diseases involving obstructions of the microcirculatory system, and deformation induced protein adsorption will alter the rigidity of their membranes. Deformation induced protein transfer will also affect adsorption of cells onto implant surfaces, and the performance of liposome based controlled release systems. Quantitative models describing this phenomenon in biomaterials do not exist. Using a simple quantitative model, we provide new insight in this phenomenon. We present data that show convincingly that for cells or droplets with diameters upwards of a few micrometers, shape deformations induce adsorption of proteins at their interface even at moderate flow rates.
    “In situ” removal of isopropanol, butanol and ethanol from fermentation broth by gas stripping
    Vrije, G.J. de; Budde, M.A.W. ; Wal, H. van der; Claassen, P.A.M. ; Lopez Contreras, Ana - \ 2013
    Bioresource Technology 137 (2013). - ISSN 0960-8524 - p. 153 - 159.
    acetobutylicum atcc 824 - clostridium-acetobutylicum - batch fermentation - product recovery - aqueous-solution - n-butanol - adsorption - acetone - conversion
    In this study, the removal of IBE from aqueous solutions by gas stripping has been characterized. The effect of one or more components in the solution on the kinetics of the separation has been studied, both at 37 °C and at 70 °C. Gas stripping has been applied to batch, repeated batch and continuous cultures of Clostridium beijerinckii grown on a glucose/xylose mixed sugar substrate mimicking lignocellulosic hydrolysates, with the aim of finding optimal conditions for a stable IBE-producing culture with high productivity. An innovative repeated-batch process has been demonstrated in which the gas-stripping is performed at 70 °C, resulting in a prolonged stable IBE culture.
    Fouling of dairy components on hydrophobic polytetrafluoroethylene (PTFE) membranes for membrane distillation
    Hausmann, A. ; Sanciolo, P. ; Vasiljevic, T. ; Weeks, M. ; Schroën, C.G.P.H. ; Gray, S. ; Duke, M. - \ 2013
    Journal of Membrane Science 442 (2013). - ISSN 0376-7388 - p. 149 - 159.
    scale formation mechanism - skimmed-milk - reverse-osmosis - whey proteins - ultrafiltration - nanofiltration - adsorption - products - systems - flux
    This study investigates fouling of membranes during membrane distillation (MD) of two model dairy feeds — skim milk and whey, as well as their major single components. Every MD experiment was conducted for 20 hat 54 C feed inlet temperature and 5 C permeate inlet temperature using PTFE membranes. Performance was assessed in terms of throughput (flux) and retention efficiency.Skim milk flux was found to be lower but stable overtime compared to whey.The study using single components as well as combinations the reofrevealed that fouling was primarily driven by proteins and calcium, but only in combination.Lactose also played a role to a lesser extent in the protein/membrane interactions, possibly due to preferential hydration,but did not interact with the membrane polymer directly. However lactose was found to deposit once an anchorpoint to the membrane was established by other components. Skim milk showed strong adhesion from its principle proteins, caseins;however salts were needed to form a thick and dense cake layer.Caseins seem to form a layer on the membrane surface that prevents other components from interacting with the membrane polymer.Wheyproteins, on the other hand, deposited to alesse rextent. In general membrane distillation was found to be a process that generates high quality water with retention of all tested components >99% while simultaneously concentrating whey or skim milk.
    Fouling mechanisms of dairy streams during membrane distillation
    Hausmann, A. ; Sanciolo, P. ; Vasiljevic, T. ; Weeks, M. ; Schroën, C.G.P.H. ; Gray, S. ; Duke, M. - \ 2013
    Journal of Membrane Science 441 (2013). - ISSN 0376-7388 - p. 102 - 111.
    calcium-phosphate - skimmed-milk - osmotic distillation - whey proteins - ultrafiltration - microfiltration - adsorption - stability - spectroscopy - precursors
    This study reports on fouling mechanisms of skim milk and whey during membrane distillation (MD) using polytetrafluoroethylene (PTFE) membranes. Structural and elemental changes along the fouling layer from the anchorpoint at the membrane to the topsurface of the fouling layer have been investigated using synchrotron IR micro-spectroscopy and electron microscopy with associated energy dispersive X-ray spectroscopy(EDS)Initial adhesion of single components on a membrane representing a PTFEsurface was observed in-situ utilizing reflectometry.Whey components were found to penetrate into the membrane matrix while skim milk fouling remained on top of the membrane. Whey proteins had weaker attractive interaction with the membrane and adhesion depended more on the presence of phosphorus near the membrane surface and throughout to establish the fouling layer. This work has given detailed insight into the fouling mechanisms of MD membranes in major dairy streams, essential for maintaining membrane distillation as operational for acceptable times, therewith allowing further development of this emerging technology.
    Foam properties of algae soluble protein isolate: Effect of pH and ionic strength
    Schwenzfeier, A. ; Lech, F.J. ; Wierenga, P.A. ; Eppink, M.H.M. ; Gruppen, H. - \ 2013
    Food Hydrocolloids 33 (2013)1. - ISSN 0268-005X - p. 111 - 117.
    air-water interfaces - tetraselmis sp - adsorption - stability - emulsions - charge
    In this study the foam properties of algae soluble protein isolate (ASPI), a mixture of mainly proteins and polysaccharides, were investigated as function of isolate concentration (0.1–1.0 mg/mL) and pH (3.0–7.0) at 10 mM and 200 mM NaCl. In addition, adsorption kinetics and dilatational elasticity at the air–water interface were studied. Whey protein isolate (WPI) and egg white albumin (EWA) were used as reference proteins. The consistent dilatational behaviour of ASPI at all pH values and ionic strengths tested indicated a similar interfacial composition at all these conditions. Adsorption kinetics, in contrast, were influenced by varying environmental conditions. At increased ionic strength and close to the theoretical isoelectric point calculated based purely on the amino acid composition of ASPI (pH 7) adsorption increased. Since similar adsorption behaviour was also observed for WPI and EWA, the interfacial properties of ASPI are most likely dominated by its protein fraction. This is further confirmed by the fact that ¿-potential measurements suggested an overall isoelectric point of ASPI below pH 3, while adsorption kinetics varied between pH 5 and pH 7 (the theoretical protein-based isoelectric point of ASPI). The overall foam stability of ASPI stabilized foams was superior to those of WPI and EWA in the pH range 5–7. In conclusion, the molecular and interfacial properties of ASPI, a mixture of proteins and polysaccharides, seem to favour the production of very stable foams in this pH range by the selective adsorption of its protein fraction to the air–water interface.
    Enhancement of Emulsifying Properties of Cuttlefish Skin Gelatin by Modification with N-hydroxysuccinimide Esters of Fatty Acids
    Aewsiri, T. ; Benjakul, S. ; Visessanguan, W. ; Encarnacion, A.B. ; Wierenga, P.A. ; Gruppen, H. - \ 2013
    Food Bioprocess Technology 6 (2013)3. - ISSN 1935-5130 - p. 671 - 681.
    in-water emulsions - fish gelatin - proteins - stability - surface - adsorption
    Cuttlefish (Sepia pharaonis) skin gelatin modified with N-hydroxysuccinimide esters of various fatty acids including capric acid (C10:0), lauric acid (C12:0), and myristic acid (C14:0) at different molar ratios was characterized and determined for emulsifying property. Fatty acid esters were incorporated into gelatin as indicated by the decrease in free amino group content. Gelatin modified with fatty acid ester had the increased surface hydrophobicity and emulsifying property with coincidental decrease in surface tension. Gelatin modified with fatty acid ester of C14:0 showed the highest surface activity, especially with the high degree of modification. Emulsion stabilized by gelatin modified with fatty acid ester of C14:0 had a smaller mean particle diameter with higher stability, compared with that stabilized by the control gelatin (without modification). Emulsion stabilized by modified gelatin remained stable at various pH (3–8) and salt concentrations (NaCl 0–500 mM). Emulsion was also stable after being heated at 50–90 °C for 30 min.
    Emulsion properties of algae soluble protein isolate from Tetraselmis sp.
    Schwenzfeier, A. ; Helbig, A. ; Wierenga, P.A. ; Gruppen, H. - \ 2013
    Food Hydrocolloids 30 (2013)1. - ISSN 0268-005X - p. 258 - 263.
    in-water emulsions - diffusing wave spectroscopy - whey-protein - physicochemical properties - stabilized emulsions - flocculation - emulsifiers - adsorption - microalgae - pectin
    To study possible applications of microalgae proteins in foods, a colourless, protein-rich fraction was isolated from Tetraselmis sp. In the present study the emulsion properties of this algae soluble protein isolate (ASPI) were investigated. Droplet size and droplet aggregation of ASPI stabilized oil-in-water emulsions were studied as function of isolate concentration (1.25–10.00 mg/mL), pH (3–7), and ionic strength (NaCl 10–500 mM; CaCl2 0–50 mM). Whey protein isolate (WPI) and gum arabic (GA) were used as reference emulsifiers. The lowest isolate concentrations needed to reach d32 = 1 µm in 30% oil-in-water emulsions were comparable for ASPI (6 mg/mL) and WPI (4 mg/mL). In contrast to WPI stabilized emulsions ASPI stabilized emulsions were stable around pH 5 at low ionic strength (I = 10 mM). Flocculation only occurred around pH 3, the pH with the smallest net droplet ¿-potential. Due to the charge contribution of the anionic polysaccharide fraction present in ASPI its droplet ¿-potential remained negative over the whole pH range investigated. An increase in ionic strength (=100 mM) led to a broadening of the pH range over which the ASPI stabilized emulsions were unstable. GA emulsions are not prone to droplet aggregation upon changes in pH or ionic strength, but much higher concentrations are needed to produce stable emulsions. Since ASPI allows the formation of stable emulsions in the pH range 5–7 at low protein concentrations, it can offer an efficient natural alternative to existing protein–polysaccharide complexes.
    Extraction of sediment-associated polycyclic aromatic hydrocarbons with granular activated carbon
    Rakowska, M.I. ; Kupryianchyk, D. ; Grotenhuis, J.T.C. ; Rijnaarts, H.H.M. ; Koelmans, A.A. - \ 2013
    Environmental Toxicology and Chemistry 32 (2013)1. - ISSN 0730-7268 - p. 304 - 311.
    environmental black carbon - soot-like materials - san-francisco bay - polychlorinated-biphenyls - surface-chemistry - pcb bioavailability - organic-compounds - marine sediment - sorption - adsorption
    Addition of activated carbon (AC) to sediments has been proposed as a method to reduce ecotoxicological risks of sediment-bound contaminants. The present study explores the effectiveness of granular AC (GAC) in extracting polycyclic aromatic hydrocarbon (PAH) from highly contaminated sediments. Four candidate GAC materials were screened in terms of PAH extraction efficiency using single-step 24-h GAC extractions, with traditional 24-h Tenax extraction as a reference. Subsequently, sorption of native PAHs to the best performing GAC 1240W (0.45–1.70¿mm) was studied for sediment only and for GAC–sediment mixtures at different GAC–sediment weight ratios, using 76-µm polyoxymethylene (POM) passive samplers. Granular AC sorption parameters for PAHs were determined by subtracting the contribution of PAH sorption to sediment from PAH sorption to the GAC–sediment mixture. It appears that the binding of PAHs and the effectiveness of GAC to reduce sediment porewater concentrations were highly dependent on the GAC–sediment mixing ratio and hydrophobicity of the PAH. Despite the considerable fouling of GAC by organic matter and oil, 50 to 90% of the most available PAH was extracted by the GAC during a 28-d contact time, at a dose as low as 4%, which also is a feasible dose in field-scale applications aimed at cleaning the sediment by GAC addition and removal.
    Sorption of perfluorooctane sulfonate to carbon nanotubes in aquatic sediments
    Kwadijk, C.J.A.F. ; Velzeboer, I. ; Koelmans, A.A. - \ 2013
    Chemosphere 90 (2013)5. - ISSN 0045-6535 - p. 1631 - 1636.
    natural organic-matter - adsorption - nanomaterials - environment - attenuation - release - surface - acids - pfos
    To date, sorption of organic compounds to nanomaterials has mainly been studied for the nanomaterial in its pristine state. However, sorption may be different when nanomaterials are buried in sediments. Here, we studied sorption of Perfluorooctane sulfonate (PFOS) to sediment and to sediment with 4% multiwalled carbon nanotubes (MWCNTs), as a function of factors affecting PFOS sorption; aqueous concentration, pH and Ca2+ concentration. Sorption to MWCNT in the sediment–MWCNT mixtures was assessed by subtracting the contribution of PFOS sorption to sediment-only from PFOS sorption to the total sediment–MWCNT mixture. PFOS Log KD values ranged 0.52–1.62 L kg-1 for sediment and 1.91–2.90 L kg-1 for MWCNT present in the sediment. The latter values are relatively low, which is attributed to fouling of MWCNT by sediment organic matter. PFOS sorption was near-linear for sediment (Freundlich exponent of 0.92 ± 0.063) but non-linear for MWCNT (Freundlich exponent of 0.66 ± 0.03). Consequently, the impact of MWCNT on sorption in the mixture was larger at low PFOS aqueous concentration. Effects of pH and Ca2+ on PFOS sorption to MWCNT were statistically significant. We conclude that MWCNT fouling and PFOS concentration dependency are important factors affecting PFOS–MWCNT interactions in sediments.
    Physical gels based on charge-driven bridging of nanoparticles by triblock copolymers
    Lemmers, M. ; Spruijt, E. ; Akerboom, S. ; Voets, I.K. ; Aelst, A.C. van; Cohen Stuart, M.A. ; Gucht, J. van der - \ 2012
    Langmuir 28 (2012)33. - ISSN 0743-7463 - p. 12311 - 12318.
    dynamic light-scattering - shear-induced gelation - nanocomposite hydrogels - formulation process - colloidal silica - aqueous-solution - reversible gels - micelles - macromolecules - adsorption
    We have prepared an aqueous physical gel consisting of negatively charged silica nanoparticles bridged by ABA triblock copolymers, in which the A blocks are positively charged and the B block is neutral and water-soluble. Irreversible aggregation of the silica nanoparticles was prevented by precoating them with a neutral hydrophilic polymer. Both the elastic plateau modulus and the relaxation time increase slowly as the gel ages, indicating an increase both in the number of active bridges and in the strength with which the end blocks are adsorbed. The rate of this aging process can be increased significantly by applying a small shear stress to the sample. Our results indicate that charge-driven bridging of nanoparticles by triblock copolymers is a promising strategy for thickening of aqueous particle containing materials, such as water-based coatings.
    Influence of lysozyme complexation with purified Aldrich humic acid on lysozyme activity
    Li, Y. ; Tan, W.F. ; Wang, M.X. ; Liu, F. ; Weng, L.P. ; Norde, W. ; Koopal, L.K. - \ 2012
    European Journal of Soil Science 63 (2012)5. - ISSN 1351-0754 - p. 550 - 557.
    streaming current detector - nica-donnan model - cationic polyelectrolytes - charge determination - substances - soil - stability - adsorption - titration - binding
    Humic acid is an important component of dissolved organic matter and in two previous papers it has been shown that purified Aldrich humic acid (PAHA) forms strong complexes with the oppositely charged protein lysozyme (LSZ). The complexation and aggregation of enzymes with humic acids may lead to changes in their activity. Therefore, the enzyme activity of LSZ in the PAHA – LSZ complex as a function of mass ratio PAHA:LSZ was investigated at two pH values (pH 5 and pH 8 where PAHA and LSZ are oppositely charged) and two ionic strengths (5 mmol l-1; 50 mmol l-1). The newly prepared complex was characterized and the mass ratios PAHA:LSZ at the isoelectric point (IEP) of the complex at the assayed conditions were obtained with the Mütek particle charge detector. The LSZ activity was measured with an assay specific for LSZ. The activity of LSZ decreased upon complex formation with PAHA and the PAHA effect on the enzyme activity was increased by the subsequent aggregation. A critical PAHA:LSZ mass ratio for the behaviour of the enzyme activity was that at the IEP of the complex. Before this mass ratio was reached the LSZ activity strongly decreased under all conditions. Beyond this mass ratio both pH and ionic strength affected the activity of LSZ in the complex. The results can be explained by the effects that pH and ionic strength have on (i) the electrostatic attraction between LSZ and PAHA in the complex and (ii) the electrostatic repulsion between the complexes. These two factors plus the hydrophobic attraction determine the structure of the complexes and the size of the aggregates and hence the screening of the active site of the protein.
    Sorption of tetracycline on organo-montmorillonites
    Liu, N. ; Wang, M.X. ; Liu, M.M. ; Liu, F. ; Weng, L.P. ; Koopal, L.K. ; Tan, W.F. - \ 2012
    Journal of Hazardous Materials 225-226 (2012). - ISSN 0304-3894 - p. 28 - 35.
    oxytetracycline - adsorption - cations - soils - clay - pharmaceuticals - metronidazole - olaquindox - mobility - surfaces
    Tetracycline (TC) is a veterinary antibiotic that is frequently detected as pollutant in the environment. Powerful adsorbents are required for removing TC. The present paper compares the TC adsorption capacity of Na-montmorillonite (Na-mont) with six organo-montmorillonites (organo-monts). Three quaternary ammonium cations (QACs) with different alkyl-chain lengths were used as modifiers. Powder X-ray diffraction indicated that the d(001) values of organo-monts increased with increasing the QACs loading and alkyl-chain length. The CECs of the organo-monts were substantially lower than that of Na-mont and decreased with QACs chain length and increased loading. The modeling of the adsorption kinetics revealed that the processes of TC adsorption on the tested samples could be well fitted by the pseudo-second-order equation. The maximum adsorption capacities of TC on the organo-monts (1000-2000 mmol/kg) were considerably higher than that on Na-mont (769 mmol/kg). Both the Langmuir and Freundlich model could fit the adsorption isotherms. The TC adsorption to the organo-monts increase significantly with decreasing the pH below 5.5 because of the electrostatic interaction, and a high QACs loading performed better than a low loading at around pH 3.
    Role of surfactants on the approaching velocity of two small emulsion drops
    Danov, K.D. ; Stoyanov, S.D. ; Vitanov, N.K. ; Ivanov, I.B. - \ 2012
    Journal of Colloid and Interface Science 368 (2012). - ISSN 0021-9797 - p. 342 - 355.
    thin liquid-films - colliding small bubbles - spherical drops - ionic surfactants - viscous-fluid - slow motion - soluble surfactants - lubrication force - oleyl alcohol - adsorption
    Here we present the exact solution of two approaching spherical droplets problem, at small Reynolds and Peclet numbers, taking into account surface shear and dilatational viscosities, Gibbs elasticity, surface and bulk diffusivities due to the presence of surfactant in both disperse and continuous phases. For large interparticle distances, the drag force coefficient, f, increases only about 50% from fully mobile to tangentially immobile interfaces, while at small distances, f can differ several orders of magnitude. There is significant influence of the degree of surface coverage, 0, on hydrodynamic resistance beta for insoluble surfactant monolayers. When the surfactant is soluble only in the continuous phase the bulk diffusion suppresses the Marangoni effect only for very low values of 0, while in reverse situation, the bulk diffusion from the drop phase is more efficient and the hydrodynamic resistance is lower. Surfactants with low value of the critical micelle concentration (CMC) make the interfaces tangentially immobile, while large CMC surfactants cannot suppress interfacial mobility, which lowers the hydrodynamic resistance between drops. For micron-sized droplets the interfacial viscosities practically block the surface mobility and they approach each other as solid spheres with high values of the drag coefficient.
    Simultaneous analysis of small organic acids and humic acids using high performance size exclusion chromatography
    Qin, X.P. ; Liu, F. ; Wang, G.C. ; Weng, L.P. - \ 2012
    Journal of Separation Science 35 (2012)24. - ISSN 1615-9306 - p. 3455 - 3460.
    spectroscopic properties - molecular-weight - iron-oxide - adsorption - substances - goethite - matter - water - polydispersity - complexation
    An accurate and fast method for simultaneous determination of small organic acids and much larger humic acids was developed using high performance size exclusion chromatography. Two small organic acids, i.e. salicylic acid and 2,3-dihydroxybenzoic acid, and one purified humic acid material were used in this study. Under the experimental conditions, the UV peaks of salicylic acid and 2,3-dihydroxybenzoic acid were well separated from the peaks of humic acid in the chromatogram. Concentrations of the two small organic acids could be accurately determined from their peak areas. The concentration of humic acid in the mixture could then be derived from mass balance calculations. The measured results agreed well with the nominal concentrations. The detection limits are 0.05 mg/L and 0.01 mg/L for salicylic acid and 2,3-dihydroxybenzoic acid, respectively. Applicability of the method to natural samples was tested using groundwater, glacier, and river water samples (both original and spiked with salicylic acid and 2,3-dihydroxybenzoic acid) with a total organic carbon concentration ranging from 2.1 to 179.5 mg C/L. The results obtained are promising, especially for groundwater samples and river water samples with a total organic carbon concentration below 9 mg C/L.
    Interfacial layers from the protein HFBII hydrophobin: Dynamic surface tension, dilatational elasticity and relaxation times
    Alexandrov, N.A. ; Marinova, K.G. ; Gurkov, T.D. ; Danov, K.D. ; Kralchevsky, P.A. ; Stoyanov, S.D. ; Blijdenstein, T.B.J. ; Arnaudov, L.N. ; Pelan, E.G. ; Lips, A. - \ 2012
    Journal of Colloid and Interface Science 376 (2012). - ISSN 0021-9797 - p. 296 - 306.
    class-ii hydrophobins - air-water-interface - trichoderma-reesei - structural-analysis - crystal-structures - curved interfaces - latex-particles - beta-casein - adsorption - rheology
    The pendant-drop method (with drop-shape analysis) and Langmuir trough are applied to investigate the characteristic relaxation times and elasticity of interfacial layers from the protein HFBII hydrophobin. Such layers undergo a transition from fluid to elastic solid films. The transition is detected as an increase in the error of the fit of the pendant-drop profile by means of the Laplace equation of capillarity. The relaxation of surface tension after interfacial expansion follows an exponential-decay law, which indicates adsorption kinetics under barrier control. The experimental data for the relaxation time suggest that the adsorption rate is determined by the balance of two opposing factors: (i) the barrier to detachment of protein molecules from bulk aggregates and (ii) the attraction of the detached molecules by the adsorption layer due to the hydrophobic surface force. The hydrophobic attraction can explain why a greater surface coverage leads to a faster adsorption. The relaxation of surface tension after interfacial compression follows a different, square-root law. Such behavior can be attributed to surface diffusion of adsorbed protein molecules that are condensing at the periphery of interfacial protein aggregates. The surface dilatational elasticity, E, is determined in experiments on quick expansion or compression of the interfacial protein layers. At lower surface pressures (
    Exploiting the spontaneous potential of the electrodes used in the capacitive mixing technique for the extraction of energy from salinity difference
    Brogioli, D. ; Ziano, R. ; Rica, R.A. ; Salerno, D. ; Kozynchenko, O. ; Hamelers, H.V.M. ; Mantegazza, F. - \ 2012
    Energy & Environmental Science 5 (2012)12. - ISSN 1754-5692 - p. 9870 - 9880.
    gradient power - water - desalination - adsorption - battery - supercapacitor - performance - storage - salt
    The "capacitive mixing" (CAPMIX) technique is aimed at the extraction of energy from the salinity difference between the sea and rivers. It is based on the voltage rise that takes place at the electrodes when changing the salt concentration of the solution in which the two electrodes are dipped. In this paper, we focus on activated carbon electrodes, produced with various methods and treatments, and we measure their behaviour in CAPMIX experiments. We find that they behave as polarizable electrodes only on time scales of the order of minutes, while on longer time scales they tend to move to a specific "spontaneous" potential, likely due to chemical redox reactions. This analysis sheds light on the charge leakage, i.e. the loss of the stored charge due to undesired chemical reactions, which is one of the main hurdles of the CAPMIX technique when performed with activated carbon electrodes. We show that the leakage finds its origin in the tendency of the electrode to move to its spontaneous potential. Our investigation allows us to completely get rid of the leakage and demonstrates the striking result that CAPMIX cycles can be performed without an external power supply.
    Fabrication of Environmentally Biodegradable Lignin Nanoparticles
    Frangville, C. ; Rutkevicius, M. ; Richter, A.P. ; Velev, O.D. ; Stoyanov, S.D. ; Paunov, V.N. - \ 2012
    ChemPhysChem 13 (2012)18. - ISSN 1439-4235 - p. 4235 - 4243.
    ultrafine titanium-dioxide - tio2 nanoparticles - epithelial-cells - in-vitro - polymers - particles - silver - ions - fibroblasts - adsorption
    We developed a method for the fabrication of novel biodegradable nanoparticles (NPs) from lignin which are apparently non-toxic for microalgae and yeast. We compare two alternative methods for the synthesis of lignin NPs which result in particles of very different stability upon change of pH. The first method is based on precipitation of low-sulfonated lignin from an ethylene glycol solution by using diluted acidic aqueous solutions, which yields lignin NPs that are stable over a wide range of pH. The second approach is based on the acidic precipitation of lignin from a high-pH aqueous solution which produces NPs stable only at low pH. Our study reveals that lignin NPs from the ethylene glycol-based precipitation contain densely packed lignin domains which explain the stability of the NPs even at high pH. We characterised the properties of the produced lignin NPs and determined their loading capacities with hydrophilic actives. The results suggest that these NPs are highly porous and consist of smaller lignin domains. Tests with microalgae like Chlamydomonas reinhardtii and yeast incubated in lignin NP dispersions indicated that these NPs lack measurable effect on the viability of these microorganisms. Such biodegradable and environmentally compatible NPs can find applications as drug delivery vehicles, stabilisers of cosmetic and pharmaceutical formulations, or in other areas where they may replace more expensive and potentially toxic nanomaterials.
    An overview of fertilizer-P recommendations in Europe: soil testing, calibration and fertilizer recommendations
    Jordan-Meille, L. ; Rubaek, G.H. ; Ehlert, P.A.I. ; Genot, V. ; Hofman, G. ; Goulding, K. ; Recknagel, J. ; Provolo, G. ; Barraclough, P. - \ 2012
    Soil Use and Management 28 (2012)4. - ISSN 0266-0032 - p. 419 - 435.
    available phosphorus - i test - phosphate - eutrophication - adsorption - management - hungary - systems - crops - olsen
    The procedure for applying phosphorus (P) fertilizer to soil can be divided into three consecutive steps: (i) Measurement of soil-P availability, (ii) calibration of the soil-P fertility level and (iii) estimation of the recommended P dose. Information on each of these steps was obtained for 18 European countries and regions with the aim of comparing P fertilizer recommendation systems at the European scale. We collected information on P fertilizer recommendations through conventional or grey literature, and personal contacts with researchers, laboratories and advisory services. We found much variation between countries for each of the three steps: There are more than 10 soil-P tests currently in use, apparent contradictions in the interpretation of soil-P test values and more than 3-fold differences in the P fertilizer recommendations for similar soil-crop situations. This last result was confirmed by conducting a simple experimental inter-laboratory comparison. Moreover, soil properties (pH, clay content) and crop species characteristics (P responsiveness) are used in some countries in the calibration and recommendation steps, but in different ways. However, there are also common characteristics: soil-P availability is determined in all countries by extraction with chemical reagents and the calibration of the soil-P test values, and the fertilizer recommendations are based on the results from empirical field trials. Moreover, the fertilizer recommendations are nearly all based on the amount of P exported in the crops. As long as rational scientific and theoretical backgrounds are lacking, there is no point in trying to synchronize the different chemical methods used. We therefore call for a mechanistic approach in which the processes involved in plant P nutrition are truly reproduced by a single standard method or simulated by sorption-desorption models.
    Enzymatic Modification of Polyethersulfone Membranes
    Nady, N. ; Franssen, M.C.R. ; Zuilhof, H. ; Boom, R.M. ; Schroën, C.G.P.H. - \ 2012
    Water 4 (2012)4. - ISSN 2073-4441 - p. 932 - 943.
    catalyzed modification - surfaces - adsorption - acid
    Enzymatic modification of polyethersulfone (PES) membranes has been found not only feasible, but also an environmentally attractive way to vary surface properties systematically. In this paper, we summarize the effect of modification layers on protein adsorption and bacterial adhesion on PES membranes and surfaces. The enzyme laccase was used to covalently bind (poly)phenolic acids to the membrane, and compared to other membrane modification methods, this method is very mild and did not influence the mechanical strength negatively. Depending on the conditions used during modification, the modification layers were capable of influencing interactions with typical fouling species, such as protein, and to influence attachment of microorganisms. We also show that the modification method can be successfully applied to hollow fiber membranes; and depending on the pore size of the base membrane, proteins were partially rejected by the membrane. In conclusion, we have shown that enzymatic membrane modification is a versatile and economically attractive method that can be used to influence various interactions that normally lead to surface contamination, pore blocking, and considerable flux loss in membranes.
    Bioconjugation of Protein-Repellent Zwitterionic Polymer Brushes Grafted from Silicone Nitride
    Nguyen, A.T. ; Baggerman, J. ; Paulusse, J.M.J. ; Zuilhof, H. ; Rijn, C.J.M. van - \ 2012
    Langmuir 28 (2012)1. - ISSN 0743-7463 - p. 604 - 610.
    biosensor applications - poly(ethylene glycol) - antibody microarrays - surface - adsorption - well - membranes - plasma - immobilization - strategies
    A new method for attaching antibodies to protein-repellent zwitterionic polymer brushes aimed at recognizing microorganisms while preventing the nonspecific adsorption of proteins is presented. The poly(sulfobetaine methacrylate) (SBMA) brushes were grafted from a-bromo isobutyryl initiator-functionalized silicon nitride (SixN4, x = 3) surfaces via controlled atom-transfer radical polymerization (ATRP). A trifunctional tris(2-aminoethyl)amine linker was reacted with the terminal alkylbromide of polySBMA chains. N-Hydroxysuccinimide (NHS) functionalization was achieved by reacting the resultant amine-terminated polySBMA brush with bifunctional suberic acid bis(N-hydroxysuccinimide ester). Anti-Salmonella antibodies were subsequently immobilized onto polySBMA-grafted SixN4 surfaces through these NHS linkers. The protein-repellent properties of the polySBMA-grafted surface after antibody attachment were evaluated by exposing the surfaces to Alexa Fluor 488-labeled fibrinogen (FIB) solution (0.1 g·L–1) for 1 h at room temperature. Confocal laser scanning microscopy (CLSM) images revealed the minimal adsorption of FIB onto the antibody-coated polySBMA in comparison with that of antibody-coated epoxide monolayers and also bare SixN4 surfaces. Subsequently, the interaction of antibodies immobilized onto polySBMA with SYTO9-stained Salmonella solution without using blocking solution was examined by CLSM. The fluorescent images showed that antibody-coated polySBMA efficiently captured Salmonella with only low background noise as compared to antibody-coated monolayers lacking the polymer brush. Finally, the antibody-coated polySBMA surfaces were exposed to a mixture of Alexa Fluor 647-labeled FIB and Salmonella without the prior use of a blocking solution to evaluate the ability of the surfaces to capture bacteria while simultaneously repelling proteins. The fluorescent images showed the capture of Salmonella with no adsorption of FIB as compared to antibody-coated epoxide surfaces, demonstrating the potential of the zwitterionic layer in preventing the nonspecific adsorption of the proteins during the detection of bacteria in complex matrices.
    Influence of buffer composition on the distribution of inkjet printed protein molecules and the resulting spot morphology
    Mujawar, L.H. ; Amerongen, A. van; Norde, W. - \ 2012
    Talanta 98 (2012). - ISSN 0039-9140 - p. 1 - 6.
    bovine serum-albumin - antibody microarrays - surfaces - performance - adsorption
    Producing high quality protein microarrays on inexpensive substrates like polystyrene is a big challenge in the field of diagnostics. Using a non-contact inkjet printer we have produced microarrays on polystyrene slides for two different biotinylated biomolecules, bovine serum albumin (BSA–biotin) and immunoglobulin-G (IgG–biotin), and studied the influence of buffer (composition and pH) on the spot morphology and signal intensity. Atomic force microscopy revealed the morphological pattern of the (biomolecule) spots printed from phosphate buffer (pH 7.4), phosphate buffered saline (pH 7.4) and carbonate buffer (pH 9.6). The spots showed an irregular crust-like appearance when printed in phosphate buffered saline (pH 7.4), mainly due to the high NaCl content, whereas spots of biomolecules printed in carbonate buffer (pH 9.6) showed a smooth morphology. In addition, the rinsing of these dried spots led to the loss of a considerable fraction of the biomolecules, leaving behind a small fraction that is compatible with the (mono)layer. It was confirmed by confocal laser microscopy that the quality of the spots with respect to the uniformity and distribution of the biomolecules therein was superior when printed in carbonate buffer (pH 9.6) as compared to other buffer systems. Particularly, spotting in PBS yielded spots having a very irregular distribution and morphology.
    Interfacial behaviour of proteins, with special reference to immunoglobulins. A physicochemical study
    Norde, W. ; Lyklema, J. - \ 2012
    Advances in Colloid and Interface Science 179-182 (2012). - ISSN 0001-8686 - p. 5 - 13.
    bovine pancreas ribonuclease - ultrafine silica particles - solid-liquid interfaces - human-plasma albumin - circular-dichroism - oriented immobilization - conformational-changes - polystyrene surfaces - adsorption - model
    Some basic elements of the adsorption of proteins on solid surfaces are briefly reviewed, emphasizing immunoglobulins. The paper focuses on the physicochemical interactions and considers the precautions that have to be taken to let the protein adsorb in a way in which it is biologically active. Contributing factors include surface pretreatment, composition of the solution, (pH, nature and concentration of electrolytes, etc.), extent of reversibility, and lateral interactions in the adsorbed state. Particular attention is paid to the option of partially pre-coating the adsorbent by irreversibly adsorbed polymers to induce the later adsorbing immune globulin molecules to assume a biologically preferred orientation and conformation.
    Hybrid Monte Carlo self-consistent field approach to model a thin layer of a polyelectrolyte gel near an adsorbing surface
    Leermakers, F.A.M. ; Bergsma, J. ; Gucht, J. van der - \ 2012
    The Journal of Physical Chemistry Part A: Molecules, Spectroscopy, Kinetics, Environment, & General Theory 116 (2012)25. - ISSN 1089-5639 - p. 6574 - 6581.
    adsorption - polymers - optimization - interface - volume - ions
    The use of thin layers of a surface bound (polyelectrolyte) hydrogels for measuring the concentration of metal ions from electrolyte solutions is our motivation for modeling such hydrogels. The gels are composed of polymeric species with conformational degrees of freedom on the nanometer scale. The polymer conformations are affected by the presence of cross-links in the gel on a five to ten times larger length scale, and the repulsive interactions generated by the charges along the chains. Here we present a hybrid computational Monte Carlo Self-consistent field (MC-SCF) approach to model such hydrogels. The SCF formalism is used to evaluate the conformational properties of the chains, implementing a freely jointed chain model, in between featureless cross-links. The Monte Carlo simulation method is used to sample the (restricted) translational degrees of freedom of the cross-links in the gel. We consider the case that the polymers in the gel have an affinity for surface positioned at the edge of the simulation volume. The polymer density decays as a power-law from the surface to the gel-density with an exponent close to -4/3. The gel features relatively large density fluctuations which is natural for a gel with a low density (f ˜ 0.035), a low degree of cross-linking (average of three chainparts per cross-link), and relatively large chains (N = 50) in between the cross-links. Some parts of the gel can break loose from the gel and sample the adjoining volume. Representative snapshots exemplify large density fluctuations, which explain the large pore size distribution observed in experimental counterparts.
    Polymer compatibility in two dimensions. Modeling of phase behavior of mixed polymethacrylate Langmuir films
    Bernardini, C. ; Cohen Stuart, M.A. ; Stoyanov, S.D. ; Arnaudov, L.N. ; Leermakers, F.A.M. - \ 2012
    Langmuir 28 (2012)13. - ISSN 0743-7463 - p. 5614 - 5621.
    field optical microscopy - interacting chain molecules - block-copolymer - statistical-theory - hybrid lipids - separation - monolayer - surface - adsorption - size
    We analyze the possibility of polymer blends undergoing phase separation in two dimensions. To this end, we investigate a model system consisting of water-supported Langmuir monolayers, obtained from binary polyalkyl-methacrylate mixtures (PXMA, where X stands for any of the type of ester side groups used: M, methyl-; E, ethyl-; B, butyl-; H, hexyl-; O, octyl-; L, lauryl-methacrylate), by means of self consistent field (SCF) calculations. In particular, we address the conditions which determine demixing and phase separation in the two-dimensional system, showing that a sufficient chain length mismatch in the ester side group moieties is able to drive the polymer demixing. When the difference in length of the alkyl chain of the ester moieties on the two types of polymers is progressively reduced, from 11 carbon atoms (PMMA/PLMA) to 4 carbons only (POMA/PLMA), the demixing tendency is also reduced. The polymer/subphase interactions affect more the distribution of the polymer coils in the POMA/PLMA blend monolayer. Mixing of the two polymers is observed, but also a partial layering along the vertical direction. We also add, to a PMMA/PLMA blended monolayer, a third component, namely, a symmetrical diblock copolymer of the type PLMA-b-PMMA. We observe adsorption of the diblock copolymer exclusively at the contact line between the two homopolymer domains, and a concomitant lowering of the line tension. The line tension varies with the chemical potential of the diblock copolymer according to Gibbs’ law, which demonstrates that PLMA-b-PMMA can act as a “lineactant” (the equivalent of a surfactant in two-dimensional systems) in the binary demixed PMMA/PLMA Langmuir monolayer.
    A self-consistent field study of a hydrocarbon droplet at the air-water interface
    Hilz, E. ; Leermakers, F.A.M. ; Vermeer, A.W.P. - \ 2012
    Physical Chemistry Chemical Physics 14 (2012)14. - ISSN 1463-9076 - p. 4917 - 4926.
    liquid-vapor interface - molecular-dynamics simulations - block-copolymer micelles - line tension - computer-simulation - surface-tension - curvature corrections - nonionic surfactants - lattice theory - adsorption
    A molecularly detailed self-consistent field (SCF) approach is applied to describe a sessile hydrocarbon droplet placed at the air–water interface. Predictions of the contact angle for macroscopic droplets follow from using Neumann's equation, wherein the macroscopic interfacial tensions are computed from one-gradient calculations for flat interfaces. A two-gradient cylindrical coordinate system with mirror-like boundary conditions is used to analyse the three dimensional shape of the nano-scale oil droplet at the air–water interface. These small droplets have a finite value of the Laplace pressure and concomitant line tension. It has been calculated that the oil–water and oil–vapour interfacial tensions are curvature dependent and increase slightly with increasing interfacial curvature. In contrast, the line tension tends to decrease with curvature. In all cases there is only a weak influence of the line tension on the droplet shape. We therefore argue that the nano-scale droplets, which are described in the SCF approach, are representative for macroscopic droplets and that the method can be used to efficiently generate accurate information on the spreading of oil droplets at the air–water interface in molecularly more complex situations. As an example, non-ionic surfactants have been included in the system to illustrate how a molecularly more complex situation will change the wetting properties of the sessile drop. This short forecast is aimed to outline and to stress the potential of the method.
    The oxidative esterification of glycerol to methyl glycerate in methanol using gold on oxidic supports: an insight in product selectivity
    Pazhavelikkakath Purushothaman, R.K. ; Haveren, J. van; Es, D.S. van; Heeres, H.J. - \ 2012
    Green Chemistry 14 (2012). - ISSN 1463-9262 - p. 2031 - 2037.
    aqueous-phase oxidation - bimetallic catalysts - commodity chemicals - carbon-monoxide - au catalysts - lactic-acid - derivatives - adsorption - conversion - kinetics
    Gold nanoparticles on different oxidic supports (TiO2, Al2O3 and ZnO) have been studied for the oxidation of glycerol in methanol, using molecular oxygen as the oxidizing agent in a batch set-up. The main oxidation products are methyl glycerate and dimethyl mesoxalate in over 95% selectivity at high glycerol conversion, indicating that C–C bond scission occurs at a significantly lower extent compared to glycerol oxidations in water. The product selectivity is a function of the support. Highest selectivity (82% at 72% conversion) to methyl glycerate is observed in the case of Au/TiO2 as the catalyst. The use of a base is not essential for the glycerol oxidation reaction to occur, although for TiO2 and Al2O3 higher initial activities are found in the presence of sodium methoxide. Au/ZnO gives comparable activity and selectivity both in the presence and absence of a base. Oxidation experiments with reaction intermediates indicate that oxidation of methyl glycerate to higher oxygenates does not occur to a significant extent in methanol. An alternative pathway for the formation of dimethyl mesoxalate involving dihydroxyacetone is proposed.
    Water Desalination Using Capacitive Deionization with Microporous Carbon Electrodes
    Porada, S. ; Weinstein, L. ; Dash, R. ; Wal, A.F. van der; Bryjak, M. ; Gogotsi, Y. ; Biesheuvel, P.M. - \ 2012
    ACS Applied Materials and Interfaces 4 (2012)3. - ISSN 1944-8244 - p. 1194 - 1199.
    carbide-derived carbon - activated carbon - brackish-water - seawater desalination - aerogel electrodes - charge efficiency - aqueous-solutions - electrosorption - technology - adsorption
    Capacitive deionization (CDI) is a water desalination technology in which salt ions are removed from brackish water by flowing through a spacer channel with porous electrodes on each side. Upon applying a voltage difference between the two electrodes, cations move to and are accumulated in electrostatic double layers inside the negatively charged cathode and the anions are removed by the positively charged anode. One of the key parameters for commercial realization of CDI is the salt adsorption capacity of the electrodes. State-of-the-art electrode materials are based on porous activated carbon particles or carbon aerogels. Here we report the use for CDI of carbide-derived carbon (CDC), a porous material with well-defined and tunable pore sizes in the sub-nanometer range. When comparing electrodes made with CDC with electrodes based on activated carbon, we find a significantly higher salt adsorption capacity in the relevant cell voltage window of 1.2–1.4 V. The measured adsorption capacity for four materials tested negatively correlates with known metrics for pore structure of the carbon powders such as total pore volume and BET-area, but is positively correlated with the volume of pores of sizes
    Multi-dimensional fractionation and characterization of crude protein mixtures: Toward establishment of a database of protein purification process development parameters
    Ahamed, T. ; Pinkse, M.W.H. ; Wielen, L.A.M. van der; Verhaert, P. ; Dedem, G. ; Eppink, M.H.M. ; Sandt, E. van de; Ottens, M. - \ 2012
    Biotechnology and Bioengineering 109 (2012)12. - ISSN 0006-3592 - p. 3070 - 3083.
    ion-exchange chromatography - expert-systems - separations - adsorption - optimization - displacers - selection - design
    A multi-dimensional fractionation and characterization scheme was developed for fast acquisition of the relevant molecular properties for protein separation from crude biological feedstocks by ion-exchange chromatography (IEX), hydrophobic interaction chromatography (HIC) and size-exclusion chromatography (SEC). In this approach, the linear IEX isotherm parameters were estimated from multiple linear salt-gradient IEX data, while. the nonlinear IEX parameters as well as the HIC isotherm parameters were obtained by the inverse method under column overloading conditions. Collected chromatographic fractions were analyzed by gel electrophoresis for estimation of molecular mass, followed by mass spectrometry for protein identification. The usefulness of the generated molecular properties data for rational decision-making during downstream process development was equally demonstrated. Monoclonal antibody (mAb) purification from crude hybridoma cell culture supernatant (HCCS) was used as case study. The obtained chromatographic parameters only apply to the employed stationary phases and operating conditions, hence prior HTS of different chromatographic resins and mobile phase conditions is still a prerequisite. Nevertheless, it provides a quick, knowledge-based approach for rationally synthesizing purification cascades prior to more detailed process optimization and evaluation.
    Manual of PEARLNEQ v5
    Boesten, J.J.T.I. ; Horst, M.M.S. ter - \ 2012
    Wageningen : Wettelijke Onderzoekstaken Natuur & Milieu (WOt-werkdocument 304)
    bodemchemie - pesticiden - adsorptie - degradatie - modellen - soil chemistry - pesticides - adsorption - degradation - models
    This manual describes the PEARLNEQ v5 software package . This package can estimate long-term sorption parameters using results of aged-sorption studies with soil, using a submodel for sorption and transformation that is identical to the submodel used for that purpose in the FOCUS_PEARL v3.3.3. The submodel assumes two types of sorption sites: equilibrium sites and non-equilibrium sites. The sorption isotherms for both sites are described with Freundlich equations. The mathematical equations describing the submodel are solved via a FORTRAN programme. An additional FORTRAN programme generates the necessary input files for the PEST optimisation package. Instructions are given how to obtain optimized parameters using an example dataset and how to obtain parameters using your own data.
    Performance of hemicellulolytic enzymes in culture supernatants from a wide range of fungi on insoluble wheat straw and corn fiber fractions
    Gool, M.P. van; Toth, K. ; Schols, H.A. ; Szakacs, G. ; Gruppen, H. - \ 2012
    Bioresource Technology 114 (2012). - ISSN 0960-8524 - p. 523 - 528.
    xylan-degrading enzymes - enzymatic-hydrolysis - aspergillus-awamori - pretreatment - cellulose - arabinoxylans - fermentation - degradation - adsorption - substrate
    Filamentous fungi are a good source of hemicellulolytic enzymes for biomass degradation. Enzyme preparations were obtained as culture supernatants from 78 fungal isolates grown on wheat straw as carbon source. These enzyme preparations were utilized in the hydrolysis of insoluble wheat straw and corn fiber xylan rich fractions. Up to 14% of the carbohydrates in wheat straw and 34% of those in corn fiber were hydrolyzed. The degree of hydrolysis by the enzymes depended on the origin of the fungal isolate and on the complexity of the substrate to be degraded. Penicillium, Trichoderma or Aspergillus species, and some non-identified fungi proved to be the best producers of hemicellulolytic enzymes for degradation of xylan rich materials. This study proves that the choice for an enzyme preparation to efficiently degrade a natural xylan rich substrate, is dependent on the xylan characteristics and could not be estimated by using model substrates.
    Laccase-catalyzed modification of PES membranes with 4-hydroxybenzoic acid and gallic acid
    Nady, N. ; Schroën, C.G.P.H. ; Franssen, M.C.R. ; Mohy Eldin, M.S. ; Zuilhof, H. ; Boom, R.M. - \ 2012
    Journal of Membrane Science 394-395 (2012)March. - ISSN 0376-7388 - p. 69 - 79.
    ultrafiltration membranes - surface modification - fungal laccases - green chemistry - water - ph - purification - adsorption - copolymers - conversion
    We here report on the performance of poly(ethersulfone) membranes modified with 4-hydroxybenzoic acid and gallic acid as substrates, and using laccase as biocatalyst under several modification conditions. The average flux of the base membrane was never reduced more than 20% (mostly below 10% reduction) by modification with 4-hydroxybenzoic acid, and not more than 9% for gallic acid. The mechanical and thermal properties of the membrane were not adversely affected by the modification method. For 4-hydroxybenzoic acid, longer modification times (i.e., hours) and higher substrate concentrations lead to modified membranes with a better protein repellence. The reaction with gallic acid is faster, but less effective in terms of the resulting protein repellence. In conclusion, the laccase-catalyzed modification of poly(ethersulfone) membranes is a mild method with low environmental impact that leads to effective protein repellence while keeping the bulk properties of the base membrane intact. This makes laccase-catalyzed modification an interesting alternative for currently used membrane modification methods.
    Analysis of the contribution of sedimentation to bacterial mass transport in a parallel plate flow chamber Part II: Use of fluorescence imaging
    Li, J.Y. ; Busscher, H.J. ; Mei, H.C. van der; Norde, W. ; Krom, B.P. ; Sjollema, J. - \ 2011
    Colloids and Surfaces. B: Biointerfaces 87 (2011)2. - ISSN 0927-7765 - p. 427 - 432.
    deposition - adhesion - adsorption - biofilms - kinetics - gene
    Using a new phase-contrast microscopy-based method of analysis, sedimentation has recently been demonstrated to be the major mass transport mechanism of bacteria towards substratum surfaces in a parallel plate flow chamber (J. Li, H.J. Busscher, W. Norde, J. Sjollema, Colloid Surf. B. 84 (2011)76). Here we describe a novel method for enumerating adhesion of fluorescent bacteria in a parallel plate flow chamber that allows direct imaging of the bacterial distribution along the length of the flow chamber, as caused by sedimentation. Imaging of fluorescence was done using macroscopic bio-optical imaging of the entire flow chamber, including top and bottom plates as well as of the flowing suspension in between. An algorithm is forwarded that allows to separate the fluorescence arising from the suspension and bottom plate and at the same time determines the single cell fluorescence from which the bacterial distribution over the entire bottom plate can be visualized. Enumeration of the numbers of bacteria adhering to the center of the glass bottom plate for a fluorescent Staphylococcus aureus strain was found to coincide with enumerations using phase-contrast microscopy. Moreover, due to the use of macroscopic bio-optical imaging, it was found that the number of adhering staphylococci increases linearly with distance from the inlet of the flow chamber, which could be explained from a simplified mass balance of convection, sedimentation and blocking near the bottom plate of the flow chamber.
    Depletion profiles for dilute solutions of linear chains, stars and H-branched molecules by self-consistent field calculations and Monte Carlo simulations
    Preisler, Z. ; Kosovan, P. ; Kuldova, J. ; Uhlik, F. ; Limpouchova, Z. ; Prochazka, K. ; Leermakers, F.A.M. - \ 2011
    Soft Matter 7 (2011)21. - ISSN 1744-683X - p. 10258 - 10265.
    polymer-chains - adsorption
    We have performed self-consistent field (SCF) calculations and Monte Carlo (MC) simulations to analyse the depletion profiles for isolated linear, star-like and H-shaped polymers in good solvent using lattice approximations in both methods. In the SCF approach the intra-molecular excluded-volume effects are accounted for using an approach that resembles Flory's method that leads to the Flory size of the chains. This gives a major improvement over the classical tanh profile, and becomes much closer to the MC results, provided that a Kuhn length of 1.5 is implemented.
    Soil processes and functions in critical zone observatories: hypotheses and experimental design
    Banwart, S. ; Bernasconi, S.M. ; Bloem, J. ; Blum, W. ; Ruiter, P.C. de; Gaans, P. van; Riemsdijk, W.H. van - \ 2011
    Vadose Zone Journal 10 (2011)3. - ISSN 1539-1663 - p. 974 - 987.
    solid-solution interface - physical quality - organic-matter - water-quality - river-basin - adsorption - catchments - (hydr)oxides - ecosystems - deposition
    European Union policy on soil threats and soil protection has prioritized new research to address global soil threats. This research draws on the methodology of Critical Zone Observatories (CZOs) to focus a critical mass of international, multidisciplinary expertise at specific field sites. These CZOs were selected as part of an experimental design to study soil processes and ecosystem function along a hypothesized soil life cycle—from incipient soil formation where new parent material is being deposited, to highly degraded soils that have experienced millennia of intensive land use. Further CZOs have been selected to broaden the range of soil environments and data sets to test soil process models that represent the stages of the soil life cycle. The scientific methodology for this research focuses on the central role of soil structure and soil aggregate formation and stability in soil processes. Research methods include detailed analysis and mathematical modeling of soil properties related to aggregate formation and their relation to key processes of reactive transport, nutrient transformation, and C and food web dynamics in soil ecosystems. Within this program of research, quantification of soil processes across an international network of CZOs is focused on understanding soil ecosystem services including their quantitative monetary valuation within the soil life cycle. Further experimental design at the global scale is enabled by this type of international CZO network. One example is a proposed experiment to study soil ecosystem services along planetary-scale environmental gradients. This would allow scientists to gain insight into the responses of soil processes to increasing human pressures on Earth's critical zone that arise through rapidly changing land use and climate.
    Dynamic water vapour sorption in gluten and starch films
    Oliver, L. ; Meinders, M.B.J. - \ 2011
    Journal of Cereal Science 54 (2011)3. - ISSN 0733-5210 - p. 409 - 416.
    polymer-solvent systems - glass-transition - diffusion - adsorption - kinetics
    Water sorption of gluten and wheat starch films as a function of water activity was studied using gravimetric step-change sorption experiments. Films of different thicknesses were used with the aim to vary the characteristic diffusion time and to get insights in the contribution of the polymer-chain rearrangement in the sorption behaviour. It is shown that both starch and gluten are in the glassy state for a water activity aw below 0.9. From comparison of the dynamical sorption curves with a Fickian diffusion model, it is shown that water diffusion in gluten films seems Fickian for aw <0.7, and non-Fickian for aw > 0.7, while for starch films, non-Fickian sorption behaviour is observed for aw > 0.1. The results show that polymer-chain rearrangement and the stress built up in the matrix play an important role in the sorption dynamics of these films. Even when the material is in the glassy state matrix relaxation phenomena play a role in the sorption behaviour of starch and gluten.
    Low Temperature Drying With Air Dehumidified by Zeolite for Food Products: Energy Efficiency Aspect Analysis
    Djaeni, M. ; Asselt, C.J. van; Bartels, P.V. ; Sanders, J.P.M. ; Straten, G. van; Boxtel, A.J.B. van - \ 2011
    International Journal of Food Engineering 7 (2011)6. - ISSN 1556-3758
    water-vapor - adsorption - multistage - dryer - performance - simulation - flow
    Developments in low temperature drying of food products are still an interesting issue; especially with respect to the energy efficiency. This research studies the energy efficiency that can be achieved by a dryer using air which is dehumidified by zeolite. Experimental results are fitted to a dynamic model to find important variables for the drying operation. The results show that ambient air temperature as well as the ratio between air flow for drying and air flow for regeneration, affect the energy efficiency significantly. Relative humidity of used air, and shift time have a minor effect on the dryer performance. From the total work, it can be noted that the dryer efficiency operated at 50-60°C achieves 75 percent, which is attractive for drying of food products.
    Verwijdering van fosfaat uit bodemwater met ijzerzand : De omhulde drain
    Koopmans, G.F. ; Chardon, W.J. ; Belder, P. ; Groenenberg, B.J. - \ 2011
    H2O : tijdschrift voor watervoorziening en afvalwaterbehandeling 44 (2011)20. - ISSN 0166-8439 - p. 35 - 38.
    grondwaterkwaliteit - fosfaatuitspoeling - eutrofiëring - drainagewater - draineerbuizen - zand - ijzer - adsorptie - waterzuivering - ijzeroxiden - oppervlaktewaterkwaliteit - veldproeven - groundwater quality - phosphate leaching - eutrophication - drainage water - drain pipes - sand - iron - adsorption - water treatment - iron oxides - surface water quality - field tests
    In het Nederlandse oppervlaktewater zijn de fosfaatconcentraties vaak te hoog en vormt eutrofiëring een groot probleem. Fosfaatuitspoeling uit landbouwgronden draagt flink bij aan de totale fosfaatbelasting van het oppervlaktewater. Met brongerichte maatregelen, zoals evenwichtsbemesting, zal in sommige delen van het landelijk gebied de hoofddoelstelling van de Kaderrichtlijn Water niet worden gerealiseerd. Hiervoor zijn aanvullende maatregelen nodig, die kunnen bijdragen aan het verbeteren van de chemische waterkwaliteit. We hebben de effectiviteit getest van een drainagebuis omhuld met ijzerzand om fosfaatuitspoeling te verminderen. Deze veldproef is uitgevoerd op een duinzandgrond in het bloembollengebied. Het gemiddelde zuiveringsrendement van de omhulde drainagebuis bedraagt 94 procent. Het omhullen van drainagebuizen met ijzerzand lijkt een veelbelovende maatregel voor het verminderen van fosfaatuitspoeling
    Humic substance charge determination by titration with a flexible cationic polyelectrolyte
    Tan, W.F. ; Norde, W. ; Koopal, L.K. - \ 2011
    Geochimica et Cosmochimica Acta 75 (2011)19. - ISSN 0016-7037 - p. 5749 - 5761.
    natural organic-matter - streaming current detector - nica-donnan model - fulvic-acid - proton-binding - colloid titration - mineral particles - light-scattering - ion-binding - adsorption
    The anionic charge of humic substances (HS) plays a major role in the interaction of HS with other components. Therefore, the potential of the polyelectrolyte titration technique to obtain the charge density of HS in simple 1–1 electrolyte solutions has been investigated. Titrations are carried out with an automatic titrator combined with the “Mütek particle charge detector” which allows determination of the Mütek potential and the pH as a function of the added amount of titrant which is a solution of poly-diallyldimethylammonium chloride (polyDADMAC), a cationic strong polyelectrolyte. When the Mütek potential reverses its sign the iso-electric point (IEP) of the polyDADMAC–HS complex is reached. The polyDADMAC/HS mass ratio at the IEP gives information on the HS charge density and from the pH changes in solution an estimate of the charge regulation in the HS–polyDADMAC complex can be obtained. In general, for polyDADMAC–HS complexes an increase in the dissociation of the acid groups of HS is found (charge regulation). The charge regulation decreases with increasing concentration of 1–1 background electrolyte. Cation incorporation can be neglected at 1–1 electrolyte concentrations ¿ 1 mmol L-1 and a 1–1 stoichiometry exists between the polyDADMAC and HS charge. However, at these low salt concentrations the charge regulation is substantial. A detailed analysis of purified Aldrich humic acid (PAHA) at pH 5 and a range of KCl concentrations reveals that the anionic charge of PAHA in the complex increases at 5 mmol L-1 KCl by 30% and at 150 mmol L-1 KCl by 12%. On the other hand, increasing amounts of K+ become incorporated in the complex: at 5 mmol L-1 KCl 5% and at 150 mmol L-1 KCl 24% of the PAHA charge is balanced by K+. By comparing at pH 5 the mass ratios polyDADMAC/PAHA in the complex at the IEP with the theoretical mass ratios of polyDADMAC/PAHA required to neutralize PAHA in the absence of charge regulation and K+ incorporation, it is found that at 50 mmol L-1 KCl the extra negative charge due to the interaction between polyDADMAC and PAHA is just compensated by K+ incorporation in the complex. Therefore, a pseudo 1–1 stoichiometry exists at about 50 mmol L-1 1–1 electrolyte concentration and only at this salt concentration polyDADMAC titrations and conventional proton titrations give identical results. Most likely this is also true for other HA samples and other pH values. For FA further study is required to reveal the conditions for which polyDADMAC and proton titrations give identical results.
    Predictive model of cationic surfactant binding to humic substances
    Ishiguro, M. ; Koopal, L.K. - \ 2011
    Colloids and Surfaces. A: Physicochemical and Engineering Aspects 379 (2011)1-3. - ISSN 0927-7757 - p. 70 - 78.
    natural organic-matter - metal-ion binding - nica-donnan model - proton binding - adsorption - acids - water - polyelectrolytes - complexation - competition
    The humic substances (HS) have a high reactivity with other components in the natural environment. An important factor for the reactivity of HS is their negative charge. Cationic surfactants bind strongly to HS by electrostatic and specific interaction. Therefore, a surfactant binding model is developed that takes both the specific and electrostatic interactions explicitly into account. The model is analogous to that of ion binding to HS with the NICA-Donnan model, but competition for the binding sites is not taken into account and the NICA-Donnan model reduces to the Langmuir–Freundlich–Hill–Donnan (LFH-D) model. The parameters of the LFH equation are the maximum binding, the affinity constant and the non-ideality constant. The non-ideality parameter accounts for both the site heterogeneity and the cooperativity due to hydrophobic interaction between surfactant molecules. The affinity constant incorporates the specific (e.g., hydrophobic) interactions between surfactant and HS. The Donnan part of the model accounts in a simple way for the electrostatic interactions by assuming that for a given set of conditions there is only one electrostatic potential that governs the behavior in the Donnan phase. The separation between the specific interactions (LHF) and the electrostatic interactions (D) is based on the so-called master curve (MC) procedure in which the binding is replotted as a function of the “free” surfactant concentration in the Donnan phase. The MC depends only on the specific interactions. Once the MC is obtained it can be fitted to the LFH equation to obtain the model parameters. Subsequently, the surfactant isotherms can be calculated with the LFH-D model. The model is tested using previously obtained data on dodecyl pyridinium chloride (DPC) and cetyl pyridinium chloride (CPC) binding to some purified humic and fulvic acids at pH about 5. The LFH-D model is well suited to describe the surfactant binding to HAs from very low concentrations up to the iso-electric point (IEP). The affinity of DPC for the different HAs allows ranking of the HAs according to their hydrophobicity. Prediction of DPC binding at other pH values also leads to good results for HA. For FAs the model can only describe the surfactant binding up to an adsorbed amount of 0.5 mol/kg. For higher binding values the LFH-D model underestimates the binding.
    Comparison of various models to describe the charge-pH dependence of poly(acrylic acid)
    Lützenkirchen, J. ; Male, J. van; Leermakers, F.A.M. ; Sjöberg, S. - \ 2011
    Journal of Chemical and Engineering Data 56 (2011)4. - ISSN 0021-9568 - p. 1602 - 1612.
    ion-binding - electrolyte-solutions - monte-carlo - polyelectrolytes - adsorption - molecules - constants - titration - sodium - simulations
    The charge of poly(acrylic acid) (PAA) in dilute aqueous solutions depends on pH and ionic strength. We report new experimental data and test various models to describe the deprotonation of PAA in three different NaCl concentrations. A simple surface complexation approach is found to be very successful: the constant capacitance model requires one pKa value and one capacitance for excellent fits to the data, with both parameters depending on ionic strength. The use of a self-consistent set of diffuse double layer parameters with one pKa for flat, spherical, and cylindrical geometry does not result in a satisfactory description of the data, and a number of adjustments to that model were tested to improve the fit. The basic Stern model (BSM) was tested with both plate and cylinder geometry. The cylinder geometry along with strong electrolyte binding was found to be superior to a similar approach involving weak electrolyte binding both in terms of goodness of fit and self-consistency of the parameters. The third approach, the non-ideal competitive consistent adsorption-Donnan (NICCA-Donnan) model, involving one functional group, allows an excellent description of the experimental data. Finally, the polyacid chain was modeled using a mechanistically more realistic self-consistent field (SCF) approach, which allows for radially inhomogeneous distributions of the charges and radial variations in the polymer density and electrostatic potential, while the functional groups can be in protonated, deprotonated, or complexed states. One functional group was insufficient for a satisfactory description of the data. With two segments (one monoprotic, the other diprotic) a reasonable description of the data, including the ionic strength dependence, is achieved, and the tendency of the size of the macro-ion with pH and ionic strength is as expected. This model has the fewest adjustable parameters and is considered the most realistic and comprehensive among the models tested
    Pickering emulsions: Wetting and colloidal stability of hairy particles - A self-consistent field theory
    Salari, J.W.O. ; Leermakers, F.A.M. ; Klumperman, B. - \ 2011
    Langmuir 27 (2011)11. - ISSN 0743-7463 - p. 6574 - 6583.
    oil-water interface - interacting chain molecules - statistical-theory - solid particles - stabilization - adsorption - polymer - phase - microcapsules - surfactants
    The assembly of sterically stabilized colloids at liquid–liquid interfaces is studied with the self-consistent field (SCF) theory using the discretization scheme that was developed by Scheutjens, Fleer, and co-workers. The model is based on a poly(methyl methacrylate) (pMMA) particle with poly(isobutylene) (pIB) grafted to the surface. The stabilizing groups on the particle surface have a significant effect on the interfacial assembly and, therefore, also on the formation and properties of Pickering emulsions. The wetting behavior of the particle is altered by the presence of the stabilizing groups, which affects the equilibrium position of the particles at the interface. The stabilizing groups can also lead to an activation barrier before interfacial adsorption, analogous to the steric repulsion between two particles. These effects are numerically solved with the SCF theory. It is commonly known that flocculating conditions enhance the interfacial adsorption and yield stable Pickering emulsions, which is confirmed in this work. Additionally, it is concluded that those conditions are not an absolute requirement. There is a window of stabilizer concentrations GpIB, 2.2–3.3 mg/m2 pIB, that shows both partial wetting and colloidal stability. The activation barrier for interfacial assembly is 140–550 kBT and is an order of magnitude higher than the colloidal stability. The difference can be attributed to the unfavorable interaction of pIB with water and a difference in geometry (plate–sphere vs sphere–sphere). This study demonstrates the interplay and provides a quantitative comparison between the wetting behavior and the colloidal stability, and it gives a better understanding of the colloidal assembly at soft interfaces and formation of Pickering emulsions in general
    Speciation of Se and DOC in soil solution and their relation to Se bioavailability.
    Weng, L.P. ; Vega, F.A. ; Supriatin, S. ; Bussink, W. ; Riemsdijk, W.H. van - \ 2011
    Environmental Science and Technology 45 (2011)1. - ISSN 0013-936X - p. 262 - 267.
    donnan membrane technique - ion-chromatography - selenium uptake - trace-metals - extracts - translocation - spectrometry - adsorption - sorption - samples
    A 0.01 M CaCl2 extraction is often used to asses the bioavailability of plant nutrients in soils. However, almost no correlation was found between selenium (Se) in the soil extraction and Se content in grass. The recently developed anion Donnan membrane technique was used to analyze chemical speciation of Se in the 0.01 M CaCl2 extractions of grassland soils and fractionation of DOC (dissolved organic carbon). The results show that most of Se (67-86%) in the extractions (15 samples) are colloidal-sized Se. Only 13-34% of extractable Se are selenate, selenite and small organic Se (
    The contribution of organic and mineral colloidal nanoparticles to element transport in a podzol soil.
    Regelink, I.C. ; Weng, L.P. ; Riemsdijk, W.H. van - \ 2011
    Applied Geochemistry 26 (2011)Suppl.. - ISSN 0883-2927 - p. S241 - S244.
    field-flow fractionation - montmorillonite - competition - separation - adsorption - speciation - water - fe
    The aim of this work is to analyze the size-distribution and composition of nanoparticles in a water-extract of a podzol B horizon. AsFlowFFF coupled to ICP–MS and a UV/VIS detector was used for particle fractionation and simultaneous measurement of the composition of the nanoparticles. Detected nanoparticles were organic and mineral particles; the mineral particles were dominated by clay and Fe-(hydr)oxides. Both organic- and inorganic particles contributed to the mobility of Fe, Al, trace metals and P. For Zn, Pb and P respectively 73%, 92% and 72% of the colloidal concentrations were associated with clay minerals. The large contribution of clay particles to the mobility of trace metals and P can be partly explained by the high amount of dispersed clay due to drying, sieving and rewetting of the soil. Inorganic nanoparticles can contribute significantly to the mobility of metals and P in soils.
    Electrospun Polyurethane Fibers for Absorption of Volatile Organic Compounds from Air
    Scholten, E. ; Bromberg, L. ; Rutledge, G.C. ; Hatton, T.A. - \ 2011
    ACS Applied Materials and Interfaces 3 (2011). - ISSN 1944-8244 - p. 3902 - 3909.
    shape-memory polyurethane - activated carbon - block-copolymers - polymer nanofibers - hard segment - adsorption - membranes - vapors - desorption - sorption
    Electrospun polyurethane fibers for removal of volatile organic compounds (VOC) from air with rapid VOC absorption and desorption have been developed. Polyurethanes based on 4,4-methylenebis(phenylisocyanate) (MDI) and aliphatic isophorone diisocyanate as the hard segments and butanediol and tetramethylene glycol as the soft segments were electrospun from their solutions in N,N-dimethylformamide to form micrometer-sized fibers. Although activated carbon possessed a many-fold higher surface area than the polyurethane fiber meshes, the sorption capacity of the polyurethane fibers was found to be similar to that of activated carbon specifically designed for vapor adsorption. Furthermore, in contrast to VOC sorption on activated carbon, where complete regeneration of the adsorbent was not possible, the polyurethane fibers demonstrated a completely reversible absorption and desorption, with desorption obtained by a simple purging with nitrogen at room temperature. The fibers possessed a high affinity toward toluene and chloroform, but aliphatic hexane lacked the necessary strong attractive interactions with the polyurethane chains and therefore was less strongly absorbed. The selectivity of the polyurethane fibers toward different vapors, along with the ease of regeneration, makes them attractive materials for VOC filtration.
    Brushes and proteins
    Bosker, W.T.E. - \ 2011
    Wageningen University. Promotor(en): Martien Cohen Stuart, co-promotor(en): Willem Norde. - [S.l.] : S.n. - ISBN 9789085859178 - 142
    biofilms - eiwitten - adsorptie - aangroeiwerende middelen - fabricage - biomaterialen - biofilms - proteins - adsorption - antifouling agents - manufacture - biomaterials

    Brushes and Proteins

    Wouter T. E. Bosker

    Protein adsorption at solid surfaces can be prevented by applying a polymer brush at the surface. A polymer brush consists of polymer chains end-grafted to the surface at such a grafting density that the polymer chains stretch out into the solution. This is schematically shown in figure 1.


    Fig. 1. Cartoons of a polymer brush. Two ways of preparation: (a) chemical grafting and (b) grafting through adsorption of block copolymers, for instance by Langmuir-Blodgett deposition (LB).

    The main parameters determining the protein resistance of a brush are the grafting density (σ), the chain length (N) and the solvent quality. The thickness of the brush is a function of these parameters: H ~ N σ1/3.

    This research is related to biofouling: 'the undesirable accumulation of proteins and cells at a surface', which starts by adsorption of proteins at the surface. Prevention of biofouling is of vital interest in medicine, where bacterial adhesion may cause severe infections on biomaterials used for implants. Treatment with antibiotics has hardly any effect. The only promising remedy against infections in this case is the prevention of a bacterial film. Because protein adsorption is the first step in this process, the research in this thesis is focused on prevention of protein adsorption by polymer brushes.

    Numerous studies over the past decades revealed that neutral polymer brushes, especially from poly(ethylene oxide) (PEO), can minimize protein adsorption. Mindful of the parameters determining the adsorbed amount mentioned above, the following three mechanisms can be identified, displayed in figure 2. Primary adsorption occurs when the diameter of the protein is (much) smaller than the distance between the polymer chains. In case of secondary adsorption, the protein is (much) bigger than the distance between the polymer chains. Ternary adsorption results from an attraction between the proteins and the polymer chains in the brush and was first discovered by Currie et al. In 1999. For a considerable time researchers have assumed a repulsion between the proteins and the polymer chains, thereby neglecting the possible ternary adsorption. However, there is increasing evidence that this attraction occurs, especially with PEO brushes. This is highlighted in this research, by adsorption studies at bimodal PEO brushes, consisting of a dense PEO brush of short chains with a varying PEO brush of long chains.

    Figure 2.
    Different mechanisms for protein adsorption at polymer brushes:

    primary, secondary and ternary adsorption.

    The main objective of this research was to investigate whether polysaccharide brushes, in particular dextran brushes, could be prepared at a solid surface and to study their protein repellency. It was suggested that brushes from these natural polymers would be more successful to prepare nonfouling surfaces with. Dextran brushes were prepared using Langmuir-Blodgett deposition (LB) and PS-dextran diblock copolymers, illustrated in figure 1. With the LB method it is possible to control both σ and N. The synthesis of the PS-dextran diblock copolymers is described in the thesis as well as the interfacial behavior. Quasi-2D aggregation occurred at the air-water interface during preparation (compression of the PS-dextran monolayer, see figure 1), resulting in inhomogeneous dextran layers at low grafting density. At higher grafting density these aggregates were pushed together to form a homogeneous dextran brush, as illustrated by AFM images. This transition from inhomogeneous to homogeneous results in non-continuous adsorption behavior at dextran brushes, in contrast to PEO brushes, as demonstrated in figure 3.


    Figure 3. Normalized adsorption of BSA (Γ/ Γ0) at dextran brushes (■) and PEO brushes (○).

    In case of dextran brushes the adsorption of BSA is constant up to a specific σ, followed by a drastic decrease, while PEO brushes show a gradual reduction.Figure 3 also demonstrates that dextran brushes are as efficient as PEO brushes in preventing protein adsorption, at high σ. This is the main conclusion of this research. It is expected that at even higher σ dextran brushes will completely suppress protein adsorption.

    Stable Protein-Repellent Zwitterionic Polymer Brushes Grafted from Silicon Nitride
    Nguyen, A.T. ; Baggerman, J. ; Paulusse, J.M.J. ; Rijn, C.J.M. van; Zuilhof, H. - \ 2011
    Langmuir 27 (2011)6. - ISSN 0743-7463 - p. 2587 - 2594.
    self-assembled monolayers - transfer radical polymerization - poly(ethylene oxide) brushes - molecular simulation - organic monolayers - biosensor applications - surface modification - adsorption - density - adhesion
    Zwitterionic poly(sulfobetaine acrylamide) (SBMAA) brushes were grafted from silicon-rich silicon nitride (SixN4, x > 3) surfaces by atom transfer radical polymerization (ATRP) and studied in protein adsorption experiments. To this aim ATRP initiators were immobilized onto SixN4 through stable Si-C linkages via three consecutive reactions. A UV-induced reaction of 1,2-epoxy-9-decene with hydrogen-terminated SixN4 surfaces was followed by conversion of the epoxide with 1,2-ethylenediamine resulting in primary and secondary amine-terminated surfaces. A reaction with 2-bromoisobutyryl bromide led to ATRP initiator-covered surfaces. Zwitterionic polymer brushes of SBMAA were grown from these initiator-coated surfaces (thickness 30 nm), and the polymer-coated surfaces were characterized in detail by static water contact angle measurements, X-ray photoelectron spectroscopy (XPS), and an atomic force microscope (AFM). The adsorption of proteins onto zwitterionic polymer coated surfaces was evaluated by in situ reflectometry, using a fibrinogen (FIB) solution of 0.1 g·L-1, and compared to hexadecyl-coated SixN4 surfaces (C16-SixN4), uncoated air-based plasma oxidized SixN4 surfaces (SiOy-SixN4), and hexa(ethylene oxide)-coated SixN4 surfaces (EO6-SixN4). Excellent protein repellence (>99%) was observed for these zwitterionic polymer-coated SixN4 surfaces during exposure to FIB solution as compared to C16-SixN4 surfaces. Furthermore, the stability of these zwitterionic polymer-coated SixN4 surfaces was surveyed by exposing the surfaces for 1 week to phosphate buffered saline (PBS) solution at room temperature. The zwitterionic polymer-coated SixN4 surfaces before and after exposure to PBS solution were characterized by XPS, AFM, and water contact angle measurements, and their protein-repelling properties were evaluated by reflectometry. After exposure to PBS solution, the zwitterionic polymer coating remained intact, and its thickness was unchanged within experimental error. No hydrolysis was observed for the zwitterionic polymer after 1 week exposure to PBS solution, and the surfaces still repelled 98% FIB as compared to C16-SixN4 surfaces, demonstrating the long-term efficiency of these easily prepared surface coatings
    Improvement of foaming properties of cuttlefish skin gelatin by modification with N-hydroxysuccinimide esters of fatty acid
    Aewsiri, T. ; Benjakul, S. ; Visessanguan, W. ; Wierenga, P.A. ; Gruppen, H. - \ 2011
    Food Hydrocolloids 25 (2011)5. - ISSN 0268-005X - p. 1277 - 1284.
    air-water-interface - proteins - proteolysis - adsorption - surfactant - ovalbumin - charge
    Conformation and foaming properties of cuttlefish skin gelatin modified by N-hydroxysuccinimide esters of different saturated fatty acids including capric acid (C10:0), lauric acid (C12:0) and myristic acid (C14:0) at different molar ratios (0.25, 0.50, 1.00 and 2.00) were investigated. Covalent attachment of fatty acids into gelatin was observed as evidenced by the decrease in amino groups. Fourier transform infrared spectroscopic study indicated the presence of alkyl group of modified gelatin. The higher increase in surface activity with coincidental increase in surface hydrophobicity was observed in gelatin modified with fatty acid ester having a longer chain, especially at the higher molar ratio. The increase in foam expansion was related with the improved surface activity mediated by the modification by N-hydroxysuccinimide esters of fatty acid.
    Effect of 1-1 electrolyte concentration on the adsorption/desorption of copper ion on synthetic birnessite
    Wang, M. ; Wang, Y. ; Tan, W. ; Liu, F. ; Feng, X. ; Koopal, L.K. - \ 2010
    Journal of Soils and Sediments 10 (2010)5. - ISSN 1439-0108 - p. 879 - 885.
    heavy-metal ions - redox reactions - oxide minerals - adsorption - manganese - fe - desorption - hydroxides - surfaces - sorption
    Oxides are ubiquitous in nature and play an important role in scavenging metal ions from soils and sediments. At the common pH range of the natural environment the well-studied Fe and Al oxides mostly carry a positive charge and adsorbed amounts of heavy metals, and their desorption percentages decrease with increasing ionic strength. The less well studied but also important Mn oxides possess negative charges in the natural environment and this will lead to a different behavior. Therefore, it is useful to further investigate how the electrolyte concentration and type affect the metal ion adsorption/desorption by Mn oxides. The phyllomanganate birnessite was synthesized with hydrochloric acid and potassium permanganate, and characterized by X-ray diffraction and transmission electron microscopy. The point of zero charge and specific surface area (SSA) were determined by, respectively, the rapid potentiometric titration method and BET-N(2) method. The adsorption was measured after shaking the samples in contact with Cu(NO(3))(2) solution for 2 h and further equilibration for 22 h at pH 4.5 and 25 +/- 1A degrees C. The 1-1 electrolyte concentrations were adjusted to 0, 0.001, 0.01, 0.1, 0.5, and 1 mol L(-1) KNO(3) or KCl. The PZC and SSA of synthetic birnessite were 2.5 and 75 m(2) g(-1), respectively. The birnessite consisted of small needle-like particles. A maximum amount of Cu(2+) adsorbed on birnessite of 208 +/- 8 mmol kg(-1) and 2.77 +/- 0.11 A mu mol m(-2) by using the BET area is obtained. The adsorption amount decreased gradually with increasing ionic strength. This is primarily due to screening of the electrostatic attraction. For the same reason the percentage of desorption of Cu(2+) previously adsorbed on birnessite increased with increasing electrolyte concentration. Furthermore, the decrease of Cu(2+) adsorption with increasing ionic strength was higher in KCl solution than in KNO(3) solution. This difference is most likely related to Cu(2+)-Cl(-) complexation. The type and concentration of 1-1 electrolyte affect the Cu(2+) adsorption/desorption characteristics on Mn oxide. The amounts of Cu(2+) adsorbed on birnessite reduced, and the desorption percentage increased with increasing 1-1 electrolyte concentration. These results are opposite to that of metal ion binding to positive Fe and Al oxides. The principal differences can be explained on the basis of generic electrostatic effects.
    Investigation of gas/liquid interface of small bubbles formed in solutions of different alkylammonium chlorides
    Sakai, M. ; Murata, T. ; Kamio, K. ; Mukae, K. ; Yamauchi, A. ; Moroi, Y. ; Sugihara, G. ; Norde, W. - \ 2010
    Colloids and Surfaces. A: Physicochemical and Engineering Aspects 359 (2010)1-3. - ISSN 0927-7757 - p. 6 - 12.
    water evaporation - aqueous-solutions - adsorption - microbubbles - surfactants - monolayers - charge
    The electrophoretic mobility of nitrogen gas bubbles was measured in solutions of different nalkylammonium chlorides in a cylindrical cell, 30 mm in diameter and 70 mm in length, rotating in order to keep the bubbles on a line of the rotation axis of the cylinder. An electric charge field was applied to the solutions through two electrodes located at both ends of the cylinder. The mobility was measured as a function of the size of bubbles. The maximum mobility U*(=v/E) and the corresponding diameter of the bubble, d(b)* were used to determine the apparent surface charge density, mat the gas/liquid interface. The surface charge density of bubbles was found (i) to be negative even in solutions of all n-alkylammonium chlorides carbon atoms, the number n of which was selected to be n=1, 2,3, and 10, and (ii) to decrease in magnitude with increasing number of carbon atoms. Decylammonium chloride (DAC: n = 10) is a typical cationic surfactant, however, the surface was revealed to still be negative, which strongly suggests that DAC molecules do not always come out to the gas/liquid interface. The change in surface charge density with the added salt concentration was analyzed, and as a result, it was found that only DAC follows the Langmuir adsorption isotherm. (C) 2010 Published by Elsevier B.V.
    Modeling of Cd Uptake and Efflux Kinetics in Metal-Resistant Bacterium Cupriavidus metallidurans
    Hajdu, R. ; Pinheiro, J.P. ; Galceran, J. ; Slaveykova, V.I. - \ 2010
    Environmental Science and Technology 44 (2010)12. - ISSN 0013-936X - p. 4597 - 4602.
    speciation dynamics - heavy-metals - ralstonia-metallidurans - marine bacterium - cadmium - zinc - bioavailability - biosorption - adsorption - ch34
    The Model of Uptake with Instantaneous Adsorption and Efflux, MUIAE, describing and predicting the overall Cd uptake by the metal-resistant bacterium Cupriavidus metallidurans CH34, is presented. MUIAE takes into account different processes at the bacteria-medium interface with specific emphasis on the uptake and efflux kinetics and the decrease in bulk metal concentration. A single set of eight parameters provides a reasonable description of experimentally determined adsorbed and internalized Cd, as well as the evolution of dissolved Cd concentrations with time, for an initial Cd concentration between 10(-8) and 10(-4) M, covering the situation of contaminated environments and heavily polluted effluents. The same set of parameters allowed successful prediction of the internalized and adsorbed Cd as a function of the measured free Cd ion concentration in the presence of natural and anthropogenic ligands. The findings of the present study reveal the key role of Cd efflux and bulk depletion on the overall Cd uptake by C. metallidurans, and the need to account for these processes to understand and improve the efficiency of the metal removal from the contaminated environment
    Effects of extraction procedures on metal binding properties of extracellular polymeric substances (EPS) from anaerobic granular sludges
    Abzac, P. D'; Bordas, F. ; Hullebusch, E. ; Lens, P.N.L. ; Guibaud, G. - \ 2010
    Colloids and Surfaces. B: Biointerfaces 80 (2010)2. - ISSN 0927-7765 - p. 161 - 168.
    activated-sludge - titration data - biosorption - cadmium - complexation - adsorption - sorption - lead - cd - constants
    The effects of the extraction procedure of extracellular polymeric substances (EPS) on their proton/metal binding properties were studied. Nine extraction procedures (one control, four physical and four chemical procedures) were applied to four types of anaerobic granular sludges. The binding capacities between the EPS and lead or cadmium were investigated at pH 7 by a polarographic method. The composition of the EPS extracts varied according to the extraction technique and the origin of the sludge. This induced differences in the pK(a)s and the binding sites density of the EPS extracts. The carry-over of the extractant in the samples strongly affects the properties of the EPS from chemical extraction protocols. Lead and cadmium seem to be bound differently with the EPS, a higher binding capacity was observed for Pb2+ than for Cd2+.
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