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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    Towards predicting the stability of protein-stabilized emulsions
    Delahaije, R.J.B.M. ; Gruppen, H. ; Giuseppin, M.L.F. ; Wierenga, P.A. - \ 2015
    Advances in Colloid and Interface Science 219 (2015). - ISSN 0001-8686 - p. 1 - 9.
    in-water emulsions - random sequential adsorption - equation-of-state - beta-lactoglobulin - light-scattering - latex-particles - quantitative description - exposed hydrophobicity - globular-proteins - diffusing wave
    The protein concentration is known to determine the stability against coalescence during formation of emulsions. Recently, it was observed that the protein concentration also influences the stability of formed emulsions against flocculation as a result of changes in the ionic strength. In both cases, the stability was postulated to be the result of a complete (i.e. saturated) coverage of the interface. By combining the current views on emulsion stability against coalescence and flocculation with new experimental data, an empiric model is established to predict emulsion stability based on protein molecular properties such as exposed hydrophobicity and charge. It was shown that besides protein concentration, the adsorbed layer (i.e. maximum adsorbed amount and interfacial area) dominates emulsion stability against coalescence and flocculation. Surprisingly, the emulsion stability was also affected by the adsorption rate. From these observations, it was concluded that a completely covered interface indeed ensures the stability of an emulsion against coalescence and flocculation. The contribution of adsorption rate and adsorbed amount on the stability of emulsions was combined in a surface coverage model. For this model, the adsorbed amount was predicted from the protein radius, surface charge and ionic strength. Moreover, the adsorption rate, which depends on the protein charge and exposed hydrophobicity, was approximated by the relative exposed hydrophobicity (QH). The model in the current state already showed good correspondence with the experimental data, and was furthermore shown to be applicable to describe data obtained from literature.
    Preparation, structure and stability of sodium caseinate and gelatin micro-particles
    Ince, A.E. ; Saglam, D. ; Venema, P. ; Linden, E. van der; Scholten, E. - \ 2015
    Food Hydrocolloids 45 (2015). - ISSN 0268-005X - p. 291 - 300.
    glucono-delta-lactone - whey-protein particles - light-scattering - physical-properties - beta-lactoglobulin - swelling behavior - phase-separation - ionic-strength - high-pressure - mixed gels
    Protein particles are promising candidates for texturing food products and can be produced in several ways. Here, we produced protein particles using a two-step emulsification method. This method is suitable to change the size of the particles and to control the protein concentration inside the particles. In this study, we prepared protein particles from two different protein sources, sodium caseinate (NaCas) and gelatin, that are gelled by acidification and cooling, respectively. The size and the internal protein concentration of the particles, their stability against heating and pH changes were studied. Although similar emulsification conditions were used to prepare the particles, NaCas particles were found to be 10 times smaller (average diameter 400 nm) than the gelatin particles (average diameter 4 µm). The internal protein concentration of the NaCas particles (16.8% w/w) is approximately twice as high compared to that of gelatin particles (7.6% w/w) (using an initial protein concentration of the solution of 10% (w/w)). The NaCas particle dispersions were found to be stable between pH 3 and pH 4. The particles disintegrated at pH values further away from the iso-electric point. Upon heating the dispersions at 90 °C, the NaCas particles were shown to be heat stable. Dispersions of gelatin particles were stable against aggregation at all pH values studied, except at pH 6, while the particles melted above 40 °C. Swelling of both particles was observed for both acidic and alkaline pH values. We conclude that emulsification method is robust for different protein sources used.
    Regulation of Acetate Kinase Isozymes and Its Importance for MixedAcid Fermentation in Lactococcus lactis
    Puri, P. ; Goel, A. ; Bochynska, A. ; Poolman, B. - \ 2014
    Journal of Bacteriology 196 (2014)7. - ISSN 0021-9193 - p. 1386 - 1393.
    streptococcus-lactis - escherichia-coli - methanosarcina-thermophila - lysine acetylation - membrane-proteins - product formation - light-scattering - in-vivo - metabolism - phosphate
    Acetate kinase (ACK) converts acetyl phosphate to acetate along with the generation of ATP in the pathway for mixed-acid fermentation in Lactococcus lactis. The reverse reaction yields acetyl phosphate for assimilation purposes. Remarkably, L. lactis has two ACK isozymes, and the corresponding genes are present in an operon. We purified both enzymes (AckA1 and AckA2) from L. lactis MG1363 and determined their oligomeric state, specific activities, and allosteric regulation. Both proteins form homodimeric complexes, as shown by size exclusion chromatography and static light-scattering measurements. The turnover number of AckA1 is about an order of magnitude higher than that of AckA2 for the reaction in either direction. The K-m values for acetyl phosphate, ATP, and ADP are similar for both enzymes. However, AckA2 has a higher affinity for acetate than does AckA1, suggesting an important role under acetate-limiting conditions despite the lower activity. Fructose-1,6-bisphosphate, glyceraldehyde- 3-phosphate, and phospho-enol-pyruvate inhibit the activities of AckA1 and AckA2 to different extents. The allosteric regulation of AckA1 and AckA2 and the pool sizes of the glycolytic intermediates are consistent with a switch from homolactic to mixed-acid fermentation upon slowing of the growth rate.
    Controlled formation of protein nanoparticles by enzymatic cross-linking of a-lactalbumin with horseradish peroxidase
    Dhayal, S.K. ; Gruppen, H. ; Vries, R.J. de; Wierenga, P.A. - \ 2014
    Food Hydrocolloids 36 (2014). - ISSN 0268-005X - p. 53 - 59.
    field-flow fractionation - beta-lactoglobulin - foaming properties - interfacial properties - light-scattering - separation - emulsions - transglutaminase - stability
    Inorganic and organic colloidal particles are known to impart much higher stability to foams and emulsions than proteins, heat-induced protein aggregates or low molar mass surfactants. In this study we show that a-lactalbumin can be enzymatically cross-linked by horse-radish peroxidase to produce nanoparticles with controlled size and meso-scale structure. Furthermore, the effects of process parameters, such as the protein concentration (10–30 g L-1), total dosed amount of hydrogen peroxide (0–10 mM), the time gap between each dosage of hydrogen peroxide (120–600 s) and ionic strength (100–200 mM), on the sizes of the nanoparticles have been investigated. The cross-linked protein nanoparticles varied in size (radius of gyration, Rg) and weight averaged molar mass (Mw), ranging between monomeric protein (~2 nm, 14.2 kDa) and nanoparticles (200 nm, 100 MDa). The speed of particle formation increased with increasing ionic strength, but their meso-scale structure remained similar. The Rg of these nanoparticles scaled as Mw0.6, indicating similar meso-scale structure (conformation) at all length scales but variation of density with size. The apparent density (internal protein concentration) of the nanoparticles was between 104 and 10 kg m-3 for Rg ~ 20 nm and Rg > 100 nm respectively.
    Diverging electrophoretic and dynamic mobility of model silica colloids at low ionic strength in ethanol
    Kortschot, R.J. ; Lyklema, J. ; Philipsen, A.P. ; Erné, B.H. - \ 2014
    Journal of Colloid and Interface Science 422 (2014). - ISSN 0021-9797 - p. 65 - 70.
    macroscopic electric-field - concentrated dispersions - charged colloids - nonaqueous dispersions - dielectric response - light-scattering - organic-solvent - cell model - spheres - suspensions
    Electroacoustics and laser Doppler electrophoresis were employed to measure the mobility of surface-modified silica colloids in ethanol as a function of the ionic strength. Sufficiently low volume fractions were chosen to exclude effects of interparticle interactions. At high ionic strength, the electrophoretic mobility µeµe is equal to the (electroacoustic) dynamic mobility µdµd at 3.3 MHz. However, the ratio µd/µeµd/µe increases significantly to ~~5 at low ionic strength. This increase may be related to the porous outer layer of the surface-modified silica spheres.
    Translational and rotational diffusion of flexible PEG and rigid dendrimer probes in sodium caseinate dispersions and acid gels
    Salami, S. ; Rondeau-Mouro, C. ; Barhoum, M. ; Duynhoven, J.P.M. van; Mariette, F. - \ 2014
    Biopolymers 101 (2014)9. - ISSN 0006-3525 - p. 959 - 965.
    glucono-delta-lactone - hydrodynamic transport-properties - nuclear-magnetic-resonance - polystyrene latex spheres - aqueous polymer-solutions - light-scattering - nmr - suspensions - gelation - microstructure
    The dynamics of rigid dendrimer and flexible PEG probes in sodium caseinate dispersions and acid gels, including both translational diffusion and rotational diffusion, were studied by NMR. Above the onset of the close-packing limit (C ~ 10 g/100 g H2O), translational diffusion of the probe depended on its flexibility and on the fluctuations of the matrix chains. The PEG probe diffused more rapidly than the spherical dendrimer probe of corresponding hydrodynamic radius. The greater conformational flexibility of PEG facilitated its motion through the crowded casein matrix. Rotational diffusion was, however, substantially less hindered than the translational diffusion and depended on the local protein–probe friction which became high when the casein concentration increased. The coagulation of the matrix led to the formation of large voids, which resulted in an increase in the translational diffusion of the probes, whereas the rotational diffusion of the probes was retarded in the gel, which could be attributed to the immobilized environment surrounding the probe. Quantitative information from PFG-NMR and SEM micrographs have been combined for characterizing microstructural details in SC acid gels.
    Predictions of Glass Transition Temperature for Hydrogen Bonding Biomaterials
    Sman, R.G.M. van der - \ 2013
    The Journal of Physical Chemistry Part B: Condensed Matter, Materials, Surfaces, Interfaces & Biophysical 117 (2013)50. - ISSN 1520-6106 - p. 16303 - 16313.
    molecular-dynamics simulations - gel sol transition - aqueous-solutions - free-volume - glycerol-water - physical-properties - positron lifetime - light-scattering - phase-behavior - starch gels
    We show that the glass transition of a multitude of mixtures containing hydrogen bonding materials correlates strongly with the effective number of hydroxyl groups per molecule, which are available for intermolecular hydrogen bonding. This correlation is in compliance with the topological constraint theory, wherein the intermolecular hydrogen bonds constrain the mobility of the hydrogen bonded network. The finding that the glass transition relates to hydrogen bonding rather than free volume agrees with our recent finding that there is little difference in free volume among carbohydrates and polysaccharides. For binary and ternary mixtures of sugars, polyols, or biopolymers with water, our correlation states that the glass transition temperature is linear with the inverse of the number of effective hydroxyl groups per molecule. Only for dry biopolymer/sugar or sugar/polyol mixtures do we find deviations due to nonideal mixing, imposed by microheterogeneity.
    On the Stability and Morphology of Complex Coacervate Core Micelles: From Spherical to Wormlike Micelles
    Kooij, H.M. van der; Spruijt, E. ; Voets, I.K. ; Fokkink, R.G. ; Cohen Stuart, M.A. ; Gucht, J. van der - \ 2012
    Langmuir 28 (2012)40. - ISSN 0743-7463 - p. 14180 - 14191.
    block-copolymer micelles - light-scattering - polyelectrolyte complexes - protein adsorption - diblock copolymer - polysulfone surfaces - polystyrene surfaces - silica - delivery - polymer
    We present a systematic study of the stability and morphology of complex coacervate core micelles (C3Ms) formed from poly(acrylic acid) (PAA) and poly(N-methyl-2-vinylpyridinium)-b-poly(ethylene oxide) (PM2VP-b-PEO). We use polarized and depolarized dynamic and static light scattering, combined with small-angle X-ray scattering, to investigate how the polymer chain length and salt concentration affect the stability, size, and shape of these micelles. We show that C3Ms are formed in aqueous solution below a critical salt concentration, which increases considerably with increasing PAA and PM2VP length and levels off for long chains. This trend is in good agreement with a mean-field model of polyelectrolyte complexation based on the Voorn-Overbeek theory. In addition, we find that salt induces morphological changes in C3Ms when the PAA homopolymer is sufficiently short: from spherical micelles with a diameter of several tens of nanometers at low salt concentration to wormlike micelles with a contour length of several hundreds of nanometers just before the critical salt concentration. By contrast, C3Ms of long PAA homopolymers remain spherical upon addition of salt and shrink slightly. A critical review of existing literature on other C3Ms reveals that the transition from spherical to wormlike micelles is probably a general phenomenon, which can be rationalized in terms of a classical packing parameter for amphiphiles.
    Effect of temperature shocks on membrane fouling in membrane bioreactors
    Brink, P. van den; Satpradit, O.A. ; Bentem, A. van; Zwijnenburg, A. ; Temmink, B.G. ; Loosdrecht, M.C.M. - \ 2011
    Water Research 45 (2011)15. - ISSN 0043-1354 - p. 4491 - 4500.
    afvalwaterbehandeling - bioreactoren - membranen - geactiveerd slib - temperatuur - vervuiling door afzetting - viscositeit - waste water treatment - bioreactors - membranes - activated sludge - temperature - fouling - viscosity - waste-water treatment - cross-flow microfiltration - flux-step method - activated-sludge - particle deposition - size distribution - light-scattering - bubble-size - performance - ultrafiltration
    Temperature is known to influence the biological performance of conventional activated sludge systems. In membrane bioreactors (MBRs), temperature not only affects the bioconversion process but is also shown to have an effect on the membrane performance. Four phenomena are generally reported to explain the higher resistance for membrane filtration found at lower temperatures: (1) increased mixed liquor viscosity, reducing the shear stress generated by coarse bubbles, (2) intensified deflocculation, reducing biomass floc size and releasing EPS into the mixed liquor, (3) lower backtransport velocity and (4) reduced biodegradation of COD. Although the higher resistance at low temperatures has been reported in several papers, the relation with supernatant composition has not been investigated before. In this paper, the composition of the soluble fraction of the mixed liquor is related to membrane performance after exposing the sludge to temperature shocks. Flux step experiments were performed in an experimental system at 7, 15, and 25° Celsius with sludge that was continuously recirculated from a pilot-scale MBR. After correcting the permeate viscosity for temperature, higher membrane fouling rates were obtained for the lower temperature in combination with low fouling reversibility. The soluble fraction of the MBR mixed liquor was analysed for polysaccharides, proteins and submicron particle size distribution. At low temperature, a high polysaccharide concentration was found in the experimental system as compared to the MBR pilot. Upon decreasing the temperature of the mixed liquor, a shift was found in particle size towards smaller particles. These results show that the release of polysaccharides and/or submicron particles from sludge flocs could explain the increased membrane fouling at low temperatures
    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.
    Prediction of the state diagram of starch water mixtures using the Flory--Huggins free volume theory
    Sman, R.G.M. van der; Meinders, M.B.J. - \ 2011
    Soft Matter 7 (2011)2. - ISSN 1744-683X - p. 429 - 442.
    glass-transition temperatures - phase-transitions - aqueous-solutions - physicochemical properties - light-scattering - molecular-weight - corn starch - thermal characterization - crystalline polymorph - scanning calorimetry
    In this paper we analyse the phase and state transitions of starch and other glucose homopolymers and oligomers using the free volume extension of the Flory–Huggins theory by Vrentas and Vrentas, combined with the Couchman–Karasz theory for the glass transition. Using scaling relations of model parameters with molar weight we have obtained accurate predictions of moisture sorption and the freezing, boiling, and melting data obtained from literature for starch, dextrans, pullulan and maltodextrins. With the estimated model parameters we can construct the complete state diagram for starch, which can now be used as a quantitative tool for design and analysis of food structuring processes.
    Size-exclusion chromatographic protein refolding: Fundamentals, modelling and operation
    Freydell, E.J. ; Wielen, L. van der; Eppink, M.H.M. ; Ottens, M. - \ 2010
    Journal of Chromatography. A, Including electrophoresis and other separation methods 1217 (2010)49. - ISSN 0021-9673 - p. 7723 - 7737.
    refractive-index detectors - nonlinear chromatography - diffusion-coefficients - liquid-chromatography - light-scattering - human proinsulin - aggregation - lysozyme - mechanism - media
    Size-exclusion chromatography (SEC) has proven its capability to refold a variety of proteins using a range of gel filtration column materials, demonstrated in the growing body of experimental evidence. However, little effort has been allocated to the development of mechanistic models describing size-exclusion chromatographic refolding reactors (SECRR). Mechanistic models are important since they provide a link between process variables like denatured and reduced protein feed concentration (C(f,D&R)), flow rate, column length, etc., and performance indicators like refolding yield (Y(N)), thereby opening the possibility for in silico design of SECRRs. A critical step, in the formulation of such models, is the selection of an adequate reaction mechanism, which provides the direct link between the separation and the refolding yield. Therefore, in this work we present a methodology using a SEC refolding reactor model, supported by a library of reaction mechanisms, to estimate a suitable reaction scheme using experimental SEC refolding data. SEC refolding data is used since it provides information about the mass distribution of monomers and aggregates after refolding, information not readily available from batch dilution refolding data alone. Additionally, this work presents (1) a systematic analysis of the reaction mechanisms considered using characteristic time analysis and Damköhler maps, revealing (a) the direct effect of a given reaction mechanism on the shape of the SEC refolding chromatogram (number of peaks and resolution) and (b) the effect that the competition between convection, refolding and aggregation is likely to have on the SEC refolding yield; (2) a comparison between the SECR reactor and the batch dilution refolding reactor based on mechanistic modeling, quantitatively showing the advantages of the former over the latter; and (3) the successful application of the modeling based strategy to study the SEC refolding data of an industrially relevant protein. In principle, the presented modeling strategy can be applied to any protein refolded using any gel filtration material, providing the proper mass balances and activity measurements are available.
    Polymers at the water/air interface, surface pressure isotherms, and molecularly detailed modeling
    Bernardini, C. ; Stoyanov, S.D. ; Cohen Stuart, M.A. ; Arnaudov, L.N. ; Leermakers, F.A.M. - \ 2010
    Langmuir 26 (2010)14. - ISSN 0743-7463 - p. 11850 - 11861.
    interacting chain molecules - air/water interface - light-scattering - langmuir monolayers - methyl-methacrylate - monomolecular films - statistical-theory - air - spread - poly(dimethylsiloxane)
    Surface pressure isotherms at the air/water interface are reproduced for four different polymers, poly-l-lactic acid (PLLA), poly(dimethylsiloxane) (PDMS), poly(methyl methacrylate) (PMMA), and poly(isobutylene) (PiB). The polymers have the common property that they do not dissolve in water. The four isotherms differ strongly. To unravel the underlying details that are causing these differences, we have performed molecularly detailed self-consistent field (SCF) modeling. We describe the polymers on a united atom level, taking the side groups on the monomer level into account. In line with experiments, we find that PiB spreads in a monolayer which smoothly thickens already at a very low surface pressure. PMMA has an autophobic behavior: a PMMA liquid does not spread on top of the monolayer of PMMA at the air/water interface. A thicker PMMA layer only forms after the collapse of the film at a relatively high pressure. The isotherm of PDMS has regions with extreme compressibility which are linked to a layering transition. PLLA wets the water surface and spreads homogeneously at larger areas per monomer. The classical SCF approach features only short-range nearest-neighbor interactions. For the correct positioning of the layering and for the thickening of the polymer films, we account for a power-law van der Waals contribution in the model. Two-gradient SCF computations are performed to model the interface between two coexistent PDMS films at the layering transition, and an estimation of the length of their interfacial contact is obtained, together with the associated line tension value.
    New directions towards structure formation and stability of protein-rich foods from globular proteins
    Purwanti, N. ; Goot, A.J. van der; Boom, R.M. ; Vereijken, J.M. - \ 2010
    Trends in Food Science and Technology 21 (2010)2. - ISSN 0924-2244 - p. 85 - 94.
    calcium caseinate dispersions - whey-protein - dietary-protein - cheddar cheese - shear-flow - beta-lactoglobulin - fibrous materials - light-scattering - spinning process - induced gelation
    Concentrated protein-rich foods have strong potential to be developed in terms of health and well-being roles. Unfortunately, limitations in creating products with the rights texture and stability hinder the use of those products by consumers. Main reason is that the formation of micro- and macrostructures in concentrated protein systems is not fully understood yet and hence not controlled. As a result, their multi-level structures are not optimal. This paper overviews possible routes to produce protein-rich foods with emphasis on options to produce protein-rich materials that have the potential to be stable and desirable in terms of the combination structure–texture–sensory. The main conclusion is that these demands could be met by introduction of well-defined heterogeneity in the product using new plasticizing components and innovative production methods.
    Structural properties and gelatinisation characteristics of potato and cassava starches and mutants thereof
    Gomand, S.V. ; Lamberts, L. ; Derde, L.J. ; Groesaert, H. ; Vandeputte, G.E. ; Goderis, B. ; Visser, R.G.F. ; Delcour, J.A. - \ 2010
    Food Hydrocolloids 24 (2010)4. - ISSN 0268-005X - p. 307 - 317.
    aspects provide insight - size-exclusion chromatography - amylose maize starches - molecular-structure - rice starches - retrogradation properties - amylopectin structure - light-scattering - refractive-index - granular starch
    The molecular size of amylopectin (AP) and amylose (AM), AP chain length distribution, crystallinity and granular structure (morphology and granule size distribution) of five wild type potato starches (wtps), five AM free potato starches (amfps), four high-AM potato starches (haps), one wild type cassava starch (wtcs) and one AM free cassava starch (amfcs) were investigated and related to their gelatinisation characteristics. Starches with higher levels of short chains [degree of polymerisation (DP) 6–9 and DP 10–14)] had lower gelatinisation onset (To), peak (Tp) and conclusion (Tc) temperatures, whereas higher contents of longer chains (DP 18–25 and DP 25–80) led to higher gelatinisation temperatures. Gelatinisation enthalpies (¿H) increased with degree of crystallinity. The granules of wtps were larger than those of amfps and haps, respectively. No differences in morphology were observed between wtps and amfps granules, but the haps granules had more irregular surfaces and showed multi-lobed granules.
    Multicompartment Nanoparticles Formed by a Heparin-Mimicking Block Terpolymer in Aqueous Solutions
    Uchman, M. ; Stepanek, M. ; Prochazka, K. ; Mountrichas, G. ; Pispas, S. ; Voets, I.K. ; Walther, A. - \ 2009
    Macromolecules 42 (2009)15. - ISSN 0024-9297 - p. 5605 - 5613.
    atomic-force microscopy - abc triblock copolymer - onion-type micelles - fluorescence correlation spectroscopy - diblock copolymers - selective solvents - light-scattering - poly(2-vinylpyridine)-block-poly(ethylene oxide) - wormlike micelles - star terpolymers
    A new amphiphilic block. terpolymer poly((sulfamate-carboxylate)isoprene)-block-polystyrene-block-poly(ethyl ene oxide), PISC230-PS52-PEO151, with a narrow molecular weight distribution (PDI = 1.05), was synthesized via the post. polymerization reaction of the anionically prepared precursor block terpolymer polyisoprene-block-polystyrene-block--poly(ethylene oxide) with chlorosulfonyl isocyanate. The formation and Structure of self-assemblies of the polyelectrolyte block terpolymer in dilute aqueous Solutions were studied by static and dynamic light scattering, atomic force and cryogenic transmission electron microscopy, fluorometry, and H-1 NMR spectroscopy. In acidic solutions, the terpolymers self-assemble into kinetically trapped multicompartment micelles, with the core consisting of discrete PS and PISC domains and PEO in the shell. If the solution pH is adjusted to the alkaline region, the multicompartment micelles undergo an irreversible transition to regular micelles, with a PS core and a mixed shell formed by PEO and PISC blocks.
    Electrostatic hierarchical co-assembly in aqueous solutions of two oppositely charged double hydrophilic diblock copolymers
    Voets, I.K. ; Keizer, A. de; Leermakers, F.A.M. ; Debuigne, A. ; Jerome, R.J. ; Detrembleur, C. ; Cohen Stuart, M.A. - \ 2009
    European Polymer Journal 45 (2009)10. - ISSN 0014-3057 - p. 2913 - 2925.
    polyion complex micelles - mediated radical polymerization - coacervation core micelles - block ionomer complexes - water-soluble complexes - polyelectrolyte complexes - poly(ethylene oxide) - light-scattering - hybrid micelles - coronal chains
    The formation of spherical micelles in aqueous solutions of poly(N-methyl-2-vinyl pyridinium iodide)-block-poly(ethylene oxide), P2MVP-b-PEO and poly(acrylic acid)-block-poly(vinyl alcohol), PAA-b-PVOH has been investigated with light scattering-titrations, dynamic and static light scattering, and 1H 2D Nuclear Overhauser Effect Spectroscopy. Complex coacervate core micelles, also called PIC micelles, block ionomer complexes, and interpolyelectrolyte complexes, are formed in thermodynamic equilibrium under charge neutral conditions (pH 8, 1 mM NaNO3, T = 25 °C) through electrostatic interaction between the core-forming P2MVP and PAA blocks. 2D 1H NOESY NMR experiments show no cross-correlations between PEO and PVOH blocks, indicating their segregation in the micellar corona. Self-consistent field calculations support the conclusion that these C3Ms are likely to resemble a ‘patched micelle’; that is, micelles featuring a ‘spheres-on-sphere’ morphology
    Effect of free calcium concentration and ionic strength on alginate fouling in cross-flow membrane filtration
    Brink, P. van den; Zwijnenburg, A. ; Smith, G. ; Temmink, B.G. ; Loosdrecht, M.C. van - \ 2009
    Journal of Membrane Science 345 (2009)1-2. - ISSN 0376-7388 - p. 207 - 216.
    extracellular polymeric substances - waste-water treatment - reverse-osmosis membranes - activated-sludge - light-scattering - sodium alginate - physical aspects - bioreactor mbr - critical flux - model
    Extracellular polymeric substances (EPS) are generally negatively charged polymers. Membrane fouling in membrane bioreactors (MBRs) by EPS is therefore influenced by the water chemistry of the mixed liquor (calcium concentration, foulant concentration and ionic strength). We used alginate as a model compound to study this fouling in detail. Flux-step experiments were performed with a flat sheet test cell, varying the free calcium concentration, total ionic strength and alginate concentration. There was a strong relation between calcium concentration and fouling rate. An increased ionic strength had no impact on fouling rate in low fouling experiments, but decreased fouling with 66–72% at high fouling conditions. Reversibility of the fouling decreased with increasing calcium concentrations to values as low as 3%. Several fouling mechanisms were identified and the reducing effect of increased ionic strength on alginate fouling was explained by competition for carboxyl groups on the alginate polymer. Further research will focus on the interaction of polysaccharides with other compounds typically present in the MBR supernatant (e.g. proteins, humic acids and sludge particles) and a more detailed analysis of the fouling layer
    Pluronic polymersomes stabilized by core cross-linked polymer micelles
    Li, F. ; Haan, L.H.J. de; Marcelis, A.T.M. ; Leermakers, F.A.M. ; Cohen Stuart, M.A. ; Sudhölter, E.J.R. - \ 2009
    Soft Matter 5 (2009). - ISSN 1744-683X - p. 4042 - 4046.
    dilute aqueous-solution - triblock copolymer - light-scattering - vesicles - delivery - solubilization - transition - system
    Vesicles from Pluronic L121 (PEO5-PPO68-PEO5) triblock copolymers were stabilized against aggregation by Pluronic P85 (PEO26-PPO40-PEO26) micelles. Both the vesicles and the micelles were reinforced by an interpenetrating polymer network from pentaerythritol tetraacrylate (PETA). AFM, electron microscopy and fluorescence labeling studies are used to investigate the morphology of the capsules. The P85 micelles are integrated into the L121 polymersome walls, while both types of Pluronic block copolymer are also non-covalently trapped in their respective interpenetrating acrylate networks. The micelle-containing vesicles retain their size upon heating until at least 33 °C. Upon cooling below room temperature the vesicles reversibly lose block copolymers. It was shown that the double-stabilized vesicles are readily internalized in HeLa and Caco-2 cells.
    Net Charge Affects Morphology and Visual Properties of Ovalbumin Aggregates
    Weijers, M. ; Broersen, K. ; Barneveld, P.A. ; Cohen Stuart, M.A. ; Hamer, R.J. ; Jongh, H.H.J. de; Visschers, R.W. - \ 2008
    Biomacromolecules 9 (2008)11. - ISSN 1525-7797 - p. 3165 - 3172.
    heat-induced denaturation - beta-lactoglobulin - light-scattering - protein aggregation - globular protein - amyloid fibrils - ionic-strength - neutral ph - gelation - prediction
    The effect of ovalbumin net charge on aggregate morphology and visual properties was investigated using chromatography, electrophoresis, electron microscopy, and turbidity measurements. A range of differently charged ovalbumin variants (net charge ranging from ¿1 to ¿26 at pH 7) was produced using chemical engineering. With increasing net charge, the degree of branching and flexibility of the aggregates decreased. The turbidity of the solutions reflected the aggregate morphology that was observed with transmission electron microscopy. Increasing the stiffness of the aggregates transformed the solutions from turbid to transparent. Artificially shielding the introduced net charge by introducing salt in the solution resulted in an aggregate morphology that was similar to that for low-net-charge variants. The morphology of heat-induced aggregates and the visual appearance of the solutions were significantly affected by net charge. We also found that the morphology of ovalbumin aggregates can be rapidly probed by high-throughput turbidity experiments.
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