Records 21 - 40 / 397
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 18.104.22.168) 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.