- N.A.M. Besseling (1)
- P.M. Biesheuvel (1)
- T.M. Birshtein (4)
- O.V. Borisov (3)
- C.I. Butré (1)
- M. Charlaganov (1)
- M.A. Cohen Stuart (3)
- A.M. Donald (2)
- G.J. Fleer (4)
- R.G. Fokkink (1)
- T. Gilich (1)
- T. Gillich (1)
- H. Gruppen (1)
- J. Gucht van der (3)
- V.A. Ivanov (1)
- P.G. Khalatur (1)
- A.R. Khokhlov (1)
- L.I. Klushin (1)
- P. Kosovan (1)
- A. Kroes-Nijboer (1)
- F.A.M. Leermakers (9)
- M. Lemmers (1)
- E. Linden van der (3)
- S. Lindhoud (1)
- E.H. Lucassen-Reynders (1)
- J. Lyklema (1)
- A.A. Mercurieva (1)
- W. Norde (1)
- J.M.P. Oever (1)
- J.P.M. Ploeg van der (1)
- A.A. Polotsky (3)
- S.W. Prescott (1)
- S.S. Rogers (2)
- O.V. Rud (2)
- V. Rud (1)
- L.M.C. Sagis (2)
- R. Schweins (1)
- N.P. Shusharina (1)
- A.M. Skvortsov (2)
- E. Spruijt (2)
- M. Textor (2)
- S. Tindemans (1)
- M. Veen van der (1)
- P. Venema (3)
- T. Vermonden (1)
- I.K. Voets (1)
- W.M. Vos de (1)
- R.J. Vries de (1)
- A.A. Well van (1)
- P.A. Wierenga (1)
- E.B. Zhulina (1)
Influence of water availability on the enzymatic hydrolysis of proteins
Butré, C.I. ; Wierenga, P.A. ; Gruppen, H. - \ 2014
Process Biochemistry 49 (2014)11. - ISSN 1359-5113 - p. 1903 - 1912.
substrate-inhibition - functional-properties - ionic-strength - amino-acid - hydration - nmr - macromolecules - mechanism - kinetics - protease
The overall rate of enzymatic protein hydrolysis decreases with increasing protein concentration (0.1–30% (w/v)) at constant enzyme/substrate ratio. To understand the role of water, the amount of available water was expressed as the ratio between free and bound water and experimentally determined from water activity and T2 relaxation time (NMR) measurements. At low protein concentrations a large excess of water is present (1.5 × 106 water molecules per protein molecule at 0.1% (w/v) whey protein isolate (WPI), but only 3984 at 30% (w/v) WPI. Assuming that 357 molecules of water are needed for full hydration of the protein, these values correspond to a 4280 and 11 times excess of water, showing that at 30% (w/v) WPI the amount of water becomes limited. At the same time, only a small decrease was observed in water activity (1.00–0.997 for 0.1–30% (w/v) WPI), and an increase of bound water measured by NMR (
Dendron brushes and dendronized polymers: a theoretical outlook
Borisov, O.V. ; Polotsky, A.A. ; Rud, V. ; Zhulina, E.B. ; Leermakers, F.A.M. ; Birshtein, T.M. - \ 2014
Soft Matter 10 (2014)13. - ISSN 1744-683X - p. 2093 - 2101.
mean-field model - monte-carlo - persistence length - scaling theory - good solvent - dendrimers - macromolecules - conformations - simulation - core
Dendron brushes are molecular structures built up of treelike macromolecules, with multiple generations of branches, grafted with a root segment to a surface (particle) or to a backbone chain (dendronized polymer) with a sufficiently high grafting density so that the dendrons interact laterally. Recent advances in the theory of dendron brushes are highlighted and complemented by insights from numerical self-consistent field modelling. Our focus is on controversial issues, which are still under debate, such as, the strain distribution in individual dendrons and the appearance of distinct populations with a different extent of stretching for dendrons in planar brushes. We anticipate that dendritic brushes (i) show a strong resistance against bending, which may manifest in a high apparent persistence length of dendronized polymers, and (ii) have an unusually large beneficial effect on the colloidal stability due to the sharp steric repulsive interaction observed when these surface layers are pushed towards the overlap.
Dendritic spherical polymer brushes: Theory and self-consistent field modeling
Rud, O.V. ; Polotsky, A.A. ; Gillich, T. ; Borisov, O.V. ; Leermakers, F.A.M. ; Textor, M. ; Birshtein, T.M. - \ 2013
Macromolecules 46 (2013)11. - ISSN 0024-9297 - p. 4651 - 4662.
polyelectrolyte brushes - scaling theory - conformations - macromolecules - dendrimers
Equilibrium structural properties of polymer brushes formed by dendrons grafted via the root segment onto spherical surfaces (dendritic spherical polymer brushes, DSPB) are studied by means of the Scheutjens–Fleer self-consistent field (SF-SCF) numerical approach and scaling analysis. In particular, we focus on the effects of the variable curvature of the surface on the polymer volume fraction distribution and extension of the individual dendrons in DSPB. A systematic comparison with spherical polymer brushes formed by linear polymer chains (LSPB) end-grafted to the surfaces of the same curvature radii is performed. We demonstrate that the difference in internal structural organization of DSPB and LSPB is most pronounced at small curvature radius of the grafting surface. In particular, the radial distribution of polymer volume fraction in DSPB is close to uniform, whereas in LSPB it decays in the radial direction following a power law. The quasi-plateau polymer volume fraction distribution in DSPB is ensured by wide radial distribution of the end segments. In contrast, in LSPB the end segments of the chains are localized preferentially close to the periphery of the brush. An increase in the curvature radius of the surface is accompanied by emerging segregation into two (or more, for larger number of generations) populations of dendrons: the less extended and the more extended ones. The former ones fill the space in the central region of the DSPB, and the latter bring the majority of the monomer units closer to the periphery of the DSPB. The theoretical results are in line with experimental findings on hydrodynamic radii of linear and dendritic poly(ethylene glycol) brushes end-grafted onto Fe3O4 nanoparticles.
Structure and dynamics of polyelectrolyte complex coacervates studied by scattering of neutrons, X-rays, and light
Spruijt, E. ; Leermakers, F.A.M. ; Fokkink, R.G. ; Schweins, R. ; Well, A.A. van; Cohen Stuart, M.A. ; Gucht, J. van der - \ 2013
Macromolecules 46 (2013)11. - ISSN 0024-9297 - p. 4596 - 4605.
gelatin/polyelectrolyte complexes - angle scattering - reversible gels - micelles - polymer - protein - macromolecules - chloride) - interface - hydrogels
We investigate the microscopic structure and density fluctuations of complex coacervates of flexible polyelectrolytes using scattering of neutrons, X-rays, and light. Poly(acrylic acid) and poly(N,N-dimethylaminoethyl methacrylate) offer a well-defined model system that allows for selective labeling and systematic variation of the strength of the attractive electrostatic interactions. Two neutron scattering experiments have been carried out: (i) we use deuterated polymeric tracers in a complex coacervate with an overall neutron scattering length density that is matched to that of the solvent, to probe the conformation of single polymer chains in the complex coacervates, and (ii) we measure complex coacervates in which all polymer chains of one type are deuterated, to probe their overall structure. The single chain static structure factors reveal that both polycations and polyanions have an ideal Gaussian chain conformation in the complex coacervates. At the same time, the overall structure is similar to that of a semidilute polymer solution, with polycations and polyanions strongly overlapping to form a network with a mesh size that is much smaller than the radius of gyration of the polymers. The mesh size decreases with decreasing salt concentration, following a scaling that is in good agreement with predictions from the corresponding salt–polymer phase diagram. These findings are confirmed by complementary X-ray scattering experiments. Finally, in all scattering experiments with light, X-rays, and neutrons, and for all polymer chain lengths and salt concentrations, we find a remarkable low-q excess scattering, following a power law with a slope close to -2. This points to the presence of equilibrium, large-scale density fluctuations in the complex coacervates. Dynamic light scattering experiments reveal two complementary diffusive modes in the complex coacervates, corresponding to fluctuations of the polymer mesh and diffusion of domains of varying density, respectively
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.
Collapse of polyelectrolyte star. Theory and modelling
Rud, O.V. ; Mercurieva, A.A. ; Leermakers, F.A.M. ; Birshtein, T.M. - \ 2012
Macromolecules 45 (2012)4. - ISSN 0024-9297 - p. 2145 - 2160.
branched polyelectrolytes - homopolymer globule - copolymer micelles - block-copolymers - polymer brushes - conformations - layer - macromolecules - surfaces - solvent
The collapse of hydrophobic polyelectrolyte stars in aqueous solutions is studied using the Scheutjens–Fleer self-consistent field (SF-SCF) approach. The hydrophobic property of the segments tends to compact the stars, whereas the presence of charges has the opposite effect. As a result, star conformations can be switched from an extended, strongly hydrated, and swollen state to a collapsed state via semicollapsed, quasi-micellar state using control parameters such as the solvent quality, specified by the Flory–Huggins parameter, the pH value or the ionic strength. More specifically, there exists a range of parameters wherein the stars have an inhomogeneous radial structure with a collapsed region, referred to as the core, and a swollen region forming the corona. In such microphase segregated state the fraction of arms of the star that form the core, or alternatively escape into the swollen corona, can be controlled. The SF-SCF analysis is complemented with analytical models to rationalize the complex phase behavior.
Reconciling lattice and continuum models for polymers at interfaces
Fleer, G.J. ; Skvortsov, A.M. - \ 2012
Journal of Chemical Physics 136 (2012)13. - ISSN 0021-9606
segmental adsorption energies - scheutjens-fleer theory - analytical approximation - depletion thickness - dilute-solution - surface - macromolecules - silica
It is well known that lattice and continuum descriptions for polymers at interfaces are, in principle, equivalent. In order to compare the two models quantitatively, one needs a relation between the inverse extrapolation length c as used in continuum theories and the lattice adsorption parameter ¿¿(s) (defined with respect to the critical point). So far, this has been done only for ideal chains with zero segment volume in extremely dilute solutions. The relation ¿¿(s)(c) is obtained by matching the boundary conditions in the two models. For depletion (positive c and ¿¿(s)) the result is very simple: ¿¿(s) = ln(1 + c/5). For adsorption (negative c and ¿¿(s)) the ideal-chain treatment leads to an unrealistic divergence for strong adsorption: c decreases without bounds and the train volume fraction exceeds unity. This due to the fact that for ideal chains the volume filling cannot be accounted for. We extend the treatment to real chains with finite segment volume at finite concentrations, for both good and theta solvents. For depletion the volume filling is not important and the ideal-chain result ¿¿(s) = ln(1 + c/5) is generally valid also for non-ideal chains, at any concentration, chain length, or solvency. Depletion profiles can be accurately described in terms of two length scales: ¿ = tanh(2)[(z + p)/d], where the depletion thickness (distal length) d is a known function of chain length and polymer concentration, and the proximal length p is a known function of c (or ¿¿(s)) and d. For strong repulsion p = 1/c (then the proximal length equals the extrapolation length), for weaker repulsion p depends also on chain length and polymer concentration (then p is smaller than 1/c). In very dilute solutions we find quantitative agreement with previous analytical results for ideal chains, for any chain length, down to oligomers. In more concentrated solutions there is excellent agreement with numerical self-consistent depletion profiles, for both weak and strong repulsion, for any chain length, and for any solvency. For adsorption the volume filling dominates. As a result c now reaches a lower limit c ˜ -0.5 (depending slightly on solvency). This limit follows immediately from the condition of a fully occupied train layer. Comparison with numerical SCF calculations corroborates that our analytical result is a good approximation. We suggest some simple methods to determine the interaction parameter (either c or ¿¿(s)) from experiments. The relation ¿¿(s)(c) provides a quantitative connection between continuum and lattice theories, and enables the use of analytical continuum results to describe the adsorption (and stretching) of lattice chains of any chain length. For example, a fully analytical treatment of mechanical desorption of a polymer chain (including the temperature dependence and the phase transitions) is now feasible.
Modeling the structure and antifouling properties of a polymer brush of grafted comb-polymers
Vos, W.M. de; Leermakers, F.A.M. ; Lindhoud, S. ; Prescott, S.W. - \ 2011
Macromolecules 44 (2011)7. - ISSN 0024-9297 - p. 2334 - 2342.
consistent-field analysis - protein adsorption - branched polymers - chain molecules - scaling theory - surface - macromolecules - behavior
Numerical self-consistent field theory is used to study the structural characteristics of a polymer brush consisting of end-grafted comb-polymers. A comb-polymer brush is shown to retain the parabolic density profile characteristic of the unbranched brush. Increasing either the number of branches or the length of the side-chains leads to an increase in the height (H) of the brush. This is partly because of the branched structure: it is more favorable to stretch the polymer backbone, while leaving the side-chains almost unstretched. The other reason for the increased stretching is simply because of the extra polymer in the brush due to the branches. We find that it does not matter how the side-chains are distributed along the backbone for the predicted density profile; it is only the total amount of polymer in the side-chains that is important. The effect of branching on the brush height can be captured in a simple scaling law: H Nb(NT/Nb)2/3, where Nb is the chain length of the polymer backbone, NT is the total chain length, thus including the side-chains, and their ratio NT/Nb is a measure for the amount of branching. The structure of the branched brush is less suitable for keeping away small particles from the grafted interface. It is, however, a good way of increasing the polymer density, and thus its antifouling properties, when the grafting density of the brush is limited
Dendritic versus linear polymer brushes: Self-consistent field modeling, scaling theory, and experiments
Polotsky, A.A. ; Gilich, T. ; Borisov, O.V. ; Leermakers, F.A.M. ; Textor, M. ; Birshtein, T.M. - \ 2010
Macromolecules 43 (2010)22. - ISSN 0024-9297 - p. 9555 - 9566.
neurofilament brush - ionic-strength - monte-carlo - chains - macromolecules - stabilization - conformation - simulation - surfaces - collapse
Equilibrium structural properties of polymer brushes formed by dendritic polymer chains (dendrons) are studied by means of Scheutjens-Fleer self-consistent field (SF-SCF) modeling and scaling analysis. Limiting cases of minimal and maximal possible losses of conformational entropy corresponding to different assumptions concerning distribution of elastic tension in the end-grafted dendrons are analyzed on the basis of the Flory-type scaling approach. The numerical SCF modeling indicates that the effective exponent of the power-law dependence for the height of dendritic brush on the grafting density differs from that derived within the Flory-type approximation. This is explained by changing of the intramolecular elastic tension distribution upon an increase in grafting density. The distributions of end and branching points are wide and exhibit multiple maxima, pointing to a broad distribution in the chain stretching. This distribution leads to monotonically decreasing overall density profiles. The theoretical results are in line with experimental findings on linear and dendritic poly(ethylene glycol) layers end-grafted onto TiO2 surfaces
Fracture of Protein Fibrils As Induced by Elongational Flow
Kroes-Nijboer, A. ; Venema, P. ; Baptist, H.G.M. ; Linden, E. van der - \ 2010
Langmuir 26 (2010)16. - ISSN 0743-7463 - p. 13097 - 13101.
transient extensional flow - beta-lactoglobulin gels - whey-protein - amyloid fibrils - induced scission - dilute-solution - ph 2 - macromolecules - heat - degradation
The length distribution of whey protein fibrils is important for application purposes. However, it is hard to influence the length distribution of whey protein fibrils during production. One way of influencing the length distribution of the mature fibrils is exposing them to an external field, like a flow field. In this research whey protein fibrils were exposed to elongational flow to fracture the fibrils. A simple experimental setup was used to establish a range of elongational strain rates. The length distribution of the fractured fibrils was determined using transmission electron microscopy and was shown to be controllable at relatively low strain rates.The length distribution of whey protein fibrils is important for application purposes. However, it is hard to influence the length distribution of whey protein fibrils during production. One way of influencing the length distribution of the mature fibrils is exposing them to an external field, like a flow field. In this research whey protein fibrils were exposed to elongational flow to fracture the fibrils. A simple experimental setup was used to establish a range of elongational strain rates. The length distribution of the fractured fibrils was determined using transmission electron microscopy and was shown to be controllable at relatively low strain rates.
Temperature effects in the mechanical desorption of an infinitely long lattice chain: Re-entrant phase diagrams
Skvortsov, A.M. ; Klushin, L.I. ; Fleer, G.J. ; Leermakers, F.A.M. - \ 2009
Journal of Chemical Physics 130 (2009). - ISSN 0021-9606 - p. 174704 - 174704.
self-avoiding walks - surface critical-behavior - field-theory approach - single-stranded-dna - monte-carlo - polymer-chain - solid-surface - adsorption - macromolecules - force
We consider the mechanical desorption of an infinitely long lattice polymer chain tethered at one end to an adsorbing surface. The external force is applied to the free end of the chain and is normal to the surface. There is a critical value of the desorption force ftr at which the chain desorbs in a first-order phase transition. We present the phase diagram for mechanical desorption with exact analytical solutions for the detachment curve: the dependence of ftr on the adsorption energy (at fixed temperature T) and on T (at fixed ). For most lattice models ftr(T) displays a maximum. This implies that at some given force the chain is adsorbed in a certain temperature window and desorbed outside it: the stretched state is re-entered at low temperature. We also discuss the energy and heat capacity as a function of T; these quantities display a jump at the transition(s). We analyze short-range and long-range excluded-volume effects on the detachment curve ftr(T). For short-range effects (local stiffness), the maximum value of ftr decreases with stiffness, and the force interval where re-entrance occurs become narrower for stiffer chains. For long-range excluded-volume effects we propose a scaling ftr~T1-(Tc-T)/ around the critical temperature Tc, where =0.588 is the Flory exponent and 0.5 the crossover exponent, and we estimated the amplitude. We compare our results for a model where immediate step reversals are forbidden with recent self-avoiding walk simulations. We conclude that re-entrance is the general situation for lattice models. Only for a zigzag lattice model (where both forward and back steps are forbidden) is the coexistence curve ftr(T) monotonic, so that there is no re-entrance
New ends to the tale of tails: adsorption of comb polymers and the effect on colloid stability
Charlaganov, M. ; Kosovan, P. ; Leermakers, F.A.M. - \ 2009
Soft Matter 5 (2009)7. - ISSN 1744-683X - p. 1448 - 1459.
interacting chain molecules - statistical-theory - field theory - interfaces - surface - layers - macromolecules - weight
In this paper we consider the classical problem of homopolymer adsorption at the solid–liquid interface and discuss its implications for colloidal stability. More specifically, our focus is on comb-like homopolymers in the strong adsorption limit. A self-consistent field analysis shows that for relatively long side chains but still much longer backbones, the adsorbed layer is dominated by the side chains near the surface, whereas at larger distances the layer has features that belong to the backbone. As a rule, homopolymer adsorption promotes flocculation of colloids. This is attributed to the long polymer chains that form bridges between the colloidal particles. However, the free ends of the chains do not participate in the bridging and thus contribute with a small repulsive term to the mainly attractive pair interaction. For comb polymers, the free ends of the side chains amplify the repulsion dramatically. As a result, in contrast to linear adsorbed homopolymers, comb polymers typically prevent flocculation
Biomolecular design elements : cortical microtubes and DNA-coated colloids
Tindemans, S. - \ 2009
University. Promotor(en): Bela Mulder. - [S.l. : S.n. - ISBN 9789085853954 - 172 p.
microtubuli - celskelet - moleculaire structuur - macromoleculen - microtubules - cytoskeleton - molecular conformation - macromolecules
This thesis deals with the self-organizing properties of systems of biomolecules.
Compression/expansion rheology of oil/water interfaces with adsorbed proteins. Comparison with the air/water surface
Benjamins, J. ; Lyklema, J. ; Lucassen-Reynders, E.H. - \ 2006
Langmuir 22 (2006)14. - ISSN 0743-7463 - p. 6181 - 6188.
liquid-liquid interface - beta-casein adsorption - air-water-interface - fluid interfaces - hexadecane/water interface - flexible proteins - drop tensiometer - layers - monolayers - macromolecules
Dynamic interfacial tensions and surface dilational moduli were measured for four proteins at three fluid interfaces, as a function of time and concentration. The proteins-ß-casein, ß-lactoglobulin, bovine serum albumin, and ovalbumin - were adsorbed from aqueous solution against air, n-tetradecane, and a triacylglycerol oil. The sinusoidal interfacial compression/expansion, at frequencies ranging from 0.005 to 0.5 Hz, was effected in a dynamic drop tensiometer suited to viscous oil phases. Generally, at interfacial pressures up to 15 mN/m, dilational moduli were purely elastic at frequencies from 0.1 Hz. In this elastic range, in-surface relaxation either was essentially completed or had not yet started within a time on the order of 10 s. Within this time span, protein exchange with the bulk solution was negligible. In cases where in-surface relaxation was completed in the imposed time, the moduli depended only on the equilibrium ¿(¿) relationship. We interpret these results in terms of a simple two-dimensional solution model, based on a Gibbs dividing surface, accounting for nonideal mixing to the first order with respect to both entropy and enthalpy. Interfacial mixing enthalpy is shown to have a major effect on the elasticity, with both quantities increasing in the sequence triacylglycerol ¿ tetradecane ¿ air. We also suggest a strong correlation between enthalpy and clean-interface tension that increases in the same order. At each interface, the enthalpy increases with increasing molecular rigidity: ß-casein ¿ ß-lactoglobulin ¿ bovine serum albumin ¿ ovalbumin. Best agreement with the experimental data was obtained with a recently extended version of the model accounting for proteins adopting smaller molecular areas with increasing surface pressure. For interfacial pressures above 15 mN/m, the moduli were generally no longer purely elastic, with viscous loss angles ranging up to 36 degrees. In this range of high pressures, the moduli depended on relaxation mechanisms for which specific kinetic models must be developed
Investigating the Permanent Electric Dipole Moment of ß-Lactoglobulin Fibrils, Using Transient Electric Birefringence
Rogers, S.S. ; Venema, P. ; Ploeg, J.P.M. van der; Linden, E. van der; Sagis, L.M.C. ; Donald, A.M. - \ 2006
Biopolymers 82 (2006)3. - ISSN 0006-3525 - p. 241 - 252.
amyloid fibrils - polyelectrolyte solutions - length distribution - protein - nmr - macromolecules - polarizability - spectroscopy - aggregation - constraints
Amyloid fibrils, which are polymeric assemblies of protein molecules, have been intensively studied on a structural level, yet due to complications such as the disorder within the molecules, several aspects of their structure remain mysterious. Similarly, the kinetics of assembly are not well understood. Here we investigate the electric dipole moment of ß-lactoglobulin fibrils, a model amyloid fibril system, by applying the technique of transient electric birefringence. This moment appears to be large, and comparable to the total moment of the constituent protein monomers if they were joined in a chain, head-to-tail, without changing conformation, suggesting an ordered joining of monomers in the fibril. Such an ordered assembly may have implications for the assembly mechanism of ß-lactoglobulin fibrils in particular, and amyloid fibrils in general
Supramolecular coordination polymers in water: rings, chains and networks
Vermonden, T. - \ 2005
University. Promotor(en): Ernst Sudhölter, co-promotor(en): Ton Marcelis. - s.l. : S.n. - ISBN 9085041481 - 128 p.
polymeren - moleculaire structuur - synthese - macromoleculen - supramoleculaire chemie - polymers - molecular conformation - synthesis - macromolecules - supramolecular chemistry
A modified Poisson-Boltmann model including charge regulation for the adsorption of ionizable polyelectrolytes to charged interfaces, applied to lysozyme adsorption on silica
Biesheuvel, P.M. ; Veen, M. van der; Norde, W. - \ 2005
The Journal of Physical Chemistry Part B: Condensed Matter, Materials, Surfaces, Interfaces & Biophysical 109 (2005)9. - ISSN 1520-6106 - p. 4172 - 4180.
electrostatic free-energy - protein adsorption - double-layer - weak polyelectrolytes - equilibrium-constants - surfaces - complexes - macromolecules - computation - particles
The equilibrium adsorption of polyelectrolytes with multiple types of ionizable groups is described using a modified Poisson-Boltzmann equation including charge regulation of both the polymer and the interface. A one-dimensional mean-field model is used in which the electrostatic potential is assumed constant in the lateral direction parallel to the surface. The electrostatic potential and ionization degrees of the different ionizable groups are calculated as function of the distance from the surface after which the electric and chemical contributions to the free energy are obtained. The various interactions between small ions, surface and polyelectrolyte are self-consistently considered in the model, such as the increase in charge of polyelectrolyte and surface upon adsorption as well as the displacement of small ions and the decrease of permittivity. These interactions may lead to complex dependencies of the adsorbed amount of polyelectrolyte on pH, ionic strength, and properties of the polymer (volume, permittivity, number, and type of ionizable groups) and of the surface (number of ionizable groups, pK, Stern capacity). For the adsorption of lysozyme on silica, the model qualitatively describes the gradual increase of adsorbed amount with pH up to a maximum value at pHc, which is below the iso-electric point, as well as the sharp decrease of adsorbed amount beyond pHc. With increasing ionic strength the adsorbed amount decreases (for pH > pHc), and pHc shifts to lower values.
Measuring the Length Distribution of a Fibril System: a Flow Birefringence Technique applied to Amyloid Fibrils
Rogers, S.S. ; Venema, P. ; Sagis, L.M.C. ; Linden, E. van der; Donald, A.M. - \ 2005
Macromolecules 38 (2005)7. - ISSN 0024-9297 - p. 2948 - 2958.
beta-lactoglobulin gels - rodlike chains subject - transient shear-flow - rheooptical response - carbon nanotubes - protein - macromolecules - polydispersity - disease - fibers
Relaxation of flow birefringence can give a direct measure of the rotational diffusion of rodlike objects in solution. With a suitable model of the rotational diffusivity, a length distribution can be sought by fitting the decay curve. We have measured the flow birefringence decay from solutions of amyloid fibrils composed of ß-lactoglobulin and extracted a length distribution using the Doi-Edwards-Marrucci-Grizzuti theory of semidilute rotational diffusion. The concentration scaling of the results shows that the fibrils diffuse as free rods: they cannot be significantly branched, sticky, or break up under dilution. The length distribution obtained shows a single broad peak, consistent with measurements of the fibrils by electron microscopy. This comparison, and combination of the experiment with an assay to find the total concentration of fibrils, allows calibration of the length scale and concentration scale of the length distribution. It is our hope that this method can be used for following the growth kinetics of amyloid fibrils in vitro and for studying the length distribution of rodlike systems in general
Adsorption of charged macromolecules on a gold electrode
Barten, D. - \ 2003
University. Promotor(en): Martien Cohen Stuart, co-promotor(en): Mieke Kleijn. - Wageningen : S.n. - ISBN 9058089282 - 104 p.
elektrodes - elektrolyten - adsorptie - macromoleculen - electrodes - electrolytes - adsorption - macromolecules
|Soluble complexes of gum arabic with alfa-lactalbumin and beta-lactoglobulin above the protein isoelectric point: analysis in terms of charge patches
Vries, R.J. de - \ 2003
In: Food Colloids, Biopolymers and Materials / Dickinson, E., Vliet, T. van, Cambridge : Royal Society of Chemistry (Special Publications 284) - ISBN 0854048715 - p. 329 - 344.
alfa-lactalbumine - bèta-lactoglobuline - arabische gom - iso-elektrisch punt - colloïdale eigenschappen - macromoleculen - alpha-lactalbumin - beta-lactoglobulin - gum arabic - isoelectric point - colloidal properties - macromolecules