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J Lyklema

Publications and source records attributed to J Lyklema.

14 recordsLinked to original sources
PubMed2000

An Improved Method for Calculating Zeta-Potentials from Measurements of the Electrokinetic Sonic Amplitude.

The surface electric properties of the commercially available silica, Monospher 1000 (Fa. Merck), have been studied by conductivity and ESA (electrokinetic sonic amplitude) experiments. It could be shown that accounting for the contribution of the stagnant layer to surface conductivity is indispensable in the interpretation of electrokinetic data at low ionic strength. A general method has been put forward which allows to take into account the total, experimentally accessible surface conductivity in the evaluation of ESA data of moderately concentrated suspensions. This includes additional conductivity measurements which serve for the independent estimation of the total relative surface conductivity. The resulting zeta-potentials are clearly higher than those obtained after neglecting the contribution of the stagnant layer to surface conductivity. In addition, the ionic mobilities of potassium and magnesium in the hydrodynamically stagnant layer have been investigated in some detail. It has been found that the ionic mobility of potassium is of the same order of magnitude as in the bulk solution while the mobility of magnesium is significantly reduced. Copyright 2000 Academic Press.

Journal Article↗
PubMed1999

Interaction between fatty acid salts and elastin: kinetics, absorption equilibrium, and consequences for elasticity.

Elastin from bovine ligamentum nuchae is incubated in aqueous solutions of sodium salts of fatty acids (FAS). The FAS are laurate, myristate, and palmitate. Absorption of FAS in the elastin network is studied as a function of time, FAS concentration, and ionic strength. The consequences of this uptake for the elasticity of the elastin are studied by static and dynamic stress-strain measurements. Generally, distinction must be made between the initial time-dependent stage (I) and the final equilibrium stage (II). In I the initial rate of absorption follows a second-order binding mechanism, with the rate constant increasing with decreasing length of the FAS. In this regime, the elasticity modulus remains more or less unaffected. Especially in regime II the absorption of FAS is enhanced by a reduction in the cross-link density in the elastin network. This is ascribed to an osmotic pressure primarily caused by the concomitant uptake of low molecular weight ions in the elastin. The absorption equilibrium can be described by Langmuir theory. The absorption affinity increases with increasing hydrocarbon chain length of the FAS, indicating the contribution of hydrophobic interaction. Although the elasticity is not lost, the modulus is now reduced and a concomitant viscous component is developed.

Animals↗
PubMed1998

Low-Frequency Dielectric Response of Polystyrene Latex Dispersions.

The low-frequency permittivity and the conductivity increments of a well-characterized polystyrene sulfate latex with constant surface charge density were measured in KCl electrolyte solutions. The ionic strength was varied in the range 0.4-6 mM. The data could be explained with one absolute surface-conductivity parameter over the complete concentration range. The titratable surface charge density correlates well with the surface conductivity, the ions in the double layer having the bulk mobility. The results are in good agreement with static conductivities of plugs composed of the same particles obtained in a previous study (1). The electrokinetic charge obtained from streaming potentials (1) in that study is significantly lower, confirming the presence of conduction behind the shear plane. In order to interpret the conductivity data, simple analytical expressions have been derived for the frequency-dependent complex conductivity of a dilute dispersion of spherical particles with relatively thin double layers (kappaa >>1, where a is the particle radius and kappa-1 the Debye screening length). The expressions are restricted to binary suspending electrolytes. However, no restrictions on the ion mobilities and ion valencies are made. Our results agree well with the numerical results of the dielectric model of Mangelsdorf and White (2, 3) and reduce to O'Brien's static conductivity results (4) in the limit of low frequencies. Copyright 1998 Academic Press.

Journal Article↗
PubMed1997

Conductivity and Dielectric Dispersion of Gram-Positive Bacterial Cells

The conductivity of bacterial cell suspensions has been studied over a wide range of ionic strengths and is interpreted in terms of their cell wall properties. The experimental data have been analyzed after improving the high kappaa double-layer theory of Fixman, by accounting for ionic mobility in the hydrodynamically stagnant layer, i.e., in the bacterial wall. Static conductivity and dielectric dispersion measurements both show that the counterions in the porous gel-like cell wall give rise to a considerable surface conductance. From a comparison of the mobile charge with the total cell wall charge it is inferred that the mobilities of the ions in the bacterial wall are of the same order but somewhat lower than those in the bulk electrolyte solution. The occurrence of surface conductance reduces the electrophoretic mobility in electrophoresis studies. If this effect is not taken into account, the zeta-potential will be underestimated, especially at low electrolyte concentrations.

Journal Article↗
PubMed1991

Thermodynamics of ion binding by proteins. Phenomenological linkage relations for binding of electrolyte and interpretation by double layer theory.

In this paper we report a new set of thermodynamic linkage relations for the binding of electrolyte by proteins. The relations are derived for protein solutions in membrane equilibrium with a reference solution, allowing a phenomenological definition of ion binding. This is an extension of Wyman's linkage theory. The theory is applied to the electrolyte dependence of proton titration curves for bovine serum albumin in KCl solution (C. Tanford, S. A. Swanson and W. S. Shore, J. Am. Chem. Soc. 77 (1955) 6414). The curves are re-analysed in terms of Esin-Markov coefficients. In addition, we discuss the interpretation of the phenomenological K+ and Cl- binding numbers in terms of a two-state binding model, in which part of the ions are thought to adsorb on specific sites at the protein surface and/or part in the diffuse layer. It is shown that the electrolyte binds largely in the diffuse layer, especially when the protein surface charge is high.

Electrolytes↗
PubMed1991

Interfacial thermodynamics of protein adsorption and ion co-adsorption. III. Electrochemistry of bovine serum albumin adsorption on silver iodide.

An experimental analysis of charge regulation in protein adsorption is presented. The model system consists of colloidal particles of the slightly water soluble salt silver iodide as the adsorbent and the protein bovine serum albumin as the adsorbate. Protein adsorption experiments corroborate earlier findings that albumin adsorbs maximally close to the isoelectric point of the protein. The adsorption is reversible with respect to protein-protein exchange. The charge regulation is studied by novel potentiometric titrations. The Galvani potential of the adsorbent, partially covered with protein, is varied by the addition of AgNO3/KI while the pH is kept constant by means of a pH-stat. It is shown that the ion co-adsorption is a linear decreasing function of the blank surface charge density. The results are consistent with thermodynamics: for the first time a few phenomenological linkage relations between the ion co-adsorptions and chemical potentials are verified experimentally. The charge regulation is interpreted in terms of a contact layer model, which explains the ion co-adsorption by compounded ion exchange equilibria in the small layer of atomic contact between adsorbed protein and surface.

Adsorption↗
PubMed1990

Statistical thermodynamics of association colloids. IV. Inhomogeneous membrane systems.

A previously developed self-consistent field theory to describe the equilibrium properties of lipid-like membranes is extended to allow the presence of inhomogeneities parallel to the membrane. Conformations of lipid molecules and foreign ('guest') molecules in the membrane are obtained by step-weighted random walk generation of the chains on a lattice, where the theory is made two-dimensional to account for the parallel inhomogeneities. No pre-assigned positions of the head groups, or other parts of the molecules, are introduced. Nearest neighbor interactions are accounted for through Flory-Huggins type interaction parameters. The theory is applied to the incorporation of trans-membrane molecules and conditions for channel formation are discussed. Lateral phase separation in membranes consisting of non-mixing lipids is also considered. Water only slightly enriches the boundary between the two lipid regions. The aliphatic chains are very well able to smoothly cover inhomogeneities in the bilayer. No indications of instability of the membrane due to the induced inhomogeneities are found.

Lipid Bilayers↗
PubMed1990

Influence of interfaces on microbial activity.

Bacterial adhesion in natural and artificial systems has been critically reviewed to investigate the influences exerted by the presence of interfaces. Numerous investigations have demonstrated that, in the presence of a solid phase, the activity of bacterial cultures is changed. Reviewing relevant literature, two problems were encountered. One is of an experimental nature. Due to lack of similarity in experimental conditions, disparate experiments often cannot be compared; their results may even appear conflicting. The other problem is of an interpretational nature: several hypothetical theories exist which try to explain the effect of surfaces on microbial activity. These theories often confuse changes in the medium and limitations in mass transfer which are due to the presence of solid surfaces (indirect influences) with changes in cell properties (direct influences). Whenever a surface is reported to influence the metabolism of bacteria, the action is found almost exclusively to be due to changes in the medium or environment and is therefore indirect. Based on data reported in the literature, and by using thermodynamic and kinetic considerations, it is concluded that so far neither experimental nor theoretical evidence exists for a direct influence of interfaces on microbial activity.

Bacteria↗
PubMed1987

The role of bacterial cell wall hydrophobicity in adhesion.

In this study, the adhesion of bacteria differing in surface hydrophobicity was investigated. Cell wall hydrophobicity was measured as the contact angle of water on a bacterial layer collected on a microfilter. The contact angles ranged from 15 to 70 degrees. This method was compared with procedures based upon adhesion to hexadecane and with the partition of cells in a polyethylene glycol-dextran two-phase system. The results obtained with these three methods agreed reasonably well. The adhesion of 16 bacterial strains was measured on sulfated polystyrene as the solid phase. These experiments showed that hydrophobic cells adhered to a greater extent than hydrophilic cells. The extent of adhesion correlated well with the measured contact angles (linear regression coefficient, 0.8).

Alkanes↗
PubMed1987

Electrophoretic mobility and hydrophobicity as a measured to predict the initial steps of bacterial adhesion.

The relationship between physiochemical surface parameters and adhesion of bacterial cells to negatively charged polystyrene was studied. Cell surface hydrophobicity and electrokinetic potential were determined by contact angle measurement and electrophoresis, respectively. Both parameters influence cell adhesion. The effect of the electrokinetic potential increases with decreasing hydrophobicity. Cell surface characteristics determining adhesion are influenced by growth conditions. At high growth rates, bacterial cells tend to become more hydrophobic. This fact can be of ecological significance for controlling the spread of bacteria throughout the environment.

Bacteria↗
PubMed1983

On the statistical thermodynamics of membrane formation.

Modifying a procedure developed by Scheutjens and Fleer (J. Phys. Chem. 83 (1979) 1619; J. Phys. Chem. 84 (1980) 178) to describe adsorption of polymers, a lattice theory is proposed to formulate the formation and properties of amphiphilic bilayer membranes. In this theory individual conformations are distinguished and lateral interactions are taken into account in a Flory-Huggins approximation. Probability distributions of head, tail and solvent segments are computed and it is shown that they are not narrow, i.e., membrane properties are subject to considerable fluctuations. The average concentration of the water in the hydrophobic core is nonzero. Various extensions, consequences and applications are proposed.

Lipid Bilayers↗