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W Norde

Publications and source records attributed to W Norde.

7 recordsLinked to original sources
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

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↗
PubMed1990

Physical chemical description of bacterial adhesion.

For the description of general bacterial adhesion phenomena two different physicochemical approaches are available. The first one, based on a surface Gibbs energy balance, assumes intimate contact between the interacting surfaces. According to this approach adhesion is solely related to the Gibbs energies of the surfaces involved. The second approach, based on colloid chemical theories (DLVO theory), allows for two types of adhesion: 1. secondary minimum adhesion, which is often weak and reversible, and 2. irreversible primary minimum adhesion. In the first case a thin water film is present between the interacting surfaces. In the DLVO approach adhesion is determined by long range interactions, i.e., Van der Waals and electrostatic interactions. Van der Waals interactions may be related to the hydrophobicity of the cell wall. For the measurement of bacterial hydrophobicity and electrokinetic potential several macroscopic methods are available. Based on a literature review of the influence of both surface characteristics on adhesion, it is concluded that the surface Gibbs energy balance approach is not adequate to describe the majority of adhesion phenomena. On the other hand the DLVO-theory describes the observations fairly well, especially in the case of reversible (secondary minimum) adhesion. The influence of adsorbing (in)organic compounds, extracellular polymers and cell surface appendages on adhesion can also be predicted by a DLVO-type approach.

Bacterial Adhesion↗
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↗