Protein adsorption surface charge density

Clay minerals or phyllosilicates are lamellar natural and synthetic materials with high surface area, cation exchange and swelling properties, exfoliation ability, variable surface charge density and hydrophobic/hydrophilic character [85], They are good host structures for intercalation or adsorption of organic molecules and macromolecules, particularly proteins. On the basis of the natural adsorption of proteins by clay minerals and various clay complexes that occurs in soils, many authors have investigated the use of clay and clay-derived materials as matrices for the immobilization of enzymes, either for environmental chemistry purpose or in the chemical and material industries. 

Keywords nanosilicas structural and adsorption characteristics surface charge density aqueous suspension particle mobility protein adsorption Proteus mirabilis... 

Gessner, A., Lieske, A., Paulke, B., and Muller, R. (2002), Influence of surface charge density on protein adsorption on polymeric nanoparticles Analysis by two-dimensional electrophoresis, Ear. J. Pharm. Biopharm., 54(2), 165-170. 

FIGURE 6.51 Surface charge density for A-300 in the aqueous suspension (CsiO2=0.2 wt%) at 0.001 M NaCl as a function of pH (measured by titration method). (Adapted from J. Colloid Interface Sci., 260, Gun ko, V.M., Mikhailova, I.V., Zarko, V.I. et al.. Study of interaction of proteins with fumed silica in aqueous suspensions by adsorption and photon correlation spectroscopy methods, 56-69,2003c, Copyright 2003, with permission from Elsevier.)... 

Electrochemical properties are other important physical surface parameters. The existing surface charge density, i.e. the surface potential, has a strong influence on protein adsorption and blood compatibility [81]. In this way the characterization of the interface charge density of a biomaterial by -potential determination delivers an important parameter for understanding blood compatibility of biomaterial surfaces [82-85]. 

Similarly for each of the other proteins, cyclic voltammograms were recorded after each addition of an aliquot of protein to the buffer solution in the electrochemical cell. The surface charge density was measured over the region which normally corresponds to a monolayer of OH during oxide formation in aqueous solutions, to the anodic end potential of 0.4 V (vs. SCE). Since this is also the rest potential of lysozyme on platinum, the surface charge densities measured to this anodic end potential may reflect the adsorption of a monolayer of protein and allow correlation with results from other experimental techniques. The calculated values of 7"for the three proteins considered in these studies are shown in Fig. 5. Plateau values in surface charge densities can be seen at low bulk concentrations... 

Surface concentrations of 1.3 mg m" for the plateau value at low bulk protein concentrations and 1.8 mg m at the higher concentrations, calculated from the surface charge density resulting from adsorption of )ff-lactoglobulin at 299 K and pH 7.0 on a platinum electrode with an anodic end potential of 0.4 V, agree very well with values in the literature... 

One of the few electrochemical investigations on proteins directly related to medical applications is that reported by Razumas et who studied adsorption of insulin on platinum from a physiological saline solution of pH 7.4 (298 K). The smallest amount of protein adsorption was found to be around the potential of zero charge of platinum. The authors compared the surface adsorption of insulin at different potentials using ellipsometric measurements and determined a surface charge density of F = 121 mg m" for insulin at a potential of 0.4 V (vs. SCE). The /"max was attained within 20-30 s after the solutions were mixed. A small decrease... 

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