Adsorption of globular model proteins to silica and methylated silica surfaces and their elutability by dodecyltrimethylammonium bromide

Abstract

The interaction between a cationic surfactant (dodecyltrimethylammonium bromide) and six model proteins adsorbed on to methylated silica and silica surfaces was investigated. The proteins were bovine serum albumin, cytochrome c, β-lactoglobulin, α-lactalbumin, lysozyme and ovalbumin. The adsorption of the proteins at pH 7 and their subsequent removal by surfactant were studied by in situ ellipsometry. The degree of desorption upon dilution and the degree of elutability were compared and no relationship between these parameters could be found, which indicates that the mechanisms behind the two ways of protein removal are quite different. Further, the degree of elutability by surfactant was related to the physicochemical properties of the proteins. It was found that the size, charge, temperature of denaturation and adiabatic compressibility influenced the degree of elutability at the hydrophilic negatively charged silica surfaces for those of the model proteins that were still adsorbed after buffer rinsing. Negatively charged proteins with high denaturation temperatures, indicating high structural stability, did not adsorb on to this surface (ovalbumin) or adsorbed to a very low degree and were desorbed upon rinsing with buffer (β-lactoglobulin). All proteins adsorbed on to the hydrophobic methylated silica and the parameters that seemed to influence the degree of elutability were size and shell hydrophobicity of the proteins.