Mutual adsorption of protein and detergent at the alumina-water interface

Abstract

Mutual adsorption of bovine serum albumin (BSA) and sodium dodecyl sulphate (SDS) at the alumina-water interface has been determined as functions of protein and detergent concentrations, ionic strength, pH and temperature of the aqueous medium. The extgent of adsorption decreases with increase of temperature. The isotherm with respect to the adsorption of protein at a fixed total concentration (C s t ) of the surfactant is S-shaped in character. The limiting value of the protein adsorption decreases with increase of C s/t. The study of adsorption at serveral values of pH and ionic strength of the medium indicates that the mutual interactions of BSA and SDS with alumina interface are significantly controlled byt ehe electrostatic effect. At a given value of C s t , extent of adsorption (Γ S) at first decreases with increase of the adsorption (Γ p) of BSA due to the competitive interaction process whereas Γ S increases with increases of Γ p in the relatively higher range of the adsorption of protein as a result of the increase of the mutual interaction of BSA and SDS at the interface. The binding ratio of SDS to BSA in the bulk phase and at the aluminawater interface respectively under identical situation have been compared at various values of the equilibrium bulk concentrations (C s) of the surfactant in solution. At low values of C s, these ratios in the two phases are of comparable order in magnitude. However, at high values of C s, the binding ratio at the interface increases enormously due to the massive cooperative interaction even though the value of this ratio in the bulk remains low.