Mutual Adsorption of Serum Albumin and Long-Chain Cationic Surfactants at the Alumina-Water Interface

Abstract

Mutual adsorption of bovine serum albumin (BSA) and different cationic surfactants from the aqueous solution to the surface of the alumina powder has been analytically studied as functions of protein concentration, pH, ionic strength and temperature of the medium. The surfactants used are cetyl trimethyl ammonium bromide (СТАB), myristyl tri-methyl ammonium bromide (MTAB), dodecyl trimethyl ammonium bromide (DTAB) and cetyl pyridinium bromide (СРB). At a given total concentration (c) of a surfactant, the extent of adsorption is found to increase with increase of BSA concentration (cp) in the bulk solution until a constant maximum value Γ p m is reached. Γ p m decreases with increase of temperature at a fixed value of с s t . Γ p m is also found to alter significantly with change of pH and ionic strength of the medium. The effects of hydrocarbon chain length as well as nature of the head groups on Г at fixed c s t have also been examined. At constant с s t the extent of adsorption (Γs)of surfactant decreases with the increase of Гp due to the competitive nature of adsorption process. The binding ratios of a surfactant to BSA at the interface and in the bulk solution have been critically compared. Such binding at the interface is massive due to the ligand-protein co-operative interaction when the surfactant concentration in the bulk is considerably low. Free energies for ligand-protein interactions and the transfer of BSA at the interface have been calculated using appropriate thermodynamic relations.