Simultaneous adsorption of gelatin and long-chain amphiphiles at solid-water interface

Abstract

Simultaneous adsorption of gelatin and anionic or cationic long-chain amphiphiles from the solution to the surface of alumina has been studied as function of protein concentration, pH, and temperature of the medium. The long-chain amphiphiles used are cetyltrimethyl ammonium bromide (CTAB), myristyltrimethyl ammonium bromide (MTAB), dodecyltrimethyl ammonium bromide (DTAB), cetylpyridinium bromide (CPB), and sodium dodecyl sulfate (SDS). At a fixed total concentration of the surfactant ( C s 1), adsorption of gelatin at the alumina-water interface increases with increase of gelatin concentration ( C p) in the bulk solution until a constant value Γ p m is reached. Γ p m changes considerably with increase of net charge of gelatin and with increase of temperature. The effects of hydrocarbon chain length and the nature of the head groups of the surfactant on Γ p m have also been critically examined. The adsorption isotherms of bovine serum albumin (BSA) and gelatin at hydrophobic graphite-water interface have been compared at different pH in presence and absence of long-chain amphiphiles. The number of moles of amphiphile ( Γ s a) associated per mole of gelatin at the interface and that ( Γ s eq) of the same surfactant bound per mole of gelatin in the bulk phase have been compared. The binding of surfactant to the protein at the interface is massive and cooperative at a critical bulk concentration of the surfactant in solution. Free energy changes of amphiphile-protein interaction in the interface have been calculated using the Tanford equation. The standard free energies for the transfer of protein from bulk solution to the alumina-water interface have been calculated using appropriate thermodynamic relations.