Influence of tetraalkylammonium salts on the adsorption kinetics of bovine serum albumin in aqueous solutions at the air-liquid interface

Abstract

Bovine serum albumin adsorption dynamics in water and in aqueous solutions of tetramethylammonium bromide, hexyltrimethylammonium bromide octyltrimethylammonium bromide, decyltrimethylammonium bromide, and dodecyltrimethylammonium bromide at the air-liquid interface was studied at a temperature of 298.15 K.The kinetics of the adsorption process of the biomolecule in water and in the aqueous alkylammonium solutions was investigated following the changes in surface tension with time. The measurements were performed on a high-precision drop volume tensiometer.The surface pressure data were adjusted with two of the most used semi-empirical kinetic models that describe the process of adsorption and allow the determination of the equilibrium adsorption parameters.The results in water and in the aqueous solutions containing tetraalkylammonium salts show that the adsorption kinetics is well described by a model consisting of three steps in which the transport of the protein in the initial stage is diffusion controlled. After some time, the rate is determined by the adsorption and the penetration of the protein at the air-liquid interface and the rearrangement of the protein at the interface; the evolution of both processes is described by steps that follow first-order rate equations.The results indicate that the overall adsorption process of bovine serum albumin BSA in water and the aqueous alkylammonium salts solutions is controlled by the second step which is the slowest of the three steps; it corresponds to the adsorption and penetration of the biomolecule at the air-liquid interface.