Activation Parameters for Kinetics of Protein Adsorption at Silica-Water Interface

Abstract

The extent of adsorption of three different proteins, lysozyme, β-lactoglobulin, and hemoglobin, from aqueous solutions to the surface of silica powder have been studied as a function of time for various values of protein concentration, pH, and temperature. The rates of adsorption in all cases have been observed to fit the first-order equation with two kinetic constants Ka1 and Ka2 . Using the Arrhenius equation, the activation energies ΔE*1 and ΔE*2 for protein adsorption have been evaluated. The corresponding values of enthalpy of activation (ΔH*), entropy of activation (ΔS*), and free energy of activation (ΔG*) have been evaluated using Eyring's equation of absolute reaction rate. It has been found that for Ka1 , ΔH*1 >T ΔS*1 and for Ka2 , TΔS*2 > ΔH*2 for all three proteins. The values of Ka1 follow the order lysozyme > β-lactoglobulin > hemoglobin, but the activation energy, enthalpy of activation, entropy of activation, and free energy of activation are found to be of the same order for the adsorption of each of the three biopolymers.