clays, BSA, adsorption

Four clays (acid activated montmorillonite K10, illite-smectite, bentonite B75 and vermiculite) were tested for the interaction with BSA solution. Clays were characterized by the infrared spectroscopy and TG/DSC analysis. The sorption of BSA was tested at concentration level 2 mg.mg-1. Conformation of BSA molecule is strongly affected by pH value of the solution and multivalent cations can probably lead to the formation of supramolecular structures. Conformational changes and supramolecular structures influence the binding of BSA on the clay surface. Montmorillonite K10 and Illite-smectite are subject to very weak hydrolysis and there is sufficient amount of BSA adsorbed on the clays? surfaces. On the other hand, bentonite and vermiculite are subject to stronger hydrolysis, pH values in the contact with solutions increase to 9, which cause adsorbed amount practically equal to 0. Adsorption kinetic and isotherms for montmorillonite K10 and Illite-smectite at pH 4.4 were measured. Adsorption of BSA on both clays corresponds to the pseudo-second-order kinetic model and the equilibration time was 90 minutes. The Langmuir isotherm model is suitable for description of equilibrium sorption data and the maximal adsorbed amounts from the Langmuir isotherm were 0.067 mg.mg-1 for montmorillonite K10 and 0.086 mg.mg-1 for illite-smectite. The isoelectric point of BSA was determined on the pH value 4.5 and it was determined that both clays are negatively charged in whole studied range of pH values. Zeta-potentials and particle distributions were measured for all studied systems (clays, BSA and clays after contact with BSA) at pH 4.4. It was found out that average particle size of the clays decreases after contact with BSA solution in all cases except of vermiculite. BSA in the solution probably attacks the clays? surface, which leads to the particle size decrease as well as this phenomenon probably influences sorption od BSA on the clays surface.