(528c) The Effect of Silica Surface Functionalizations On Lysozyme Adsorption

Chromatography is a standard protein separation method in the pharmaceutical industry. A deeper understanding of the surface interactions between the protein and the stationary phase has the potential to increase the efficiency of these chromatographic separations. Therefore, the effect of different surface functionalities on protein adsorption was studied using model adsorption systems. Silica of known pore size and geometry was functionalized with different surface groups to test the effects of the surface chemistry on lysozyme adsorption. Lysozyme adsorption experiments were conducted using 0.02M potassium phosphate buffer at pH 7 at room temperature; these conditions were chosen to minimize solution interaction. Adsorption on acid-washed silica was used as a control. For example, samples of acid-washed silica were functionalized with either carboxyl or amine groups. The carboxyl group changed the adsorption isotherm from Type II (observed for acid-washed silica) to Type I. The amine group prevented lysozyme adsorption. The amine-functionalized surface was also used to graft amino acids onto the surface using peptide synthesis methods, creating an amide bond with the surface amine group. Amino acids with similar R groups to the carboxyl and amine functionalities were selected. Lysozyme adsorption on glycine (R = H), aspartic acid (R = CH₂-COOH), and lysine (R = (CH₂)₄-NH₂) is compared to adsorption on the native acid-washed silica as well as the carboxyl- and amine-functionalized surfaces. The lysozyme was shown to follow different patterns of adsorption depending on the surface functionalities.