(322e) Unusual Interfacial Activation of Burkholderia Cepacia Lipase Immobilized in Nanopores of Sba-15 Silica
ABSTRACT: Ordered mesoporous silicas are currently being investigated as promising novel hosts for enzyme immobilization to improve enzyme stability and activity. In the present study we report the immobilization and enzymatic activity of Burkholderia Cepacia lipase immobilized in ordered mesoporous SBA-15 silicas possessing 55 Å, 80 Å, and 240 Å diameter pores. The lipase activity in p-nitrophenylacetate (p-NPA) hydrolysis was investigated as a function of the SBA-15 pore size, enzyme loading and the nature of the surface functional groups. It was observed that the enzymatic activity decreased as a result of lipase adsorption on the external surface of the 55 Å pore SBA-15 host, while the activity was preserved when lipase was immobilized inside the large mesopores (240 Å). We further investigated the SBA-15 hosts functionalized with n-butyl, amine (-NH2), and sulfonic acid (-SO3H) groups. The functionalized materials were characterized by SAXS, N2 adsorption-desorption isotherm data, scanning electron microscopy (SEM) and elemental analysis. The interfacial activation of B. Cepacia lipase was found to be strikingly different depending on the surface functional group. In particular, lipase (pI~4.5) immobilized on the sulfonic acid-functionalized SBA-15 host (~21 nm) showed unusually high activity at pH 7. Studies on the effects of sulfonic acid ligand density, host endcapping, lipase loading, and pH will be presented. Based on these results, it is postulated that electrostatic interactions between sulfonic acid moieties and the Ser-His-Asp catalytic triad enhances the enzymatic activity for hydrolysis.