Immobilization of enzymes on fumed silica nanoparticles for applications in nonaqueous media.

ABSTRACT

Enzymatic catalysis in nonaqueous media is considered as an attractive tool for the preparation of a variety of organic compounds of commercial interest. This approach is advantageous for numerous reasons including the enhanced stability of some substrates and products in solvents, sometimes improved selectivity of the enzyme, and reduction of unwanted water-dependent side reactions since little water is present. Due to the poor solubility of enzymes in these media, mass transfer limitations are sometimes present, leading to low apparent catalytic activity. Immobilization on solid supports has been successfully applied to overcome enzyme solubility issues by increasing the accessibility of substrates to the enzymes' active sites. We have developed a simple immobilization protocol that uses fumed silica as support. Fumed silica is an inexpensive nanostructured material with unique properties including large surface area and exceptional adsorptive affinity for organic macromolecules. Our protocol is performed in two main steps. First, the enzyme molecules are physically adsorbed on the surface of the non-porous fumed silica nanoparticles with the participation of silanol groups (Si-OH) and second, water is removed by lyophilization. The protocol has been successfully applied to both s. Carlsberg and Candida antarctica lipase B (CALB). The resulting fumed silica-based nanobiocatalysts of these two enzymes were tested for catalytic activity in hexane. The transesterification of N-acetyl-L -phenylalanine ethyl ester was the model reaction for s. Carlsberg nanobiocatalysts. The simple esterification of geraniol and the enantioselective transesterification of (RS)-1-phenylethanol were the model reactions for CALB nanobiocatalysts. The observed catalytic activities were remarkably high and even exceeded those of commercially available preparations.