Use of a Lipase to Synthesize Silica Gels in a Hydrophobic Organic Solvent

Abstract

Biocatalytic and chemical catalytic reactions in solutions of lauric acid, 1-octanol and tetramethoxysilane (TMOS) in hydrophobic isooctane and in the presence of the lipase from Burkholderia cepacia, was studied by gas chromatography. Two types of silica gels could be obtained and the chemical and biochemical transformations leading to their formation were elucidated. In a first type of gelation, biocatalytic esterification between lauric acid and alcohol slowly produced some water which in turn hydrolyzed TMOS. Simultaneously, a transesterification reaction between 1-octanol and TMOS grafted octyl groups on the silica precursor. This induced a gelation of hydrophobic silica throughout the complete isooctane solvent volume. A second type of silica gel formed when no 1-octanol was added and only in the presence of the enzyme. This type of gel was hydrophilic and separated from the isooctane layer. Gas chromatographic analysis showed that it could only be formed as a result of hydrolysis reaction between lauric acid and TMOS, directly catalyzed by the lipase itself. Therefore, in this second type of gelation process, the metal-organic compound TMOS itself appeared as a direct enzymatic substrate.