Catalytic activity of Burkholderia (Pseudomonas) cepacia encapsulated in silica aerogels in esterification and hydrolysis as a function of the gel and solvent hydrophobicities

Lipase from Burkholderia (formerly Pseudomonas) cepacia was encapsulated in silica aerogels dried by the supercritical method with CO2. Aerogels with hydrophilic and hydrophobic functionalities were made by combining different proportions of tetramethoxysilane and methyltrimethosysilane as the silicon precursors. These aerogels were tested in the esterification of lauric acid by I-octanol, as well as in the hydrolysis reaction of octyl laurate. These catalytic tests were carried out in two different solvents, namely water saturated isooctane or dioxane containing different initial water concentrations. The adsorption of the esterification and hydrolysis reactants, taken separately, on the most active aerogel in water saturated isooctane was studied. The results showed that for esterification as well as for hydrolysis, the most active gels were the hydrophobic ones, independent of the solvent or water proportion used. Esterification reaction was much faster in water saturated isooctane, whereas hydrolysis was favored in dioxane, with the highest water concentration, as expected from the thermodynamics. As for the adsorption results, they showed that the reactant most taken by the gel is lauric acid. This study showed that the acid is not only adsorbed, but seems to undergo a reaction with the gel. (C) 2002 Elsevier Science B.V. All rights reserved.