In recent years many studies have shown, that entrapment of lipases in sol-gel matrices have resulted in heterogeneous biocatalysts having significantly enhanced enzyme activities. In this work we investigated the influence of sol-gel encapsulation and organic solvents on lipase stability and activity in esterification reactions.

Lipases produced by microorganisms Aspergillus oryzae and Porcine pancreas were used as catalysts for esterification of stearic acid with aliphatic alcohols and 7-hydroxy-6-hydroxymethyl-2-oxabicyclo(3,3,0)octane-3-one with vinylacetate.

The silica prepolymer for lipase entrapment was prepared from tetramethoxysilane, methyltrimethoxysilane and propyltrimethoxysilane under acidic conditions. The porosity of the catalysts was changed by modification of the silane: water ratio. The silica matrices were characterized by measurement of porosity and specific surface.

In esterification of stearic acid with alcohols, the catalytic activity of lipases, free and entrapped, decreased in the range ethanol > 1-propanol > 1-butanol. The solvent hydrofobicity increased the activity of free lipases as well as lipases immobilized by sol-gel process (acetone

The esterification of 7-hydroxy-6-hydroxymethyl-2-oxabicyclo(3,3,0)octane-3-one (intermediate of the prostaglandin synthesis) with vinylacetate in acetone and THF had the regioselectivity 95%. The enantiomeric excess desired for the following step in prostaglandin synthesis was reached by modification of reaction conditions.

We can conclude that esterifications catalysed by lipases entrapped in silica-organic matrices is positively influenced by the hydrofobicity of silica precursors and solvents. Accessibility of lipase active centre was increased by higher porosity and probably also by smaller volume of solvent molecule. The matrix porosity and content of organosilanes need to be kept in optimal limits because of the mechanical stability of matrices and low losses of entrapped lipase required for the reusability of the catalyst.

[1] Kuncová, G., Guglielmi, M., Dubina, P., Šafar, B., Coll.Czech.Chem.Comm. 60, 1573-1577, 1995.

[2] Reetz, M. T., Zonta, A., Simpelkamp, J., German patent P44 08 152.9.