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Abstract

Lipases can be efficiently entrapped in the pores of hydrophobic silicates by a simple and cheap sol–gel process in which a mixture of a hydrophobic alkylsilane RSi(OCH₃)₃ and Si(OCH₃)₄ is hydrolyzed under basic conditions in the presence of the enzyme. Additives such as isopropanol, polyvinyl alcohol, cyclodextrins, ionic liquids or surfactants enhance the efficiency of this type of lipase-immobilization. The main area of application of these heterogeneous biocatalysts concerns esterification or transesterification in organic solvents, ionic liquids, or supercritical carbon dioxide. Rate enhancements (relative to the traditional use of lipase powders) of several orders of magnitude have been observed, in addition to higher thermal stability. The lipase-immobilizates are particularly useful in the kinetic resolution of chiral esters, enantioselectivity often being higher than what is observed when using the commercial forms of these lipases (powder or classical immobilizates). Thus, due to the low price of sol–gel entrapment, the excellent performance of the lipase-immobilizates, and the ready recyclability, the method is industrially viable.