The original procedure for the encapsulation of lipases in sol-gel materials produced by the fluoride-catalyzed hydrolysis of mixtures of RSi(OCH 3 ) 3 and Si(OCH 3 ) 4 has been improved considerably. This involves higher enzyme loading, variation of the alkylsilane precursor, and the use of additives such as isopropyl alcohol, 18-crown-6, Tween 80 ¾ , methyl-b-cyclodextrin and/or KCl. A dramatic increase in enzyme activity is observed.The sol-gel lipase immobilizates are also excellent catalysts in the kinetic resolution of chiral alcohols and amines, recycling without any substantial loss in enantioselectivity and a residual activity of 70% being possible even after 20 reaction cycles.

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For the first time FTIR spectroscopy has been applied to the measurement of enantiomeric purity. The underlying concept is based on the use of pseudo-enantiomers that are (13)C-labeled at appropriate positions. Upon applying Lambert-Beer's law in the determination of the concentrations of both enantiomers, the ee values are accessible, accuracy to within +/-5 % of the true values being possible. The application of a commercially available high-throughput FTIR system results in a slightly decreased accuracy (+/-7% for the ee values), but this allows a throughput of up to 10000 samples per day. The method is of interest in the area of combinatorial symmetric catalysis and directed evolution of enantioselective enzymes.

The entrapment of lipases in hydrophobic silicate matrices formed by sol-gel mediated hydrolysis of RSi(OCH3)3/Si(OCH3)4 as originally reported in 1996 has been improved over the years by a number of modifications. In the production of second-generation sol-gel lipase immobilizates, a variety of additives during the sol-gel process leads to increased activity and enhanced stereoselectivity in esterifying kinetic resolution. Recent advances in this type of lipase immobilization are reviewed here, in addition to new results regarding the sol-gel entrapment of the lipase from Burkholderia cepacia. It constitutes an excellent heterogeneous biocatalyst in the acylating kinetic resolution of two synthetically and industrially important chiral alcohols, rac-sulcatol and rac-trans-2-methoxycyclohexanol. The observation that the catalyst can be used 10 times in recycling experiments without losing its significant activity or enantioselectivity demonstrates the practical viability of the sol-gel approach.