Fine-tuning the second generation sol–gel lipase immobilization with ternary alkoxysilane precursor systems

The sol–gel immobilization of Celite-supported lipase from Pseudomonas fluorencens (Lipase AK) was systematically studied using ternary silane precursor systems consisting of alkyltriethoxysilane (alkylTEOS), phenyltriethoxysilane (PhTEOS) and tetraethoxysilane (TEOS). The parameters investigated were the surface coverage at various enzyme-Celite ratios (between 1:1 and 1:10) and the effect of molar ratio of alkylTEOS (alkyl = propyl, hexyl, octyl, 1H,1H,2H,2H-perfluorooctyl, decyl, dodecyl, octadecyl), PhTEOS and TEOS (seven series of alkylTEOS:PhTEOS:TEOS from 0.1:0.9:1 to 0.9:0.1:1 in 0.1 steps) on the catalytic properties of the sol–gel biocatalysts. For comparison, the corresponding binary systems (1:1 molar ratios of alkylTEOS:TEOS and PhTEOS:TEOS) were also studied. The ternary and binary sol–gel lipase preparations were evaluated by their catalytic behavior in enantiomer selective acetylation of racemic 1-phenylethanol and 2-heptanol. For each alkylTEOS precursor, one or more alkylTEOS/PhTEOS/TEOS ternary systems were superior biocatalysts compared to the corresponding alkylTEOS/TEOS preparations. The best overall results were achieved with the medium-chain octylTEOS and perfluorooctylTEOS-containing ternary systems.