Effect of imprinting sol–gel immobilized lipase with chiral template substrates in esterification of (R)-(+)- and (S)-(−)-glycidol

To prepare an immobilized lipase effective for enantioselective esterification of glycidol with n-butyric acid in organic media, hybrid gel-entrapped lipase on Celite was prepared by the sol–gel method and pretreated with chiral template substrates. When n-butyltrimethoxysilane, (n-BuTrMOS) as an organic silane precursor, was mixed with tetramethoxysilane (TMOS) at a molar ratio of 4:1, the hybrid gel-entrapped lipase on Celite showed three times higher activity than the deposited lipase on Celite as a control. The pretreatment of this immobilized lipase with a hydrophobic enantiomer such as (R)-(−)-2-octanol brought about a selective enhancement of the activity for the esterification of (R)-(+)-glycidol, whereas such pretreatment hardly affected the activity for the esterification of (S)-(−)-glycidol. Consequently, the relative initial enantiomeric activity (RIEA) of the hybrid gel-entrapped lipase on Celite, defined as a ratio of the initial esterification rate of (R)-(+)-glycidol to that of (S)-(−)-glycidol, changed between 0.76 and 2.0. In addition, increasing the concentration of (R)-(−)-2-octanol as a template substrate, increased the activity and RIEA, and showed maximum values with the addition of 21 mM of (R)-(−)-2-octanol.