Abstract:

Cetyl trimethyl ammonium bromide/sorbitan monostearate(Span-60) microemulsion-based gel(CTAB/Span-60 MBG) having good stability in aqueous solution was successfully prepared. The mass percentage of Span-60 in emulsifier mixture（EM, the mixture of n-butanol and Span-60） was determined. The catalytic activity and stereoselectivity of lipase immobilized in CTAB/Span-60 MBG were tested using the esterification of hexanoic acid and hexanol, the hydrolysis of α-glyceryl monostearate and the stereoselective esterification of racemic ibuprofen and octanol as probes, respectively. The results showed that CTAB/Span-60 MBG with good mechanical strength could be achieved when the mass percentage of Span-60 in EM was less than 57%. In organic solvent, the catalytic esterification activity of lipase in this MBG increased gradually with the increase of the content of Span-60 in EM at the first stage and reached maximum at 35% and then decreased slightly with further increase of the content, and was higher than that in CTAB MBG, within the investigated content of Span-60. This immobilized lipase could catalyze the hydrolysis of α-glyceryl monostearate in aqueous solution and the reaction conversion rate didn′t change any more after 24 h. The catalytic hydrolytic activity decreased by 13.68% after 9 re-usage times. This suggests that lipase in CTAB/Span-60 MBG could be separated and reused. Lipase in this MBG also selectively catalyzed S-enantiomer ibuprofen to S-enantiomer ester and the excessive enantiomeric product(eee) of the latter gradually decreased with the proceeding of the reaction, but showing better stereoselectivity than CTAB MBG. As a promising carrier for immobilizing lipase, CTAB/Span60 MBG could be used in biosynthesis and biotransformation not only in organic solvent but also in aqueous solution.

Key words: microemulsion-based gel (MBG), immobilized lipase, catalytic activity, enantioselectivity, reaction conversion rate, enantiomeric excess (eee)