The Catalytic Activity and Stereoselectivity of Lipase Immobilized in Cetyl Trimethyl Ammonium Bromide/Sorbitan Monostearate Microemulsion-based Gel

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.