十六烷基三甲基溴化铵/山梨醇酐硬脂酸酯微乳液凝胶固定化脂肪酶的催化活性及立体选择性

制备了能在水溶液中长时间稳定存在的十六烷基三甲基溴化铵/山梨醇酐硬脂酸酯（CTAB/Span-60）微乳液凝胶（MBG），确定了Span-60在乳化剂EM（正丁醇与Span-60的混合物）中的质量分数范围；分别以正己酸与正己醇的酯化反应、α-单硬脂酸甘油酯的水解反应、消旋布洛芬与正辛醇的不对称酯化反应为指示反应，研究了CTAB/Span-60 MBG固定化脂肪酶的催化活性及立体选择性。 结果表明，Span-60在EM中的质量分数小于57%时可形成机械强度较好的CTAB/Span-60 MBG；其固定化脂肪酶在有机溶剂中的酯化活性随EM中Span-60含量的增加先是逐渐增大，35%时最大，后又逐渐小幅度降低，在所考察的Span-60含量范围内均比在CTAB MBG中高；在水溶液中固定化脂肪酶能顺利催化α-单硬脂酸甘油酯的水解反应，24 h后反应转化率不再随反应时间的延长而增加，其水解活性在重复使用9次后仅降低13.68%，表明CTAB/Span-60 MBG固定化脂肪酶能够顺利进行分离并重复使用；此体系的脂肪酶也选择性地催化生成S-构型布洛芬辛酯，产物对映体过量值（eee）随反应的进行缓缓下降，但降幅不大，即其立体选择性要比在CTAB MBG中高。 因此，CTAB/Span-60 MBG作为脂肪酶固定化载体既可用于有机溶剂中又可用于水溶液中的生物合成与生物转化反应，扩大了微乳液凝胶固定化脂肪酶的应用范围。

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

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.