新型离子液体中脂肪酶催化薄荷醇选择性酯化

Lipase-Catalyzed Enantioselective Esterification of(±)-Menthol in Novel Ionic Liquids

设计合成了6种新型对称烷基咪唑六氟磷酸盐离子液体。以脂肪酶Candida antarctica催化(±)-薄荷醇和丙酸酐立体选择性酯化反应为模型反应,考察反应介质对酶行为的影响。结果发现,在1,3-二正辛基咪唑六氟磷酸盐([Dn OIM][PF6])中酶的活性与立体选择性明显高于其他离子液体和正己烷。因此,[Dn OIM][PF6]被选择作为反应介质。通过优化实验,得到最佳反应条件为:反应温度30℃,70 mg脂肪酶,3.0 m L离子液体,底物(±)-薄荷醇与丙酸酐物质的量比1∶1,反应时间20 h。此时,反应转化率与e.e.(p-)值分别可达48.1%与98.1%。酶在[Dn OIM][PF6]中的稳定性是正己烷的4.3倍,且重复使用7次后催化活性没有显著降低。荧光光谱和圆二色谱研究结果表明,酶在[Dn OIM][PF6]中有较大的酶蛋白质分子裸露程度和良好的二级结构稳定性。

Six novel symmetrical alkylimidazolium hexafluorophosphate ionic liquids（ILs） were designed and synthesized in this study. The enantioselective esterification of（±）-menthol with propionic anhydride catalyzed by Canadida rugosa lipase was used as a model reaction to investigate the catalytic characterization of the lipase in different medium. The results indicated that the activity and selectivity of the lipase in the ionic liquid 1,3-di（n-octyl）imidazolium hexafluorophosphate（[Dn OIM][PF6]） is obviously higher than that in other ILs and hexane. Therefore,[Dn OIM][PF6] was chosen as the medium for the reaction. By investigating various factors on the conversion of（±）-menthol,the optimal conditions were determined as reaction temperature of 30 ℃,70 mg lipase,3.0m L ionic liquid,menthol and propionic anhydride with the molar ratio of 1∶1,and reaction performed for 20 h. Under this optimal condition,the conversion of（±）-menthol and enantiomeric excess of（-）-menthyl propionate was up to 48.1% and 98.1%,respectively. The stability of the lipase in IL was4.3-fold than that in hexane. Furthermore,the activity of IL and the lipase were not substantial diminution after recycled 7 times. Meanwhile,fluorescence spectroscopy and circular dichroism results showed that the lipase in IL had bigger exposure levels of amino acid residues and excellent secondary structure stability.