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

DOI：10.3969/j.issn.1673-1689.2015.09.006

中文关键词: 离子液体 脂肪酶 立体选择性酯化 薄荷醇

英文关键词: ionic liquid, lipase, enantioselective esterification, (±)-menthol

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中文摘要:

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([DnOIM][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，[DnOIM][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 mL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[DnOIM][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[DnOIM][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。

英文摘要:

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([DnOIM][PF6]) is obviously higher than that in other ILs and hexane. Therefore，[DnOIM][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，3.0 mL 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 was 4.3-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.

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