Ionic Liquid Medaited Activation of Enzymatic Reactions

我们发现，当一种新型离子液体，即咪唑聚氧乙烯（10）十六烷基硫酸酯，以3至10摩尔%的浓度与底物相对，在洋葱伯克霍尔德菌脂肪酶催化下，使用醋酸乙烯在二异丙醚或己烷溶剂体系中进行仲醇酯交换反应时，获得了增强的对映选择性。此外，我们还发现，当这种离子液体包被脂肪酶时，在保持良好的对映体选择性的同时，脂肪酶也获得了显著的加速。在脂肪酶催化的反应中，实现加速和增强对映体选择性的方法仅有有限的实例报道：PEG涂层可以加速反应，但没有显著增强对映体选择性；此外，甲苯作为溶剂对某些底物的对映选择性增强，但对反应没有明显的激活作用。我们只用28mg的IL和1.0 g的脂肪酶来制备我们的IL - 1包被的脂肪酶PS；那笔钱实在是少得可怜。我们认为这可能是由于IL的特殊性质，因为它由咪唑阳离子和阴离子聚乙二醇硫酸盐组成，这两部分可能共同促进脂肪酶的激活。这是我们使用离子液体激活脂肪酶方法的主要概念。离子液体是目前公认的用于脂肪酶催化反应的溶剂，但是，离子液体的反应速度比传统的有机溶剂慢，这是离子液体的一个严重缺点。为了克服这一问题，人们尝试进化出适合脂肪酶催化反应的磷离子液体；制备了几种类型的磷酸盐，并对其作为脂肪酶催化反应溶剂的性能进行了评价。以2-甲氧基乙基（三正丁基）磷-二（三氟甲磺酰基）亚胺（[MEB_< 3 bbb_0 P][NTf_2]）为溶剂，在脂肪酶ps催化下实现了仲醇的快速酯交换反应，首次实现了反应速率优于在二异丙醚中的反应速率。少

We discovered that enhanced enantioselectivity was obtained when a novel ionic liquid, i.e. imidazolium polyoxyethylene(10) cetyl sulfate was added at 3 to 10 mol% vs. substrate in the Burkholderia cepacia lipase-catalyzed transesterification of sec-alcohols using vinyl acetate in diisopropyl ether or a hexane solvent system. Further, we found that a remarkable acceleration was also obtained when the lipase was coated with this ionic liquid while still maintaining excellent enantioselectivity. There have been reported only limited examples of means to achieve both acceleration and enhanced enantioselectivity of lipase-catalyzed reaction: PEG coating could accelerate the reaction but caused no significant enhanced enantioselectivity; also, using toluene as solvent caused enhanced enantioselectivity for some substrates but caused no significant activation of the reaction. We used only 28 mg of IL for 1.0 g of lipase in preparing our IL1-coated-lipase PS; the amount was really a trace. We … More assume this might be due to the special nature of IL because it consists of imidazolium cation with anionic PEG sulfate and both parts might cooperatively contribute to the activation of the lipase. This is the main concept of our lipase activation method using an ionic liquid.Ionic liquids are now recognized as solvents for use in lipase-catalyzed reactions, however, there still remains a serious drawback in that the rate of reaction in an ionic liquid is slower than that in a conventional organic solvent. To overcome this problem, attempts have been made to evolve phosphonium ionic liquids appropriate for lipase-catalyzed reaction; several types of phosphonium salts have been prepared and their capability evaluated for use as solvent for the lipase-catalyzed reaction. Very rapid lipase PS-catalyzed transesterification of secondary alcohols was obtained when 2-methoxyethyl(tri-n-butyl)phosphonium bis(trifluoromethanesulfonyl)imide ([MEB_<u3>P][NTf_2]) was used as solvent, affording the first example of a reaction rate superior to that in diisopropyl ether. Less