Ionic Liquid Medaited Activation of Enzymatic Reactions

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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