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A rational design of phosphonium ionic liquid for ionicliquidcoated-lipase (IL1-PS)-catalyzed reaction has been investigated: veryrapid transesterification of secondary alcohols was accomplished whenIL1-PS was used as catalyst in tributyl((2-methoxyethoxy)methyl)phosphoniumbis(trifluoromethanesulfonyl)amide ([P444MEM][NTf2]) or N-ethyl-N-((2-methoxyethoxy)methyl)-N-methylethanaminium bis(trifluoromethanesulfonyl)amide([N221MEM][NTf2]) as solvent with excellentenantioselectivity. It was also revealed that ammonium ionic liquidinfluenced the lipase reactivity more strongly than phosphonium ionicliquids. Increased Kcatvalue was suggestedto be the most important factor at work in IL1-PS in these ionic liquidsolvents. The Kcatvalue of (S)-1-phenyethanol in [N444MEM][NTf2] was similarto that of i-Pr2O, and 1.6-fold accelerationwas achieved for (R)-1-phenylethanol. On the otherhand, the Kmvalue for (R)-isomer in [N444MEM][NTf2] was slightly largerthan the reaction in i-Pr2O, while itwas significantly reduced for (S)-isomer. These resultssuggest that solvent provides a certain impact on the reactivity ofthe enzyme protein of IL1-PS. [ABSTRACT FROM AUTHOR]