Abstract
BACKGROUND: Enzymes may exhibit enhanced activity, stability and selectivity in ionic liquids, depending on the properties of the liquid. The physical–chemical properties of ionic liquids, however, may be modified by altering the anion or cation in the ionic liquid. This feature is a key factor for realizing successful reactions. In this work, a new ionic liquid, 1‐isobutyl‐3‐methylimidazolium hexafluorophosphate (abbreviated as [i‐C~4~mim][PF~6~]), was synthesized and investigated as a novel medium for the transesterification reaction of 2‐phenylethanol with vinyl acetate catalyzed by pseudomonas capaci lipase. As contrasts, the reaction was also carried out in two reference solvents; the isomeric ionic liquid [i‐C~4~mim][PF~6~], 1‐butyl‐3‐methylimidazolium hexafluorophosphate (abbreviated as [C~4~mim][PF~6~]), and hexanes.
RESULTS: As reaction medium, [i‐C~4~mim][PF~6~] was best among the three solvents. The initial reaction rate, the equilibrium conversion of 2‐phenylethanol and the half‐lifetime of the lipase in [i‐C~4~mim][PF~6~] medium were about 1.5, 1.2 and 3‐fold that obtained in [C~4~mim][PF~6~] medium, respectively. The lipase in [i‐C~4~mim][PF~6~] medium was recycled 10 times without substantial diminution in activity.
CONCLUSION: The ionic liquid [i‐C~4~mim][PF~6~] has good biocompatibility, and can be used widely as green media in various biocatalysis reactions to improve the activity and stability of enzymes. Besides hydrophobicity and nucleophilicity, the spatial configuration of ionic liquids is also considered a key factor effecting the behaviour of the enzyme in ionic liquids. Copyright © 2008 Society of Chemical Industry