Outstanding activation of an enzyme in ionic liquids (ILs) has been demonstrated by covalent modification with comb-shaped poly(ethylene glycol) (PEG) (PM13). Candida rugosa lipase modified with PM13 (PM13-CRL) was readily solubilized in all the ILs tested ([Emim][Tf2N], [C2OC1mim][Tf2N] and [C2OHmim][Tf2N]) containing 0.5% (v/v) of water, whereas native lipase did not dissolve in any of the ILs. The results for transesterification of 2-phenyl-1-propanol with vinyl acetate using lipase in ILs revealed that the PM13-CRL conjugate exhibits a high catalytic activity while suspended native lipase shows little activity. The hydrophobicity of ILs somewhat affected the enzyme activity and a more hydrophobic IL such as [Emim][Tf2N] was preferable for the lipase reaction, as was also observed in enzymatic reaction in conventional organic solvents. The enzyme activities in ILs were much higher than those in organic solvents, the excellent activity being associated with unique properties such as the hydrophobicity and the high polarity of ILs. Furthermore, the PM13--CRL conjugate exhibited a high storage stability in [Emim][Tf2N].
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