Effect of hydrophobic [BMIM][PF6] on enzymatic synthesis of amyl caprylate catalyzed by lipase from R. miehei in organic solvent was studied. The relevance of the enzyme activity and the conformational changes were investigated by means of the fluorescence spectra of the enzyme. It was found that the lipase-catalyzed esterification in alkanes is more efficient than in aromatic hydrocarbons. The initial reaction rate decreases with the increase of logP when logP was 1.5~3.5. [BMIM][PF6] (1% of caprylic acid, w/w) induced a 15% decrease in the initial reaction rate for all assayed reactions executed in different organic solvents, which indicates that the effect of [BMIM][PF6] on the reaction is only related to its addition rather than the solvent it was with. Further more, the initial reaction rate decreased with the increase of the dosage of [BMIM][PF6] (1%~3% of caprylic acid, w/w) employed in the reactions carried out in nonane. The fluorescence spectra analysis indicates that the conformation change coordinates to the enzyme activity.

Key words: lipase, ionic liquid, initial rate, esterification