Enhanced enantioselectivity of Candida rugosa lipase in ionic liquids as compared to organic solvents

Candida rugosa lipase has shown to retain catalytic activity in ionic liquids. In this work, enantioselectivity of this enzyme in the esterification of 2-substituted-propanoic acids and 1-butanol is compared in ionic liquids and organic solvents. The role of solvent hydrophobicity (log P), water content and the effect of substituents are evaluated. Optimal water concentration in the reaction media was determined, where the enzyme shows maximal activity and enantioselectivity. Enantioselectivity can be improved when chlorine substituent was replaced by slightly bigger size bromine. Contrary to reactions in common organic solvents, there was no need for purification steps following the reaction in ionic liquids in order to recycle the enzyme. In 1-butyl-3-methyl-imidazolium-hexafluoro-phosphate ([bmim]PF6) and 1-octyl-3-nonyl-imidazolium-hexafluoro-phosphate ([onim]PF6) ionic liquids, C. rugosa lipase could be recycled five times without appreciable activity or enantioselectivity losses.