Solvent effects on the enantioselectivity of the thermophilic lipase QLM in the resolution of ( R, S)-2-octanol and ( R, S)-2-pentanol

Abstract

The thermophilic lipase QLM-catalyzed resolution of ( R, S)-2-octanol and ( R, S)-2-pentanol via transesterification was carried out in various organic solvents, and the solvent effects on the enzyme's enantioselectivity were investigated. A significant negative correlation between the enantiomeric ratio, E, and the size of the solvent molecules was observed. The highest E value, 21, was obtained in the small molecular-sized solvent dichloromethane when ( R, S)-2-octanol was resolved with vinyl acetate as acyl donor. Thermodynamic analysis indicated that the difference in activation free energy between the two enantiomers was about 25.5% lower in dichloromethane than in the solvent-free system, and the change in the difference in activation entropy between the enantiomers was the main contributor to the changes in E values with the molecular size of solvents.