pH Memory of Immobilized Lipase for (±)-Menthol Resolution in Ionic Liquid

Magnetic DEAE-GMA-EDMA microspheres were prepared via suspension polymerization and used for the immobilization of Candida rugosa lipase by ion exchange. The effect of pH values on the immobilization of lipase was investigated. Resolution of (+/-)-menthol in the hydrophobic ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate was performed by immobilized lipase-catalyzed enantioselective esterification with propionic anhydride as acyl donor. The effects of pH condition at lipase immobilization on the conversion and enantioselectivity were investigated. As a result, pH memory of the immobilized lipase for catalyzing (+/-)-menthol resolution in the ionic liquid was observed. Better conversion and the best enantioselectivity were obtained with the immobilized lipase prepared at pH 5.0. Under the condition, (-)-menthyl propionate with enantiomeric excess of >90% was obtained. Moreover, the enantioselectivity of the immobilized lipase decreased gradually with increasing pH value.