No abstract

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.

The regioselective acylation of pyridoxine catalyzed by immobilized lipase (Candida Antarctica) in 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM]PF 6 ) has been investigated, and compared with that in acetonitrile (ACN). The acetylation of pyridoxine using acetic anhydride in [BMIM]PF 6 gave comparable conversion of pyridoxine to 5-monoacetyl pyridoxine with considerably higher regioselectivity (93%-95%) than that in ACN (70%-73%). Among the tested parameters, water activity (a w ) and temperature have profound effects on the reaction performances in either [BMIM]PF 6 or ACN. For the reaction in [BMIM] PF 6 , higher temperature (50uC-55uC) and lower a w (,0.01) are preferable conditions to obtain better conversion and regioselectivity. Mass transfer limitation and intrinsic kinetic from the ionic nature of ionic liquids (ILs) may account for a different rate-temperature profile and a lower velocity at lower temperature in [BMIM]PF 6 -mediated reaction. Moreover, consecutive batch reactions for enzyme reuse also show that lipase exhibited a much higher thermal stability and better reusability in [BMIM]PF 6 than in ACN, which represents another advantage of ILs as an alternative to traditional solvents beyond green technology.