Resolution of (±)-menthol by immobilized Candida rugosa lipase on superparamagnetic nanoparticles

Lauric acid-stabilized magnetic particles were prepared by coprecipitation in the presence of lauric acid and used for the covalent immobilization of Candida rugosa lipase via carbodiimide activation. Size analysis by transmission electron microscopy (TEM) and measurement of magnetization curves revealed that the immobilized lipase was superparamagnetic. Resolution of (±)-menthol was performed by the immobilized lipase-catalyzed enantioselective esterification with propionic anhydride. Effects of various reaction parameters, such as enzyme load, solvents, water activity, substrate concentration, reaction time and temperature, on the conversion as well as enantioselectivity were investigated. As a result, (−)-menthyl propionate with a yield higher than 96% and over 88% enantiomeric excess of products was obtained. Better conversion and enantioselectivity could be expected for the immobilized lipase-catalyzed reaction performed at 30 °C for 2.5 h with 0.2 mol/l of (±)-menthol. Hexane was found to be the most suitable solvent, and the activity as well as enantioselectivity of the immobilized lipase decreased gradually with increasing water activity. Good durability of the immobilized lipase to catalyze the resolution of (±)-menthol was also observed.