Activity, stability and enantioselectivity of lipase-coated microcrystals of inorganic salts in organic solvents

Lipase-coated microcrystals of inorganic salts were prepared by dissolving enzymes in buffers and then mixing with 3 volumes of saturated salt solutions followed by drop-wise addition into polar precipitating organic solvents. The Mucor javanicus lipase-coatcd microcrystals did not show any activity for esterification of lauric acid with 1-propanol in isooctane when NaCl and Na2SO4 were used as the salts but showed much higher activity than the enzyme powder when KCl (10.0 times) and K2SO4 (5.8 times) were used as the salts and precipitated in 1-propanol. Acetonitrile was found to be the best precipitating solvent for preparing M. javanicus lipase-coated microcrystals, with enzyme activities 26.2 and 22.4 times higher than that of the enzyme powder when KCl and K2SO4 were used as precipitating salts, respectively. The presence of water in the precipitating solvents markedly decreased the enzyme activity. The M. javanicus lipase-coated microcrystals prepared using K2SO4 as the salt and acetonitrilc as the precipitating solvent was as active at 80 degrees C as at 40 degrees C. No significant improvement in enantioselectivity of Candida rugosa lipase-coated microcrystals was observed for transesterification of 1-phenylethanol with vinyl acetate in hexane when the microcrystals were prepared by dissolving the enzymes in salt solutions containing 25% (v/v) of acetone or 2-propanol before precipitating in polar solvents.