Immobilized Lipase Catalysed Resolution Of (±)-Menthol In Nonaqueous Phase

Lauric acid-stabilized magnetic nanoparticles were prepared and used for the lipase immobilization. The nanoparticles were characterized by transmission electron microscopy and magnetic measurements. The observations indicated that the particles were superparamagnetic. Magnetic sedimentation of the nanoparticles was achieved within 0.6 min in organic media, 200 times faster than the gravitational sedimentation. The lauric acid on the particles provided a hydrophobic interface for the lipase immobilization, and the conformational changes of the immobilized lipase induced by interaction with the hydrophobic interface yielded an "open structure". Candida rugosa lipase(CRL) was immobilized to the magnetic carrier at up to 717 U/g carrier, 1.8 times higher than the free lipase containing the same protein. The activity amelioration indicated the occurrence of "interface activation". The pH dependencies of the immobilized and free lipases were also investigated, of which the optimum pH were determined. Moreover, better stability of the immobilized lipase for the hydrolysis of olive oil was observed.There are numerous advantages of conducting enzymatic conversions in organic solvents over in water. Optically active menthyl propionate of (-)-menthol was synthesized by enantioselective esterification of (±)-menthol using immobilized CRL as a biocatalylst. Substrate conversion, enantiomeric ratio(E), and enatiomeric excess percentage (e.e.%) were estimated by the analysis of gas chromatography equipped with a chiral column. Effects of various reaction parameters, such as water activity, enzyme load, type of acyl donor, solvent specie, time and temperature, on the conversion as well as enantioselectivity were studied. n-Hexane was found to be the most suitable solvent. Propionic acid anhydride gave better conversion compared to other acyl donor used in the present study. It is experimentally verified that lower water activity in organic solvent provided higher substrate conversion, E and e.e.%. They are 37.8%, 11.9 and 84.9%, respectively.