The crude and purified Lipase OF from Candida rugosa were immobilized on silica gel by adsorption or adsorption/cross linking. The effect of Tween 80 on the enantioselective hydrolysis of Ketoprofen ester by immobilized lipase was examined. It is found that Tween 80 is effective in improving both the catalytic efficiency and the enantioselectivity of the immobilized lipase, where the conversion increases 3～4 folds and the enantiomeric ratio of the purified lipase increases from 10 to >100. Stability of the immobilized lipase decreases in the presence of Tween 80. This problem, however, can be solved by further cross linking of the adsorbed enzyme with glutaraldehyde. After six circles of repeated use in batch reaction, the conversion decreased from 61% to 37% and the enantioselectivity of the lipase remains constant.
The enantiomeric ratio ( E ) is frequently used to characterize the enantioselectivity in enzyme-catalyzed kinetic resolution. In this paper two methods are evaluated in terms of accuracy, sensitivity towards E and its distribution.For the equation of Chen et al , the probability of r(ee p)∈[0.5, 1.0], the influence on E of enanatiomeric excess of product ( ee p), nearly reaches 0.75.The probability of r(ee p)∈[0.7,1.0] exceeds one half.All r(ee p) values are higher than 0.6 at conversion ratio ( C ) below 50%. For the equation of Rakels et al , the majority of r(ee p) exceeds 0.6 when ee s, enantiomeric excess of substrate is lower and ee p is higher.During the final phase of a reaction when ee s is large, the changes of ee s have greater effects on E than that of ee p,but the probabilities for the above two cases do not exceed 0.5.In addition, there are quite a few situations in which r(ee p) is equal to 0.4,0.5 and 0.6. This is the most distinguished discrimination of two methods and may also be the primary reason for which the latter is superior to the former.
