ORGANIC-REACTIONS CATALYZED BY IMMOBILIZED LIPASES .1. HYDROLYSIS OF 2-ARYL PROPIONIC AND 2-ARYL BUTYRIC ESTERS WITH IMMOBILIZED CANDIDA-CYLINDRACEA LIPASE

The alteration of the selectivity of enzymes due to the immobilization methodology is discussed. The hydrolysis of esters of (R,S) 2-phenyl propionic and 2-phenyl butyric acids has been used as a reaction test. Lipases from Candida cylindracea immobilized on agarose and alumina h ave been used as enzymatic derivatives. The stirring speed, [Substrate ] / [Enzyme] ratio and pH are the main variables that control the proc ess. An increase in the stirring speed, a diminution of the [Substrate ]/ [Enzyme] ratio and pH =7.0 favours the hydrolysis of esters. The ef fect of the support on the enzymatic activity is discussed. Inorganic supports such as Al2O3 or SiO2 stabilize the oil/water interface actin g in the same way as Na(I) or Ca(II) in the case of native enzyme. Enz ymatic derivative on Al2O3 is the most interesting biocatalyst. The ef fect of the alkyl chain of the ester is not related to the steric hind rance but to the stability of the microemulsion. The butyl ester is th e most interesting ester for carrying out the hydrolysis. A model of t he ester-active site interaction is proposed to explain the increase o bserved in the stereoselectivity of the hydrolysis of (R,S)-ester. Hig h enantioselective hydrolysis of the racemates (yielding S(+) isomer; ee greater than or equal to 98%) can be achieved using the immobilized derivatives.