SOLVENT POLARITY INFLUENCES PRODUCT SELECTIVITY OF LIPASE-MEDIATED ESTERIFICATION REACTIONS IN MICROAQUEOUS MEDIA

Esterification reactions were evaluated by using lipases from Rhizomuc or miehei (Lipozyme IM20) and Pseudomonas cepacia (PS-30) with equimol ar levels (1.77 mmol) of undecanoic acid and glycerol or 1,3-propanedi ol (1,3-PD) or 1,2-propanediol (1,2-PD) in organic solvents of log P ( partition coefficient between 1-octanol/water) values of (-0.33-4.5. R eaction yields (percentage of esterified undecanoate) with glycerol ra nged from 1.4 to 72%, with greatest yields observed in solvents of log P 4.0-4.5 for Lipozyme, whereas the PS-30 lipase was similarly effect ive (27-38% yield) over the full range of solvent polarities. For both enzymes, as solvent apolarity increased, so did the extent of acylati on of glycerol in the final product mixture. Reaction yields with 1,3- PD ranged from 8.1 to 64% for Lipozyme and from 18 to 84% for PS-30 li pase, with greatest yields observed for both enzymes in solvents of lo g P values in the range 1.2-5.0. For both lipases, the shift to greate r solvent apolarity was accompanied by an increased molar ratio of dia cylated-1,3-PD/monoacylated-1,3-PD in the product mixture. Reaction yi elds with 1,2-PD ranged from 2.5 to 45% for Lipozyme and from 12 to 52 % for PS-30 lipase, with greatest yields observed in solvents of log P values in the ranges 1.4-1.9 and 1.4-4.5, respectively. The shift to greater solvent apolarity was accompanied by an increased molar ratio of diacylated-1,2-PD:monoacylated-1,2-PD in the product mixture, excep t for Lipozyme in the three most apolar solvents (log P of 3.5-4.5) in which there was a general attenuation of activity. These results sugg est the existence of a solvent polarity influence on reaction product selectivity in multiproduct reactions, which can be partially explaine d on the basis of differential solvation and extraction properties of solvents.