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

摘要

Esterification reactions were evaluated by using lipases from Rhizomucor miehei (Lipozyme IM20) and Pseudomonas cepacia (PS-30) with equimolar levels (1.77 mmol) of undecanoic acid and glycerol or 1,3-propanediol (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. Reaction yields (percentage of esterified undecanoate) with glycerol ranged 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 effective (27-38% yield) over the full range of solvent polarities. For both enzymes, as solvent apolarity increased, so did the extent of acylation 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 lipase, with greatest yields observed for both enzymes in solvents of log P values in the range 1.2-5.0. For both lipases, the shift to greater solvent apolarity was accompanied by an increased molar ratio of diacylated-1,3-PD/monoacylated-1,3-PD in the product mixture. Reaction yields 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, except 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 suggest the existence of a solvent polarity influence on reaction product selectivity in multiproduct reactions, which can be partially explained on the basis of differential solvation and extraction properties of solvents. [References: 41]