Different aspects of solvent engineering in lipase catalysed esterifications

A microbial lipase from Pseudomonas sp., immobilized on an ACR-silica gel, has been used as catalyst for esterification reactions in organic solvents which were largely different in some fundamental physico-chemical characteristics. The results obtained were compared with the same reactions carried out in supercritical carbon dioxide. Significant variations in conversion values as function of log Pmow of the solvent (dielectric constants and Hildebrand solubility parameters not providing consistent results) seem to demonstrate the importance of the enzyme-water content on the mechanism of action as in terms of conformations arrangements as well as in terms of substrates partition equilibrium with the polar matrix. Differently, the conversions and enantioselectivity of the reactions in the supercritical fluid, always higher than in organic solvents, could be attributed to the specific properties of the medium in terms of low viscosity and surface pressure values and higher diffusivity of substrates in the supercritical phase.