Modelling the microenvironment of a lipase immobilized in polyurethane foams

Abstract

The effects of partition of substrates and product on the modelling of the microenvironment of an immobilized lipase were evaluated using Response Surface Methodology. The esterification of butyric acid with ethanol in n-hexane, catalyzed by Candida rugosa lipase immobilized in two biocompatible and relatively hydrophilic polyurethane foams (“Hypol FHP 2002™” and “Hypol FHP 5000™”) was used as the model system. For each set of initial conditions, the final concentration of substrates and ethyl butyrate in the microenvironment, at equilibrium, Cmicro, were estimated by mass balancing bulk and foams. The Cmicro values obtained were used to estimate the corresponding partition coefficients of ethanol (PEtOH), butyric acid (PBA) and ester (PEB), between the foams (microenvironment) and the bulk medium. Foams containing previously inactivated lipase, as well as lipase-free foams were used. For both substrates, Cmicro values were, in the majority of the experiments, higher than their macroenvironmental counterparts. The lowest Cmicro values were observed with the less hydrophilic foam (“FHP 5000”). A decrease of CmicroEtOH in both foams and CmicroBA in “FHP 5000” foams, was obtained upon lipase immobilization. PEB values were, in all cases, close to zero. This is beneficial in terms of the shift in reaction equilibrium, product recovery and alleviation of product inhibition effects.