BIOCATALYSIS USING GELATIN MICROEMULSION-BASED ORGANOGELS CONTAINING IMMOBILIZED CHROMOBACTERIUM-VISCOSUM LIPASE

Chromobacterium viscosum (CV) lipase was immobilized in gelatin-contai ning Aerosol-OT (AOT) microemulsion-based organogels (MBGs). The behav ior of this novel, predominantly hydrophobic matrix as an esterificati on catalyst has been examined. The biocatalyst was most effective when the MBG was granulated to yield gel particles of similar to 500 mu m diameter, providing a total surface area of ca. 10(6) mm(2) per 10 cm( 3) of gel. The gel was generally contacted with a solution of the subs trate(s) in a hydrocarbon oil. Under most conditions reaction was not diffusion limited. Apparent lipase activity was influenced by certain compositional changes in the MEG, but most significantly when the R va lue, the mole ratio of water to surfactant, was altered. Higher activi ties were observed at lower R values. Although gels of lowest R value expressed the highest condensation activity, such formulations were ph ysically unsuitable as immobilization matrices due to their proximity to the gel-solution phase boundary. MBGs of intermediate R values (bet ween 60 and 80) were considered most suitable because they offer relat ively high condensation activity and good physical stability. The gela tin concentration also exerted a small but measurable influence on the observed condensation rates. Apparent lipase activity was also influe nced to some extent by the nature of the parent hydrocarbon used to pr epare the MEG. Higher activities were obtained using formulations deri ved from isooctane and cyclohexane rather than the n-alkanes. Condensa tion activities expressed by CV lipase in the MBGs were broadly compar able to those expressed in the analogous parent water-in-oil (w/o) mic roemulsions. The MBGs functioned effectively in neat substrate solutio ns, but the condensation activity expressed by the MBGs in a series of successive batch syntheses was adversely affected by the formation an d retention of the water coproduct. Selective removal of the water was achieved using a concentrated solution of dry reverse micelles, which resulted in recovery of lost activity. Pretreatment of lipase-contain ing MBGs resulted in the formation of MBGs with enhanced catalytic pro perties and modified compositions, which could not otherwise have been prepared using the conventional procedure. (C) 1997 John Wiley & Sons , Inc.