Candida antarctica lipase B chemically immobilized on epoxy-activated micro- and nanobeads:: Catalysts for polyester synthesis

Candida antarctica Lipase B (CALB) was covalently immobilized onto epoxy-activated macroporous poly(methyl methacrylate) Amberzyme beads (235 mu m particle size, 220 angstrom pore size) and nanoparticles (nanoPSG, diameter 68 nm) with a poly(glycidyl methacrylate) outer region. Amberzyme beads allowed CALB loading up to 0.16 g of enzyme per gram of support. IR microspectroscopy generated images of Amberzyme-CALB beads showed CALB is localized within a 50 mu m thick loading front. IR microspectroscopy images, recorded prior to and after treatment of Amberzyme-CALB with DMSO/aqueous Triton X-100, are similar, confirming-that CALB is largely chemically linked to Amberzyme. The activity of CALB immobilized on Amberzyme, Lewatit (i.e., Novozym 435 catalyst), and nanoPSG was assessed for lactone ring-opening and step-condensation polymerizations. For example, the percent conversion of epsilon-caprolactone using the same amount of enzyme catalyzed by Amberzym-CALB, Novozym 435, and nanoPSG-CALB for 20 min was 7.0, 16, and 65%, respectively. Differences in CALB reactivity were discussed based on resin physical parameters and availability of active sites determined by active site titrations. Regardless of the matrix used and chemical versus physical immobilization, epsilon-CL ring-opening polymerizations occur by a chain growth mechanism without chain termination. To test Amberzyme-CALB stability, the catalyst was reused over three reaction cycles for epsilon-CL ring-opening polymerization (70 degrees C, 70 min reactions) and glycerol/1,8-octanediol/adipic acid polycondensation reactions (90 degrees C, 64 h). Amberzyme-CALB was found to have far better stability for reuse relative to Novozym 435 for the polycondensation reaction.