Kinetics and Mechanism of Candida antarctica Lipase B Catalyzed Solution Polymerization of ε-Caprolactone

Abstract

Studies of the kinetics and mechanism of Candida antarctica Lipase B (CALB) catalyzed -caprolactone ( -CL) polymerizations in toluene were performed. The kinetic plot of ln ([M]0/[M]t) vs time was carried out to 96% -CL conversion and Mn 11 970. The plot is linear (r 2 ) 0.998), indicating that termination did not occur and the propagation rate is first order with respect to monomer concentration. Changes in the water (e.g., initiator) concentration did not change the polymerization rate but did change the number of chains [R-OH]. Thus, the polymerization is zero order with respect to [R-OH] and initiator concentration. A plot of ln k app vs ln [enzyme] gave 0.7 as the reaction order of the enzyme concentration. The apparent activation energy for Novozyme-435 catalyzed -CL polymerization in toluene is 2.88 kcal mol -1 . This is well below 10.3 kcal mol -1 , the activation energy for aluminum alkoxide catalyzed -CL polymerization in toluene. Upward deviation from linearity for Mn vs fractional -CL conversion and decreases in the number of chains was accentuated by low enzyme water contents and high monomer conversion. These results are consistent with a competition between ring-opening chain-end propagation and chain growth by steplike polycondensations. CALB was irreversibly inhibited by modification with paraoxon at the lipase active site (Ser105). The modified enzyme was no longer active for the polymerization. This supports that the polymerizations studied herein occurred by catalysis at the active serine residue (Ser105) and not by other chemical or nonspecific protein-mediated processes.

Enzymatic Synthesis of Polyesters via Ring-Opening Polymerization

“…The rate-determining step of the overall polymerization is the formation of the EM. Similar mechanisms were also examined and verified [48,91,92].…”

Polymers in the Pharmaceutical Applications - Natural and Bioactive Initiators and Catalysts in the Synthesis of Biodegradable and Bioresorbable Polyesters and Polycarbonates

“…Lipases could also catalyze ROP of cyclic monomers, with different ring sizes as well as monomers containing substituents in the ring: -methyl--propiolactone (1), -butyrolactone (2), -caprolactone (3), -methyl-valerolactone (4), 1,4-dioxan-2-one (5), -caprolactone (6), -ethyl--caprolactone (7), -heptanolactone (8), -decalactone (9), -dodecalactone (10) Coŕdova et al, 1999;Divakar, 2004;Dong, 1998Dong, , 1999Gorke et al, 2007;Henderson et al, 1996;Kobayashi, 2001aKobayashi, , 2001bKobayashi, , 2009MacDonald et al, 1995;Marcilla et al, 2006;Matsumoto et al, 1999;Mei et al, 2003;Namekawa et al, 1999;Rokicki, 2000;Sivalingam & Madras, 2004;Van Der Mee et al, 2006). Lipases can accommodate a wide variety of synthetic substrates and still be able to show stereo-and regio-selectivity.…”

“…The yield of the obtained polymers varied from 10 to 100%. The preferred lipase system generally used is a physically immobilized form of Candida Antarctica, commercially available as Novozyme-435 (Barrera-Rivera et al, 2009;Coŕdova et al, 1999;Divakar, 2004;Dong, 1998Dong, , 1999Gorke et al, 2007;Henderson et al, 1996;Kobayashi, 2001aKobayashi, , 2001bKobayashi, , 2009MacDonald et al, 1995;Marcilla et al, 2006;Matsumoto et al, 1999;Mei et al, 2003;Namekawa et al, 1999;Sivalingam & Madras, 2004;Van Der Mee et al, 2006).…”

Hydrolases Part I: Enzyme Mechanism, Selectivity and Control in the Synthesis of Well-Defined Polymers

“…3) [60][61][62][63][64]94]. Initiation of the polymerization occurs by deacylation of the acyl-enzyme intermediate by an appropriate nucleophile such as water or an alcohol to produce the corresponding ω-hydroxycarboxylic acid or ester.…”

“…However, the polydispersities (polydispersity index, PDI, was typically between 1.5 and 2.0) suggested a limited control during the polymerization. Moreover, at high substrate conversions (>80%), deviations from linearity appeared that were attributed to concomitant condensation reactions [64]. In fact, most papers dealing with lipase-catalyzed ROP report a PDI in the range of 2.0 for unprecipitated samples, showing that side reactions also occur during the ROP.…”