Humicola insolens Cutinase-Catalyzed Lactone Ring-Opening Polymerizations: Kinetic and Mechanistic Studies

Abstract

This paper explores reaction kinetics and mechanism for immobilized Humicola insolenscutinase (HIC), an important new biocatalyst that efficiently catalyzes non-natural polyester synthetic reactions. HIC, immobilized on Lewatit, was used as catalyst for epsilon-caprolactone (CL) and omega-pentadecalactone (PDL) ring-opening polymerizations (ROPs). Plots of percent CL conversion vs time were obtained in the temperature range from 50 to 90 degrees C. The kinetic plot of ln([M]0/[M]t) vs time (r2 = 0.99) for HIC-catalyzed bulk ROP of CL was linear, indicating that chain termination did not occur and the propagation rate is first order with respect to monomer concentration. Furthermore, linearity to 90% conversion for M(n) vs fractional CL conversion is consistent with a chain-end propagation mechanism. Deviation from linearity above 90% conversion indicates that a competition between ring-opening chain-end propagation and chain growth by steplike polycondensations takes place at high monomer conversion. HIC was inactive for catalysis of L-lactide and (R,S)-beta-butyrolactone ROP. HIC-catalyzed ROP of epsilon-CL and PDL in toluene were successfully performed, giving high molecular weight poly(epsilon-caprolactone) and omega-poly(pentadecalactone). In addition, the relative activities of immobilized Candida antarctica lipase B (CALB) and HIC for epsilon-CL and PDL polymerizations are reported herein.

Ring-opening polymerization of ɛ-caprolactone catalyzed by a novel thermophilic lipase from Fervidobacterium nodosum

“…A large increase in FNL activity for -caprolactone polymerization was found when the reaction temperature increased from 60 • C to 90 • C. After 72 h, the monomer conversion increased from 76% at 60 • C to almost 100% at 90 • C. The increased monomer conversion values at higher temperatures were probably caused by the decreased diffusion constraints in the reaction mixture and increased water molecules accessible in the chain initiation reaction. Compared with the complete loss of enzymatic activity of HIC at temperatures more than 70 • C [31], FNL was highly thermostable, and could efficiently catalyze the ring-opening polymerization of -caprolactone at much higher temperatures. This would be of great significance for the simultaneous, single-step chemoenzymatic synthesis of novel polymers.…”

Highly efficient ring-opening polymerization of ɛ-caprolactone catalyzed by a recombinant Escherichia coli whole-cell biocatalyst

“…For example, it has been reported that the polymerization of -caprolactone using Novozym 435 in toluene at 70 • C for 4 h produced poly(-caprolactone) with an isolated yield of 85% and a number-average molecular weight (Mn) of 44,800 g/mol [13]. Recently, a novel cutinase from H. insolens was explored with promising polyester synthesis activity, with Mn value of the synthesized poly(-caprolactone) of 24,900 g/mol at 70 • C for 24 h [15,17]. Despite these impressive results, enzymatic polymerization remains in the research and development stage, in part due to the high cost of producing and immobilizing these lipases.…”

Greener Oxidation of Alcohols, Glycosides and Sulfides

“…Phthalides and their analogs have shown interesting biological activities including antifungal and cytotoxic activities (11,12). These lactones also have potential utility in polymer chemistry as they make interesting substrates for ring opening polymerization of lactones to polyesters (13,14). One possible explanation could be the initial formation of a monoaldehyde that reacts with the intramolecular hydroxymethyl group to form a hemiacetal that is then oxidized to the observed lactone (Scheme 4).…”