title: 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.
authors.affiliation: Department of Chemistry, Kenyon College, Gambier, Ohio 43022, USA.
authors.forename: Mo
authors.initials: M
authors.lastname: Hunsen
authors.forename: Azim
authors.initials: A
authors.lastname: Abul
authors.forename: Wenchun
authors.initials: W
authors.lastname: Xie
authors.forename: Richard
authors.initials: R
authors.lastname: Gross
mesh_terms: D002265:Carboxylic Ester Hydrolases / Q000737:chemistry / Q000493:pharmacokinetics*; D002384:Catalysis; D007783:Lactones / Q000737:chemistry / Q000493:pharmacokinetics*; D003904:Mitosporic Fungi / Q000201:enzymology; D011108:Polymers / Q000737:chemistry / Q000493:pharmacokinetics*
chemical_list: D007783:Lactones; D011108:Polymers; D002265:Carboxylic Ester Hydrolases; C019952:cutinase