Substrate Report for: epsilon-caprolactone

Enzyme-catalyzed ring-opening polymerization of lactones is a method of increasing interest for the synthesis of polyesters. In the present work, we investigated which changes in the structure of Candida antarctica lipase B (CaLB) shift the catalytic equilibrium between esterification and hydrolysis towards polymerization. Therefore, we present two concepts: (i) removing the glycosylation of CaLB to increase the surface hydrophobicity; and (ii) introducing a hydrophobic lid adapted from Pseudomonas cepacia lipase (PsCL) to enhance the interaction of a growing polymer chain to the elongated lid helix. The deglycosylated CaLB (CaLB-degl) was successfully generated by site-saturation mutagenesis of asparagine 74. Furthermore, computational modeling showed that the introduction of a lid helix at position Ala148 was structurally feasible and the geometry of the active site remained intact. Via overlap extension PCR the lid was successfully inserted, and the variant was produced in large scale in Pichia pastoris with glycosylation (CaLB-lid) and without (CaLB-degl-lid). While the lid variants show a minor positive effect on the polymerization activity, CaLB-degl showed a clearly reduced hydrolytic and enhanced polymerization activity. Immobilization in a hydrophobic polyglycidol-based microgel intensified this effect such that a higher polymerization activity was achieved, compared to the "gold standard" Novozym((R)) 435.

A novel method to synthesize poly(sigma-caprolactone) (PCL) through a three-step, lipase-mediated chemo-enzymatic reaction from cyclohexanone using an immobilized lipase from Trichosporon laibacchii (T. laibacchii) CBS5791 was developed. The immobilized preparation with 1280 U. g(-1) used here was obtained by a method of purification and in situ immobilization where the crude intracellular lipase (cell homogenate) was subjected to partial purification by an aqueous two-phase system (ATPS) consisting of 12% (w/w) polyethylene glycol (PEG) 4000 and 13% (w/w) potassium phosphate (K(2)HPO(4)) and then in situ immobilization directly on diatomite from the top PEG-rich phase of ATPS. In this multi-step process, the sigma-caprolactone (sigma-CL) produced by lipase-mediated one-pot two-step chemo-enzymatic oxidation of cyclohexanone was directly subjected to in situ ring-opening polymerization (ROP) started by adding highly hydrophobic solvents. It is necessary to note that sigma-CL synthesis and its subsequent ROP were catalyzed by the same lipase. The impact of various reaction parameters, e.g., solvent, cyclohexanone: hydrogen peroxide molar ratio, hydrogen peroxide forms and reaction temperature were investigated. Toluene was selected as a preferred solvent due to supporting the highest molecular weight (M(n) = 2168) and moderate sigma-CL conversion (65.42%). Through the optimization of reaction conditions, PCL was produced with a M(n) of 2283 at 50 degreesC for 24 h. These results reveal that this lipase-mediated direct ring-opening polymerization of in situ formed sigma-CL is an alternative route to the conventional synthesis of PCL.

The enzymatic ring-opening copolymerization of sigma-caprolactone (sigma-CL) and beta-lactam by using Candida antarctica lipase B (CAL-B) as catalyst was studied. Variation of the feed ratios of 25:75, 50:50, and 75:25 of sigma-CL/beta-lactam was performed. The products contain poly(sigma-CL-co-beta-lactam) and the homopolymers of poly(sigma-CL) and poly(beta-lactam). The structure of the copolymers was determined by MALDI-ToF MS. Poly(sigma-CL-co-beta-lactam) has an alternating and random structure consisting of alternating repeating units with oligo(sigma-CL) or oligo(beta-lactam). The highest fraction of the alternating copolymers resulted from the reaction with a feed ratio 50:50. The copolymer is a semicrystalline polymer with a Tm at 124 degreesC and Tgs at -15 and 50 degreesC. Interestingly, the copolymer also demonstrated cold crystallization at 29 and 74 degreesC, after quenching the sample from the melt in liquid nitrogen.

Enzyme-catalyzed ring-opening polymerization of lactones is a method of increasing interest for the synthesis of polyesters. In the present work, we investigated which changes in the structure of Candida antarctica lipase B (CaLB) shift the catalytic equilibrium between esterification and hydrolysis towards polymerization. Therefore, we present two concepts: (i) removing the glycosylation of CaLB to increase the surface hydrophobicity; and (ii) introducing a hydrophobic lid adapted from Pseudomonas cepacia lipase (PsCL) to enhance the interaction of a growing polymer chain to the elongated lid helix. The deglycosylated CaLB (CaLB-degl) was successfully generated by site-saturation mutagenesis of asparagine 74. Furthermore, computational modeling showed that the introduction of a lid helix at position Ala148 was structurally feasible and the geometry of the active site remained intact. Via overlap extension PCR the lid was successfully inserted, and the variant was produced in large scale in Pichia pastoris with glycosylation (CaLB-lid) and without (CaLB-degl-lid). While the lid variants show a minor positive effect on the polymerization activity, CaLB-degl showed a clearly reduced hydrolytic and enhanced polymerization activity. Immobilization in a hydrophobic polyglycidol-based microgel intensified this effect such that a higher polymerization activity was achieved, compared to the "gold standard" Novozym((R)) 435.

A novel method to synthesize poly(sigma-caprolactone) (PCL) through a three-step, lipase-mediated chemo-enzymatic reaction from cyclohexanone using an immobilized lipase from Trichosporon laibacchii (T. laibacchii) CBS5791 was developed. The immobilized preparation with 1280 U. g(-1) used here was obtained by a method of purification and in situ immobilization where the crude intracellular lipase (cell homogenate) was subjected to partial purification by an aqueous two-phase system (ATPS) consisting of 12% (w/w) polyethylene glycol (PEG) 4000 and 13% (w/w) potassium phosphate (K(2)HPO(4)) and then in situ immobilization directly on diatomite from the top PEG-rich phase of ATPS. In this multi-step process, the sigma-caprolactone (sigma-CL) produced by lipase-mediated one-pot two-step chemo-enzymatic oxidation of cyclohexanone was directly subjected to in situ ring-opening polymerization (ROP) started by adding highly hydrophobic solvents. It is necessary to note that sigma-CL synthesis and its subsequent ROP were catalyzed by the same lipase. The impact of various reaction parameters, e.g., solvent, cyclohexanone: hydrogen peroxide molar ratio, hydrogen peroxide forms and reaction temperature were investigated. Toluene was selected as a preferred solvent due to supporting the highest molecular weight (M(n) = 2168) and moderate sigma-CL conversion (65.42%). Through the optimization of reaction conditions, PCL was produced with a M(n) of 2283 at 50 degreesC for 24 h. These results reveal that this lipase-mediated direct ring-opening polymerization of in situ formed sigma-CL is an alternative route to the conventional synthesis of PCL.

The enzymatic ring-opening polymerization of lactones is a method of increasing interest for the synthesis of biodegradable and biocompatible polymers. In the past it was shown that immobilization of Candida antarctica lipase B (CaLB) and the reaction medium play an important role in the polymerization ability especially of medium ring size lactones like sigma-caprolactone (sigma-CL). We investigated a route for the preparation of compartmentalized microgels based on poly(glycidol) in which CaLB was immobilized to increase its esterification ability. To find the ideal environment for CaLB, we investigated the acceptable water concentration and the accessibility for the monomer in model polymerizations in toluene and analyzed the obtained oligomers/polymers by NMR and SEC. We observed a sufficient accessibility for sigma-CL to a toluene like hydrophobic phase imitating a hydrophobic microgel. Comparing free CaLB and Novozym((a)) 435 we found that not the monomer concentration but rather the solubility of the enzyme, as well as the water concentration, strongly influences the equilibrium of esterification and hydrolysis. On the basis of these investigations, microgels of different polarity were prepared and successfully loaded with CaLB by physical entrapment. By comparison of immobilized and free CaLB, we demonstrated an effect of the hydrophobicity of the microenvironment of CaLB on its enzymatic activity.

The enzymatic ring-opening copolymerization of sigma-caprolactone (sigma-CL) and beta-lactam by using Candida antarctica lipase B (CAL-B) as catalyst was studied. Variation of the feed ratios of 25:75, 50:50, and 75:25 of sigma-CL/beta-lactam was performed. The products contain poly(sigma-CL-co-beta-lactam) and the homopolymers of poly(sigma-CL) and poly(beta-lactam). The structure of the copolymers was determined by MALDI-ToF MS. Poly(sigma-CL-co-beta-lactam) has an alternating and random structure consisting of alternating repeating units with oligo(sigma-CL) or oligo(beta-lactam). The highest fraction of the alternating copolymers resulted from the reaction with a feed ratio 50:50. The copolymer is a semicrystalline polymer with a Tm at 124 degreesC and Tgs at -15 and 50 degreesC. Interestingly, the copolymer also demonstrated cold crystallization at 29 and 74 degreesC, after quenching the sample from the melt in liquid nitrogen.

A unified kinetic pathway for the enzyme-catalyzed polymerization and degradation of poly(sigma-caprolactone) was developed. This model tracks the complete distribution of individual chain lengths, both enzyme-bound and in solution, and successfully predicts monomer conversion and the molecular mass distribution as a function of reaction time. As compared to reported experimental data for polymerization reactions, modeled kinetics generate similar trends, with ring-opening rates and water concentration as key factors to controlling molecular mass distributions. Water is critically important by dictating the number of linear chains in solution, shifting the molecular mass distribution at which propagation and degradation equilibrate. For the enzymatic degradation of poly(sigma-caprolactone), the final reaction product is also consistent with the equilibrium dictated by the propagation and degradation rates. When the modeling framework described here is used, further experiments can be designed to isolate key reaction steps and provide methods for improving the efficiency of enzyme polymerization.

Enzymatic ring-opening polymerization of lactones was achieved by using lipase as catalyst. The polymerization of epsilon-caprolactone by Pseudomonas fluorescens lipase at 60 C in bulk for 10 days afforded a polyester with average molecular weight of 7.0 x 103. From 1H and 13C NMR analysis, the polymer possesses the terminal structure of a carboxylic acid group at one end and a hydroxyl group at the other.