Modeling Enzymatic Kinetic Pathways for Ring-Opening Lactone Polymerization
Peter M. Johnson, Santanu S. Kundu, Kathryn L. Beers
A unified kinetic pathway for the enzyme catalyzed polymerization and degradation of poly(ε-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 manipulating molecular mass distributions. Water is critically important by controlling the number of linear chains in solution, shifting the molecular mass distribution at which propagation and degradation equilibrate. For the enzymatic degradation of poly(ε-caprolactone), the final reaction product is consistent with the equilibrium dictated by the propagation and degradation rates. Using the modeling framework described here, further experiments can be designed to isolate key reaction steps and provide methods for improving the efficiency of enzyme polymerization.