Uzir, Mohamad Hekarl; (2005) Dynamic modelling and simulation of biocatalytic reactions. Doctoral thesis , UCL (University College London).

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Abstract

Enzyme catalysis is of key importance in the synthesis of new fine chemicals. The use of enzymes to undertake chemical conversion has become commonplace among pharmaceutical companies alongside conventional catalysis. This is mainly due to the working conditions of enzyme-catalysed reactions, the specificity as well as stereo- and regio- selectivity of enzymes as biocatalysts. Many novel techniques have been developed to carry out such catalysis ranging from a simple batch reactor to a complex fiuidised bed reactor. Evaluating these techniques requires experimental work and repeat experiments and through these, optimised conditions could be achieved for better yield and productivity. Experimental work is costly and the only cost-effective method is to introduce computer-based experiments via mathematical modelling. For this purpose, a complete kinetic study based on mechanisms of general enzyme-catalysed reactions was established and the Michaelis-Menten type kinetics has been used as the basis of the steady-state analysis. Prior to the steady-state kinetics, dynamic analyses of enzyme-catalysed reactions were also undertaken and this has led to the understanding of the quasi steady-state assumption that governed the model. New conditions were proposed for the validity of this assumption and the stability of enzyme-catalysed reactions. In this work, Baeyer-Villiger monooxygenase enzyme-catalysed synthesis of optically pure lactone was used as a model system. A complete model of the rate expression of Baeyer-Villiger reaction was devised. This provided the foundation of the fed-batch whole cell process model carried out as the main part of this work. The effect of substrate and product inhibitions was integrated into this model system and an outcome comparable to that of the experimental data was achieved. The whole cell process system has been found to be affected by membrane diffusivity during the course of reaction. This has led to the introduction of diffusion coefficients for both substrate and product into the process model. A simple enzyme-catalysed reaction-diffusion system was successfully modelled and numerically solved. Finally, stability analysis was carried out in order to prove and understand the particular biocatalytic process system.

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