ISBN 978-3-8439-3538-8

978-3-8439-3538-8, Reihe Thermodynamik

Matthias Voges
Effects of Concentration and Additives on Thermodynamic Equilibria of Enzyme-Catalyzed Reactions

174 Seiten, Dissertation Technische Universität Dortmund (2018), Softcover, A5

Zusammenfassung / Abstract

Enzyme-catalyzed reactions are attractive alternatives to chemically-catalyzed routes. However, many enzyme-catalyzed reactions are limited by the thermodynamic reaction equilibrium, what results in low reaction yields. Thus, thermodynamic characterizations of enzyme-catalyzed reactions and investigations of influencing factors on reaction equilibria (and therewith on product yields) are indispensable.

In this work, the influence of temperature, pH value, concentrations of reacting agents and additives on the reaction equilibrium of the following enzyme-catalyzed model reactions were investigated: acetophenone+2-propanol⇌1-phenylethanol+acetone; L-alanine+2-oxoglutarate ⇌L-glutamate+pyruvate; 1-phenylethylamine+cyclohexanone⇌acetophenone+cyclohexylamine. First, the standard Gibbs energy of reaction and the equilibrium constant of each reaction were determined. Second, the influence of the reaction temperature and of the pH value on the reaction equilibrium was shown. From the temperature dependency, it was shown that the three reactions within this work are endothermic. The experimentally-observed influence of the pH value on the reaction equilibrium could be described by means of protonation/ deprotonation of the reacting agents quantitatively. Third, it is shown that the total molalities and the ratio of the initial reactant molalities are influencing the reaction equilibria of the three model reactions. Fourth, a significant effect of the concentration and type of additives (natural solutes and Ionic Liquids) on the reaction equilibria and yields of the model reactions is shown. The fact that the reaction equilibria of the enzyme-catalyzed model reactions were found to depend on reaction conditions was caused by non-unity activity coefficients of the reacting agents. ePC-SAFT-predicted activity coefficients allowed predicting the respective effect of the reaction condition on reaction equilibria and therewith on the yields. The predictions are in excellent agreement with the experiments.

Thus, this work demonstrates the importance of taking thermodynamic non-idealities into account for accurate descriptions of equilibrium-limited reactions and the potential of thermodynamic models in process design as a predictive tool for yield limitations on enzyme-catalyzed reactions.