Experimental and Computational Studies on the Mechanism of Transition-Metal-Catalyzed Oxidation and Halogenation Processes

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Bacterial catechol dioxygenases are enzymes responsible for the conversion of hydroxylated aromatic into acyclic compounds and therefore play a central role within the degradation of aromatic compounds. These nonheme iron and similar copper enzymes catalyze the oxidative cleavage of aromatic C-C bonds and, depending on the position of the reactive C-C bond with respect to the hydroxyl groups of the catechol substrate, are classified into intradiol- and extradiol-cleaving catechol dioxygenases. Based on low molecular weight model compounds with bispidine-type ligands and with humic acid derivatives, we will thoroughly analyze the reaction mechanisms and product distributions. Moreover, organic substrates are transferred by the same catalyst systems to halogenated compounds, and these reactions will also be studied in detail. These studies will involve kinetic experiments, labeling studies, the trapping of reactive intermediates and their full spectroscopic characterization at low temperature and computational work to derive the relevant potential energy surfaces of the reactions and to compute the spectroscopic properties of interesting intermediate states. The detailed mechanistic information on a molecular basis of bispidine model systems will be used to model the reactivities of iron complexes without supporting bispidine ligands, and these results will be compared with similar studies of other groups within the DFG Research Group.