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Date of Award
Jeremy J. Kodanko
This dissertation is divided into two chapters, the first chapter includes an introduction to reactive oxygen species and their reactions with proteins. The introduction also covers metal-based oxidants, including both heme and non-heme enzymes that activate dioxygen as well as complexes that mimic these enzymes. The work discussed in chapter one concerns the synthesis of amino acid substrates that mimic amino acid residues. Substrates synthesized were derived from Gln, Asn, Ile, Cys and Tyr. Once synthesized, these substrates were reacted with [FeIV(O)(N4Py)]2+ under pseudo-first order conditions. The mechanisms for the reactions of the most reactive substrates were investigated. Electron-transfer proton-transfer and hydrogen atom transfer mechanisms are suggested for the substrates derived from Cys and Tyr, respectively, for their reaction with [FeIV(O)(N4Py)]2+. An electrophilic aromatic substitution mechanism is suggested for the mechanism of the reaction of the substrate derived from Phe with [FeIV(O)(N4Py)]2+.
The second chapter focuses on the oxidation of glutathione by metal-based oxidants, both single turnover and catalytic reactions. The introduction discusses the importance of glutathione in biology and the mechanism of its oxidation by copper ions. The discussion sections cover two related projects. The first is the single turnover oxidation of glutathione by [FeIV(O)(N4Py)]2+, which includes the characterization of the intermediate [FeIII(SG)(N4Py)]2+ by UV-Vis and EPR spectroscopy as well as high resolution time-of-flight mass spectrometry. The kinetics of the reaction were investigated through the use of kinetic modeling software and a mechanism was proposed for this oxidation. The second section is a discussion of the catalytic oxidation of glutathione by metal-based oxidants. Initial catalyst screens were conducted and [FeIITPA]2+ and [FeIIN4Py]2+ represent target complexes for further investigations. Antioxidant enzyme studies with catalase and superoxide dismutase show that hydrogen peroxide and superoxide are not involved before the rate-determining step of the oxidation. Also, no pH dependence was observed for the reaction of glutathione with [FeIITPA]2+, however, a slight pH dependence was observed for [FeIIN4Py]2+. These results suggest possible differences in mechanisms for the oxidation of GSH by iron complexes of N4Py and TPA, most likely due to denticity differences.
Campanali, Ashley Ann, "Synthesis Of N-Acetyl And C-Tert-Butyl Natural Amino Acid Substrates That Mimic Residues Of Polypeptides And Their Reactivity With [feiv(o)(n4py)]2+: Kinetic And Mechanistic Investigations" (2011). Wayne State University Dissertations. Paper 194.