Electronic and Geometric Structure of Biological Spin Centers Investigated with EPR Spectroscopy
Hayes, Ellen Cambron
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In this dissertation, the fundamental concepts and techniques of electron paramagnetic resonance (EPR) spectroscopy, which are important for understanding electronic structure and relating it to geometric structure, are presented in Chapter 1. Following this are five chapters each dedicated to a separate topic where EPR spectroscopy was a central tool in studying the properties of biologically relevant systems. Chapter 2 focuses on the study of tryptophan radicals in small peptide systems. The studies aim to understand how microenvironment influences the electronic structure (through measuring magnetic and electrochemical properties) of these radicals. In Chapter 3, the identity of an unknown organic radical in the active site of the enzyme spore photoproduct lyase (SPL) is investigated. This radical is believed to be a part of a radical transfer chain involved in the repair of photodamaged DNA by the enzyme SPL. In Chapter 4, closely related to the topics of Chapter 3, the pathway of DNA photodamage by ultraviolet light is investigated. The damaged DNA is believed to form through a radical recombination process amenable to study with EPR spectroscopy. Chapter 5 discusses the magnetic properties of an intermediate formed during O-O bond activation and cleavage by a small molecule MnII compound. Results of EPR spectroscopy suggest the intermediate is a MnIIIMnIV dimer and aim to characterize the bridging motif and protonation state of the MnIIIMnIV dimer. Finally, Chapter 6 presents a study of a small molecule CuII-alkoxide compound relevant for understanding CuII mediated alcohol oxidations (which occur in enzymes such as galactose oxidase). A detailed electronic structure characterization was carried out by using single-crystal EPR spectroscopy in tandem with magnetic circular dichroism spectroscopy, resonance Raman spectroscopy, and density functional theory calculations.
- Chemistry