Modeling the Active Sites of Copper Monooxygenase Enzymes

Abstract

Mechanistic investigation of copper-oxygen intermediates relevant to the oxygenation reactions of copper monooxygenase enzymes is a long-standing goal of bioinorganic chemists. To elucidate and understand the key species in copper monooxygenase pathways, small molecule synthetic chemistry has been employed to discretely generate and characterize individual species of interest. In Chapter 1, previous enzymatic and modeling work with respect to copper monooxygenase chemistry is discussed and current mechanistic proposals are explored in detail. Chapter 2 describes modeling studies of monocopper sites and the influence of secondary sphere hydrogen bonding interactions on their redox behavior. A series of monocopper complexes with secondary sphere hydrogen bond interactions were determined to result in large increases of the electrochemical potentials of the CuIII/CuII redox couple when compared to non-hydrogen bound analogs. The hydrogen bonding model systems provide evidence for the structure-function relationship of secondary coordination influences on metal-containing active sites. Chapter 3 discusses development of a previously undescribed dinucleating macrocyclic ligand, designed to support dicopper-oxygen cores relevant to the enzyme particulate methane monooxygenase (pMMO). Attempts to generate dicopper-hydroxo type cores resulted in hydrolytic products found to be dicopper complexes that were crystallographically characterized. Observed “paddle wheel” type configurations with cis-labile coordination sites in the dicopper complexes represent a class of compounds with diverse coordination chemistry. The final chapter (Chapter 4) describes the synthesis and characterization of a formal CuIII-alkylperoxo core utilizing spectroscopic and computational methods. The CuIII-alkylperoxo complex has been shown to undergo proton-coupled electron-transfer (PCET) reactions with weak O-H bond substrates. The CuIII-alkylperoxo core is considered to be a model system of a CuIII-OOH core, proposed to be a possible reactive intermediate in lytic polysaccharide monooxygenase (LPMO).