Mossbauer and EPR Studies of Biological Oxygen Activation

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With this award, the Chemistry of Life Processes Program in the Chemistry Division supports Dr. Eckard Munck from Carnegie Mellon University to conduct spectroscopic and theoretical studies of iron-containing enzymes and synthetic complexes that activate molecular oxygen. The studies involve characterization of reaction intermediates of the enzymes 2,3 homoprotocatechuate dioxygenase, 1,2 benzoate dioxygenase and methane monooxygenase; each of these proteins is a representative of a large class of enzymes that carry out catalytic reactions of fundamental importance. The studies focus on trapping short-lived (milliseconds) intermediates in high oxidations states such as iron(IV) and iron(V and involve low temperature Mossbauer and Electron Paramagnetic Resonance experiments, complemented by density functional theory calculations. Further studies are aimed at trapping putative iron(V) intermediates in water oxidation reactions, one of the great challenges in inorganic chemistry. Information gained from these investigations is expected to provide crucial insights into the mechanisms of high oxidation state chemistry.Many catalytic reactions carried out by iron-containing enzymes in mammalian and bacterial organisms pass through states that contain as reactive species short-lived intermediates for which the iron atom is in an iron(IV) or iron(V) state bound to an oxo group derived from atmospheric oxygen. Mossbauer spectroscopy is a powerful tool to characterize these states in unprecedented detail. The spectra can be analyzed to yield a large number of parameters that characterize the oxidation state and the electronic structure of the iron. These parameters can be evaluated by quantum chemical methods to yield insights into the reactivity of these entities. Information gleaned from studies of the enzymes can be used by chemists to design synthetic complexes that either mimic the biological systems or perform functions that extend the range of the latter. The projects are carried out as collaborations between physicists, chemists and biochemists, providing training for graduate students and postdoctoral fellows of four collaborating groups as they acquire a broad perspective of an integrative approach to biological research. The research will be the basis of tutorial presentations to graduate students at Carnegie Mellon University, seven groups at the University of Minnesota as well to 70-80 graduate students at the 2014 Penn State Bioinorganic Workshop.