Spectroscopy of Metal containing Biomolecules and Biomimetic complexes involved in Oxygen and Water Activation

Metalloenzymes catalyze the transformation of substrates while activating O2 and H2O in key reactions of metabolic and photosynthetic processes. Electron Paramagnetic Resonance (EPR) and Mossbauer spectroscopies are used to characterize the heme enzyme Tryptophan Dioxygenase (TDO), which catalyzes a critical ring-opening step in the pathway of NAD biosynthesis in humans. The present work demonstrates the existence of two dominant inequivalent heme species in reduced and oxidized states of the enzyme. This is consistent with a dimer of dimer protein quaternary structure that now extends to the electronic properties of the hemes. This work presents a new description of the heme interactions with the protein, which must be considered during the general interpretation of physical data as it relates to kinetics, mechanism, and function of TDO.;Synthetic biomimetic complexes provide insight into the electronic and magnetic properties of short-lived reactive intermediates that are otherwise hard to trap in proteins. This work presents a characterization of a series of biomimetic Mn/Fe complexes of the same ligand set for oxidation states +2, +3, +4 and +5 (Mn) allowing comparison of electronic parameters of the metal in d5 to d2 electronic states in the same environment. Density Functional Theory (DFT) calculations give good agreement with specific experimentally determined properties, thereby providing connections to the structure. The Fe+4 and Mn+5 complexes are the first EPR detection of these metal states. High-valent Fe+4 species are key catalytic intermediates in enzymatic reactions involving O2 and a Mn+5 center has been postulated in Photosystem II for H2O oxidation. The ability to detect such species with EPR, coupled with quantitative simulations provides a new probe for detection of the reactive intermediates in enzymes.