Research described in this proposal will be aimed at: * understanding how structure influences the function of metalloenzyme active sites. * determining if there is a correlation between structure, properties (such as spin-state), and reactivity. Questions we will be attempting to address include: * What ligand environment is needed to stabilize the low-spin state of nitrite hydratases (NHases)? What influence, if any, does spin-state have on reactivity? How do the sulfurs influence these properties? What role do the amidates play in NHase? What is the mechanism by which NHase hydrates nitrites? What role, if any, does the conserved Ser-OH (or Thr-OH in Co-NHases) play in the mechanism of NHase? What role, if any, do the conserved arginines play in the mechanism of NHase? Does superoxide reduction by superoxide reductases (SORs) proceed via an Fe(III)-OOH intermediate? What role, if any, does the conserved glutamate play in the mechanism of SOR? How do inhibitors N3- and CN- inhibit SOR activity? Is the positioning of the Cys in SOR, traps with respect to the open binding site, important in promoting function? We plan to explore these questions by: * examining the reactivity of synthetic model complexes, and attempting to correlate this with structure and properties, such as spin- state and electronic structure, by systematically altering the structure of our ligands. * ligands will, in some cases, incorporate pendent alcohol or guanidinium arms, as models for the nearby serine and arginines in NHase. * reactivity of these models with subtrates RCN (NHase), OH- (NHase), O2- (SOR) and inhibitors (N3- , NO, CN-, RC02-) will be examined. * reactivity of these models will be compared on the basis of kinetic and thermodynamic studies. * reactivity will be monitored spectrophotometrically, at low temperature, and by EPR. * kinetics data will be obtained using stopped-flow techniques, and NMR line-shape analysis.

National Institute of Health (NIH)
National Institute of General Medical Sciences (NIGMS)
Research Project (R01)
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Metallobiochemistry Study Section (BMT)
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Preusch, Peter C
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University of Washington
Schools of Arts and Sciences
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Rees, Julian A; Bjornsson, Ragnar; Kowalska, Joanna K et al. (2017) Comparative electronic structures of nitrogenase FeMoco and FeVco. Dalton Trans 46:2445-2455
Kowalska, Joanna K; Nayyar, Brahamjot; Rees, Julian A et al. (2017) Iron L2,3-Edge X-ray Absorption and X-ray Magnetic Circular Dichroism Studies of Molecular Iron Complexes with Relevance to the FeMoco and FeVco Active Sites of Nitrogenase. Inorg Chem 56:8147-8158
Villar-Acevedo, Gloria; Lugo-Mas, Priscilla; Blakely, Maike N et al. (2017) Metal-Assisted Oxo Atom Addition to an Fe(III) Thiolate. J Am Chem Soc 139:119-129
Rees, Julian A; Martin-Diaconescu, Vlad; Kovacs, Julie A et al. (2015) X-ray Absorption and Emission Study of Dioxygen Activation by a Small-Molecule Manganese Complex. Inorg Chem 54:6410-22
Brines, Lisa M; Coggins, Michael K; Poon, Penny Chaau Yan et al. (2015) Water-soluble Fe(II)-H2O complex with a weak O-H bond transfers a hydrogen atom via an observable monomeric Fe(III)-OH. J Am Chem Soc 137:2253-64
Kovacs, Julie A (2015) Tuning the Relative Stability and Reactivity of Manganese Dioxygen and Peroxo Intermediates via Systematic Ligand Modification. Acc Chem Res 48:2744-53
Coggins, Michael K; Martin-Diaconescu, Vlad; DeBeer, Serena et al. (2013) Correlation between structural, spectroscopic, and reactivity properties within a series of structurally analogous metastable manganese(III)-alkylperoxo complexes. J Am Chem Soc 135:4260-72
Coggins, Michael K; Sun, Xianru; Kwak, Yeonju et al. (2013) Characterization of metastable intermediates formed in the reaction between a Mn(II) complex and dioxygen, including a crystallographic structure of a binuclear Mn(III)-peroxo species. J Am Chem Soc 135:5631-40
Coggins, Michael K; Toledo, Santiago; Kovacs, Julie A (2013) Isolation and characterization of a dihydroxo-bridged iron(III,III)(?-OH)2 diamond core derived from dioxygen. Inorg Chem 52:13325-31
Coggins, Michael K; Brines, Lisa M; Kovacs, Julie A (2013) Synthesis and structural characterization of a series of Mn(III)OR complexes, including a water-soluble Mn(III)OH that promotes aerobic hydrogen-atom transfer. Inorg Chem 52:12383-93

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