title: Characterization of Oxygen Bridged Manganese Model Complexes Using Multifrequency (17)O-Hyperfine EPR Spectroscopies and Density Functional Theory.
abstract: Multifrequency pulsed EPR data are reported for a series of oxygen bridged (μ-oxo/μ-hydroxo) bimetallic manganese complexes where the oxygen is labeled with the magnetically active isotope (17)O (I = 5/2). Two synthetic complexes and two biological metallocofactors are examined: a planar bis-μ-oxo bridged complex and a bent, bis-μ-oxo-μ-carboxylato bridge complex; the dimanganese catalase, which catalyzes the dismutation of H2O2 to H2O and O2, and the recently identified manganese/iron cofactor of the R2lox protein, a homologue of the small subunit of the ribonuclotide reductase enzyme (class 1c). High field (W-band) hyperfine EPR spectroscopies are demonstrated to be ideal methods to characterize the (17)O magnetic interactions, allowing a magnetic fingerprint for the bridging oxygen ligand to be developed. It is shown that the μ-oxo bridge motif displays a small positive isotropic hyperfine coupling constant of about +5 to +7 MHz and an anisotropic/dipolar coupling of -9 MHz. In addition, protonation of the bridge is correlated with an increase of the hyperfine coupling constant. Broken symmetry density functional theory is evaluated as a predictive tool for estimating hyperfine coupling of bridging species. Experimental and theoretical results provide a framework for the characterization of the oxygen bridge in Mn metallocofactor systems, including the water oxidizing cofactor of photosystem II, allowing the substrate/solvent interface to be examined throughout its catalytic cycle.
authors.affiliation: Max-Planck Institute for Chemical Energy , Stiftstr. 34-36 , Mülheim an der Ruhr, DE-45470 Germany.
authors.forename: Leonid
authors.initials: L
authors.lastname: Rapatskiy
authors.affiliation: Max-Planck Institute for Chemical Energy , Stiftstr. 34-36 , Mülheim an der Ruhr, DE-45470 Germany.
authors.forename: William M
authors.initials: WM
authors.lastname: Ames
authors.affiliation: Max-Planck Institute for Chemical Energy , Stiftstr. 34-36 , Mülheim an der Ruhr, DE-45470 Germany.
authors.forename: Montserrat
authors.initials: M
authors.lastname: Pérez-Navarro
authors.affiliation: Max-Planck Institute for Chemical Energy , Stiftstr. 34-36 , Mülheim an der Ruhr, DE-45470 Germany.
authors.forename: Anton
authors.initials: A
authors.lastname: Savitsky
authors.affiliation: Department of Biochemistry and Biophysics, Stockholm University , Stockholm SE-106 91, Sweden.
authors.forename: Julia J
authors.initials: JJ
authors.lastname: Griese
authors.affiliation: Max-Planck Institute for Chemical Energy , Stiftstr. 34-36 , Mülheim an der Ruhr, DE-45470 Germany.
authors.forename: Thomas
authors.initials: T
authors.lastname: Weyhermüller
authors.affiliation: Max-Planck Institute for Chemical Energy , Stiftstr. 34-36 , Mülheim an der Ruhr, DE-45470 Germany.
authors.forename: Hannah S
authors.initials: HS
authors.lastname: Shafaat
authors.affiliation: Department of Biochemistry and Biophysics, Stockholm University , Stockholm SE-106 91, Sweden.
authors.forename: Martin
authors.initials: M
authors.lastname: Högbom
authors.affiliation: Max-Planck Institute for Chemical Energy , Stiftstr. 34-36 , Mülheim an der Ruhr, DE-45470 Germany.
authors.forename: Frank
authors.initials: F
authors.lastname: Neese
authors.affiliation: Max-Planck Institute for Chemical Energy , Stiftstr. 34-36 , Mülheim an der Ruhr, DE-45470 Germany.
authors.forename: Dimitrios A
authors.initials: DA
authors.lastname: Pantazis
authors.affiliation: Max-Planck Institute for Chemical Energy , Stiftstr. 34-36 , Mülheim an der Ruhr, DE-45470 Germany.
authors.forename: Nicholas
authors.initials: N
authors.lastname: Cox
mesh_terms: D004578:Electron Spin Resonance Spectroscopy; D008345:Manganese / Q000737:chemistry*; D008958:Models, Molecular; D009942:Organometallic Compounds / Q000737:chemistry*; D010100:Oxygen / Q000737:chemistry*; D011789:Quantum Theory
chemical_list: D009942:Organometallic Compounds; D008345:Manganese; D010100:Oxygen