title: EPR properties of mixed-valent mu-oxo and mu-hydroxo dinuclear iron complexes produced by radiolytic reduction at 77 K.
abstract: Radiolytic reduction at 77 K of oxo/hydroxo-bridged dinuclear iron(III) complexes in frozen solutions forms kinetically stabilized, mixed-valent species in high yields that model the mixed-valent sites of non-heme, diiron proteins. The mixed-valent species trapped at 77 K retain ligation geometry similar to the initial diferric clusters. The shapes of the mixed-valent EPR signals depend strongly on the bridging ligands. Spectra of the Fe(II)OFe(III) species reveal an S = 1/2 ground state with small g-anisotropy as characterized by the uniaxial component (gz-gav/2 < 0.03) observable at temperatures as high as approximately 100 K. In contrast, hydroxo-bridged mixed-valent species are characterized by large g-anisotropy (gz-gav/2 > 0.03) and are observable only below 30 K. Annealing at higher temperatures causes structural relaxation and changes in the EPR characteristics. EPR spectral properties allow the oxo- and hydroxo-bridged, mixed-valent diiron centers to be distinguished from each other and can help characterize the structure of mixed-valent centers in proteins.
authors.affiliation: WR Wiley Environmental Molecular Science Laboratory, Pacific Northwest National Laboratory, Richland, WA 99352-0999, USA.
authors.forename: R M
authors.initials: RM
authors.lastname: Davydov
authors.forename: J
authors.initials: J
authors.lastname: Smieja
authors.forename: S A
authors.initials: SA
authors.lastname: Dikanov
authors.forename: Y
authors.initials: Y
authors.lastname: Zang
authors.forename: L
authors.initials: L
authors.lastname: Que
authors.forename: M K
authors.initials: MK
authors.lastname: Bowman
mesh_terms: D016880:Anisotropy; D004578:Electron Spin Resonance Spectroscopy; D005615:Freezing; D006422:Hemerythrin / Q000737:chemistry* / Q000378:metabolism / Q000528:radiation effects; D007501:Iron / Q000737:chemistry* / Q000378:metabolism / Q000528:radiation effects; D010105:Oxygenases / Q000737:chemistry* / Q000378:metabolism / Q000528:radiation effects; D012264:Ribonucleotide Reductases / Q000737:chemistry* / Q000378:metabolism / Q000528:radiation effects; D013696:Temperature
chemical_list: D006422:Hemerythrin; C019004:methemerythrin; D007501:Iron; D010105:Oxygenases; C021555:methane monooxygenase; D012264:Ribonucleotide Reductases