title: Elucidating the protonation site of vanadium peroxide complexes and the implications for biomimetic catalysis.
abstract: Coordination complexes of vanadium(5+) played a key role in understanding the structure and mechanism of vanadium-dependent haloperoxidases, particularly the effects of protonation on peroxide coordination to dioxovanadium(5+) species, and in the activation of the peroxo-oxovanadium(5+) complex for substrate oxidation. There has been no spectroscopic evidence that could test the presence of a hydroxo intermediate in a catalytically active oxovanadium(5+) complex. Herein we report the use of the pre-edge transition in X-ray absorption spectroscopy as a spectroscopic signature for V=O bonding. Displacement of oxo donors with hydrogen peroxide or chloride donors dramatically decreases the pre-edge intensity, confirming that the source of the intense pre-edge feature is closely related to the -bonding associated with the V=O. Protonation of a catalytically active tripodal amine oxovanadium(5+) complex has no affect on the pre-edge intensity and, therefore, rules out the possibility of a hydroxo intermediate in the catalytic cycle.
authors.affiliation: Department of Chemistry and Biophysics Research Division, University of Michigan, Ann Arbor, Michigan 48109-1055, USA.
authors.forename: Curtis J
authors.initials: CJ
authors.lastname: Schneider
authors.forename: James E
authors.initials: JE
authors.lastname: Penner-Hahn
authors.forename: Vincent L
authors.initials: VL
authors.lastname: Pecoraro
mesh_terms: D032701:Biomimetics / Q000379:methods*; D002384:Catalysis; D008956:Models, Chemical; D008968:Molecular Conformation; D010084:Oxidation-Reduction; D010545:Peroxides / Q000737:chemistry*; D011522:Protons; D013057:Spectrum Analysis; D013237:Stereoisomerism; D014638:Vanadates / Q000737:chemistry*; D014639:Vanadium / Q000737:chemistry*; D014965:X-Rays
chemical_list: D010545:Peroxides; D011522:Protons; D014639:Vanadium; D014638:Vanadates