title: XANES evidence against a manganyl species in the S3 state of the oxygen-evolving complex.
abstract: Manganyl Mn=O species have been suggested as possible intermediates in photosynthetic water oxidation and as the reactive species in asymmetric olefin epoxidation. The first X-ray absorption spectrum for a MnV=O complex is reported. Comparison of the EXAFS data for Na[MnV=O(HMPAB) with those for lower-valent Mn complexes suggests that EXAFS measurements and edge-energy measurements are unlikely to have sufficient sensitivity to reliably reflect the presence of Mn=O species. In contrast, the preedge transition for Na[MnV=O(HMPAB) is 4-fold more intense than the most intense preedge transition observed for nonmanganyl complexes. This increase in intensity is shown to be sufficiently sensitive to allow detection of a manganyl species if it is formed. These data together with published data for the photosynthetic oxygen-evolving complex provide strong evidence against the presence of manganyl Mn=O species in the oxygen-evolving complex through the S3 state.
authors.affiliation: Department of Chemistry and the Biophysics Research Division, The University of Michigan, Ann Arbor, MI 48109-1055, USA.
authors.forename: Tsu-Chien
authors.initials: TC
authors.lastname: Weng
authors.forename: Wen-Yuan
authors.initials: WY
authors.lastname: Hsieh
authors.forename: Erich S
authors.initials: ES
authors.lastname: Uffelman
authors.forename: Scott W
authors.initials: SW
authors.lastname: Gordon-Wylie
authors.forename: Terrence J
authors.initials: TJ
authors.lastname: Collins
authors.forename: Vincent L
authors.initials: VL
authors.lastname: Pecoraro
authors.forename: James E
authors.initials: JE
authors.lastname: Penner-Hahn
mesh_terms: D008345:Manganese / Q000737:chemistry*; D010084:Oxidation-Reduction; D010100:Oxygen / Q000737:chemistry*; D045332:Photosystem II Protein Complex / Q000737:chemistry*; D013052:Spectrometry, X-Ray Emission
chemical_list: D045332:Photosystem II Protein Complex; D008345:Manganese; D010100:Oxygen