XANES evidence against a manganyl species in the S3 state of the oxygen-evolving complex.
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.
Weng
Tsu-Chien
TC
Department of Chemistry and the Biophysics Research Division, The University of Michigan, Ann Arbor, MI 48109-1055, USA.
Hsieh
Wen-Yuan
WY
Uffelman
Erich S
ES
Gordon-Wylie
Scott W
SW
Collins
Terrence J
TJ
Pecoraro
Vincent L
VL
Penner-Hahn
James E
JE
D008345:Manganese / Q000737:chemistry*; D010084:Oxidation-Reduction; D010100:Oxygen / Q000737:chemistry*; D045332:Photosystem II Protein Complex / Q000737:chemistry*; D013052:Spectrometry, X-Ray Emission
D045332:Photosystem II Protein Complex; D008345:Manganese; D010100:Oxygen