期刊
CHEMICAL SCIENCE
卷 5, 期 8, 页码 3064-3071出版社
ROYAL SOC CHEMISTRY
DOI: 10.1039/c4sc00453a
关键词
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资金
- NIH [GM50781, GM49970]
- Office of Science, Basic Energy Sciences (BES), Division of Chemical Sciences, Geosciences and Biosciences, Department of Energy [DE-AC02-05CH11231]
- DOE Office of Biological and Environmental Research
- National Institutes of Health
- National Center for Research Resources
- Biomedical Technology Program [P411RR001209]
- NATIONAL CENTER FOR RESEARCH RESOURCES [P41RR001209] Funding Source: NIH RePORTER
- NATIONAL INSTITUTE OF GENERAL MEDICAL SCIENCES [R37GM050781, R01GM049970, R29GM049970, R01GM077387, R01GM050781] Funding Source: NIH RePORTER
Photosynthetic water oxidation is catalyzed by a Mn4O5Ca cluster with an unprecedented arrangement of metal ions in which a single manganese center is bonded to a distorted Mn3O4Ca cubane-like structure. Several mechanistic proposals describe the unique manganese center as a site for water binding and subsequent formation of a high valent Mn-oxo center that reacts with a M-OH unit (M = Mn or Ca-II) to form the O-O bond. The conversion of low valent Mn-OHn (n = 1, 2) to a Mn-oxo species requires that a single manganese site be able to accommodate several oxidation states as the water ligand is deprotonated. To study these processes, the preparation and characterization of a new monomeric Mn-IV-OH complex is described. The Mn-IV-OH complex completes a series of well characterized Mn-OH and Mn-oxo complexes containing the same primary and secondary coordination spheres; this work thus demonstrates that a single ligand can support mononuclear Mn complexes spanning four different oxidation states (II through V) with oxo and hydroxo ligands that are derived from water. Moreover, we have completed a thermodynamic analysis based on this series of manganese complexes to predict the formation of high valent Mn-oxo species; we demonstrated that the conversion of a Mn-IV-OH species to a Mn-V-oxo complex would likely occur via a stepwise proton transfer-electron transfer mechanism. The large dissociation energy for the (MnO)-O-IV-H bond (similar to 95 kcal mol(-1)) diminished the likelihood that other pathways are operative within a biological context. Furthermore, these studies showed that reactions between Mn-OH and Mn-oxo complexes lead to non-productive, one-electron processes suggesting that initial O-O bond formation with the OEC does not involve an Mn-OH unit.
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