Where Water is Oxidized to Dioxygen: Structure of the Photosynthetic Mn4Ca Cluster from X-ray Spectroscopy

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Light-driven oxidation of water to dioxygen in plants, algae and cyanobacteria iscatalyzed within photosystem II (PS II) by a Mn4Ca cluster. Although the cluster has been studied by many different methods, the structure and the mechanism have remained elusive. X-ray absorption and emission spectroscopy and EXAFS studies have been particularly useful in probing the electronic and geometric structure, and the mechanism of the water oxidation reaction. Recent progress, reviewed here, includes polarized X-ray absorption spectroscopy measurements of PS II single crystals. Analysis of those results has constrained the Mn4Ca cluster geometry to a setof three similar high-resolution structures. The structure ... continued below

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Yano, Junko; Yano, Junko & Yachandra, Vittal K. October 24, 2007.

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Light-driven oxidation of water to dioxygen in plants, algae and cyanobacteria iscatalyzed within photosystem II (PS II) by a Mn4Ca cluster. Although the cluster has been studied by many different methods, the structure and the mechanism have remained elusive. X-ray absorption and emission spectroscopy and EXAFS studies have been particularly useful in probing the electronic and geometric structure, and the mechanism of the water oxidation reaction. Recent progress, reviewed here, includes polarized X-ray absorption spectroscopy measurements of PS II single crystals. Analysis of those results has constrained the Mn4Ca cluster geometry to a setof three similar high-resolution structures. The structure of the cluster from the present study is unlike either the 3.0 or 3.5 Angstrom-resolution X-ray structures or other previously proposed models. The differences between the models derived from X-rayspectroscopy and crystallography are predominantly because of damage to the Mn4Ca cluster by X-rays under the conditions used for structure determination by X-ray crystallography. X-ray spectroscopy studies are also used for studying the changes in the structure of the Mn4Ca catalytic center as it cycles through the five intermediate states known as the Si-states (i=0-4). The electronic structure of the Mn4Ca cluster has been studied more recently using resonant inelastic X-ray scattering spectroscopy (RIXS), in addition to the earlier X-ray absorption and emission spectroscopy methods. These studies are revealing that the assignment of formaloxidation states is overly simplistic. A more accurate description should consider the charge density on the Mn atoms that includes the covalency of the bonds and delocalization of the charge over the cluster. The geometric and electronic structure of the Mn4Ca cluster in the S-states derived from X-ray spectroscopy are leading to a detailed understanding of the mechanism of the O-O bond formation during the photosynthetic water splitting process.

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  • Journal Name: Inorganic Chemistry; Journal Volume: 47; Journal Issue: 6; Related Information: Journal Publication Date: March 17, 2008

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  • Report No.: LBNL-665E
  • Grant Number: DE-AC02-05CH11231
  • Office of Scientific & Technical Information Report Number: 934987
  • Archival Resource Key: ark:/67531/metadc894957

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  • October 24, 2007

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  • Sept. 27, 2016, 1:39 a.m.

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  • Sept. 30, 2016, 7:18 p.m.

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Yano, Junko; Yano, Junko & Yachandra, Vittal K. Where Water is Oxidized to Dioxygen: Structure of the Photosynthetic Mn4Ca Cluster from X-ray Spectroscopy, article, October 24, 2007; Berkeley, California. (digital.library.unt.edu/ark:/67531/metadc894957/: accessed October 22, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.