| 1. |
- Pushkar, Yulia, et al.
(författare)
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Structure and orientation of the Mn4Ca cluster in plant photosystem II membranes studied by polarized range-extended X-ray absorption spectroscopy
- 2007
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Ingår i: Journal of Biological Chemistry. - : AMER SOC BIOCHEMISTRY MOLECULAR BIOLOGY INC. - 0021-9258 .- 1083-351X. ; 282:10, s. 7198-7208
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Tidskriftsartikel (refereegranskat)abstract
- X-ray absorption spectroscopy has provided important insights into the structure and function of the Mn4Ca cluster in the oxygen-evolving complex of Photosystem II (PS II). The range of manganese extended x-ray absorption fine structure data collected from PS II until now has been, however, limited by the presence of iron in PS II. Using a crystal spectrometer with high energy resolution to detect solely the manganese K alpha fluorescence, we are able to extend the extended x-ray absorption fine structure range beyond the onset of the iron absorption edge. This results in improvement in resolution of the manganese-backscatterer distances in PS II from 0.14 to 0.09 angstrom. The high resolution data obtained from oriented spinach PS II membranes in the S-1 state show that there are three di-mu-oxo-bridged manganese-manganese distances of similar to 2.7 and similar to 2.8 angstrom in a 2:1 ratio and that these three manganese-manganese vectors are aligned at an average orientation of similar to 60 degrees relative to the membrane normal. Furthermore, we are able to observe the separation of the Fourier peaks corresponding to the similar to 3.2 angstrom manganese-manganese and the similar to 3.4 angstrom manganese-calcium interactions in oriented PS II samples and determine their orientation relative to the membrane normal. The average of the manganese-calcium vectors at similar to 3.4 angstrom is aligned along the membrane normal, while the similar to 3.2 angstrom manganese-manganese vector is oriented near the membrane plane. A comparison of this structural information with the proposed Mn4Ca cluster models based on spectroscopic and diffraction data provides input for refining and selecting among these models.
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| 2. |
- Smolentsev, Grigory, et al.
(författare)
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X-ray emission spectroscopy to study Ligand Valence Orbitals in Mn coordination complexes
- 2009
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Ingår i: Journal of the American Chemical Society. - : ACS Publications. - 0002-7863 .- 1520-5126. ; 131:36, s. 13161-13167
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Tidskriftsartikel (refereegranskat)abstract
- We discuss a spectroscopic method to determine the character of chemical bonding and for the identification of metal ligands in coordination and bioinorganic chemistry. It is based on the analysis of satellite lines in X-ray emission spectra that arise from transitions between valence orbitals and the metal ion 1s level (valence-to-core XES). The spectra, in connection with calculations based on density functional theory (DFT), provide information that is complementary to other spectroscopic techniques, in particular X-ray absorption (XANES and EXAFS). The spectral shape is sensitive to protonation of ligands and allows ligands, which differ only slightly in atomic number (e.g., C, N, O...), to be distinguished. A theoretical discussion of the main spectral features is presented in terms of molecular orbitals for a series of Mn model systems: [Mn(H2O)6]2+, [Mn(H2O)5OH]+, and [Mn(H2O)5NH3]2+. An application of the method, with comparison between theory and experiment, is presented for the solvated Mn2+ ion in water and three Mn coordination complexes, namely [LMn(acac)N3]BPh4, [LMn(B2O3Ph2)(ClO4)], and [LMn(acac)N]BPh4, where L represents 1,4,7-trimethyl-1,4,7-triazacyclononane, acac stands for the 2,4-pentanedionate anion, and B2O3Ph2 represents the 1,3-diphenyl-1,3-dibora-2-oxapropane-1,3-diolato dianion.
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| 3. |
- Yano, Junko, et al.
(författare)
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High-resolution structure of the photosynthetic Mn4Ca catalyst from X-ray spectroscopy
- 2008
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Ingår i: Philosophical Transactions of the Royal Society of London. Biological Sciences. - : ROYAL SOC. - 0962-8436 .- 1471-2970. ; 363:1494, s. 1139-1147
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Tidskriftsartikel (refereegranskat)abstract
- The application of high-resolution X-ray spectroscopy methods to study the photosynthetic water oxidizing complex, which contains a unique hetero-nuclear catalytic Mn4Ca cluster, is described. Issues of X-ray damage, especially at the metal sites in the Mn4Ca cluster, are discussed. The structure of the Mn4Ca catalyst at high resolution, which has so far eluded attempts of determination by X-ray diffraction, X-ray absorption fine structure (EXAFS) and other spectroscopic techniques, has been addressed using polarized EXAFS techniques applied to oriented photosystem II (PSII) membrane preparations and PSII single crystals. A review of how the resolution of traditional EXAFS techniques can be improved, using methods such as range-extended EXAFS, is presented, and the changes that occur in the structure of the cluster as it advances through the catalytic cycle are described. X-ray absorption and emission techniques (XANES and K beta emission) have been used earlier to determine the oxidation states of the Mn4Ca cluster, and in this report we review the use of X-ray resonant Raman spectroscopy to understand the electronic structure of the Mn4Ca cluster as it cycles through the intermediate S-states.
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| 4. |
- Yano, Junko, et al.
(författare)
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Where water is oxidized to dioxygen: : Structure of the photosynthetic Mn4Ca cluster
- 2006
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Ingår i: Science. - : AMER ASSOC ADVANCEMENT SCIENCE. - 0036-8075 .- 1095-9203. ; 314:5800, s. 821-825
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Tidskriftsartikel (refereegranskat)abstract
- The oxidation of water to dioxygen is catalyzed within photosystem II ( PSII) by a Mn4Ca cluster, the structure of which remains elusive. Polarized extended x-ray absorption fine structure (EXAFS) measurements on PSII single crystals constrain the Mn4Ca cluster geometry to a set of three similar high-resolution structures. Combining polarized EXAFS and x-ray diffraction data, the cluster was placed within PSII, taking into account the overall trend of the electron density of the metal site and the putative ligands. 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.
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| 5. |
- Zein, Samir, et al.
(författare)
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Focusing the view on nature's water-splitting catalyst
- 2008
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Ingår i: Philosophical Transactions of the Royal Society of London. Biological Sciences. - : ROYAL SOC. - 0962-8436 .- 1471-2970. ; 363:1494, s. 1167-1177
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Tidskriftsartikel (refereegranskat)abstract
- Nature invented a catalyst about 3 Gyr ago, which splits water with high efficiency into molecular oxygen and hydrogen equivalents (protons and electrons). This reaction is energetically driven by sunlight and the active centre contains relatively cheap and abundant metals: manganese and calcium. This biological system therefore forms the paradigm for all man-made attempts for direct solar fuel production, and several studies are underway to determine the electronic and geometric structures of this catalyst. In this report we briefly summarize the problems and the current status of these efforts and propose a density functional theory-based strategy for obtaining a reliable high-resolution structure of this unique catalyst that includes both the inorganic core and the first ligand sphere.
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