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Metal oxidation states in biological water splitting
Umeå University, Faculty of Science and Technology, Department of Chemistry.
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2015 (English)In: Chemical Science, ISSN 2041-6520, E-ISSN 2041-6539, Vol. 6, no 3, 1676-1695 p.Article in journal (Refereed) Published
Abstract [en]

A central question in biological water splitting concerns the oxidation states of the manganese ions that comprise the oxygen-evolving complex of photosystem II. Understanding the nature and order of oxidation events that occur during the catalytic cycle of five Si states (i = 0-4) is of fundamental importance both for the natural system and for artificial water oxidation catalysts. Despite the widespread adoption of the so-called "high-valent scheme"-where, for example, the Mn oxidation states in the S-2 state are assigned as III, IV, IV, IV-the competing "low-valent scheme" that differs by a total of two metal unpaired electrons (i.e. III, III, III, IV in the S-2 state) is favored by several recent studies for the biological catalyst. The question of the correct oxidation state assignment is addressed here by a detailed computational comparison of the two schemes using a common structural platform and theoretical approach. Models based on crystallographic constraints were constructed for all conceivable oxidation state assignments in the four (semi) stable S states of the oxygen evolving complex, sampling various protonation levels and patterns to ensure comprehensive coverage. The models are evaluated with respect to their geometric, energetic, electronic, and spectroscopic properties against available experimental EXAFS, XFEL-XRD, EPR, ENDOR and Mn K pre-edge XANES data. New 2.5 K Mn-55 ENDOR data of the S-2 state are also reported. Our results conclusively show that the entire S state phenomenology can only be accommodated within the high-valent scheme by adopting a single motif and protonation pattern that progresses smoothly from S-0 (III, III, III, IV) to S-3 (IV, IV, IV, IV), satisfying all experimental constraints and reproducing all observables. By contrast, it was impossible to construct a consistent cycle based on the low-valent scheme for all S states. Instead, the low-valent models developed here may provide new insight into the over-reduced S states and the states involved in the assembly of the catalytically active water oxidizing cluster.

Place, publisher, year, edition, pages
2015. Vol. 6, no 3, 1676-1695 p.
Keyword [en]
PAULA JC, 1986, JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, V108, P4002 l Rhitankar, 2013, BIOCHEMISTRY, V52, P7703 sunoki Masami, 2011, JOURNAL OF PHOTOCHEMISTRY AND PHOTOBIOLOGY B-BIOLOGY, V104, P100 auss Andre, 2012, PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF, PAULA JC, 1987, JOURNAL OF THE CHEMICAL SOCIETY-FARADAY TRANSACTIONS I, V83, P3635 llier W, 2000, BIOCHEMISTRY, V39, P4399 ussac Alain, 2009, JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, V131, P5050 pitz Christopher, 2014, NATURE, V513, P261 harieva Ivelina, 2011, ENERGY & ENVIRONMENTAL SCIENCE, V4, P2400 ena Yasufumi, 2011, NATURE, V473, P55 trie Simon, 2012, PHYSICAL CHEMISTRY CHEMICAL PHYSICS, V14, P11333
National Category
Chemical Sciences
Identifiers
URN: urn:nbn:se:umu:diva-100978DOI: 10.1039/c4sc03720kISI: 000349832600009OAI: oai:DiVA.org:umu-100978DiVA: diva2:795822
Available from: 2015-03-17 Created: 2015-03-16 Last updated: 2017-12-04Bibliographically approved

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Messinger, Johannes

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