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  Metal oxidation states in biological water splitting

Krewald, V., Retegan, M., Cox, N., Messinger, J., Lubitz, W., DeBeer, S., et al. (2015). Metal oxidation states in biological water splitting. Chemical Science, 6(3), 1676-1695. doi:10.1039/C4SC03720K.

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Krewald, Vera1, Author           
Retegan, Marius1, Author           
Cox, Nicholas2, Author           
Messinger, Johannes3, Author
Lubitz, Wolfgang2, Author           
DeBeer, Serena1, Author           
Neese, Frank1, Author           
Pantazis, Dimitrios A.1, Author           
1Research Department Neese, Max Planck Institute for Chemical Energy Conversion, Max Planck Society, ou_3023886              
2Research Department Lubitz, Max Planck Institute for Chemical Energy Conversion, Max Planck Society, ou_3023873              
3Department of Chemistry, Chemical Biological Center (KBC), Umeå University, 90187 Umeå, Sweden, ou_persistent22              


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 Abstract: 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 S2 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 S2 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 55Mn ENDOR data of the S2 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 S0 (III, III, III, IV) to S3 (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.


Language(s): eng - English
 Dates: 2014-12-012015-01-092015-03-01
 Publication Status: Published in print
 Pages: 20
 Publishing info: -
 Table of Contents: -
 Rev. Type: Peer
 Identifiers: DOI: 10.1039/C4SC03720K
 Degree: -



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Title: Chemical Science
  Other : Chem. Sci.
Source Genre: Journal
Publ. Info: Cambridge, UK : Royal Society of Chemistry
Pages: - Volume / Issue: 6 (3) Sequence Number: - Start / End Page: 1676 - 1695 Identifier: ISSN: 2041-6520
CoNE: https://pure.mpg.de/cone/journals/resource/2041-6520