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          Institute: MPI für bioanorganische Chemie     Collection: MPI für bioanorganische Chemie     Display Documents



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ID: 712891.0, MPI für bioanorganische Chemie / MPI für bioanorganische Chemie
Metal oxidation states in biological water splitting
Authors:Krewald, Vera Lucia; Retegan, Marius; Cox, Nicholas; Messinger, Johannes; Lubitz, Wolfgang; DeBeer, Serena; Neese, Frank; Pantazis, Dimitrios A.
Language:English
Date of Publication (YYYY-MM-DD):2015
Title of Journal:Chemical Science
Journal Abbrev.:Chem. Sci.
Volume:6
Issue / Number:3
Start Page:1676
End Page:1695
Review Status:Internal review
Audience:Experts Only
Abstract / Description: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.
Comment of the Author/Creator:Date: 2015, 2015
External Publication Status:published
Document Type:Article
Version Comment:Automatic journal name synchronization
Communicated by:N. N.
Affiliations:MPI für bioanorganische Chemie
Identifiers:ISI:000349832600009 [ID No:1]
ISSN:2041-6520 [ID No:2]
DOI:10.1039/c4sc03720k [ID No:3]
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