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Issue 32, 2012
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Modelling the metal atom positions of the Photosystem II water oxidising complex: a density functional theory appraisal of the 1.9 Å resolution crystal structure

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Abstract

Density functional theory (DFT) calculations are reported for a set of model compounds intended to represent the structure of the Photosystem II (PSII) water oxidising complex (WOC) as determined by the recent 1.9 Å resolution single crystal X-ray diffraction (XRD) study of Umena et al. In contrast with several other theoretical studies addressing this structure, we find that it is not necessary to invoke photoreduction of the crystalline sample below the S1 ‘resting state’ in order to rationalise the observed WOC geometry. Our results are consistent with crystallised PSII in the S1 state, with S1 corresponding to either (MnIII)4 or (MnIII)2(MnIV)2 as required by the two competing paradigms for the WOC oxidation state pattern. Of these two paradigms, the ‘low-oxidation-state’ paradigm provides a better match for the crystal structure, with the comparatively long Mn(2)–Mn(3) distance in particular proving difficult to reconcile with the ‘high-oxidation-state’ model. Best agreement with the set of metal–metal distances is obtained with a S1 model featuring μ-O, μ-OH bridging between Mn(3) and Mn(4) and deprotonation of one water ligand on Mn(4). Theoretical modelling of the 1.9 Å structure is an important step in assessing the validity of this recent crystal structure, with implications for our understanding of the mechanism of water oxidation by PSII.

Graphical abstract: Modelling the metal atom positions of the Photosystem II water oxidising complex: a density functional theory appraisal of the 1.9 Å resolution crystal structure

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Article information


Submitted
30 Mar 2012
Accepted
21 Jun 2012
First published
21 Jun 2012

Phys. Chem. Chem. Phys., 2012,14, 11333-11343
Article type
Paper

Modelling the metal atom positions of the Photosystem II water oxidising complex: a density functional theory appraisal of the 1.9 Å resolution crystal structure

S. Petrie, P. Gatt, R. Stranger and R. J. Pace, Phys. Chem. Chem. Phys., 2012, 14, 11333
DOI: 10.1039/C2CP41020F

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