Model of the Oxygen Evolving Complex Which Is Highly Predisposed to O–O Bond Formation

2018 ◽  
Vol 9 (12) ◽  
pp. 3525-3531 ◽  
Author(s):  
Yulia Pushkar ◽  
Katherine M. Davis ◽  
Mark C. Palenik
Keyword(s):  
Bond Formation ◽  
Oxygen Evolving Complex ◽  
Oxygen Evolving

Electronic structure of the oxygen-evolving complex in photosystem II prior to O-O bond formation

Science ◽  
2014 ◽  
Vol 345 (6198) ◽  
pp. 804-808 ◽  
Author(s):  
N. Cox ◽  
M. Retegan ◽  
F. Neese ◽  
D. A. Pantazis ◽  
A. Boussac ◽  
...  
Keyword(s):  
Electronic Structure ◽  
Photosystem Ii ◽  
Bond Formation ◽  
Oxygen Evolving Complex ◽  
Oxygen Evolving

Large-scale QM/MM calculations of the CaMn4O5 cluster in the S3 state of the oxygen evolving complex of photosystem II. Comparison between water-inserted and no water-inserted structures

2017 ◽  
Vol 198 ◽  
pp. 83-106 ◽  
Author(s):  
Mitsuo Shoji ◽  
Hiroshi Isobe ◽  
Takahito Nakajima ◽  
Yasuteru Shigeta ◽  
Michihiro Suga ◽  
...  
Keyword(s):  
Photosystem Ii ◽  
Water Oxidation ◽  
Large Scale ◽  
Geometrical Structure ◽  
Bond Formation ◽  
Oxygen Evolving Complex ◽  
Computational Results ◽  
Hydroxide Anion ◽  
The Right ◽  
Oxygen Evolving

Large-scale QM/MM calculations were performed to elucidate an optimized geometrical structure of a CaMn4O5 cluster with and without water insertion in the S3 state of the oxygen evolving complex (OEC) of photosystem II (PSII). The left (L)-opened structure was found to be stable under the assumption of no hydroxide anion insertion in the S3 state, whereas the right (R)-opened structure became more stable if one water molecule is inserted to the Mn4Ca cluster. The optimized Mna(4)–Mnd(1) distance determined by QM/MM was about 5.0 Å for the S3 structure without an inserted hydroxide anion, but this is elongated by 0.2–0.3 Å after insertion. These computational results are discussed in relation to the possible mechanisms of O–O bond formation in water oxidation by the OEC of PSII.

scholarly journals Photosynthetic water oxidation: binding and activation of substrate waters for O–O bond formation

2015 ◽  
Vol 185 ◽  
pp. 37-50 ◽  
Author(s):  
David J. Vinyard ◽  
Sahr Khan ◽  
Gary W. Brudvig
Keyword(s):  
Water Oxidation ◽  
Bond Formation ◽  
Oxygen Evolving Complex ◽  
Amino Acid Residues ◽  
Water Binding ◽  
State Dependent ◽  
Oxygen Evolving ◽  
Electronic And Structural Properties ◽  
Photosynthetic Water Oxidation ◽  
Insight Into

Photosynthetic water oxidation occurs at the oxygen-evolving complex (OEC) of Photosystem II (PSII). The OEC, which contains a Mn4CaO5inorganic cluster ligated by oxides, waters and amino-acid residues, cycles through five redox intermediates known as Sistates (i= 0–4). The electronic and structural properties of the transient S4intermediate that forms the O–O bond are not well understood. In order to gain insight into how water is activated for O–O bond formation in the S4intermediate, we have performed a detailed analysis of S-state dependent substrate water binding kinetics taking into consideration data from Mn coordination complexes. This analysis supports a model in which the substrate waters are both bound as terminal ligands and reactviaa water-nucleophile attack mechanism.

Alternative mechanisms for O2release and O–O bond formation in the oxygen evolving complex of photosystem II

2015 ◽  
Vol 17 (18) ◽  
pp. 12168-12174 ◽  
Author(s):  
Xichen Li ◽  
Per E. M. Siegbahn
Keyword(s):  
Photosystem Ii ◽  
Transition State ◽  
Bond Formation ◽  
Oxygen Evolving Complex ◽  
Competitive Mechanism ◽  
The One ◽  
Oxygen Evolving

A new transition state for O2release has been found. An alternative, nearly competitive, mechanism for O–O bond formation is described, which is very similar to the one previously suggested.

scholarly journals The S3 State of the Oxygen-Evolving Complex: Overview of Spectroscopy and XFEL Crystallography with a Critical Evaluation of Early-Onset Models for O–O Bond Formation

Inorganics ◽  
2019 ◽  
Vol 7 (4) ◽  
pp. 55 ◽  
Author(s):  
Dimitrios A. Pantazis
Keyword(s):  
Experimental Evidence ◽  
Early Onset ◽  
Density Functional ◽  
Structural Information ◽  
Bond Formation ◽  
Critical Evaluation ◽  
Catalytic Cycle ◽  
Oxygen Evolving Complex ◽  
X Ray ◽  
Oxygen Evolving

The catalytic cycle of the oxygen-evolving complex (OEC) of photosystem II (PSII) comprises five intermediate states Si (i = 0–4), from the most reduced S0 state to the most oxidized S4, which spontaneously evolves dioxygen. The precise geometric and electronic structure of the Si states, and hence the mechanism of O–O bond formation in the OEC, remain under investigation, particularly for the final steps of the catalytic cycle. Recent advances in protein crystallography based on X-ray free-electron lasers (XFELs) have produced new structural models for the S3 state, which indicate that two of the oxygen atoms of the inorganic Mn4CaO6 core of the OEC are in very close proximity. This has been interpreted as possible evidence for “early-onset” O–O bond formation in the S3 state, as opposed to the more widely accepted view that the O–O bond is formed in the final state of the cycle, S4. Peroxo or superoxo formation in S3 has received partial support from computational studies. Here, a brief overview is provided of spectroscopic information, recent crystallographic results, and computational models for the S3 state. Emphasis is placed on computational S3 models that involve O–O formation, which are discussed with respect to their agreement with structural information, experimental evidence from various spectroscopic studies, and substrate exchange kinetics. Despite seemingly better agreement with some of the available crystallographic interpretations for the S3 state, models that implicate early-onset O–O bond formation are hard to reconcile with the complete line of experimental evidence, especially with X-ray absorption, X-ray emission, and magnetic resonance spectroscopic observations. Specifically with respect to quantum chemical studies, the inconclusive energetics for the possible isoforms of S3 is an acute problem that is probably beyond the capabilities of standard density functional theory.

scholarly journals Mechanism and energy diagram for O–O bond formation in the oxygen-evolving complex in photosystem II

2007 ◽  
Vol 363 (1494) ◽  
pp. 1221-1228 ◽  
Author(s):  
Per E.M Siegbahn
Keyword(s):  
Photosystem Ii ◽  
Bond Formation ◽  
Oxygen Radical ◽  
Oxygen Evolving Complex ◽  
Spin Alignment ◽  
Energy Diagram ◽  
Oxo Ligand ◽  
Oxygen Evolving ◽  
Rate Limiting ◽  
Good Agreement

The recent finding of a transition state with a significantly lower barrier than previously found, has made the mechanism for O–O bond formation in photosystem II much clearer. The full mechanism can be described in the following way. Electrons and protons are ejected from the oxygen-evolving complex (OEC) in an alternating fashion, avoiding unnecessary build-up of charge. The S 0 –S 1 and S 1 –S 2 transitions are quite exergonic, while the S 2 –S 3 transition is only weakly exergonic. The strong endergonic S 3 –S 4 transition is a key step in the mechanism in which an oxygen radical is produced, held by the dangling manganese outside the Mn 3 Ca cube. The O–O bond formation in the S 4 -state occurs by an attack of the oxygen radical on a bridging oxo ligand in the cube. The mechanism explains the presence of both a cube with bridging oxo ligands and a dangling manganese. Optimal orbital overlap puts further constraints on the structure of the OEC. An alternating spin alignment is necessary for a low barrier. The computed rate-limiting barrier of 14.7 kcal mol −1 is in good agreement with experiments.

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