scholarly journals A ligand field chemistry of oxygen generation by the oxygen-evolving complex and synthetic active sites

2007 ◽  
Vol 363 (1494) ◽  
pp. 1293-1303 ◽  
Author(s):  
Theodore A Betley ◽  
Yogesh Surendranath ◽  
Montana V Childress ◽  
Glen E Alliger ◽  
Ross Fu ◽  
...  
Keyword(s):  
Water Oxidation ◽  
Active Sites ◽  
Ligand Field ◽  
Oxygen Evolving Complex ◽  
Oxygen Generation ◽  
Bond Forming ◽  
Oxygen Oxygen ◽  
Functional Models ◽  
High Valent ◽  
Oxygen Evolving

Oxygen–oxygen bond formation and O 2 generation occur from the S 4 state of the oxygen-evolving complex (OEC). Several mechanistic possibilities have been proposed for water oxidation, depending on the formal oxidation state of the Mn atoms. All fall under two general classifications: the AB mechanism in which nucleophilic oxygen (base, B) attacks electrophilic oxygen (acid, A) of the Mn 4 Ca cluster or the RC mechanism in which radical-like oxygen species couple within OEC. The critical intermediate in either mechanism involves a metal oxo, though the nature of this oxo for AB and RC mechanisms is disparate. In the case of the AB mechanism, assembly of an even-electron count, high-valent metal-oxo proximate to a hydroxide is needed whereas, in an RC mechanism, two odd-electron count, high-valent metal oxos are required. Thus the two mechanisms give rise to very different design criteria for functional models of the OEC active site. This discussion presents the electron counts and ligand geometries that support metal oxos for AB and RC O–O bond-forming reactions. The construction of architectures that bring two oxygen functionalities together under the purview of the AB and RC scenarios are described.

scholarly journals Nano-sized manganese oxides as biomimetic catalysts for water oxidation in artificial photosynthesis: a review

2012 ◽  
Vol 9 (75) ◽  
pp. 2383-2395 ◽  
Author(s):  
Mohammad Mahdi Najafpour ◽  
Fahimeh Rahimi ◽  
Eva-Mari Aro ◽  
Choon-Hwan Lee ◽  
Suleyman I. Allakhverdiev
Keyword(s):  
Hydrogen Production ◽  
Water Splitting ◽  
Water Oxidation ◽  
Active Sites ◽  
Manganese Oxides ◽  
Metal Compounds ◽  
Functional Models ◽  
Current Densities ◽  
Conversion Efficiencies ◽  
Manganese Compounds

There has been a tremendous surge in research on the synthesis of various metal compounds aimed at simulating the water-oxidizing complex (WOC) of photosystem II (PSII). This is crucial because the water oxidation half reaction is overwhelmingly rate-limiting and needs high over-voltage (approx. 1 V), which results in low conversion efficiencies when working at current densities required for hydrogen production via water splitting. Particular attention has been given to the manganese compounds not only because manganese has been used by nature to oxidize water but also because manganese is cheap and environmentally friendly. The manganese–calcium cluster in PSII has a dimension of about approximately 0.5 nm. Thus, nano-sized manganese compounds might be good structural and functional models for the cluster. As in the nanometre-size of the synthetic models, most of the active sites are at the surface, these compounds could be more efficient catalysts than micrometre (or bigger) particles. In this paper, we focus on nano-sized manganese oxides as functional and structural models of the WOC of PSII for hydrogen production via water splitting and review nano-sized manganese oxides used in water oxidation by some research groups.

New Linear High-Valent Tetranuclear Manganese-Oxo Cluster Relevant to the Oxygen-Evolving Complex of Photosystem II with Oxo, Hydroxo, and Aqua Coordinated to a Single Mn(IV)

2005 ◽  
Vol 44 (25) ◽  
pp. 9567-9573 ◽  
Author(s):  
Chen ◽  
Marie-Noëlle Collomb ◽  
Carole Duboc ◽  
Geneviève Blondin ◽  
Eric Rivière ◽  
...  
Keyword(s):  
Photosystem Ii ◽  
Oxygen Evolving Complex ◽  
High Valent ◽  
Oxygen Evolving

scholarly journals Simulation of the isotropic EXAFS spectra for the S2 and S3 structures of the oxygen evolving complex in photosystem II

2015 ◽  
Vol 112 (13) ◽  
pp. 3979-3984 ◽  
Author(s):  
Xichen Li ◽  
Per E. M. Siegbahn ◽  
Ulf Ryde
Keyword(s):  
Photosystem Ii ◽  
Water Oxidation ◽  
Density Functional ◽  
Structural Changes ◽  
Complete Agreement ◽  
Oxygen Evolving Complex ◽  
Chemical Modeling ◽  
Oxygen Evolving ◽  
High Degree ◽  
Exafs Spectra

Most of the main features of water oxidation in photosystem II are now well understood, including the mechanism for O–O bond formation. For the intermediate S2 and S3 structures there is also nearly complete agreement between quantum chemical modeling and experiments. Given the present high degree of consensus for these structures, it is of high interest to go back to previous suggestions concerning what happens in the S2–S3 transition. Analyses of extended X-ray adsorption fine structure (EXAFS) experiments have indicated relatively large structural changes in this transition, with changes of distances sometimes larger than 0.3 Å and a change of topology. In contrast, our previous density functional theory (DFT)(B3LYP) calculations on a cluster model showed very small changes, less than 0.1 Å. It is here found that the DFT structures are also consistent with the EXAFS spectra for the S2 and S3 states within normal errors of DFT. The analysis suggests that there are severe problems in interpreting EXAFS spectra for these complicated systems.

scholarly journals Recent pulsed EPR studies of the Photosystem II oxygen-evolving complex: implications as to water oxidation mechanisms

2004 ◽  
Vol 1655 ◽  
pp. 158-171 ◽  
Author(s):  
R.David Britt ◽  
Kristy A Campbell ◽  
Jeffrey M Peloquin ◽  
M.Lane Gilchrist ◽  
Constantino P Aznar ◽  
...  
Keyword(s):  
Photosystem Ii ◽  
Water Oxidation ◽  
Oxygen Evolving Complex ◽  
Pulsed Epr ◽  
Oxygen Evolving ◽  
Oxidation Mechanisms
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