Water exchange in manganese-based water-oxidizing catalysts in photosynthetic systems: From the water-oxidizing complex in photosystem II to nano-sized manganese oxides

Abstract

The water-oxidizing complex (WOC), also known as the oxygen-evolving complex (OEC), of photosystem II in oxygenic photosynthetic organisms efficiently catalyzes water oxidation. It is, therefore, responsible for the presence of oxygen in the Earth's atmosphere. The WOC is a manganese-calcium (Mn₄CaO₅(H₂O)₄) cluster housed in a protein complex. In this review, we focus on water exchange chemistry of metal hydrates and discuss the mechanisms and factors affecting this chemical process. Further, water exchange rates for both the biological cofactor and synthetic manganese water splitting are discussed. The importance of fully unveiling the water exchange mechanism to understand the chemistry of water oxidation is also emphasized here. This article is part of a special issue entitled: photosynthesis research for sustainability: keys to produce clean energy.

From manganese complexes to nano-sized manganese oxides as water-oxidizing catalysts for artificial photosynthetic systems: Insights from the Zanjan team

“…The experiments show that the water molecules from the solvent or OH groups on the surface of the Mn oxides are necessary for water oxidation (Fig. 3) [46]. In other experiments with different ratios of water to acetonitrile, we observed water oxidation is a first order reaction on the concentration of water (Fig.…”

“…[45], Copyright (2015) by Elsevier. OH moieties couple to form oxygen [46]. We hypothesize that there are many MneOH fragments on the surface of the Mn oxides, and if the mechanism i is the true mechanism for oxygen evolution, we expect that at least for the first few seconds, and before water exchange by acetonitrile, water oxidation should be observed.…”

“…3 occurs [46]. In this mechanism, oxygen is formed by the nucleophilic attack of water molecules on an Mn]O or Mn-OH moiety.…”

Photobiological hydrogen production and artificial photosynthesis for clean energy: from bio to nanotechnologies

“…Recently, several biomimetic approaches to artificial photosynthesis have been proposed for the photo catalytic oxidation of water molecules to generate H 2 and O 2 (Allakhverdiev et al 2010a;Najafpour et al 2014b). As we mentioned above, natural photosynthesis acts as the base for the artificial photosynthesis to design solar energy conversion systems.…”

“…H 2 , the simplest and most abundant element, meets the requirements to be an energy source. It has higher energy content per unit mass than alternative fuels; it can be readily produced as a gas from various resources (Esper et al 2006;Kotay and Das 2008;Allakhverdiev et al 2010a, b;Allakhverdiev 2012;Najafpour and Allakhverdiev 2012;Azwar et al 2014;Najafpour et al 2014b) and, when combusted, generates only water. H 2 can be used as a good transportation fuel, because H 2 gas-based fuel cells can be more efficient in power generation than Fig.…”