Dioxygen water oxidation

In contrast the oxo-ruthenium complex c ,c -[ (bpy)2Runl(0H2) 2(//-0)]4+ and some of its derivatives are known to be active catalysts for the chemical or electrochemical oxidation of water to dioxygen.464-472 Many studies have been reported473 181 on the redox and structural chemistry of this complex for understanding the mechanism of water oxidation. Based on the results of pH-dependent electrochemical measurements, the basic structural unit is retained in the successive oxidation states from Rum-0 Ru111 to Ruv O Ruv.466... 

This scheme, set up with reactions in dichloromethane, gave spin adducts from several of the nucleophiles discussed above (F, Cl", AcO, CN, tetramethylsuccinimide anion and triethyl phosphite), provided UV light was employed. With filtered light of A > 435 nm, no spin adducts were detected. This is expected, since PBN cannot then be excited. With water as the nucleophile, only benzoyl nitroxide [9] was seen, indicating that any HO-PBN" disappears too rapidly to be detectable 10 s in acetonitrile) and/or that its rate of formation from PBN +ConW is too low (see above). The complication that nucleophilic addition-oxidation might compete was ruled out experimentally in dichloromethane, but detected for fluoride ion in chloroform, using dioxygen to oxidize the intermediate hydroxylamine anion. 

The oxidation of water to dioxygen occurs as the consequence of Photosystem 11-dependent generation of a very strong oxidant. Protons liberated by the water-oxidation reaction then contribute to the thylakoid transmembrane electrochemical gradient that drives ATP synthesis. Brudvig et aL describe how flash-induced proton-release measurements have resolved key steps that provide insights on how the 02-evolving center of PSll mediates this four-electron oxidation of water. 

Manganese is an element that is essential for life. It is present at the active site of many en2ymes [4, 5]. Those en2ymes in which the metal center is involved in a redox process are manganese catalase [101], peroxidase [102], and SOD [103]. In addition, a cluster containing four Mn and one Ca atoms in the water-oxidizing center (WOC) of PSII is the site at which dioxygen is produced photosynthetically on Earth [3,104]. 

Although these cobalt species do not in themselves activate dioxygen, they do exhibit similarities to the proposed structures of manganese complexes that may be involved in photosynthetic water oxidation... 

Photosynthetic water oxidation in PSII involves the binding of two water molecules, the removal of four electrons and four protons from the Mn complex/sub-strate (water) entity, 0-0 bond formation, and dioxygen release. 

The Wacker process is based on three reactions oxidation of ethylene by Pd2+ in water, oxidation of Pd° to Pd2+ by Cu2+, and oxidation of Cu+ by dioxygen to Cu2+. These reactions are shown by 8.1 to 8.3. Note that if the three reactions are summed up, the net reaction becomes one mole of ethylene and half a mole of oxygen, giving one mole of acetaldehyde. Both palladium and copper ions shuttle between two oxidation states to act as the catalysts. 

In Photsystem II, the water oxidation with evolution of dioxygen occurs under the action of a relatively mild oxidant the cation of chlorophyll which is the product of one-electron oxidation with redox potential E0 = 1.1 eV (Anderson, 2001). The potentials of the oxidation of water by one-, two- and four electron mechanisms are equal to 2.7 V (hydroxyl radical), 1.36 V (hydrogen proxide), and 0.81 (dioxygen). Enclosed in... 

By far the most important role of manganese in nature is its direct involvement in the photocatalytic, four-electron oxidation of water to dioxygen in green plant photosynthesis, an essential process for the maintenance of life. Pirson, in 1937, first discovered the requirement of manganese in photosynthesis by showing that plants grown in a Mn-deficient medium lost their water oxidation capacity (184). During the next four decades, several researchers showed that two photosystems, photosystem I (PSI) and photosystem II (PSII), were involved in photosynthesis and that 02 evolution and Mn were localized at PSII (for a review, see Ref. 185). 

This section gives a brief overview of some of the more important properties of the binary oxides of the elements. Some of the more important aspects that must be considered in evaluating a compound are its thermodynamic stability and chemical reactivity, particularly with respect to oxidation or reduction as well as reactivity with such constituents of the atmosphere as dioxygen, water vapor, and carbon dioxide, since these factors will determine the commercial availability of the compound and the need for any particular precautions in its handling or storage in the laboratory. 

This work > is of importance in relevant to the water oxidation reaction in the photosynthetic membrane. The oxidation of two water molecules to evolve dioxygen in photosystem II is understood to be realized by an enzymatic organization of a special Mn cluster in a protein architecture This oxygen... 

The water oxidation experiment to evolve dioxygen was reported using trinuclear ruthenium complexes with higher turnover numbers. The higher... 

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