Water oxidation dimer

The primary synthetic route proceeds via oxidative dimerization of 2-aminoan-thraquinone in the presence of an alkali hydroxide. 2-aminoanthraquinone, for instance, is fused with potassium hydroxide/sodium hydroxide at 220 to 225°C in the presence of sodium nitrate as an oxidant. New techniques involve air oxidation of 1-aminoanthraquinone at 210 to 220°C in a potassium phenolate/sodium acetate melt or in the presence of small amounts of dimethylsulfoxide. A certain amount of water which is formed during the reaction may be removed by distillation in order to improve both efficiency and yield. 

Preparation of 4-Nitrosoheptane Dimer (Bromine Water Oxidation) [43]... 

Due to the historical importance of the initial stages of silicon oxidation to microelectronics fabrication, there has been a great deal of interest in the reaction of the water oxidant on the Si(100)-2 x 1 surface. A number of studies have shown that water adsorbs in a dissociated state consisting of OH(a) and H(a) species adsorbed on the Si surface dimer at room temperature [60-69]. More recent studies have closely investigated the mechanism of water oxidation. A series of density functional theory calculations (DFT) calculations by Konecny and Doren indicated that water first molecularly adsorbs through one of its lone pairs in a weakly bound precursor state, then transfers a proton to form OH(a) and H(a) species on the surface dimer [43]. The pathway to proton transfer is found to be unactivated with respect to the entrance channel, which suggests that OH(a) and H(a) are the dominant surface species at room temperature, in agreement with the previous experimental work [60-69]. 

Oxidation of arylmethyl ketoximes by phenyliodoso diacetate in glacial acetic acid was second order overall, first order each in substrate and oxidant.145 Iodine allowed the oxidative dimerization of glycine ester enolates with low to moderate diastereoselec-tivity that is consistent with kinetic control.146 Although malonic acid is not oxidized by iodate under acidic conditions, oxidation proceeds in the presence of catalytic ruthenium(III). A mechanism is put forward to account for the observed orders of reaction.147 The rate of periodate oxidation of m-toluidine in acetone-water increases with ionic strength.148... 

A rationalization for the formation of 10 is presented in Scheme 4. The crucial feature is that lithiation of the oxide 7 occurs at two different sites, in both of which internal coordination to lithium is important. When lithiation occurs on the 6-carbon, giving 13, formation of the dienylphosphine oxide 11 results, and hence anion 12 arises. Upon quenching with water the dimeric dioxide 10 is formed. In a separate experiment, addition of benzaldehyde led to isolation of a trienylphosphine oxide whose formation we take to be further evidence for the anion 12. 0... 

Hurst JK. Water oxidation catalyzed by dimeric ja-oxo bridged ruthenium diimine complexes. Coord Chem Rev 2005 249 313-28. 

Liu F, Concepcion JJ, Jurss JW, Cardolaccia T, Templeton JL, Meyer TJ. Mechanisms of water oxidation from the blue dimer to photosystem II. Inorg Chem. 2008 47(6) 1727-52. 

The available data do not permit an unambiguous definition of either the OEC structure or the mechanism of water oxidation. It is possible, however, to construct a model consistent with both the known chemistry of Mn and the available data and to use this model to make testable predictions concerning OEC structure. The present structural results are consistent with, if not proof of, the dimer-of-dimers model of the OEC (11). Within this model, we attribute the 2.7-A feature to the intradimer Mn-Mn distances and the 3.3-A feature to an interdimer Mn-Mn distance. The EXAFS finding that there are two to three (per 4 Mn) 2.7-A Mn-Mn distances (65) is consistent with the presence of two Mn(/i-0)2Mn dimers. The 3.3-A feature, which disappears on hy-droquinone treatment (see Figure 10), is attributed to an interdimer Mn-Mn distance. This distance is typical of oxo- or oxocarboxylato-... 

A variety of models for the sequence of events which occur in the OEC during water splitting has been reviewed recently [15,16]. In general, these models are based on a dimeric Mn cluster and feature water oxidation to produce bound, par-... 

These structural characteristics mean that the dendrimer porphyrin can be used to mimic the function of the heme protein - its ability to bind to oxygen. A dendrimer porphyrin with an Fe(II) ion can stably trap oxygen via coordination with imidazole ligands. The oxygen was reversibly trapped within the dendrimer, and it can be released when the oxygen in the surrounding solvent was removed. The dendrimer sphere shields the porphyrin part from the outer environment. Therefore, side effects such as irreversible oxidation of the porphyrin by water and dimerization of the oxygen-bound porphyrins can be suppressed. 

Fig. 5. Water oxidation redox cycle using the dimer ruthenium complex...

It is noted that the linearly oxo-bridged trinuclear ruthenium complex [NH3)5Ru-0-Ru(NH3)4-0-Ru(NH3)5] + (Ru "-Ru Ru", called Ru-red) is a better catalyst for water oxidation than the dimer ruthenium complexes in homogeneous solution The Ru" -Ru -Ru " is oxidized electrochemically... 

Meyer et al. - reported the catalytic activity of oxo-bridged dimer ruthenium complex, [bpy)2(H20)Ru0Ru(H20)(bpy)2] , towards water oxidation to... 

Nafion film coated on an ITO electrode to understand the structural transformations of the dimer in the Nafion coating during the catalytic water oxidation process . The absorption spectral changes observed during the oxidation scan from 0.4 to 1.4 V (s. SCE) (Fig. lOA) showed a decrease in the absorbance at 655 nm with simultaneous increase in the absorbance at around 450 nm with clear isosbestic points at 430 and 545 nm. In the reductive scan from 1.4 to 0.4 V (vs. SCE) (Fig. lOB), the absorbance at 655 nm increased and a simultaneous decrease in the absorbance at 450 nm was observed with an isosbestic point at 555 nm. The absorbance at 655 nm was almost recovered back. Initially the oxidation of the dimer complex H20-Ru" -Ru "-0H2 leads to the formation of H20-Ru "-Ru -0H2 with an absorption maximum at around 450 nm and further oxidation at higher positive potentials must lead to Ru -Ru formation in a successive oxidation process. The Ru -Ru would be rapidly reduced by water molecules to produce H20-Ru -Ru -0H2 at pH 1. The same in situ spectrocyclic voltammetry experiments at pH 9.3 showed an absorption maximum at around 500 nm with the formation of H20-Ru" -Ru -OH in the Nafion film. In relevant to the absorbances at 450... 

The reactions observed for the dimer complex adsorbed in a Nafion film coated on an ITO electrode at different pH by in situ absorption spectral measurements are summarized as shown in Fig. 11. At higher positive potentials and at potentiostatic conditions, a band at around 450 nm was observed indicating the formation of H20-Ru "-Ru -OH2 at acidic conditions and formation of H20-Ru" "-Ru -OH at basic conditions in addition to the absorbance at 655 nm. This shows that during the catalytic water oxidation process, the diaquo dimer complex exists as an intermediate. In a Nafion polymer membrane, the metal complex is isolated and experiences a micro-heterogeneous environment imposed by hydrophobic fluorocarbon moiety and... 

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