O2 oxidation

The elemental reaction used to describe a redox reaction is the half reaction, usually written as a reduction, as in the following case for the reduction of oxygen atoms in O2 (oxidation state 0) to H2O (oxidation state —2). The half-cell potential, E°, is given in volts after the reaction ... 

Both Fe and Al form insoluble oxides that precipitate from solution. Overall, then, O2 oxidizes each... 

Exposure of s.o. samples to NH3-NO at 623 K, caused a slight reduction of V to V v, whereas exposure to NO-NH3-O2, did not affect the vanadium oxidation state. Exposure of reduced samples (CO at 623 K) to NH3-NO caused slight oxidation, whereas exposure to NO-NH3-O2 oxidized all V . ... 

Solid-oxide fuel cell Ion-conducting ceramic (yttrium stabilised zircon oxide) O2- (oxide) 800-1000... 

X lO M s (neutral ligands) to 6 x lO M s for -t-3 charged entering ions.Dilute solutions (<0.1 mM) of the aqua complex should be used to avoid complications of polynuclear formation. In addition, O2 oxidizes Fe(CN)5H20 fairly rapidly in acid solution ... 

Figure 8.7 Combustion products particle size distributions for O2 oxidizer tests 1 — 02/Ar, 2 — H2O...

In the case of O2 oxidation of a,-unsaturated esters, there is a small but significant solvent effect on the variation of the ene products . Hydrogen abstraction from the methyl group which is geminal to the ester functionality in compound 79 (equation 2), producing 79a, decreases substantially as the solvent polarity increases. For example, the ratio of ene products 79a/79b decreases by a factor of 5 in going from carbon tetrachloride to the more polar solvent DMSO. 

Early studies have shown that tryptophan, tyrosine, histidine, methionine and cysteine, either as free amino acids or as components of peptides, are excellent substrates for O2 oxidation reactions. Usually, reaction of O2 with amino acids is mostly described in terms of chemical quenching with the exception of tryptophan, for which collisional deactivation as the result of physical quenching is not neghgible. The rate constants of O2 toward the main reactive amino acids that show a strong solvent dependence are reported in Table 2 for neutral aqueous solutions with values within the range 0.8-3.7... 

Thus, the long-lived hydroperoxide 128 derived from Tyr endoperoxide in Gly-Tyr-Gly upon O2 oxidation is formed and decays only slightly after a several-month incubation period at room temperature, leading to the corresponding alcohol 129 (equation 63). 

The properties of the semiquinone from of the ETF isolated from the methylotrophic bacterium resemble those of the bacterial flavodoxins with the exception that flavodoxins form neutral semiquinones whereas this ETF forms an anionic semiquinone. Nearly quantitative anionic semiquinone formation is observed either in the presence of excess dithionite or when excess trimethylamine and a catalytic amount of trimethylamine dehydrogenase are added. Of interest is the apparent stability of the anionic semiquinone towards oxidation by O2 but not to oxidizing agents such as ferricyanide. This appears to be the first example of an air-stable protein-bound anionic flavin semiquinone. Future studies on the factors involved in imparting this resistance to O2 oxidation by the apoprotein are looked forward to with great interest. 

Controlled O2 oxidation of the MoIII,ni IV,lv tetramer yields a product which titrates for MoIV and from an incomplete X-ray crystal study appears to be basically the same tetrameric structure, except that all the bridging ligands are now fi-oxo. This Mo tetramer is also an intense red colour, Figure 10. The reduction potential for the couple involving the two tetrainers is +0.07 V. Rapid reactions of both tetramers with 02 are of interest in that there is no site for binding unless the coordination number increases. Mild oxidants such as [Co(NH3)5Cl]2+ react rapidly (fi/2 < 1 min) with both tetramers to give the Mo)1 dimer. 

The arguments just presented suggest that all n-type semiconductor photoanodes which resist corrosion under conditions of H2O to O2 oxidation must have (a) stable elemental component(s) at low pH. Moreover, since the oxide dissolution reaction is associated with essentially the same H+/0= interactions, the low pH stability limit will be at approximately the same value (P stable 3). 

The rate constants of O catalytic dismutation, determined for the nitroxides tested, increased with [H+], indicating that OOH, but not O2 oxidizes nitroxide ... 

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