Oxygen atom donor

Manganese Water Splitting, Oxygen Atom Donor... 

The similarity of the structure of peroxynitrous acid to the simplest peroxy acid, per-oxyformic acid, immediately raised the question as to its relative reactivity as an oxygen atom donor. This became particularly relevant when it was recognized that the 0—0 bond dissociation energy (AG° = 21 kcalmoR ) of HO—ONO was much lower than that of more typical peroxides. Consequently, peroxynitrous acid (HO-ONO) can be both a one- and two-electron oxidant. Since the 0-0 bond in HO-ONO is so labile, its chemistry is also consistent in many cases with that of the free hydroxyl radical. 

Although water oxide, once formed, proved to be a remarkably efficient oxygen atom donor, it is quite likely that it is simply too high in energy to be a viable oxidant. A second problem with the preliminary calculations by Bach and coworkers" is that NH3 is not a realistic nucleophile for such studies it is what was feasible at that time. This inadequacy has only recently been ameliorated by Ottolina and Carrea , who used the more nucleophilic trimethylamine (TMA) as the attacking nucleophile and got an entirely different and much more chemically realistic hypersurface for the HO—OH oxidation of amines. The prior results at the MP2 level compared favorably with the results of the B3LYP/6-31-I-G method, so the basic problem was in the nucleophile and not with the... 

Wille demonstrated recently the utility of S04 as an oxygen atom donor when it was reacted with two different ten-membered alkynes 24 (equation 22) and 27 (equation 23) . This is the first example of transfer of oxygen atom from peroxydisulfate ion. 

The active oxidizing species is the 8 oxoiron complex formed on the action of the single-oxygen-atom donor. The interaction of 8 with the alkane results in hydrogen... 

The kinetics of oxidation of aldehydes by the Fenton reagent [Fe(II)-H202-0H-] have been studied.89 It has been suggested that different reactivities of PhIO in iron(III)-porphyrin-catalysed alkene epoxidation may be due to the formation of a more reactive iron(IV)-0-IPh complex.90 The iron(m) complex of tetrakis(3,5-disulfonato-mesityl)porphyrin catalyses the oxidative degradation of 2,4,6-trichlorophenol to 2,6-dichloro-l,4-benzoquinone with KHSO5 as the oxygen atom donor a peroxidase-type oxidation is thought to be involved.91... 

One important discrepancy should be noted between photochemical and chemical ion radical reactions. In the photochemical mode, an oxidized donor and a reduced acceptor remain in the same cage of a solvent and can interact instantly. In the chemical mode, these initial products of electron transfer can come apart and react separately in the bulk solvent. For example, one-electron oxidation of phenylbenzyl sulfide results in formation of the cation radical both in the photoinduced reaction with nitromethane and during treatment with ammoniumyl species. Sulfide cation radicals undergo fragmentation in the chemical process, but they form phenylbenzyl sulfoxide molecules in the photochemical reaction. The sulfoxide is formed at the expense of the oxygen atom donor. The latter comes from the nitromethane anion radical and is directly present in the solvent cage. As for the am-... 

This reactivity suggests that although these complexes effectively catalyze a reaction that likely proceeds by a coupled electron proton transfer, they appear to be relatively poor oxygen atom donors. 

Model studies clearly demonstrate that oxo transfer is a viable mechanism for many of the enzyme reactions shown in Table 2d. However, primarily because of difficulties in labeling studies, it has not yet proved possible to validate oxo transfer as a physiologically relevant enzymatic mechanism. Although it has been possible to oxidize and reduce molybdenum centers using certain oxygen atom donors or acceptors, these experiments serve only to demonstrate that such processes are possible and not that they are part of the physiologically relevant pathway [231,233],... 

Although oxo transfer allows the oxidation of enzyme substrates in biological model systems [196,198,231], the ultimate source of the oxygen incorporated by molybdenum or tungsten enzymes is water (Eq. 19). As such, in the absence of an oxygen atom donor,... 

The peroxidase activity of PGHS is comparable to that of better known peroxidases such as horseradish peroxidase (HRP). The catalytic cycle of HRP is shown in Figure 5 [9], Its first step is the formation of an intermediate very often found in hemoproteins by transfer of an oxygen atom from various oxygen atom donors to the Fe(III) heme (Eq. 6). It is a high-valent iron-oxo species, at least formally a Fe(V)=0 complex. In fact, the detailed electronic structure of this intermediate depends on the environment of the heme provided by the protein. In HRP, this intermediate (called compound I) is a (porphyrin radical-cation)-Fe(IV)=0 complex, as shown by many spectroscopic techniques [9],... 

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