Oxygen superoxide ion

Katayama Y, Sekiguchi K, Yamagata M, Miura T (2005) Electrochemical behavior of oxygen/ superoxide ion couple in 1-butyl-l-methylpyrrolidinium bis(trifluoromethylsulfonyl) imide room-temperature molten salt. J Electrochem Soc 152 E247-E250... 

Peroxide and superoxide ions have recently been identified in molten systems. These ions are formed by the oxidation of oxide ions by oxygen or oxy-anions such as nitrate (see Reference 11). 

The principal product of the reaction of the alkali metals with oxygen varies systematically down the group (Fig. 14.15). Ionic compounds formed from cations and anions of similar radius are commonly found to he more stable than those formed from ions with markedly different radii. Such is the case here. Lithium forms mainly the oxide, Li20. Sodium, which has a larger cation, forms predominantly the very pale yellow sodium peroxide, Na202. Potassium, with an even bigger cation, forms mainly the superoxide, K02, which contains the superoxide ion, O,. ... 

It should be noted that dissociation of surface complexes of oxygen in polar solvents on semireduced ZnO films is presumably justified from the thermodynamic point of view as oxygen adsorption heat on ZnO and electron work function are [58] 1 and approximately 5 eV respectively while the energies of affinity of oxygen molecules to electron, to solvation of superoxide ion and surface unit charge zinc dope ions are 0.87, 3.5, and higher than 3 eV, respectively [43]. 

Hyperfine interaction has also been used to study adsorption sites on several catalysts. One paramagnetic probe is the same superoxide ion formed from oxygen-16, which has no nuclear magnetic moment. Examination of the spectrum shown in Fig. 5 shows that the adsorbed molecule ion reacts rather strongly with one aluminum atom in a decationated zeolite (S3). The spectrum can be resolved into three sets of six hyperfine lines. Each set of lines represents the hyperfine interaction with WA1 (I = f) along one of the three principal axes. The fairly uniform splitting in the three directions indicates that the impaired electron is mixing with an... 

M.E. Poever and B.S. White, Electrolytic reduction of oxygen in aprotic solvents the superoxide ion. Electrochim. Acta. 11, 1061-1067 (1966). 

D.T. Sawyer and J.L. Roberts, Electrochemistry of oxygen and superoxide ion in dimethyl sulfoxide at platinum, gold, and mercury electrodes. J. Electroanal. Chem. 12, 90-101 (1966). 

P.F. Knowles, J.F. Gibson, F.M. Pick, and R.C. Bray, Electron-spin-resonance evidence for enzymic reduction of oxygen to a free radical, the superoxide ion. Biochem. J. Ill, 53-58 (1969). 

T. Ohsaka, F. Matsumoto, and K. Tokuda, An electrochemical approach to dismutation of superoxide ion using a biological model system with a hydrophobic/hydrophilic interface, in Frontiers of Reactive Oxygen Species in Biological and Medicine (K. Asaka and T. Yoshikawa, eds), pp. 91—93. Elsevier Science B.V. Oxford (1994). 

The 02 ion is known as the superoxide ion, and it is produced when oxygen reacts with potassium, rubidium, and cesium. 

In order to rationalize the complex reaction mixtures in these slurry reactions the authors suggested that irradiations of the oxygen CT complexes resulted in simultaneous formation of an epoxide and dioxetane36 (Fig. 34). The epoxide products were isolated only when pyridine was co-included in the zeolite during the reaction. Collapse of the 1,1-diarylethylene radical cation superoxide ion pair provides a reasonable explanation for the formation of the dioxetane, however, epoxide formation is more difficult to rationalize. However, we do point out that photochemical formation of oxygen atoms has previously been observed in other systems.141 All the other products were formed either thermally or photochemically from these two primary photoproducts (Fig. 34). The thermal (acid catalyzed) formation of 1,1-diphenylacetaldehyde from the epoxide during photooxygenation of 30 (Fig. 34) was independently verified by addition of an authentic sample of the epoxide to NaY. The formation of diphenylmethane in the reaction of 30 but not 31 is also consistent with the well-established facile (at 254 nm but not 366 or 420 nm) Norrish Type I... 

Superoxide ions, 02, are readily formed by the transfer of electrons from Fs centers on MgO or from Mo(V) on Mo/Si02 to molecular oxygen (7, 9). The value of g3 for 02 is particularly sensitive to the crystal field gradient at the surface and thus varies from one metal oxide to another (10). In fact, the spectrum of 01 on MgO indicates that the ions are held at four distinctly different sites (11,12). The oxygen-17 hyperfine splitting (Table I) for 170170- on MgO confirms that both oxygen atoms are equivalent, on supported molybdenum the atoms are nonequivalent, suggesting a peroxy-type bond to the metal (7,13). 

Alkanes—Continued reactions—Continued with ozonide ions, 135 with superoxide ions, 134-35 role of oxygen ions in oxidation. 138-41 Alkenes, reactions with oxygen ions, 134 with ozonide ions, 135 with superoxide ions, 134-35 Aluminosilicate gels, alkali cations, 241... 

Nitroimidazoles (such as metronidazole and misonidazole) can enhance the porphyrin sensitized Type I photooxidations83 that is, electron transfer from the sensitizer to the oxygen molecule is facilitated to give more of the superoxide ion (Scheme 6). The Type II mechanism operates by energy transfer from the sensitizer to afford the singlet oxygen84. 

Whereas several l-aryl-4-nitroimidazoles are found to be good sensitizers for superoxide ion formations85 (Type I photooxidation), only l-phenyl-2-methyl-4-nitroimidazole 140 is a photosensitizer for singlet oxygen, i.e. by energy transfer of type II photooxidation (equation 70). 

Really, as illustrated in Scheme 5, the irreversible oxidation of these oxygenated complexes can involve either a one-electron or a two-electron process. This depends upon the fact that the reaction of the oxygenated complex to regenerate the non-oxygenated complex can proceed through the release of a superoxide ion or an oxygen molecule. 

Table 2 The reactivity of complexes [M(triphos)(catecholate)J+ (M=Co, Rh, Ir) with molecular oxygen as a function of the catecholate/ semiquinone oxidation potential. I=no reactivity 11= the oxygenated complex regenerates the initial complex in the quinone form by release of superoxide ion III = the oxygenated complex regenerates the initial complex in the quinone form by release of molecular oxygen...

Electron-transfer chains in plants differ in several striking aspects from their mammalian counterparts. Plant mitochondria are well known to contain alternative oxidase that couples oxidation of hydroquinones (e.g., ubiquinol) directly to reduction of oxygen. Semiquinones (anion-radicals) and superoxide ions are formed in such reactions. The alternative oxidase thus provides a bypass to the conventional cytochrome electron-transfer pathway and allows plants to respire in the presence of compounds such as cyanides and carbon monoxide. There are a number of studies on this problem (e.g., see Affourtit et al. 2000, references therein). 

Besides the enzyme, the superoxide ion can also be an electron donor. The ion arises as a result of detoxication of xenobiotics (xenobiotics are outsiders, which are involved in the chain of metabolism). Xenobiotics yield anion-radicals by the neutralizing influence of redox proteins. Oxygen (inhaled with air) takes an unpaired electron off from a part of these anion radicals and forms the superoxide ion. The superoxide ion plays its own active role in biochemical reactions. 

The majority of the enzyme-catalyzed reactions discussed so far are oxidative ones. However, reductive electron transfer reactions take place as well. Diaphorase, xanteneoxidase, and other enzymes as well as intestinal flora, aquatic, and skin bacteria—all of them can act as electron donors. Another source of an electron is the superoxide ion. It arises after detoxification of xenobiotics, which are involved in the metabolic chain. Under the neutralizing influence of redox proteins, xenobiotics yield anion-radicals. Oxygen, which is inhaled with air, strips unpaired electrons from these anion-radicals and gives the superoxide ions (Mason and Chignell 1982). 

Recent research into the ter Meer reaction (Shugalei and Tselinskii 1994) has demonstrated that it actually chooses the chain ion-radical mechanism. Chain branching is attributed to air oxygen, after transformation into the superoxide ion (O2 see Section 1.7.1). The whole process of substitution in the aqueous-alkaline buffer medium is expressed by a 14-step sequence summed in Scheme 4.36. 

As seen from Scheme 5.13, not the initial substrate, but rather its anion-radical undergoes methoxylation. This produces the anion-radical of the a complex, which is oxidized by oxygen into the conventional anionic a complex carrying no unpaired electron. This stage generates the superoxide ion, which later competes advantageously with the methoxide ion for the starting 2,4-dinitrochlorobenzene to reduce it into the anion-radical. 

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