Superoxide ion radical

Superoxide dismutase enzymes are functional dimers of molecular weight (Mr) of approximately 32 kDa. The enzymes contain one copper ion and one zinc ion per subunit. Superoxide dismutase (SOD) metalloenzymes function to disproportionate the biologically harmful superoxide ion-radical according to the following reaction ... 

Trace amounts of Cu(II) were reported to catalyze the oxidation of I-to I2 (156) and the phosphinate ion (H2P02) to peroxodiphosphate ion (PDP), which could be present as P20g, HP20 or H2P20f (757). Individual kinetic traces showed some unusual patterns in these reactions, such as the variation between first- and zeroth-order kinetics with respect to the formation of I2 under very similar conditions, or an autocatalytic feature in the concentration profiles of PDP, but these events were not studied in detail. The catalytic effect was interpreted in terms of a Cu(II) / Cu(I) redox cycle and the superoxide ion radical,... 

The major in situ process that results in the formation of H202 is undoubtedly photochemical (e.g., 12, 15, 49, 50). Photochemical formation of H202 in fresh and salt waters probably results from the disproportionation of the superoxide ion radical, 02 (8, 9, 15, 51, 52). The kinetics of superoxide disproportionation are well established (53), and its steady-state concentration can be calculated. Because of the known effects of superoxide ion in cells (47), its presence in surface waters may be important in biologically mediated processes. However, other sources, such as biological formation (e.g., 45, 54), redox chemistry (21, 24, 29, 31, 32), wet (e.g., 55) and dry (50, 56, 57) deposition, and surfaces (e.g., 58) may also be important. 

Organic radicals formed in these reactions may further react with oxygen (in an aerated medium as in water treatment) to yield organic peroxyl radicals that can eventually react with compounds present in the medium to release the superoxide ion radical (see route through 5 in Fig. 6 see also the work of von Sonntag and Schuchmann [122] for more details about peroxyl radical reactions). In these cases, compounds that react with the hydroxyl radical are known to be promoters of ozone decomposition because the superoxide ion radical consumes ozone at a fast rate [see reaction (63) above]. On the contrary, if the reaction between hydroxyl radical and compound M does yield inactive radicals, M is known as a scavenger or inhibitor of ozone decomposition (see route to 4 in Fig. 6). Many natural substances such as humic substances and carbonates are known to possess such a role [121]. However, the case of carbonate ion is rather special because it reacts with hydroxyl radicals to yield the carbonate ion radical ... 

The double role as scavenger and initiator, observed for hydrogen peroxide in the 03/H202 system, has also been reported in the UV/H202 system. It should be noted that hydrogen peroxide does not inhibit the ozone decomposition and Eq. (75) is valid only in the cases that ozone is present in the reaction mixture and the process is chemically controlled (low concentrations of hydrogen peroxide). This is because reactions of hydrogen peroxide with the hydroxyl radical release the superoxide ion radical that... 

CD spectroscopy has also been used to study the metal-binding and reactivity properties of iron- and manganese-containing SODs. These enzymes metabolize the superoxide ion radical O2 into molecular oxygen and hydrogen peroxide. The Fe- and Mn-SOD enzymes are strictly metal specific. Jackson and Brunold show that, despite the fact that Fe replacement of Mn in the Mn-SOD enzyme [(Mn Fe)-SOD] results in an inactive enzyme, the CD spectrum of wild-type Fe-SOD and (Mn - Fe)-SOD are remarkably similar. This suggests that the destroyed enzyme activity, upon replacement of the metal, does not occm via distortion of the enzyme active site. 

O.C. Zafiriou (1990). Chemistry of superoxide ion-radical (02 ) in seawater. I. pK (HOO) and uncatalyzed dismutation kinetics studied by pulse radiolysis. Mar. Chem., 30,31-43. 

Restoration of the Fe + ions takes place in the Fe +reduction process provided by the superoxide ion radicals, O2 ... 

The last topic was concerned with the ESR spectra of the superoxide ion radical (02 ) which is one of the most important oxide radical intermediates in catalysis and has been extensively studied by means of ESR spectroscopy. Some important characteristics of the g-values and the hyperfine structiu e due to (/ = 7/2) label-... 

The main mechanisms of the appearance of the active radical forms of oxygen (ROS) in the body are usually related to the distortion of the functioning of the electron transport chains (ETC) of the mitochondria or microsomes. The functions of the mitochondrial ETC are a realization of the subsequent oxidation-reduction reactions of the electron transfer from the substrate of oxidation to the oxygen as a final electron acceptor. At the same time, two-electron reduction of to H O takes place, which is why the free radicals (very reactive species with free valence) should not appear. However, it was shown in [19,20] that the normal electron transfer in the mitochondria (two-electron reduction of O ) is inevitably spontaneously intermpted, during which only one-electron reduction of takes place and superoxide ion-radical appears. This radical is not very reactive, but when we discuss the mechanism of the potential harm of O, it is usually referred on the reaction 6.6 ... 

Write the Lewis structure of each of the following species and indicate which are radicals (a) the superoxide ion, Oz ... 

Starke, P.E., and Farber, J.L. (1985). Ferric iron and superoxide ions are required for the killing of cultured hepatocytes by hydrogen peroxide. Evidence for the participation of hydroxyl radicals formed by an iron catalyzed Haber-Weiss reaction. J. Biol. Chem. 260, 10099-10104. 

Indeed, when present in concentrations sufficient to overwhelm normal antioxidant defences, ROS may be the principal mediators of lung injury (Said and Foda, 1989). These species, arising from the sequential one-electron reductions of oxygen, include the superoxide anion radical, hydrogen peroxide, hypochlorous ions and the hydroxyl radical. The latter species is thought to be formed either from superoxide in the ptesence of iron ions (Haber-Weiss reaction Junod, 1986) or from hydrogen peroxide, also catalysed by ferric ions (Fenton catalysis Kennedy et al., 1989). 

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). 

Other cationic surfactants such as TTAB, DTAB, DODAB, STAC, CEDAB, and DDDAB have been used in CL reactions with less frequency. Thus, tetradecyltrimethylammonium bromide [TTAB] has been used to increase the sensitivity of the method to determine Fe(II) and total Fe based on the catalytic action of Fe(II) in the oxidation of luminol with hydrogen peroxide in an alkaline medium [47], While other surfactants such as HTAB, hexadecylpiridinium bromide (HPB), Brij-35, and SDS do not enhance the CL intensity, TTAB shows a maximum enhancement at a concentration of 2.7 X 10 2 M (Fig. 11). At the same time it was found that the catalytic effect of Fe(II) is extremely efficient in the presence of citric acid. With regard to the mechanism of the reaction, it is thought that Fe(II) forms an anionic complex with citric acid, being later concentrated on the surface of the TTAB cationic micelle. The complex reacts with the hydrogen peroxide to form hydroxy radical or superoxide ion on the... 

He is the author of Superoxide Ion Chemistry and Biological Implications (Volumes 1 and 2, CRC Press, 1989 1990) and the co-author of several jointed books on free radicals. He has published about 100 works. 

Dioxygen oxidizes transition metal ions in the lower valence state generating the hydroxyperoxyl radicals or superoxide ions [155,156]. The thermodynamic characteristics of these reactions are presented in Table 10.6. It is seen that all cited reactions are endothermic, except for the reaction of the cuprous ion with 02. The reaction of the ferrous ion with dioxygen has a sufficiently low enthalpy (28 kJ mol 3). 

The reaction proceeds as a chain process involving the peroxyl radical and superoxide ion [284],... 

The superoxide ion is a very weak hydrogen atom abstractor, which cannot continue the chain, and is destroyed via disproportionation with any peroxyl radical. So, the studies of the mechanisms of cyclic chain termination in oxidation processes demonstrate that they, on the one hand, are extremely diverse and, on the other, that they are highly structurally selective. The 20 currently known mechanisms are presented in Table 16.6. 

The ground state (0 kJ/mol) for the CL molecule is represented by the term symbol 3v . The first excited state (92 kJ/mol above the ground state) is a 1 singlet (electrons spin paired with both electrons in either the n x or the n y level). The 1 v state with paired spin electrons, one each in the 7i v and n y levels, is the next excited level 155 kJ/mol above the ground state. Reduction of 02 by one electron yields the superoxide ion (02), a radical anion. Reduction by two electrons yields the peroxide ion, (02 ). Bond lengths and bond orders for these are given in Table 4.2. As noted in equation 4.2, the reduction potential for 02 in the presence of protons is thermodynamically favorable. Therefore, reversible binding of O2 to a metal can only be achieved if competition with protons and further reduction to superoxide and peroxide are both controlled.8... 

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... 

Figure 5.2. Pathways of oxygen reduction. The sequential reduction of molecular oxygen, ultimately to water, is shown. Abbreviations 02 % superoxide free radical H202, hydrogen peroxide OH, hydroxide ion -OH, hydroxyl free radical e, electron H+, hydrogen ion. Singlet states of oxygen are also shown as i +02and Ag02.

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