Anions superoxide radical anion

Fig. 8.9 Possible mechanisms of the bioluminescence reaction of dinoflagellate luciferin, based on the results of the model study (Stojanovic and Kishi, 1994b Stojanovic, 1995). The luciferin might react with molecular oxygen to form the luciferin radical cation and superoxide radical anion (A), and the latter deproto-nates the radical cation at C.132 to form (B). The collapse of the radical pair might yield the excited state of the peroxide (C). Alternatively, luciferin might be directly oxygenated to give C, and C rearranges to give the excited state of the hydrate (D) by the CIEEL mechanism. Both C and D can be the light emitter.

Fig. 3. a) First order plot of oxygen uptake in the Methylene-blue (MB)-sensitized photooxidation of GA 8.4 pM and 1.3 mM histidine (control) in phosphate buffer pH 7. b) Percentage radical scavenging activity for the control molecule Trolox and GA at pH 7.4 in phosphate buffer 10 mM (hydroxyl radical) and pH 10 in sodium carbonate buffer 50 mM (anion superoxide radical). 

A significant amount of the 02 metabolized by the human organism is converted to the highly reactive superoxide radical anion 02. Endogenous overproduction of 02 may cause considerable... 

Triantis T, Stelakis A, Dimotikali D and Papadopoulos K. 2005. Investigations on the antioxidant activity of fruit and vegetable aqueous extracts on superoxide radical anion using chemiluminescence techniques. Anal Chim Acta 536(1-2) 101-105. 

P., Oxidative denitrification of N-omega-hydroxy-L-arginine by the superoxide radical anion, Biochem. J. 317 (1996), p. 17-21... 

Step 3. O2 binds, but can also dissociate. If it dissociates, the enzyme reverts to the heme Fe3+ resting state and generates superoxide radical anion in the process. 

In contrast, antioxidant enzymes can efficiently counteract all UV-induced ROS (Aguilera et al. 2002). These enzymes are represented by superoxide dismutase (SOD), catalase and glutathione peroxidase as well as those involved in the ascorbate-glutathione cycle, such as ascorbate peroxidase, mono-dehydroascorbate reductase, dehydroascorbate reductase and glutathione reductase. One of the most important classes of antioxidant enzymes is the SOD family, which eliminate noxious superoxide radical anions. Different metalloforms of SOD exist (Fe, Mn, CuZn and Ni), which due to their intracellular localisation protect different cellular proteins (Lesser and Stochaj 1990). 

Spin trapping of the superoxide radical anion, as well as that of hydroperoxyl and hydroxyl radicals and related species will be considered later in connection with biological chemistry (pp. 52-54). 

The hydroperoxyl radical formed, "00H, has a pKg of 4.75 and exists in water as a superoxide radical anion 02 Either species in water dismutates to produce O2 and hydrogen peroxide, H2O2, or, possibly, react with dissolved or adsorbed phenol. Dilute H2O2 does... 

A type I one-electron photo-oxidation of methionine-methionine-containing peptides by triplet carboxybenzophenone in air-saturated aqueous solution has been reported the S+ radical cation that is formed then reacts with the other Met-S to form an S-S three-electron complex which reacts with superoxide radical anion before hydrolysis to Met(=0)-Met(=0) bis-sulfoxide. Alternatively, cyclization of the A-terminal NH2 on to the S can occur to give a three-electron S-N complex which can react with superoxide radical anion to give a cyclic sulfonium intermediate. 

The mechanism of the electron transfer from electron donor such as MV to producing molecular hydrogen and catalyzed by Au [187] or Pt clusters [188], and that of the disproportionation reaction of the superoxide radical anion O2 by Pt clusters in solution or supported on colloidal Ti02 particles [189], have been studied by pulse radiolysis. 

Cathodic reduction of oxygen is the most convenient method of production of the superoxide radical-anion,. The properties of this important species have been well reviewed and key references to the extensive work on the electrochemistry of oxygen are contained therein. Of immediate significance is the large cathodic shift in E° for the 0 /0 couple which accompanies a change from aqueous to aprotic solvent (e.g. DMF, DMSO, and MeCN) this is interpreted in terms of relatively weak solvation in aprotic media which enhances the nucleophilicity of the superoxide anion. However, in the presence of acids the chemistry of superoxide is dominated by the disproportionation shown in equation 1. 

As indicated in Fig. 16.2, in addition to energy transfer, chemical reactions of excited UCs ( UC, 3UC ) may lead to the formation of other reactive oxygen species (ROS) that may react with organic pollutants. Such ROS include DOM-derived oxyl- and peroxyl radicals (RO , ROO ), superoxide radical anions (02 ) that may be further reduced to H202, and hydroxyl radicals (HO ). In the case of HO , however, DOM is a net sink rather than a source. Finally, some of the 3UC may react directly with certain more easily oxidizable pollutants (see below). 

The reaction serves as an illustrative example of the synthetic utilization of the Te(II)—>Te(IV) two-electron shuttle. Another promising application is seen in photodynamic therapy in which tellurapyrylium dyes 119 can function as photosensitizers to produce either singlet oxygen or superoxide radical-anions (via electron transfer), thereby serving as cytotoxic agents. An important useful property of tellurapyrylium dyes is their absorbance in the near-infrared region where biological tissues are most important. 

Perkins MJ (1996) A radical reappraisal of Gif reactions. Chem Soc Rev 25 229-236 Phulkar S, Rao BSM, Schuchmann H-P, von Sonntag C (1990) Radiolysis of tertiary butyl hydroperoxide in aqueous solution. Reductive cleavage by the solvated electron, the hydrogen atom, and, in particular, the superoxide radical anion. Z Naturforsch 45b 1425-1432 Pimblott SM, LaVerne JA (1997) Stochastic simulation of the electron radiolysis of water and aqueous solutions. J Phys Chem A 101 5828-5838... 

Chatgilialoglu C, Castelhano AL, Griller D (1985) Structures and optical absorption spectra of some sulfuranyl radicals in solution. J Org Chem 50 2516-2518 D Alessandro N, Bianchi G, Fang X, Jin F, Schuchmann H-P, von Sonntag C (2000) Reaction of superoxide with phenoxyl-type radicals. J Chem Soc Perkin Trans 2 1862-1867 Das S, von Sonntag C (1986) Oxidation of trimethylamine by OH radicals in aqueous solution, as studied by pulse radiolysis, ESR and product analysis. The reactions of the alkylamine radical cation, the aminoalkyl radical and the protonated aminoalkyl radical. Z Naturforsch 41b 505-513 Das S, Schuchmann MN, Schuchmann H-P, von Sonntag C (1987) The production of the superoxide radical anion by the OH radical-induced oxidation of trimethylamine in oxygenated aqueous solution. The kinetics of the hydrolysis of (hydroxymethyl)dimethylamine. Chem Ber 120 319-323... 

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