Radical, hydrogen peroxide

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). 

Sostaric et al. [67] also found that dissolution of CdS could be achieved through sonochemical reduction of the sulphur by hydroxyl radicals, hydrogen peroxide and superoxide ... 

Nitrosoarenes are readily formed by the oxidation of primary N-hydroxy arylamines and several mechanisms appear to be involved. These include 1) the metal-catalyzed oxidation/reduction to nitrosoarenes, azoxyarenes and arylamines (144) 2) the 02-dependent, metal-catalyzed oxidation to nitrosoarenes (145) 3) the 02-dependent, hemoglobin-mediated co-oxidation to nitrosoarenes and methe-moglobin (146) and 4) the 0 2-dependent conversion of N-hydroxy arylamines to nitrosoarenes, nitrosophenols and nitroarenes (147,148). Each of these processes can involve intermediate nitroxide radicals, superoxide anion radicals, hydrogen peroxide and hydroxyl radicals, all of which have been observed in model systems (149,151). Although these radicals are electrophilic and have been suggested to result in DNA damage (151,152), a causal relationship has not yet been established. Nitrosoarenes, on the other hand, are readily formed in in vitro metabolic incubations (2,153) and have been shown to react covalently with lipids (154), proteins (28,155) and GSH (17,156-159). Nitrosoarenes are also readily reduced to N-hydroxy arylamines by ascorbic acid (17,160) and by reduced pyridine nucleotides (9,161). 

Wang S Y and Jiao HJ. 2000. Scavenging capacity of berry crops on superoxide radicals, hydrogen peroxide, hydroxyl radicals, and singlet oxygen. J Agric Food Chem 48 5677-5684. 

Colquhoun and Schumacher [98] have shown that y-linolcnic acid and eicosapentaenoic acid, which inhibit Walker tumor growth in vivo, decreased proliferation and apoptotic index in these cells. Development of apoptosis was characterized by the enhancement of the formation of reactive oxygen species and products of lipid peroxidation and was accompanied by a decrease in the activities of mitochondrial complexes I, III, and IV, and the release of cytochrome c and caspase 3-like activation of DNA fragmentation. Earlier, a similar apoptotic mechanism of antitumor activity has been shown for the flavonoid quercetin [99], Kamp et al. [100] suggested that the asbestos-induced apoptosis in alveolar epithelial cells was mediated by iron-derived oxygen species, although authors did not hypothesize about the nature of these species (hydroxyl radicals, hydrogen peroxide, or iron complexes ). 

The absence of substituents with free radical scavenging properties in most of the (3-blockers makes doubtful their efficacy as powerful antioxidants. Arouma et al. [293] tested the antioxidative properties of several 3-blockers in reactions with superoxide, hydroxyl radicals, hydrogen peroxide, and hypochlorous acid. It was demonstrated that most of the compounds tested were inactive in these experiments. Nonetheless, propranolol, verapamil, and flunarizine effectively inhibited iron ascorbate-stimulated microsomal lipid peroxidation and all drugs (excluding flunarizine) were effective scavengers of hydroxyl radicals. Contrary to Janero et al. [292], these authors did not find the inhibition of xanthine oxidase by propranolol. It was concluded that 3-blockers are not the effective in vivo antioxidants. 

Joshi, AA Locke, BR Arce, P Finney, WC. Formation of hydroxyl radicals, hydrogen peroxide and aqueous electrons by pulsed streamer corona discharge in aqueous solution. Journal of Hazardous Materials, 1995 41,3-30. 

Iron(II) hydroxyl radical, hydrogen peroxide determination, 641... 

The self-peroxidation reactions of Cu,Zn-SOD provide a particularly novel mechanism for the formation of protein radicals. Hydrogen peroxide is generated during the reaction cycle of the enzyme ... 

Bannister, J, V., Hill, H. A. O. (eds.) Chemical and Biochemical Aspects of Superoxide and Superoxide Dismutase, New York-Amsterdam-Oxford, Elsevier/North-Holland, 1980, p. 414 Fridovich, I. Oxygen radicals, hydrogen peroxide, and oxygen toxicity. In Free Radicals in Biology, Vol. I (Pryor, W. A., ed.). New York-San Francisco-London, Academic Press, 1976, pp. 239-277... 

Scavenger is a term used for substrates reacting with hydroxyl radicals that do not yield species that propagate the chain reaction. Scavengers can hinder oxidation by consuming hydroxyl radicals, hydrogen peroxide, and UV light. 

This remarkably low reactivity of triplet oxygen is in sharp contrast with the reactivity of other oxygen-centered radicals. Hydrogen peroxide (D(O-H) =87.1 kcal/mol) or aliphatic alcohols such as methanol (D(O-H) = 104kcal/mol), for instance, have much stronger O-H bonds than the hydroperoxyl radical, and the corresponding oxyl radicals will usually quickly and irreversibly abstract hydrogen atoms from alkanes to yield alkyl radicals (Table 3.1). 

Fridovitch, I., "Oxygen Radicals, Hydrogen Peroxide and Oxygen Toxicity", In Free Radicals in Biology Pryor, W.A., Ed. Academic Press New York, NY, 1976, Vol. 1 pp 239-277. 

Usually, EPR signals of the radicals and the paramagnetic metal ions of the lattice are superimposing as it has been observed in [29-33, 40-42, etc.]. In many cases for generating radicals hydrogen peroxide H202 was used, as well as illumination, heat treatment in the presence of 02 and reduction by CO or H2. It follows from Table 8.3 that ... 

Fridovich, I. 1976. Oxygen radicals, hydrogen peroxide and oxygen toxicity. In Free Radicals in Biology, Vol. 1 (W.A. Pryor, ed.), pp. 239-277, Academic Press, New York. 

Fig. 8-3. Reduction of oxygen by a one-electron transfer mechanism. Each of the four reaction steps involves addition of one electron and one proton, giving rise to peroxy radicals, hydrogen peroxide, and hydroxyl radicals as intermediate products (a). The crifresponding organic species are formed when oxygen reacts with organic radicals R- (b).

Monosaccharides can oxidise when catalysed by trace amounts of transition metals, generating free radicals, hydrogen peroxide and reactive dicarbonyls directly [27]. The process of glucose oxidation can lead to protein damage by free radicals and by covalent binding of the carbonyl products of the process to protein components (see below) (Fig. 5). 

In the zeolite, owing to the lack of multimolecular degradation, oxidation of water by [Ru(bpy)3] + becomes possible. The reaction is slow, and hydroxyl radicals, hydrogen peroxide and superoxide are created as intermediates. In plant photosynthesis, an Mn-based water-splitting catalyst system in which the reaction with water only occurs after four electrons have been stored in the water-splitting enzyme... 

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