Reduction hydroxyl radical

Alkyl hydroperoxides give alkoxy radicals and the hydroxyl radical. r-Butyl hydroperoxide is often used as a radical source. Detailed studies on the mechanism of the decomposition indicate that it is a more complicated process than simple unimolecular decomposition. The alkyl hydroperoxides are also sometimes used in conjunction with a transition-metal salt. Under these conditions, an alkoxy radical is produced, but the hydroxyl portion appears as hydroxide ion as the result of one-electron reduction by the metal ion. ... 

In broad terms, the following types of reactions are mediated by the homolytic fission products of water (formally, hydrogen, and hydroxyl radicals), and by molecular oxygen including its excited states—hydrolysis, elimination, oxidation, reduction, and cyclization. 

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). 

The reduction of Fe(III) by carotenoids may have deleterious consequences. The reduced iron Fe(II) can react with hydrogen peroxide leading to the formation of hydroxyl radical, the most reactive free radical encountered in biological systems (Equation 15.10) ... 

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). 

This conclusion is partly true because superoxide is unable to abstract hydrogen atom even from the most active bisallylic positions of unsaturated compounds, while perhydroxyl radical abstracts H atom from linoleic, linolenic, and arachidonic fatty acids with the rate constants of 1-3 x 1031 mol-1 s-1 [24], However, the superoxide damaging activity does not originate from hydrogen atom abstraction reactions but from one-electron reduction processes, leading to the formation of hydroxyl radicals, peroxynitrite, etc, and in these reactions perhydroxyl cannot compete with superoxide. 

Of course, superoxide may reduce ferric to ferrous ions and by this again catalyze hydroxyl radical formation. Thus, the oxidation of ferrous ions could be just a futile cycle, leading to the same Fenton reaction. However, the competition between the reduction of ferric ions by superoxide and the oxidation of ferrous ions by dioxygen depends on the one-electron reduction potential of the [Fe3+/Fe2+] pair, which varied from +0.6 to —0.4 V in biological systems [173] and which is difficult to predict.)... 

There are various pathways for free radical-mediated processes in microsomes. Microsomes can stimulate free radical oxidation of various substrates through the formation of superoxide and hydroxyl radicals (the latter in the presence of iron) or by the direct interaction of chain electron carriers with these compounds. One-electron reduction of numerous electron acceptors has been extensively studied in connection with the conversion of quinone drugs and xenobiotics in microsomes into reactive semiquinones, capable of inducing damaging effects in humans. (In 1980s, the microsomal reduction of anticancer anthracycline antibiotics and related compounds were studied in detail due to possible mechanism of their cardiotoxic activity and was discussed by us earlier [37], It has been shown that semiquinones of... 

Hydroxy-10,12-octadecadienoic acid, which is formed by the reduction of 9-HPODE, was identified in the erythrocyte membrane phospholipid of diabetic patients [83]. It was suggested that this compound was formed as a result of glucose-induced oxidative stress in the reaction of hydroxyl radicals with linoleic acid. 

Several studies suggest that LA and DHLA form complexes with metals (Mn2+, Cu2+, Zn2+, Cd2+, and Fe2+/Fe3+) [215-218]. However, in detailed study of the interaction of LA and DHLA with iron ions no formation of iron LA complexes was found [217]. As vicinal dithiol, DHLA must undoubtedly form metal complexes. However, the high prooxidant activity of DHLA makes these complexes, especially with transition metals, highly unstable. Indeed, it was found that the Fe2+-DHLA complex is formed only under anerobic conditions and it is rapidly converted into Fe3+ DHLA complex, which in turn decomposed into Fe2+ and LA [217]. Because of this, the Fe3+/DHLA system may initiate the formation of hydroxyl radicals in the presence of hydrogen peroxide through the Fenton reaction. Lodge et al. [218] proposed that the formation of Cu2+ DHLA complex suppressed LDL oxidation. However, these authors also found that this complex is unstable and may be prooxidative due to the intracomplex reduction of Cu2+ ion. 

Spin trapping has been widely used for superoxide detection in various in vitro systems [16] this method was applied for the study of microsomal reduction of nitro compounds [17], microsomal lipid peroxidation [18], xanthine-xanthine oxidase system [19], etc. As DMPO-OOH adduct quickly decomposes yielding DMPO-OH, the latter is frequently used for the measurement of superoxide formation. (Discrimination between spin trapping of superoxide and hydroxyl radicals by DMPO can be performed by the application of hydroxyl radical scavengers, see below.) For example, Mansbach et al. [20] showed that the incubation of cultured enterocytes with menadione or nitrazepam in the presence of DMPO resulted in the formation of DMPO OH signal, which supposedly originated from the reduction of DMPO OOH adduct by glutathione peroxidase. 

Ionizing radiations (a, ft and y) react unselectively with all molecules and hence in the case of solutions they react mainly with the solvent. The changes induced in the solute due to radiolysis are consequences of the reactions of the solute with the intermediates formed by the radiolysis of the solvent. Radiolysis of water leads to formation of stable molecules H2 and H2O2, which mostly do not take part in further reactions, and to very reactive radicals the hydrated electron eaq, hydrogen atom H" and the hydroxyl radical OH" (equation 2). The first two radicals are reductants while the third one is an oxidant. However there are some reactions in which H atom reacts similarly to OH radical rather than to eaq, as e.g. abstraction of an hydrogen atom from alcohols, addition to a benzene ring or to an olefinic double bond, etc. 

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