Radical Fenton reaction

There is a more serious problem for the [Fe(H20)6]2+ complex in acidic medium, which needs more efficient oxidants than 02. In such a case H202 is sufficient for regenerating Fem with simultaneous formation of hydroxyl radicals (Fenton reaction) ... 

Minisci, Galli and co-workers have studied a variety of radical reactions which result in the formation of organic azides. These processes commonly involve the interaction of an organic peroxide, an alkene, and azide ion in the presence of a ferrous-ferric redox system. The initial step is the reduction of the peroxide by Fe " " to form a free alkoxy radical (Fenton reaction, equation 104). 

Cleavage of H2O2 by Fe " ions generates OH radicals (Fenton reaction) (Scheme 1), which are the most reactive ROS species [113]. 

Floyd, R.A. Zs-Nagy (1984). Formation of long lived hydroxyl free radical adducts of proline and hydroxyproline in a Fenton reaction. Biochimica Bio-physica Acta, 790, 94-7. 

As strong metal ion chelators due to their catechol structure, tea flavonoids are able to bind and thus decrease the level of free cellular ferric and ferrous ions, which are required for the generation of reactive oxygen radicals via the Fenton reaction (Yang and Wang, 1993). 

Humans Hydrogen peroxide has been used as an enema or as a cleaning agent for endoscopes and may cause mucosal damage when applied to the surface of the gut wall. Hydrogen peroxide enteritis can mimic an acute ulcerative, ischaemic or pseudomembranous colitis, and ranges from a reversible, clinically inapparent process to an acute, toxic fulminant colitis associated with perforation and death (Bilotta and Waye, 1989). It is conceivable that anecdotal reports of exacerbation of IBD by iron supplementation (Kawai et al. 1992) are mediated by hydroxyl radical production by the Fenton reaction. 

The antiulcer agent rebamipide ((2-(4-chlorobenzoy-lamino)-3-[2(lH)-quinolinon-4-yl]propionic acid) dose-dependently decreased hydroxyl radical signal generated by the Fenton reaction in an e.s.r. study. Rebamipide is active as a hydroxyl radical scavenger and inhibitor of superoxide production by neutrophils (Yoshikawa etal., 1993). 

Spin trapping EPR technique and UV-Vis spectroscopy have been used (Polyakov et al. 2001b) to determine the relative rates of reaction of carotenoids with OOH radicals formed by the Fenton reaction in organic solvents. The Fe3+ species generated via the Fenton reaction... 

FIGURE 9.1 EPR spectra of spin adducts recorded during the Fenton reaction in DMSO at different H202 concentrations ([FeClJ = 1 mM), (1), (2), and (3) are OH, OOH, and CH3 radicals, respectively. 

Polyakov, N. E., T. V. Leshina et al. (2001c). Carotenoids as scavengers of free radicals in a Fenton reaction, antioxidants or pro-oxidants. Free Rad. Biol. Med. 31 398-404. 

In the presence of trace amounts of iron, superoxide can then reduce Fe3+ to molecular oxygen and Fe2+. The sum of this reaction (equation 2) plus the Fenton reaction (equation 1) produces molecular oxygen plus hydroxyl radical, plus hydroxyl anion from superoxide and hydrogen peroxide, in the presence of catalytic amounts of iron - the so-called Haber-Weiss reaction (equation 3) (Haber and Weiss, 1934). 

Ferrous iron, by its reaction with hydrogen peroxide in the Fenton reaction, can yield the toxic hydroxyl radical, OH, which will further potentiate oxygen toxicity. 

Reactions of Hydroxyl and Hydroxyl-Like Radicals Produced by the Fenton Reaction with Nucleic Acids... 

It has been thought for a long time that the major route from superoxide to reactive free radicals is the superoxide-dependent Fenton reaction (Reactions 1 and 2) ... 

For a long time one question remained unanswered the efficiency of the Fenton reaction as the in vivo producer of hydroxyl radicals due to the low rate of Reaction (2) (the rate constant is equal to 42.11 mol 1 s 1 [18]). It is known that under in vitro conditions the rate of Fenton reaction can be sharply enhanced by chelators such as EDTA, but for a long time no effective in vivo chelators have been found. From this point of view new findings obtained by Chen and Schopfer [19] who found that peroxidases catalyze hydroxyl radical formation in plants deserve consideration. These authors showed that horseradish peroxidase (HRP) compound III is a catalyst of the Fenton reaction and that this compound is one to two orders of magnitude more active than Fe EDTA. 

The rate constant for Reaction (3) is in the range of 108 to 1091 mol-1s-1 [20]. Therefore, Reactions (3) and (4) may significantly enhance the concentration of ferrous ions and make Fenton reaction a better competitor with the peroxynitrite-inducible damage [21]. The formation of hydroxyl radicals in the reaction of superoxide with mitochondrial aconitase has... 

The formation of hydroxyl or hydroxyl-like radicals in the reaction of ferrous ions with hydrogen peroxide (the Fenton reaction) is usually considered as a main mechanism of free radical damage. However, Qian and Buettner [172] have recently proposed that at high [02]/ [H202] ratios the formation of reactive oxygen species such as perferryl ion at the oxidation of ferrous ions by dioxygen (Reaction 46) may compete with the Fenton reaction (2) ... 

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