Fenton reaction structure

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). 

Lipid peroxidation is probably the most studied oxidative process in biological systems. At present, Medline cites about 30,000 publications on lipid peroxidation, but the total number of studies must be much more because Medline does not include publications before 1970. Most of the earlier studies are in vitro studies, in which lipid peroxidation is carried out in lipid suspensions, cellular organelles (mitochondria and microsomes), or cells and initiated by simple chemical free radical-produced systems (the Fenton reaction, ferrous ions + ascorbate, carbon tetrachloride, etc). In these in vitro experiments reaction products (mainly, malon-dialdehyde (MDA), lipid hydroperoxides, and diene conjugates) were analyzed by physicochemical methods (optical spectroscopy and later on, HPLC and EPR spectroscopies). These studies gave the important information concerning the mechanism of lipid peroxidation, the structures of reaction products, etc. 

The Fenton reaction may also be used site-specifically, e.g. for the sequence-specific cleavage of DNA with the help of benzopyridoindole-EDTA intercalator forming triple-helical structures (Marchand et al. 2000). 

Ruppert, G., Bauer, R., Heisler, G., Novalic, S. (1993) Mineralization of cyclic organic water contaminants by the photo-Fenton reaction-influence of structure and substituents. Chemosphere 27(8), 1339-1347. 

Szulbinski WS. Fenton reaction of iron chelates involving polyazacyclononane. The ligand structure effect. Pol J Chem 2000 74 109-124. 

Parra S, Guasaquillo I, Enea O, et al. Abatement of an azo dye on structured C-nafion/ Fe-ion surfaces by photo-Fenton reactions leading to carboxylate intermediates with a remarkable biodegradability increase of the treated solution. J Phys Chem B 2003 107 ... 

Hydroxyl radical may hydroxylate tyrosine to 3,4-dihydroxyphenylalanine (DOPA). DOPAs are the main residues corresponding to protein-bound reducing moieties able to reduce cytochrome c, metal ions, nitro tetrazolium, blue and other substrates (S32). Reduction of metal ions and metalloproteins by protein-bound DOPA may propagate radical reactions by redox cycling of iron and copper ions which may participate in the Fenton reaction (G9). Abstraction of electron (by OH or peroxyl or alkoxyl radicals) leads to the formation of the tyrosyl radical, which is relatively stable due to the resonance effect (interconversion among several equivalent resonant structures). Reaction between two protein-bound tyrosyl radicals may lead to formation of a bityrosine residue which can cross-link proteins. The tyrosyl radical may also react with superoxide, forming tyrosine peroxide (W13) (see sect. 2.6). 

These footprinting analyses, based on enzymic and chemical digestion, are now widely used to define DNA (and RNA) and their complexes with various ligands. Recently active radical probes have been used as footprinting agents in protection assays in a variety of systems (e.g., Tullius and Dombroski, 1986 Chalepakis and Beato, 1989 Hayes and Tullius, 1989 Schickor et al., 1990). Such probes rely on active radical intermediates, most likely hydroxyl radicals, released by Fe(II) in the presence of an electron donor, probably via a Fenton reaction. In addition, hydroxyl radicals also appear to react with DNA in a conformation-specific manner which may allow some prediction of DNA secondary structure (see Burkhoft and Tullius, 1987 Zorbas et al., 1989 Lu et al., 1990). 

Hydroxyl radical induced strand scission is used for probing of the ribose moiety. The probe is insensitive to local conformations and not useful for detailed structural predictions however, the nonselective reactivity and small size makes hydroxyl radical probing a powerful approach for footprinting proteins on RNA. Recently methods have been developed where the hydroxyl radicals are generated locally by attaching the iron ion, which catalyses the radical formation in the Fenton reaction, to specific sites on RNA binding proteins. RNA located in the neighborhood of the tethered Fe2+ will then be modified selectively.7,8... 

The study of Fenton-like reactions is significant for biological systems. Csapski et al. studied the Fenton reaction in the presence of [Cu(I)(phenanthroline)2] and DNA 102). They showed that the Cu(I) complex binds to DNA, the double helical structure of which was degraded by either the OH radical or [Cu(III)(phenanthroline)2], which is formed via the oxidation of [Cu(IXphenanthroline)2] by H2O2. 

Several studies indicate that catechins and procyanidins are powerful scavengers of ROS. Some findings regarding the antioxidant activity of proanthocyanidins are listed in Ref. [100]. Other antioxidant mechanisms are the chelation of transition metals, as well as the mediation and inhibition of enzymes. The metal-chelating activity of proanthocyanidins is thought to be due to their capacity to reduce the concentration, and thus the oxidative activity, of hydroxyl radicals formed by Fenton reaction catalyzed by iron or copper. Flavanols also influence oxidative stress via enzyme modification and modulation of cell signaling pathways the extent of the effect relies greatly on flavanol structure-related protein reactivity [101]. 

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