Fenton-type reactions

Consequently, the antioxidant activity of GA in biological systems is still an unresolved issue, and therefore it requires a more direct knowledge of the antioxidant capacity of GA that can be obtained by in vitro experiments against different types of oxidant species. The total antioxidant activity of a compound or substance is associated with several processes that include the scavenging of free radical species (eg. HO, ROO ), ability to quench reactive excited states (triplet excited states and/ or oxygen singlet molecular 1O2), and/or sequester of metal ions (Fe2+, Cu2+) to avoid the formation of HO by Fenton type reactions. In the following sections, we will discuss the in vitro antioxidant capacity of GA for some of these processes. 

Destruction of chromophoric and nonchromophoric pollutants in pulp and paper effluents may be achieved by advanced oxidation methods such as photocatalysis, photo-oxidation using hydrogen peroxide (H202)/UV or ozone (Osj/UV systems, Fenton-type reactions, wet oxidation, and by employing strong oxidants such as ozone. 

Rodriguez, J. Contreras, D. Parra, C. Freer, J. Baeza, J. Duran, N. Pulp mill effluent treatment by Fenton-type reaction catalyzed by iron complexes. Water Sci. Technol. 1999, 40 (11-12), 351-355. 

Hydroxymethanesulfonic acid (HMSA) is a complex formed from formaldehyde and S(IV). It has been detected in atmospheric liquids (i.e., rain and snow). The complex has high resistance to oxidation by oxygen as well as ferric ions and oxygen. Martin et al. (1989) first studied the oxidation of HMSA. Graedel et al. (1986) proposed that Fenton-type reactions are possible in atmospheric liquid water. 

Ferryl species are well-documented and play a major role in P-450-type systems. In general, Fe(II)-containing enzymes try to avoid the formation of -OH in their reaction with H202. A similar situation seems to prevail in the case of Fe2+ complexed by DTPA (Rahhhal and Richter 1988), and one has to be keep in mind when discussing Fenton and Fenton-type reactions that complexation and possibly also the pH may shift the Fenton reaction from OH to Fe(IV) as the reactive intermediate. 

Table 2.3. Rate constants of Fenton-type reactions. For further details see Goldstein et al. (1993) and Koppenol (1994) ...

Gilbert BC, Harrington G, Scrivens G, Silvester S (1997) EPR studies of Fenton-type reactions in copper-peroxide. In Minisci F (ed) Free radicals in biology and environment. Kluwer, Dordrecht, pp 49-62... 

These dramatic discrepancies mentioned above may also be of some relevance in biological systems, where these probes have been widely used (see below). If OH were formed in biological systems by Fenton-type reactions, these probe molecules could strongly overestimate (or underestimate) the OH production in these systems. 

Mundy CJ, Colvin ME, Quong AA (2002) Irradiated guanine a Car-Parinello molecular dynamics study of dehydrogenation in the presence of an OH radical. J Phys Chem A 106 10063-10071 Murata-Kamiya N, Kamiya H, Muraoka M, Kaji H, Kasai H (1998) Comparison of oxidation products from DNA components byy-irradiation and Fenton-type reactions. J Radiat Res 38 121-131 Nabben FJ, van der Stroom HA, Loman H (1983) Inactivation of biologically active DNA by isopropanol and formate radicals. Int J Radiat Biol 43 495-504 Nakashima M, Hayon E (1979) Rates of reaction of inorganic phosphate radicals in solution. J Phys Chem 74 3290-3291... 

With Cu2+, H2O2 and ascorbate, a Fenton-type reaction is initiated. In the presence of DNA, the copper is bound to DNA and an addition of OH scavengers such as DMSO suppresses this reaction only marginally as shown with a polyly-sine-bound fluorescent OH probe (Makrigiorgos 1999). 

It is noteworthy that in the presence of H202 not only iron and copper, but also nickel and cobalt induce DNA damage via a Fenton-type reaction (Nacker-dien et al. 1991). 

Although soluble guanylyl cyclase is commonly considered to be the only primary chemical receptor for NO, heme proteins can react with NO in a variety of oxidation states. For example, NO can complex at near diffusion control with hypervalent iron states formed in Fenton-type reactions (63-65). 

Puppo A. Effect of flavenoids on hydroxyl radical formation by Fenton-type reactions influence of the iron chelator. Phytochemistry 1992 31 85-88. 

Fig. 87 Copper-catalyzed synthesis of alkoxyamines by a Fenton-type reaction...

Fujihira M, Satoh Y, OsaT. Heterogeneous photocatalytic reactions on semiconductor materials. III. Effect of pH and Cu2+ ions on the photo-Fenton type reaction. Bull Chem Soc Jpn 1982 55 666-71. 

In the absence of strong chelating agents, lactoferrin, transferrin and ceruloplasmin do not promote hydroxyl-radical production at pH 7.4 [158,159], which is consistent with their protecting role at sites of inflammation. At present, the possible involvement of ferritin and that of the iron-transit pool in Fenton-type reactions cannot be excluded, and this may be of great importance in some pathophysiological situations such as post-ischemic reperfusion of tissues. 

Fenton type reactions are particularly important in atmospheric waters [10], which are acidic. An additional source of hydroxyl radical that is significant only when using UV light of wavelength shorter than about 300 nm (i.e. in the case of water treatment using UV lamps, but not for sunlight) is represented by photolysis of hydrogen peroxide ... 

As stressed throughout this book, lipid oxidation is one of the more important biological radical processes. Being a chain reaction, only low concentrations of initiators are required, and it has been argued that an important initiator may be a Fenton type reaction. 

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