Hydroxyl radical nitric acid

Polyphenols can act as antioxidants by a number of potential pathways. The most important is likely to be by free radical scavenging, in which the polyphenol can break the radical chain reaction. Polyphenols are effective antioxidants in a wide range of chemical oxidation systems, being capable of scavenging peroxyl radicals, alkyl peroxyl radicals, superoxide, hydroxyl radicals, nitric oxide and peroxynitrate in aqueous and organic environments [121]. This activity is due to the ability of donating an H atom from an aromatic hydroxyl group to a free radical, and the major ability of an aromatic structure to support an unpaired electron by delocalization around the 7i-electron system. Phenolic acids... 

Methionine also represents an important and early target for oxidation, where end products include the sulphoxide and the sulphone. In addition to the hydroxyl radical, hypochlorous acid, nitric oxide and singlet oxygen are all capable of eliciting this change. 

Free radicals produced in vivo include superoxide, the hydroxyl radical, nitric oxide, oxygen-centered organic radicals such as peroxyl and alkoxyl radicals, and sulfur-centered thiyl radicals. Other oxygen-containing reactive species that are not radicals are also formed. These include hydrogen peroxide, peroxynitrite, and hypochlorous acid. While these are not radical species, they are actually or potentially damaging oxidants. The collective term ROS is often used to describe both radical and nonradical species. 

Peroxonitrous acid can decompose by two pathways isomerization to nitric acid, and dissociation into the hydroxyl radical and nitrogen dioxide. 

Mahoney, L.R (1970). Evidence for the formation of hydroxyl radicals in the isomerisation of pemittous acid to nitric acid in aqueous solutions. J. Am. Chem. Soc. 92, 5262-5263. 

Peroxynitrite easily oxidizes nonprotein and protein thiyl groups. In 1991, Radi et al. [102] have shown that peroxynitrite efficiently oxidizes cysteine to its disulfide form and bovine serum albumin (BSA) to some derivative of sulfenic acid supposedly via the decomposition to nitric dioxide and hydroxyl radicals. Pryor et al. [124] suggested that the oxidation of methionine and its analog 2-keto-4-thiomethylbutanic acid occurred by two competing mechanisms, namely, the second-order reaction of sulfide formation and the one-electron... 

It should be noted that Reaction (4) is not a one-stage process.) Both free radical N02 and highly reactive peroxynitrite are the initiators of lipid peroxidation although the elementary stages of initiation by these compounds are not fully understood. (Crow et al. [45] suggested that trans-ONOO is protonated into trans peroxynitrous acid, which is isomerized into the unstable cis form. The latter is easily decomposed to form hydroxyl radical.) Another possible mechanism of prooxidant activity of nitric oxide is the modification of unsaturated fatty acids and lipids through the formation of active nitrated lipid derivatives. 

Finally, nitrogen dioxide is oxidized to nitric acid in a number of ways. For example, it may react with a hydroxyl radical, producing the acid ... 

Brown, S. S., R. K. Talukdar, and A. R. Ravishankara, Reconsideration of the Rate Constant for the Reaction of Hydroxyl Radicals with Nitric Acid, J. Phys. Chem. A 103, 3031-3037 (1999b). 

The UV spectrum of nitrite at acidic pH is unusual. Nitrite at neutral to alkaline pH has a single peak at 356 nm, which is converted to a series of multiple peaks at acidic pH (Fig. 15). Normally, a UV peak is broadened by a combination of vibrational and more closely spaced rotational quantum states. However, light in the near UV region can separate nitrous acid into hydroxyl radical and nitric oxide. 

Fig. 7.3 Reactions showing the generation of ROS during lipid peroxidation and oxidative stress. Hydroxyl radical ( OH) lipid radical ( lipid), peroxyl radical (lipid-OO ) lipid peroxide (lipid-OOH) nitric oxide ( NO) nitrogen dioxide (N02) peroxynitrite anion (ONOO-) hypochlorous acid (HOC1), and hydrogen peroxide (H202)...

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