Hydroperoxyl radicals HOO

Recently, perhydroxyl (hydroperoxyl) radical HOO has been wittily named by de Grey [23] as the forgotten radical. Although the concentration of perhydroxyl radical should be many times lower than that of the superoxide (about 1000 times smaller at pH 7.8), this radical always presents in solution, in equilibrium with superoxide ... 

There is not room here to discuss the detailed mechanisms by which exposure to radiation causes adverse responses. Much of the effects of radiation result from its interaction with water to produce active species that include superoxide (Oi), hydroxyl radical (HO-), hydroperoxyl radical (HOO), and hydrogen peroxide (H202). These species oxidize cellular macromolecules. When DNA is so affected, mutagenesis and carcinogenesis may result. Ionizing radiation can also interact with organic substances to produce a carbonium ion, such as +CH3, that can alkylate nitrogenous bases on DNA. 

The hydroperoxyl radical (HOO-) is the conjugate acid of superoxide ion (02 ) (equation 93) and constitutes about 1% of the 02 that is formed in aqueous systems at pH 7. Although the 0-0 bond of HOO- traditionally is viewed to be the same as the single a bond of HO-OH (A//dbe, 51 kcalmoH ), its bond energy (AHdbe) is about 85kcalmoH, which is more consistent with the 1.5 bond order of 02. However, HOO- is unstable in protic media (such as water and alcohols) and rapidly decomposes via het-erolytic and homolytic disproportionation (equations 94 and 95). ... 

The Me" transition metal ion can be oxidized further, for example, Fe(II), Cu(I), or Ti(III), and can activate oxidative cleavage of hydrogen peroxide, as in the Fenton mechanism. It was suggested that the hydroperoxyl radical, HOO, is the species that attacks the membrane. As will be clearly seen below, some of the transition metal ions may react directly with the sulfonic groups of the membrane, thus providing an additional degradation pathway. 

The last reaction is significant in that it is responsible for the disappearance of much atmospheric CO and because it produces the hydroperoxyl radical HOO. One of the major inorganic reactions of the hydroperoxyl radical is the oxidation of NO ... 

Hydroxyl radical (HO ), which reacts with some hydrocarbons at rates that are almost diffusion-controlled (meaning that if a molecule collides with a hydroxyl radical they react), is the predominant reactant in early stages of smog formation. Significant contributions are made by hydroperoxyl radical (HOO ) and O3 after smog formation is well under way. 

Work by Harbour, Chow and Bolton (1974) on the spin adducts of superoxide (or HOO )13 with nitrones paved the way for a number of investigations of superoxide and hydroperoxyl radical chemistry. Harbour and Bolton (1975) used DMPO to trap superoxide formed by spinach chloroplasts in the presence of 02. The signal strength was greatly enhanced when methylviologen was present, consistent with the hypothesis that this bis-pyridinium dication accepts an electron from the primary acceptor of photoprotein I, and then transfers it to molecular oxygen. 

The alkylperoxyl radical can be expected to react with sulfur amino acids by mechanisms similar to those for HOO- and HO-. Reactions of the hydroxyl and hydroperoxyl radicals have been more extensively studied because of their importance in radiation biochemistry. Thus, for cysteine, glutathione, and sulfhydryl proteins,... 

The hydroperojg l radieal, HOO% is an intermediate in some important chemical reactions. In addition to its production by the reactions discussed above, in polluted atmospheres, hydroperoxyl radical is made by the following two reactions, starting with photol5Tic dissociation of formaldehyde to produce a reactive formyl radical ... 

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