Hydroxyl radical radiolysis product

Pulse radiolysis results (74) have led other workers to conclude that adsorbed OH radicals (surface trapped holes) are the principal oxidants, whereas free hydroxyl radicals probably play a minor role, if any. Because the OH radical reacts with HO2 at a diffusion controlled rate, the reverse reaction, that is desorption of OH to the solution, seems highly unlikely. The surface trapped hole, as defined by equation 18, accounts for most of the observations which had previously led to the suggestion of OH radical oxidation. The formation of H2O2 and the observations of hydroxylated intermediate products could all occur via... 

The attack on the aromatic nucleus by hydroxyl radicals is probably analogous to that by phenyl and methyl radicals, Eq. (34a,b). Evidence that the first step is the addition of hydroxyl radical to benzene, rather than abstraction of a hydrogen atom, has recently been adduced from a study of the radiolysis of water-benzene mixtures. The familiar addition complex may undergo two reactions to form the phenolic and dimeric products respectively, Eq. (34a,b). Alternative mechanisms for the formation of the dimer have been formulated, but in view of the lack of experimental evidence for any of the mechanisms further discussion of this problem is not justified. 

Owing to the reactions of the initial primary radiolysis products among themselves, as in Eqs. (11-58)—(11-62), it is usually necessary to add another reagent to remove the unwanted ones. For example, to study reactions of e alone, one must work in neutral or basic solution to avoid its destruction by HsO+ (see Problem 11-12). Also, hydroxyl radicals and hydrogen atoms are removed from the system by prior addition of terf-butyl alcohol to give noninterfering products,... 

In a pulse radiolysis study of solutions of CdS of different particle size, the rate of reaction of the OH radical with the colloidal particles was studied as well as the absorption spectrum of the products The hydroxyl radical reacts on its first encounter... 

Radicals can react with bases via hydrogen atom abstraction or, more commonly, by addition to the pi bonds in the heterocyclic nucleobases (Scheme 8.1). These reactions have been extensively studied in the context of hydroxyl radical (HO ), which is generated by y-radiolysis of water. When DNA is exposed to the hydroxyl radical, approximately 80% of the reactions occur at the bases. Many base damage products arising from the reaction hydroxyl radical with DNA have been characterized (Fig. 8.2). ... 

The gamma-radiation-induced oxidation of 2-propanol has been investigated. Acetone and hydrogen peroxide are the principal products and arise via a chain reaction in aqueous acid solutions at high concentrations of 2-propanol. In neutral solutions of 2-propanol and in solutions of methanol and ethanol, no such chain reactions are observed. The reasons for this are discussed along with the implications of the results for the hydroxyl radical yield in water radiolysis. 

The production of ethylene from methional (3-thiomethylpropanal) was induced by the oxidation of xanthine by dioxygen catalysed by xanthine oxidase The second-order rate constant for the reaction of hydroxyl radicals with methional was estimated by pulse radiolysis to amount to 8.2 x lO s while the superoxide anion reacted more slowly The short lag period of the ethylene production induced by the oxidation of xanthine could be overcome by the addition of small amounts of hydrogen peroxide. The reaction was inhibited by SOD or by catalase, and by scavengers of hydroxyl radicals, so that the Haber-Weiss reaction was implicated... 

Because hydroxyl radicals have indiscriminate reactivity, they can react with almost all types of organic and inorganic compounds. Most aromatic compounds undergo radical attack on the aromatic ring in a manner similar to that of benzene systems. The products and the rate constants for hydroxyl radical attack on aromatic compounds are listed in Table 5.11. The data were obtained from the pulse radiolysis studies (Buxton et al., 1988). 

Owen RW, Wimonwatwatee T, Spiegelhalder B, Bartsch H (1996) A high performance liquid chromatography system for quantification of hydroxyl radical formation by determination of dihydroxy benzoic acids. Eur J Cancer Prevention 5 233-240 Pan X-M, Bastian E, von Sonntag C (1988) The reactions of hydroxyl radicals with 1,4- and 1,3-cyclohexadiene in aqueous solution. A pulse radiolysis and product study. Z Naturforsch 43b 1201—1205... 

Janik I, Ulanski P, Flildenbrand K, Rosiak JM, von Sonntag C (2000) Hydroxyl-radical-induced reactions of poly(vinyl methyl ether) a pulse radiolysis, EPR and product study in deoxygenated and oxygenated aqueous solutions. J Chem Soc Perkin Trans 2 2041-2048 Jayson GG, Stirling DA, Swallow AJ (1971) Pulse- and X-radiolysis of 2-mercaptoethanol in aqueous solution. Int J Radiat Biol 19 143-156... 

Bansal KM, Patterson LK, Schuler RH (1972) Production of halide ion in the radiolysis of aqueous solutions of the 5-halouracils. J Phys Chem 76 2386-2392 Barnes JP, Bernhard WA (1994) One-electron-reduced cytosine in acidic glasses conformational states before and after proton transfer. J Phys Chem 98 887-893 Barvian MR, Greenberg MM (1992) Independent generation of the major adduct of hydroxyl radical and thymidine. Examination of intramolecular hydrogen atom transfer in competition with thiol trapping.Tetrahedron Lett 33 6057-6060... 

SCHEME 4.1 Schematics of radiolysis and reducing species. As a result of ionization of the water molecule, hydroxyl radicals and hydrated electrons are formed. The final radiolytic yield depends on the secondary reactions in spurs and on the presence of other compounds. See Refs 25,26,190, and 191 for the detailed discussion and references. Solvated electrons are mobile enough to escape spurs and to react with the heme protein complexes even at 77K. All other reactive products of radiolysis are immobilized in the solid solvent matrix, or trapped by radical quenchers. 

The radiolysis of water produces hydrated electrons (e q, G = 2.9), hydrogen atoms (G = 0.55) and hydroxyl radicals (G = 2.8) which react with the solute molecules. In addition, the radiolysis of aqueous solutions also yields H202 (G = 0.75), gaseous hydrogen (G = 0.45) and hydronium ions (H30+, G = 2.9). In most cases the molecular products do not interfere with the reactions of the radicals. To study the reaction of one radical with the solute without interference from other radicals, scavengers for the other radicals should be added7-10. 

The facile oxidation of organic substrates in the presence of a Fenton system is believed to be due to the production of the hydroxyl radical, as mentioned earlier. Consequently, a number of techniques have been employed to generate the species independently of any iron centres. Two techniques worthy of a mention are photolysis and radiolysis. Photolytic activation can be used to cause homolysis of the peroxygen bond because peroxides have a relatively broad absorption band above 300 nm (Figure 2.13).29... 

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