Radiation-induced reduction

An almost complete description of both OH radical-mediated and one-electron oxidation reactions of the thymine moiety (3) of DNA and related model compounds is now possible on the basis of detailed studies of the final oxidation products and their radical precursors. Relevant information on the structure and redox properties of transient pyrimidine radicals is available from pulse radiolysis measurements that in most cases have involved the use of the redox titration technique. It may be noted that most of the rate constants implicating the formation and the fate of the latter radicals have been also assessed. This has been completed by the isolation and characterization of the main thymine and thymidine hydroperoxides that arise from the fate of the pyrimidine radicals in aerated aqueous solutions. Information is also available on the formation of thymine hydroperoxides as the result of initial addition of radiation-induced reductive species including H" atom and solvated electron. 

The specificity of the radiation-induced reduction of metal ion precursors into metal atoms, which then coalesce into clusters, is attributable to strong reducing agents such as the... 

Among the nonnoble metals that can be synthesized by radiation-induced reduction in solution, nickel raises some difficulties because the atom formation and aggregation processes undergo the competition of oxidation reactions of highly reactive transients, such as monovalent Ni ion, Ni atom, and the very first nickel oligomers. Nevertheless, in... 

The possible formation of an alloyed or a core-shell cluster depends on the kinetic competition between, on one hand, the irreversible release of the metal ions displaced by the excess ions of the more noble metal after electron transfer and, on the other hand, the radiation-induced reduction of both metal ions, which depends on the dose rate (Table 5). The pulse radiolysis study of a mixed system [66] (Fig. 7) suggested that a very fast and total reduction by the means of a powerful and sudden irradiation delivered for instance by an electron beam (EB) should prevent the intermetal electron transfer and produce alloyed clusters. Indeed, such a decisive effect of the dose rate has been demonstrated [102]. However, the competition imposed by the metal displacement is more or less serious, because, depending on the couple of metals, the process may not occur [53], or, on the contrary, may last only hours, minutes, or even seconds [102]. 

Radiation Induced Reduction of Metal Ions in Frozen Aqueous Solutions... 

NishimotoS, Ide H, WadaT, KagiyaT (1983a) Radiation-induced hydroxylation of thymine promoted by electron-affinic compounds. Int J Radiat Biol 44 585-600 Nishimoto S, Ide H, Nakamichi K, Kagiya T (1983b) Radiation-induced reduction of thymidine in aqueous solution Isolation and characterization of a novel dimeric product. J Am Chem Soc 105 6740-6741... 

Nishimoto S, Ide H, Nakamichi K, Otsuki N, Kagiya T (1983c) Radiation-induced reductive conversion of 5-bromo-6-hydroxythymine to thymine promoted by transition metal salts in deaerated aqueous solution. Chem Lett 1441-1444... 

Nishimoto S, Ide H, Otsuki N, Nakamichi K, Kagiya T (1985) Radiation-induced reduction of thymine derivatives in aqueous solution. Part 4. Promoted transformation of thymine glycol into thymine by aromatic amines and low-valent transition metal salts. J Chem Soc Perkin Trans 2 1127-1134... 

The radiation-induced reduction of/ -toluenediazonium ions by methanol (Packer et al., 1971) involves a chain reaction propagating by (66) and (67). 

High-performance liquid chromatography (HPLC) has been used to analyze metronidazole [1435-1437], misonidazole [1309,1438], and other nitroimidazoles [1435, 1439] in body fluids or pharmaceutical dosage forms. HPLC analysis of effect of hypoxic-cell radiosensitizer misonidazole on the radiation-induced reduction of DNA bases (thymine, cytosine, and adenine) has been carried out [1440, 1441], HPLC was employed to characterize different nitroimidazoles [327, 366, 388,409, 450, 1442-1444], nitropyrazoles [246, 301], nitrothiazoles [366], l-aryl(hetaryl)-4-nitro-l,2,3-triazoles [601], nitrobenzimidazoles [707], nitrobenzofurazans [774, 1445-1449], nitrobenzotriazoles [1450],... 

Due to a kinetic competition between inter-metallic electron transfer and radiation-induced reduction of mixed metal ions, it was shown, thanks to radiolysis, that the core-shell or alloyed structure of a bimetallic nanoparticle depends not only on the redox potentials of the mixed systems but also on the metal ions reduction rate which is controlled by the dose rate. 

Experiments on the radiation-induced reduction of the functionalized fullerene car-boxylate, C6oC(COO-)2, in aqueous media were unsuccessful, despite the use of a concentration range that should guarantee rapid fullerene reduction (e.g., as found for Ceo-y-CD, C6o-surfactant, and C6o-vesicle) [89, 90]. In particular, the absorption at ca 700 nm, attributable to the initially generated hydrated electron, remained... 

Marignier J.-L., Belloni J., Delcourt M.-O., Chevalier J.-P, New microaggregates of non noble metals and alloys prepared by radiation-induced reduction. Nature, 1985,317,344-345. Belloni J., Marignier J.-L., Delcourt M.-O., Minana M., Non noble metal catalytic microaggregates, a method for their preparation and their application in the catalysis ofthe photoreduction of water., US Pat. 1986, 4,629,709. Belloni J., Marignier J.-L., Delcourt M.-O., Minana M., New mono or multimetal microaggregates, a method for their preparation and their application in the catalysis of the photoreduction of water, US Patent 1987,4745094. 

MARIGNIER, J. L., BELLONI, J., DELCOURT, M. O., CHEVALIER, J. P., Microaggregates of Non-Noble Metals and Bimetallic Alloys Prepared By Radiation-Induced Reduction , Nature 1985, 317, 344-345. 

Reduction Typical fullerene solvents are organics of low or medium polarity, such as toluene, benzonitrile, chlorinated hydrocarbons and CS2. In contrast, fullerenes are poorly soluble in polar solvents, including various alcohols. In polar solvents a spontaneous and irreversible cluster formation is noticed, yielding aggregates of various sizes. In aqueous solutions, [60]fullerene and its higher homologous, are practicable insoluble. It should be noted that most of the listed solvents cannot per se be employed for radiation-induced reduction studies. 

Tabic 1 Rate Constant for the Radiation-Induced Reduction of 50 in Organic Solvents (12,13)... 

The atoms are produced in deaerated solution by radiation-induced reduction of the metal ion precursors. The species solvated electrons e, ", and H atoms arising from the radiolysis of water are strong reducing agents (E°(H20/e3 ) = - 2.87 V he E°(H /H) = - 2.3 V he- They easily reduce metal ions up to the zero-valent state ... 

Metal clusters supported on solid supports are easier to use as catalysts. However, the mechanism of their action is inferred mostly indirectly from their efficiency. Multimetallic clusters are known to present enhanced catalytic properties relative to pure metals, specially when the catalyzed reaction process includes several steps. The method of radiation-induced reduction provides a powerful way to obtain homodisperse, small and alloyed clusters. 

Nichipor, H., Dashouk, E., Yermakov A computer simulation of the kinetics of high temperature radiation induced reduction of NO. Radiat. Phys. Chem. 54(3), 307-315 (1999)... 

Jackson, E. M., Weaver, B. D., Summers, G. R, Shapiro, R, and Burke, E. A. 1995a. Radiation-induced reduction and pair breaking in high-T,. superconductors. Phys. Rev. Lett. 74(15) 3033-3036. 

Synthesis of Metallic NPs by Radiation-Induced Reduction and Their Applications.454... 

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