Primary radiation induced products

This review has spanned many years of work devoted to the attempts to understand the effects of radiation damage to DNA. The emphasis has been on the use of EPR/ENDOR spectroscopy to reveal the structures of the primary radiation induced products in DNA. ENDOR was invented before 1960, but it took quite some time before this technique was used to study problems in radiation biology. The basic reason is that complex equipment had to be designed and tested that permits the irradiation and examination of small single crystals at helium temperatures. The apparatus was only completed around 1975 by Bernhard and co-workers in Rochester, and by Huttermann and co-workers in Regensburg. 

In the section on model compounds there are discussions about thymine, cytosine and guanine nucleotides. To date there have been no detailed EPR/ENDOR experiments on an adenine nucleotide because of the inability to grow good single crystals. The structure of 5 -dAMP hexahydrate is known from a crystal structure study [113]. It would be very interesting to analyze the primary radiation induced products in 5 -dAMP at helium temperature to see if there is actually spin density on both the phosphate and the adenine base for the oxidation product as reported in the theoretical study by Hou et al. [104],... 

Before discussing the types of radicals actually observed in DNA, it is important to first summarize the work on model systems. These include studies of irradiated nucleosides and nucleotides from which one can usually determine the structures of the free radical products. The emphasis here will be to summarize the results on EPR/ENDOR studies of irradiated DNA bases at low temperatures in efforts to study the primary radiation-induced defects. 

Several recent papers have reported Density Functional Theory (DFT) calculations on the primary oxidation and reduction products observed in irradiated single crystals of the common nucleobases Thymine, Cytosine, Guanine, and Adenine. The theoretical calculations include estimates of spin densities and isotropic and anisotropic hyperfine couplings which can be compared with experimental results (obtained from detailed EPR/ENDOR experiments). In many cases the theoretical and experimental results agree rather well. In other cases there are discrepancies between the theoretical and experimental results. Herein the successes and failures of using DFT to calculate spin densities and hyperfine couplings of the primary radiation induced free radicals observed in the nucleobases will be discussed. 

The areas where the use of the track model has been found particularly expedient are (1) LET variation of product yields in the radiation chemistry of liquids (2) the yield of escaped ions and its variation with particle LET (3) energy loss in primary excitations and ionizations (4) radiation-induced luminescence and (5) particle identification. 

In 2002, Kanno and Taylor successfully developed a simple one-pot procedure using MnOi/NHiOMe-HCl for the conversion of activated primary alcohols into O-methyl oximes (Scheme 11). They also developed a modification using Amberlyst 15-supported alkoxylamines, which can be employed to prepare other types of 0-aUcyl oximes as well as the parent hydroxylamines. This latter procedure has been used as the cornerstone of an efficient synthesis of the antifungal natural product citaldoxime 11 (Scheme 11). Citaldoxime is an antifungal natural product first obtained as a radiation-induced stress metabolite of Citrus sinensis , and later isolated from the roots of several different citrus plants. ... 

The synthesis and characterization of the hydrogenation product of polystyrene (PS), poly(cyclohexylethylene) (PCHE), have been the subject of persistent research efforts. The earliest published report on this material dates to 1929, with new work appearing steadily up to the present. The primary motivation for saturating the phenyl rings in polystyrene is the potential to improve the stability of polystyrene with respect to oxidative and radiation-induced degradation. It has now also been established that the hydrogenation of polystyrene leads to a substantial increase in the glass transition temperature (Tg). 

The intense primary y radiation due to nuclear fission, the secondary y radiation emitted by the fission and activation products and the radiation from the fission products give rise to radiation-induced chemical reactions. The most important reaction is the radiation decomposition of water in water-cooled reactors, leading to the formation of H2, H2O2 and O2. Many substances dissolved in the water influence the formation of H2 (Fig. 11.18). In most closed coolant systems equipment for... 

Origin of different nature of both kinds of primary products of radiolysis was found in different size of spurs, as the centers of radiation induced chemical reactions were called. The... 

Superoxide dismutases are able to protect cells from damaging effects caused by radiation 3i8-32o> reaction was proposed, in which SOD removes reactive oxygen species, generated by the irradiation and thus preventing the organisms from an attack by primary radicals or their reaction products, respectively Other reports on the radioprotective effect include the induction of superoxide dismutase in irradiated whole organs However, a radiation-induced SOD synthesis was not... 

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