title: Qualitative and quantitative analyses of the decomposition products that arise from the exposure of thymine to monochromatic ultrasoft X rays and 60Co gamma rays in the solid state.
abstract: HPLC analyses of condensed thymine irradiated with monochromatic synchrotron ultrasoft X rays in the energy region around nitrogen and oxygen K-shell edges were performed. Cobalt-60 gamma rays were used as a reference radiation. The radiation chemical dose response of each separated thymine decomposition product was also determined. Uracil (U), 5-(hydroxymethyl)uracil (HMU), 5,6-dihydrothymine (DHT), 5-formyluracil (foU) and four main unknown products were found in the HPLC chromatogram of the sample irradiated with ultrasoft X rays in vacuo. Similar spectra of the products were also found in the gamma-ray experiment; however, some unknown products that appeared after elution of the thymine peak were significantly larger than those in the ultrasoft X- ray experiment. This result indicates the difference in radiation quality. The G value of DHT produced by gamma radiation was 10 times larger than those produced by the ultrasoft X- ray photons with energies of 395 and 407 eV corresponding to below and on the nitrogen K-shell edge, respectively. This result suggests that the differences in the photon energy and/ or in the energy spectra of the secondary electron between ultrasoft X rays and gamma rays are causing differences in the process of the radiation chemistry. Moreover, the yields of all the thymine decomposition products induced by 538 eV photons (oxygen K-shell edge) were significantly smaller than those induced by photons around the nitrogen K-shell edge. The K-shell excitation of oxygen in thymine may efficiently promote the production of small thymine fragments susceptible to desorption from the sample.
authors.affiliation: Radiation Risk Laboratory, Department of Health Physics, Japan Atomic Energy Research Institute, 2-4 Shirakatashirane, Tokai, Naka, Ibaraki 319-1195, Japan. kakamatu@riskest.tokai.jaeri.go.jp
authors.forename: Ken
authors.initials: K
authors.lastname: Akamatsu
authors.forename: Kentaro
authors.initials: K
authors.lastname: Fujii
authors.forename: Akinari
authors.initials: A
authors.lastname: Yokoya
mesh_terms: D002138:Calibration; D002851:Chromatography, High Pressure Liquid; D003037:Cobalt Radioisotopes; D004247:DNA / Q000528:radiation effects*; D004249:DNA Damage; D004260:DNA Repair; D004307:Dose-Response Relationship, Radiation; D005720:Gamma Rays; D008956:Models, Chemical; D009584:Nitrogen / Q000737:chemistry; D010100:Oxygen / Q000378:metabolism; D010432:Pentoxyl / Q000031:analogs & derivatives* / Q000032:analysis; D017785:Photons; D013053:Spectrophotometry / Q000379:methods; D017356:Synchrotrons; D013941:Thymine / Q000031:analogs & derivatives* / Q000032:analysis / Q000737:chemistry; D013997:Time Factors; D014498:Uracil / Q000031:analogs & derivatives* / Q000032:analysis / Q000737:chemistry; D014965:X-Rays
chemical_list: D003037:Cobalt Radioisotopes; C007777:5-formyluracil; C008055:5-hydroxymethyluracil; D014498:Uracil; C042836:5,6-dihydrothymine; D010432:Pentoxyl; D004247:DNA; D009584:Nitrogen; D013941:Thymine; D010100:Oxygen