ESR and ENDOR of free radicals in X-irradiated barbituric acid |
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| Affiliation: | 1. School of Chemistry, EaStCHEM and Centre of Magnetic Resonance, University of St Andrews, St Andrews KY16 9ST, United Kingdom;2. Energy Safety Research Institute, Swansea University, Fabian Way, Swansea, SA1 8EN, United Kingdom;1. Department of Pharmaceutical Engineering, Department of Biomedical Engineering, Jiangsu Key Laboratory of Drug Screening, China Pharmaceutical University, Nanjing 210009, PR China;2. Liver Cancer Institute, Zhongshan Hospital, Fudan University, Key Laboratory of Carcinogenesis and Cancer Invasion, Ministry of Education, Key Laboratory of Epigenetics and Metabolism, Ministry of Science and Technology, and Institutes of Biomedical Sciences, Fudan University, Shanghai 200032, PR China;3. Department of Medicinal Chemistry, China Pharmaceutical University, Nanjing 210009, PR China;4. Shanghai ChemPartner Co. Ltd., Zhangjiang Hi-Tech Park, Shanghai 201203, PR China |
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| Abstract: | Free radicals from dihydrate and dideuterate crystals and from anhydrous powder of barbituric acid X-irradiated between 77 K and room temperature have been studied by ESR and ENDOR spectroscopy. Four different species were characterized. In dihydrate crystals, small amounts of molecular anions were found to be formed in addition to the major radical which results from elimination of a hydrogen from the C(5)-methylene group. The α-hydrogen coupling in the latter as well as its weak intra- and intermolecular proton interactions were investigated in detail by ENDOR. The cation of barbituric acid was observed in dideuterate crystals between 77 K and 130 K. Isothermal decay curves indicated its transformation into the deuterated analog of the R2Ċ(5)-H fragment upon warming. The dose-yield relationship of dihydrate and anhydrous powder suggested a stabilization of this radical via interaction with the crystal water. Both the transformation and the stabilization mechanisms were supported by ENDOR-findings on weakly coupled protons. |
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