Interaction of the Radiosensitizer Paranitroacetophenone with Radiation-Induced Radicals on Nucleic Acid Components

• Published in: Radiation research 1976-02, Vol.65 (2), p.250-267
• Main Authors: Michaels, Howard B., Rasburn, Eric J., Hunt, John W.
• Format: Article
• Language: English
• Subjects: Absorption spectra; Acetophenones; Adducts; Anions; Deoxyribose - radiation effects; Electron transfer; Electrons; Free Radicals; Hydroxylation; Nucleic Acids - radiation effects; Pyrimidines; Radiation Effects; Radiation-Sensitizing Agents; Radiolysis; Ribose - radiation effects; Solutes; Uracil - radiation effects
• ISSN: 0033-7587; 1938-5404
• DOI: 10.2307/3574199

The techniques of optical and conductiometric pulse radiolysis were used to investigate the reactions of PNAP with the free radicals produced by ·OH attack on uracil, dihydrouracil, ribose, and deoxyribose. Electron transfer from sugar radicals to PNAP occurs with moderate efficiency, the yields being 37 and 23% for deoxyribose and ribose, respectively. In the case of uracil and dihydrouracil, however, the radicals produced by reaction with ·OH do not transfer an electron to PNAP; instead, an addition product with the sensitizer is probably formed. This transient product absorbs strongly in the near uv. A comparison with other electron-affinic sensitizers, namely, nifuroxime and menaquinone, indicates that radical addition reactions, and not electron-transfer reactions, are of major significance in the interaction of these sensitizers with the radicals produced by ·OH attack on nucleic acid bases. Reports in the literature used as evidence in support of the electron-transfer mechanism are shown to be faulty, due to improper analysis of the experimental data. An attempt is made in this paper to rationalize the various results reported for electron-affinic sensitizers.