Quantitative E.S.R.-measurements of Radiation-induced Radicals in Nucleic-acid Bases and Pentoses

Abstract

Cytosine, 5-methylcytosine, 5-hydroxymethylcytosine, thymine, uracil, 5-bromouracil, adenine, hypoxanthine, guanine, xanthine, D-ribose and D-2-deoxyribose have been irradiated as dry crystalline powders at about 100°k and 300°k and investigated by electron-spin-resonance spectrometry. First derivative spectra of each substance were recorded at 9·4 kMc/sec after x- and gamma-irradiation with a whole range of doses up to 10 Mr. Qualitative results include new structural details of spectra confirming the richness of hyperfine structure in methyl containing compounds, but emphasis has been placed on quantitative determinations. G-values obtained from the initial linear parts of dose effect curves range from 0·1–1·0 for bases and 4–6 for pentoses after irradiation at room temperature. Although somewhat higher radical yields are often found if irradiations and measurements are executed at low temperature, these yields always decrease on warming-up to room temperature below the values given above. After irradiation at room temperature, the radical-concentrations in all bases lacking a methyl group deviate from a linear dependence on radiation dose above 0·3 Mr and attain a constant level, although linearity up to at least 1 Mr is observed with bases containing a methyl group and with pentoses. At low temperature linearity is found up to 1 Mr for all bases and pentoses except 5-bromouracil, for which the corresponding value is 0·5 Mr.