Quantitative E.S.R.-measurements of Radiation-induced Radicals in Nucleotides

Abstract

The nucleotides deoxycytidine-5′-monophosphate, thymidine-5′-monophosphate · Ca, deoxyadenosine-5′-monophosphate · NH₄ and deoxyguanosine-5′-monophosphate · Na₂ have been irradiated as dry crystalline powders at room temperature and subsequently investigated by electron-spinresonance spectrometry. First derivative spectra of each substance were recorded at 9·4 kMc/sec after doses of x- and gamma-rays up to 10 Mr had been given. Qualitative results include new structural details of nucleotide spectra, and these exhibit a close resemblance to spectra of nucleosides containing the same base. G-values determined from the initial linear parts of curves showing radical-concentration against radiation dose-range from 2 to 5. Departure from linearity occurs at about 1 Mr. Results on nucleotides, nucleosides, nucleic acid bases and D-2-deoxyribose are compared. While the spectral hyperfine structure is characteristic of the nucleic acid bases, G-values and dose-effect curves for radical-concentration are typical of the pentose moiety. This result is tentatively explained by fast radical-transfer from the ribose to the base.