Free Radical Formation in Crystals of 2′-Deoxyguanosine 5′-Monophosphate Irradiated at 15 K: An ESR Study

Radiation-induced radicals in single crystals of 2′-deoxyguanosine 5′-monophosphate (5′-dGMP) at 15 K have been studied by electron spin resonance (ESR) spectroscopy. At low temperatures three radicals were analyzed in detail. The negatively charged π anion of the guanine base completely dominated the spectra. Weaker resonances were due to an alkoxy radical with the spin density in the${\rm C}_{3^{\prime}}-{\rm O}_{3}$region of the sugar moiety as well as another sugar-centered radical. The anion rapidly decayed upon exposure to uv light at 15 K or by annealing above 25 K. In both cases no successor radical was observed. The second sugar-centered radical decays at 200 K with a concomitant appearance of the resonance from the C8H-addition radical. By annealing at 295 K the latter resonance was the only one observed. After irradiation at 295 K, however, an additional resonance from a sugar-centered radical, which has been analyzed previously by B. Rakvin and J. N. Herak (Radiat. Res. 88, 240-250 (1981)) was observed. A reinvestigation of this resonance was performed.