OH-induced Free Radicals in Purine Nucleosides and Their Homopolymers: E.S.R. and Spin-trapping with 2-methyl-2-nitrosopropane

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Abstract
Free radicals produced by X-irradiation of N2O-saturated aqueous solutions of purine nucleosides (2''-deoxyadenosine, adenosine, 2''-deoxyguanosine, 3''-deoxyadenosine, guanosine and inosine) and the corresponding homopolymers (poly A and poly I) have been investigated by the technique of spin-trapping and e.s.r. spectroscopy. 2-Methyl-2-nitrosopropane was used as a spin-trap. For 2''-deoxyadenosine and 2''-deoxyguanosine, the resulting spin-adducts were separated by Bio-Gel P-2 column chromatography and analysed by e.s.r. spectroscopy. For homopolymers, e.s.r. spectra were recorded at 50.degree. C after enzymatic digestion to obtain signals with narrower line width. The e.s.r. signal consisting of only a primary triplet without further splittings, which is consistent with assignment to the trapping of an H-abstraction radical at the C4'' position of the sugar moiety, was observed in all cases. For 2''-deoxyguanosine an e.s.r. signal consisting of a secondary triplet was observed. Examinations using other spin-trapping reagents such as PBN, 4-PyOBN and DMPO provided no positive evidence supporting the proposal that this was due to an .alpha.-nitrogen. The e.s.r. signal consisting of a secondary doublet which further splits into a doublet was observed for 2''-deoxyadenosine, adenosine, 3''-deoxyguanosine, 2''-deoxyguanosine, and inosine, and tentatively associated with a radical centered in the sugar moiety.