ESR OF SULFUR-SUBSTITUTED PURINES AND NUCLEOSIDES - IONIC RADICALS IN MERCAPTOPURINE CRYSTALS AT 77-K

Single crystals of the sulfur-containing purine base derivative 6-methyl-mercaptopurine (6MeMP) have been irradiated by 4.0 MeV electrons and studied by electron spin resonance techniques at 77 K. A light-sensitive resonance has been analyzed, and the ESR data suggest that the resonance is due to a π radical with resolved hyperfine coupling from a protons on C 2 and C8 and from one nitrogen atom. The spin densities are approximately 0.35 and 0.17 on C2 and C8 and 0.08 on the nitrogen atom. This interpretation is supported by a comparison of simulated and observed spectra, and, in combination with molecular orbital calculations, it is suggested that the species responsible for the light-sensitive resonance is the anion (electron adduct) radical. Radical formation in different sulfur-containing purines is discussed and compared to that in the unsubstituted purine bases. © 1979 American Institute of Physics.