ESR and ENDOR study of the guanine cation: Secondary product in 5′-dGMP

Previous ESR studies of x-irradiated single crystals of 2′-deoxyguanosine-5′-monophosphate have indicated the presence of a radical thought to be formed by deprotonation of a primary base cation at N1. In this communication are reported some results of detailed ESR and ENDOR experiments at 10 K conflicting with the above results. One of the radicals detected exhibited two α-proton type couplings. The data analysis shows that one coupling is due to the exchangeable proton of the extra-annular NH2 group, while the other is due to the proton bonded at C8. The experimental spin densities were ρ(N10)=0.33, and ρ(C8)=0.18. The results agree reasonably well with the INDO calculated spin density distribution of a radical formed by deprotonation at N10 of a primary cation radical. The radical is stable on warming to about 200 K where it anneals rapidly.