Free radicals from single crystals of deoxyguanosine 5'-monophosphate (Na salt) irradiated at low temperatures.

In single crystals of the DNA nucleotide 2'deoxyguanosine-5'phosphate (5'dGMP) X- or gamma-irradiated at 4.2 K or 15 K, two primary radical species can be discriminated and assigned to the cation and anion of the guanine base, G(+) and G(-). Both species are unstable. G(-) partially transforms into a secondary radical at 4.2 K, the latter being the precursor to the dominant 300 K species formed by net H-addition to carbon C8. The secondary radical, together with another intermediate appearing at 77 K and perhaps connected with the anion decay could not be structurally identified. The guanine cation G(+) transforms upon annealing to temperatures above 77 K into a more stable species by deprotonation at position N1.