Electron paramagnetic resonance studies of irradiated D-glucose-6-phosphate ions: relevance to DNA

Abstract

Exposure of disodium D-glucose-6-phosphate to ⁶⁰Co γ-rays at 77 K gave a major centre identified by its EPR spectrum as the parent phosphoranyl radical, formed by electron addition to phosphorus. Several carbon-centred radicals were also detected and their structures discussed. The expected primary electron-loss centre, (RO)PO^˙–₃ was not detected, and probably reacted by hydrogen-atom abstraction with a neighbouring sugar unit. On annealing, the phosphoranyl radicals were converted into two other phosphorus-centred radicals, one of which is identified as the ^˙PO^2–₃ radical formed by loss of RO^–. The other species, formed in comparable yields is probably also a phosphoryl radical centre.

Dilute solutions in methanol or CD₃OD gave only dissociative electron capture, giving R^˙ radicals, as detected by EPR spectroscopy, plus phosphate ions. There was no evidence for phosphoranyl or phosphoryl radical formation. This switch in mechanism of electron capture between the disodium salt and methanolic solutions illustrates the major control exerted by the medium on reaction mechanism in such systems. These results are of significance with respect to processes of radiation damage to DNA. In particular, they confirm that electron addition to phosphate does not occur as a process of significance in irradiated DNA. Reasons for this are discussed.