Radiation damage to nucleosides and nucleotides. I. An ESR study of uridine-5'-phosphate.2Na+ single crystals.

TLDR: Single crystals of the disodium salt of uridine-5'-phosphate were irradiated by 4.0-MeV electrons and studied by electron spin resonance spectroscopy in the temperature range 77 to 310 K, suggesting that the radical reaction I ..-->… IV takes place at approximately 130 K and the reaction II ..-->.. III at 150 K.

Abstract: Single crystals of the disodium salt of uridine-5'-phosphate were irradiated by 4.0-MeV electrons and studied by electron spin resonance spectroscopy in the temperature range 77 to 310 K. At 77 K two resonances were observed. The dominating resonance (I) is ascribed to the electron adduct (anion) radical of the uracil base. The main hyperfine interaction observed is a coupling between the unpaired electron and the proton bonded to C/sub 6/. The other resonance (II) exhibits a large g-value anisotropy and two almost isotropic doublet couplings. This resonance is probably due to a secondary alkoxy-type radical formed by a net loss of hydrogen from O/sub 3/' in the sugar moiety. At 270 K three resonances were observed. One (III) is due to a radical formed by hydrogen abstraction from C/sub 5'/ in the sugar moiety, whereas the other two (IV,V) are probably hydrogen addition radicals at the uracil base. Radical IV is the dihydrouracil-5-yl radical formed by a net hydrogen addition to the C/sub 6/ position, whereas radical V tentatively is ascribed to the 6-yl radical. The light-induced conversion V ..-->.. IV took place at 270 K, whereas the reverse heat-induced process was not observed in the temperature range studied. Preliminary more » annealing studies of crystals irradiated at 77 K suggest that the radical reaction I ..-->.. IV takes place at approximately 130 K and the reaction II ..-->.. III at 150 K. « less