engleski

Sigma radicals in gamma-irradiated single crystals of 2-thiothymine

Thioanalogs of the nucleic-acid bases are known photosensitive probes and good traps of radiation energy. Radiation-induced sulfur-centered free radicals stabilized on the base thioanalogs molecules are of the cationic origin. Their electronic configuration is of the pi type, unless an electron-donating group, like Cl-, is added to the sulfur atom, forming the sigma sigma* "three-electron " S therefore Cl bond. The sigma radical observed in irradiated 2-thiothymine is formed simply by deprotonation of the pristine cation radical. The 2 sigma character of the radical is determined from the nature of the g tensor and the A(N-14) coupling tensor and their relation to the radical skeleton. The deprotonation of the cation radical takes place at N(3) rather than at N(1), generally observed in the irradiated pyrimidine natural bases and their other thioanalogs.

EPR spectroscopy; 2-thiothymine; sigma radicals

nije evidentirano