X - Irradiation of DNA Components: Yield and Identity of Stabilized Radicals

Nayana Jayatilaka

Department of Physics and Astronomy, Georgia State University

Clear explanation of radiation-induced free-radical mechanisms in DNA is important to understanding the ultimate effects of radiation on DNA. The objectives of this work are to measure the radiation-induced free-radical yields and to identify the radicals stabilized at liquid helium temperature. Radical yields (G-values) were estimated for X-irradiated single crystals of Cytosine monohydrate, 5-fluorouracil:1-methylcytosine, hypoxanthine HCl.H2O and 9-ethylguanine using Electron Paramagnetic Resonance (EPR) methods. Identification is underway of radicals stabilized at 10K in X-irradiated single crystals of the sodium salt of guanosine (Na:Guanosine) and 9-ethylguanine (9EtG) using EPR, electron nuclear double resonance (ENDOR) and field swept ENDOR (FSE) techniques. Immediately after the irradiation at 10K, there was clear evidence for two radical forms in Na:Guanosine and at least one in 9EtG. Future plans are to extend this work to DNA oligomer crystals.