Becker, D., Bryant-Friedrich, A., Trzasko, C. and Sevilla, M. D. Electron Spin Resonance Study of DNA Irradiated with an Argon-Ion Beam: Evidence for Formation of Sugar Phosphate Backbone Radicals. Radiat. Res. 160, 174–185 (2003).

In this study, the effects of high-LET radiation on DNA were investigated and compared with the effects of γ radiation. Hydrated DNA samples at 77 K were irradiated with argon-ion beams (³⁶Ar or ⁴⁰Ar beam at energies between 60 and 100 MeV/nucleon). The individual free radicals formed were identified and their yields were investigated by electron spin resonance spectroscopy. Argon-ion irradiation resulted in lower yields of base ion radicals and higher yields of neutral radicals than γ irradiation. A hitherto unknown species was assigned to the radical formed by C–O bond rupture at the deoxyribose C3′, resulting in a sugar carbon-centered radical. A previously characterized phosphorus-centered radical was also found. The formation of each of these species was accompanied by an immediate strand break. G values, k values, and analyses for the individual yields of neutral radicals and ion radical composition for argon-ion-irradiated hydrated DNA are reported and compared to those found previously for γ-irradiated DNA. The lower G values and k values for ion radicals and the higher fraction of neutral radicals found for argon-ion-irradiated DNA are attributed to differences in track structure inherent in the two radiations.