Gamma and ion-beam irradiation of DNA: Free radical mechanisms, electron effects, and radiation chemical track structure

The focus of our laboratory's investigation is to study the direct-type DNA damage mechanisms resulting from gamma-ray and ion-beam radiation-induced free radical processes in DNA which lead to molecular damage important to cellular survival. This work compares the results of low LET (gamma-) and high LET (ion beam) radiation to develop a chemical track structure model for ion-beam radiation damage to DNA. Recent studies on protonation states of cytosine cation radicals in the N1-substituted cytosine derivatives in their ground state and 5-methylcytosine cation radicals in ground as well as in excited state are described. Our results exhibit a radical signature of excitations in 5-methylcytosine cation radical. Moreover, our recent theoretical studies elucidate the role of electron-induced reactions (low energy electrons (LEE), presolvated electrons (e(pre)(-)), and aqueous (or, solvated) electrons(e(aq)(-))). Finally DFT calculations of the ionization potentials of various sugar radicals show the relative reactivity of these species. (C) 2016 Elsevier Ltd. All rights reserved.