Damage Induced by Proton Collisions on Building Blocks of Life

Analysis of the mechanism involved at the molecular level in the action of radiations on biomolecular systems is of main interest in cancer therapy research. Ion-induced ionization appears at the early stage of damage before fragmentation of the biomolecule. We have investigated such a reaction step focusing on the ionization of the biomolecule by charge transfer from the incident ion. Taking account of the great impact in proton-therapy treatments, we have considered proton-induced collisions, looking at a series of different biomolecular targets, mainly the DNA and RNA building blocks with on a one hand the nucleobases uracil and thymine, and on the other hand the 2-deoxy-D-ribose sugar skeleton in both furanose and pyranose forms. The study has been extended to possible precursors of the nucleobases, 2-aminooxazole and hydantoin, recently observed in space. The question of the reactivity and stability of prebiotic compounds in astrophysical environments is indeed crucial if one considers the possibility of an exogen origin of life. In proton-rich regions of space, collisions with protons could be fundamental. The calculations have been performed by means of ab initio quantum chemistry molecular methods followed by a semi-classical collision treatment in a wide collision energy range. The present analysis provides information on the respective behavior of the different biomolecular targets which may identify qualitative trends in proton-induced damage.