Electron-Induced Dissociation of the Potential Radiosensitizer 5-Selenocyanato-2′-deoxyuridine

Abstract

5-Selenocyanato-2′-deoxyuridine (SeCNdU) is a recently proposed radiosensitizer based on 2′-deoxyuridine (dU) with the electron-affinic selenocyanato (−SeCN) side group attached at the C5 position of uracil. Since electron interaction processes may be an important source of DNA damage by ionizing radiation, we have studied low-energy dissociative electron attachment to SeCNdU in the gas phase. Negative ion formation has been obtained by means of mass spectrometry, where a rich fragmentation pattern is observed even at ∼0 eV. The reaction pathways exhibiting the highest ion yields are C4N2O2H2Se•– and CN–, both involving a cleavage of the Se–CN bond. The heaviest fragment anion observed is C9N2O5H10Se•–, where besides the charged species, the hydrogen and cyano radicals are also formed. Further decomposition channels also yield the highly reactive hydroxyl radical, which possesses a high DNA damage potential. All observed channels have experimentally determined onsets at 0 eV, which are supported by calculations performed at the M06-2X/aug-cc-pVTZ level. The calculations comprise the thermochemical thresholds at standard and experimental (428.15 K, 3 × 10–11 atm) conditions together with the adiabatic electron affinities. The present study shows that low-energy electrons very effectively decompose SeCNdU upon attachment of thermal electrons, producing a large variety of charged fragments and radicals.