XANES spectral changes of hydrated deoxyribose induced by K-shell ionization of oxygen

We investigated the initial process of DNA strand breakage induced by ionizing radiation by recording XANES spectra of hydrated deoxyribose (dR) films before and after K-shell ionization of oxygen. The experiments were performed on beamline BL23SU at SPring-8, Japan. The hydrated dR films were prepared by exposing the cooled dR film surface to water vapor. The XANES spectra were then obtained by measuring the sample drain current. The soft X-ray irradiation treatment led to an increase in the intensity of the π*(C=O) peak (around 532 eV) and a decrease in the intensity of the σ*(C–O) peak (around 538 eV). Furthermore, a characteristic peak was observed at around 534–536 eV. in the hydrated dR film after irradiation. This peak, which was ascribed to a newly formed carboxyl group, was not observed in the XANES spectrum of the dry dR film after irradiation. This carboxyl group was considered to originate from the reaction of a nearby water molecule with the carbonyl group produced by the direct ionization of dR. This structure may be formed at the strand- break termini of DNA after radiation damage. Therefore, waters of hydration may play a protective role against irreparable strand breakage.