Decomposition of 2-deoxy-D-ribose by ultrasoft x-ray and low energy electron impact

The process of DNA damage induced by low energy electrons progresses through various stages. By using the similar energy of monochromatic ultrasoft X-rays as a source of the damage induction, we can select the specific process like an Auger event on a specific atom by a core level excitation in such a complicated process. In this study, oxygen K-shell excitation for 2-deoxy-D-ribose molecule was performed by both ultrasoft X-ray irradiation and low energy electron irradiation, and compared the subsequent desorption of positive ions from the sample thin film irradiated by a quadrupole mass spectrometer in a vacuum. As the desorbed ions from 2-deoxy-D-ribose, H+, CH 2+, CH 3+, C 2 H 2+, C 2 H 3+, CO+, CHO+, CH 3 O+, C 3 H3+, C 2 HO+, C 2 H 2 O+, C 2 H 3 O+and C 3 H 3 O+were observed by 538 eV photon impact. On the other hand, the low energy electron impact showed similar mass pattern with that for the photon impact, however, significantly high H+ion yield were observed compared with other ion species. Some of these ions are related to simultaneous bond scission at particular C-C and C-O (or C-C) bond in the furanose ring structure in 2-deoxy-D-ribose molecule indicating that the photon or electron impact in above oxygen K-edge region causes an intense destruction of the furanose ring structure. The relatively higher yield of H+ion induced by the electron impact is thought to attribute to a different collision mode of the electron impact from that of the photon impact. Inelastic scattering of electron could efficiently induce the H+ desorption from 2-deoxy-D-ribose. It seems that H+ ion plays an important role, such as generation of protonated or deprotonated radicals, in DNA damage process. By comparing the data from the different radiation sources, the mechanism of DNA strand breaks and base damages through the degradation of 2-deoxy-D-ribose by oxygen K-excitation will be discussed