EPR study of unpaired electron species produced in DNA thin film by K-shell ionization of nitrogen and oxygen

Yokoya, Akinari; Fujii, Kentaro; Fukuda, Yoshihiro; Ukai, Masatoshi*

In order to clarify the photoelectric effect of nitrogen and oxygen atom on DNA damage induction and succeeding mutation induction, unpaired electron species produced in DNA and nucleobases have been studied using an electron paramagnetic resonance (EPR) spectrometer. Thin films of calf thymus DNA and evaporated thymine and cytosine bases were irradiated in the EPR cavity installed in vacuum chamber connected to a soft X-ray beamline in SPring-8 (BL23SU) with synchrotron soft X-rays around nitrogen and oxygen K-edge. Short-lived EPR signals were observed only during irradiation. The photon energy dependences of the yield of these short-lived species arising in nucleobase films are very similar to those of fine structure of photoabsorption spectra (XANES), though that for DNA film is different from XANES of DNA. The origin of these short-lived species will be discussed.