酸素及び窒素のK殻イオン化によりDNA関連分子薄膜中に生じた不対電子種のEPR観測

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

横谷 明徳; 藤井 健太郎; 福田 義博; 鵜飼 正敏*

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

これまで、DNAを構成する窒素や酸素のK殻励起により生じる、照射中にのみ観測される短寿命の不対電子を有する分子種を測定し、これが突然変異の誘発の原因となる化学的に安定なDNAの分子変化(損傷)にどのように固定されて行くのかを明らかにすることを目的として、SPring-8の軟X線ビームライン(BL23SU)に設置した電子常磁性共鳴(EPR)装置を用いたラジカル生成機構の研究を行ってきた。今回、仔牛胸腺DNAの薄膜及び核酸塩基(チミン及びシトシン)の蒸着試料を作成し、EPR装置を用いて真空中で単色軟X線を試料に照射しながらEPRの"その場"測定を行ったのでその結果を報告する。

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.