Novel analytical study for reaction intermediates in the primary radiation interaction of DNA using a synchrotron radiation induced luminescence spectroscopy

To identify the precise molecular processes to induce DNA lesions, we attempt a novel spectroscopy of luminescence excitation (LEX) induced by soft X-ray synchrotron radiation, which is a non-destructive analysis of the reaction intermediates in the elementary reaction pathway of damage induction and self-organized restoration. Using a liquid micro-jet technique to introduce aqueous samples in a vacuum chamber, we measure UV-visible luminescence from nucleotide solution as a function of the soft X-ray energy from nitrogen to oxygen K-edge region. The LEX intensities for the nucleotide solutions are significantly enhanced in the soft X-ray region (410-530 eV) which is ascribed to the K-shell excitation/ionization of nitrogen atoms in the nucleobases. Furthermore, the LEX spectra do not show any signature of X-ray absorption near-edge structure (XANES) of the nucleobases. This is because the luminescence intensities collected from the integral area of micro-jet only reflect a quantum yield of luminescence of the absorbed X-ray into UV-visible light irrespective of the absorption cross sections, i.e., of XANES. Thus the present result is the first evidence of luminescence as a result of X-ray absorption of aqueous nucleotides