Mechanisms of molecular changes in amino acids due to inner shell ionization

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It was reported that the radiobiological effects are enhanced when monochromatic soft X-rays corresponding to the absorption edges of the constituent atoms are irradiated. We have been studying this enhancement mechanism. In this research, we investigated the mechanisms of molecular changes of sulfur-containing amino acids irradiated with monochromatic soft X-rays around sulfur K-shell absorption edge, expecting that this might be a underlying mechanism of the biological enhancement.Research results are summarized as follows.a)Covalent bonds including the inner shell ionized atom are cleaved more effectively than the other bonds.b)Carbon-sulfur bonds are sensitive not only to the photoabsorption of sulfur but also to that of the other constituent atoms.c)When irradiated in aqueous solution, OH adducts of the fragments are observed.d)Cleavage efficiency of the sulfur-carbon bond is not affected by the addition of OH radical scavenger, indicating that cleavage of the bond mainly occurs via direct action of the radiation.Since we could not identify the all fragments observed in the HPLC chart, we are considering new identification methods such as the use of radioisotope tracers.