Soft X-ray induced decomposition of phenylalanine and tyrosine: A comparative study

The pristine state and soft X-ray induced decomposition of two aromatic amino acids, viz. phenylalanine and tyrosine, have been studied by means of XPS and NEXAFS. The spectroscopic data on the radiation decomposition have been supplemented by a mass-spectral analysis of desorbed species in the residual gas. Despite very similar chemical structures, the two amino acids show a drastically different behavior towards ionizing radiation: phenylalanine degrades very quickly whereas tyrosine shows a prominent stability against radiation damage. Reasons for this difference are discussed in relation to radical-mediated reactions responsible for the decomposition