A paradigm study for assessment of phenylalanine's damage under arc-discharge irradiation

Energetic ions induce important biological effects and the research into radiolysis of amino acids can help to clarify radiolysis of proteins. For this purpose, arc-discharge induced radiolysis of the benzyl-containing aromatic amino acid phenylalanine in aqueous solution was studied and the damage was assessed quantitatively. The energetic ions were produced by arc-discharge in nitrogen and argon atmosphere. The arc-discharge induced chemical reactions of the biomolecule in aqueous solution were detected and analyzed by means of UV-Vis absorption, fluorescence, Fourier transformation infrared (FTIR) spectroscopy and high performance liquid chromatography (HPLC). Based on the multiple spectroscopic approach, the damage can be evaluated in a more reliable and convenient way. The fluorescence analysis in this case appears to be a more direct indicator for the assessment of damage, where it reveals that the damage increases with the irradiation time exponentially. On the contrary, the 'plateau region' or 'saddle-shape' apparently shown both in our rough absorption analysis and ninhydrin reaction test, similar to the previously reported feature of the dose effect for low-energy-ion induced damage, may be just a consequence with varied reactions and processes involved at different stages. This work thus demonstrated that application of appropriate combination of spectroscopic tools can effectively dissect the diversity of the radiolysis reaction system and assess the biomolecular damage properly.