Electron-spin-resonance Study of Radiation-induced Radicals in Aromatic and Aliphatic Amino Acids and Peptides

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Abstract
Electron-spin-resonance spectrometry at room and at low temperature (100°k) has been used to determine the free-radical yield in the x-irradiated dipeptide glycylglycine, and the aromatic amino acids L-tyrosine and L-tryptophane. Molecular mixtures of L-tyrosine and glycylglycine, as well as L-tryptophane and glycylglycine prepared by freeze-drying of aqueous solutions, have also been studied by this method. The quantitative results obtained with the latter do not support the idea of intermolecular transfer of radicals or excitation energy between the different constituents of the mixtures. As opposed to this, when the aromatic amino acids are bound to glycine by a peptide bond to form glycyl-L-tyrosine and glycyl-L-tryptophane, a marked protection of the aliphatic chain by the aromatic ring system is observed.