Electron Spin Resonance Studies of Radiation Effects on Polyamino Acids

The effects of ionizing radiation on eighteen polyamino acids were examined with the ESR method. In about half of these it was found possible to interpret the ESR observed at room temperature as arising from free radicals formed by loss of the H from the --CHR-- group of the polypeptide chain. In the others, the room-temperature ESR signals seem to arise from a damaged side chain or R group. The ESR obtained at 77 un. Concent 85% K are generally different from those obtained in room-temperature experiments and may arise often from charged or ionized molecules. Oxygen was found to alter or quench the ESR of all the polyamino acids studied, some more rapidly than others. The alteration of the signal is thought to be caused by a conversion of the radical X to peroxide radicals X-O--O. The later decay of the signal probably results from the release of H atoms, that escape through the lattice, and the consequent conversion of the polymeric free radicals to stable molecules.