Radiation Induced Free Radicals in Alanine and Some Related Amino Acids. Electron Spin Resonance Studies.

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Abstract
Free radicals induced by ionizing radiation in polycrystalline samples of a-alanine and some related amino acids were studied by electron spin resonance (ESR) techniques. The results show that the observed spectra, very often represent the composite pattern of more than one radical. Qualitative changes occur in the ESR spectra, demonstrating that secondary processes take place at a fairly slow rate in the solid state. The number of induced radicals has been measured as a function of the radiation dose as well as of the time after the end of the exposure. The dose effect curves are straight lines up to a certain dose level and then flatten out. This occurs before any saturation effects are to be expected. Time studies demonstrate the surprisingly high stability of radicals induced and trapped within solid amino acids. For the amino acids studied, 5-50 electron volts were found necessary to induce one primary radical with lifetime long enough to be observed. These low values seem to imply that the radicals originate not only from ioniza -tions, but also from excitation processes which are subsequently followed by rupture of chemical bonds. Conceivably the radical fragments induced may take part in reactions with intact neighbor molecules, a circumstance which may explain the observed qualitative changes in the resonance patterns.

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