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

Abstract

Free radicals, radioinduced in polycrystalline samples of alpha - alanine and some related amino acids, were studied by electron spin resonance techniques. The results show that the observed spectra very often represent the composite pattern of more than one radical. Qualitative changes occur in the electron spin resonance spectra, demonstrating that secondary processes take place at a fairly slow rate in the solid state. The number of induced radicals was 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 ionizations, 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 circumstancemore » which may explain the observed qualitative changes in the resonance patterns. (auth)« less