Ultraviolet Photobleaching of Free Radicals Created in γ-Irradiated Amino Acids

Abstract

The electron paramagnetic resonance spectra of γ-irradiated single crystals of organic materials are often complicated by the creation of more than one free radical. Some complex EPR spectra have been simplified by exposing the damaged crystals to intense ultraviolet light. In glycine, the damaging radiation creates $\dot{{\rm C}}{\rm H}_{2}{\rm COO}^{-}$ and ${\rm N}^{+}{\rm H}_{3}\dot{{\rm C}}{\rm HCOO}^{-}$. A 15-second exposure to uv light removes the $\dot{{\rm C}}{\rm H}_{2}{\rm COO}^{-}$ radical. In threonine, γ-irradiation creates two free radicals, neither of which have been previously identified. A one minute exposure to uv light temporarily removes one radical making it possible to identify the other radical as ${\rm CH}_{3}\dot{{\rm C}}({\rm OH}){\rm CH}({\rm N}^{+}{\rm H}_{3}){\rm COO}^{-}$. In malonic acid, malonamide, and adipic acid, unstable radicals are removed by uv photobleaching. When β-alanine is γ-irradiated at room temperature several unstable radicals are created. Exposure to uv l...