An electron spin resonance study of free radical reactions in gamma-irradiated n-acetyl-l-valine

Abstract

The radicals formed on γ radiolysis of N-acetyl-L-valine in the polycrystalline state at 77 K, at ambient temperature (303 K), and on subsequent warming over the range 77–440 K are reported. Radical anions CH 3C(O -)NHCH(CH(CH 3) 2)COOH and neutral radicals CH 3CONHCH(CH(CH 3) 2), believed to be decomposition products of radical cations, were observed at 77 K. On warming the radical anions decay to nonparamagnetic species while the neutral radicals abstract hydrogen from parent molecules to produce the radicals CH 3CONHC(CH(CH 3) 2)COOH and CH 3CONHCH(C(CH 3) 2)COOH. The α-carbon radicals are the predominant radical species at room temperature. Further warming causes these radicals to decay over the temperature range 350– 440 K. A mechanism for the radiation degradation is suggested, based upon the identification of the radical intermediates and the measurement of their concentrations, and the observation, that the major volatile product is carbon dioxide.