Electron Spin Resonance Studies of Elementary Processes in Radiation- and Photo-chemistry: Part 11.—Radical Reactions of α-Aminobutyric Acid between 26 and 440 K

Abstract

Irradiation of α-aminobutyric acid single crystals with 60Co γ-rays at 26 to 77 K results in the trapping of the protonated molecular-anion CH3CH2CH(NH3+)CO2H–(R1). During thermal annealing to 440 K, six further radicals are formed, including CH3CH2ĊHCO2H(R4), ĊH2CH2CH(NH+3)CO–2(R2), CH3ĊHCH(NH+3)CO–2(R3) and (CH3)2ĊCO2H(R7). The conversion of R1 to R4 and then to R2 and R3 occurs between 100 and 145 K by processes involving only 8–17 kJ mol–1“activation” energy and determined largely by steric considerations. The conversion of R3 to R7 has been followed isothermally between 330 and 365 K and the decay of R7 between 390 and 430 K. These processes have “activation” energies of 71 ± 7 and 83 ± 5 kJ mol–1 respectively and are likely to involve some translational motion of the radicals. A possible mechanism for the radiolysis is discussed.