Electron spin resonance study on the decay of low-temperaure radicals produced by x-irradiation of β-alanine, glycine, and L-threonine

Monocrystals of β-alanine, glycine, and L-threonine have been observed by electron spin resonance after x-irradiation near 770K and first-order rate constants of five radical decays and one growth obtained. In β-alanine the decay over a temperature range of 980K to 1880K of a signal attributed to (NH3)CH2CH2 was found to have an activation energy ΔE of 2.6 +- 0.5 kcal/mole and a pre-exponential factor k0 of 15 Hz. In glycine the decay between 1270K and 1480K of an absorption believed due to (NH2)CH2COO- was determined to have ΔE of 7.0 +- 0.7 kcal/mole and k0 of 6.4 x 108 Hz. In L-threonine, two low-temperature radicals of uncertain identity were monitored over the range of 1060K to 1450K and found to have ΔE values of 2.7 +- 1.5 and 3.3 +- 1.5 kcal/mole, respectively, and k0 values of 1.0 x 105 and 3.3 x 104 Hz, respectively, with the first value in each case for the radical with the smaller splitting. The kinetics of both the appearance at 2140K to 2540K and decay between 3410K and 4170K of a signal attributed to the stable 3000K radical in L-threonine, (CH3)C(OH)CH(NH3)COO-, have been measured. The ΔE values found were 4.2 +- 2.2 and 9.2 +- 5.8 kcal/mole, respectively and the k0 values found were 4.5 x 102 and 3.2 x 104 Hz, respectively