Structure and recombination of radicals in amino acid crystals

Decay kinetics, of the free radicals produced in crystalline amino acids by x-irradiation, was studied in the temperature range 250 to 1850C. The decay data could not be fitted to a first order rate law. Second order plots indicated two distinct second order processes: the initial faster process and the major slightly slower process. The initial process was of short duration at higher temperatures and at all temperatures it was responsible for the decay of 25 to 30 percent of the initial number of radicals. A vacancy controlled bulk diffusion mechanism is proposed for the major process and the initial process is postulated to be a conformationally favoured bulk diffusion process. L-Arginine HCl monohydrate on x-irradiation at room temperature shows radicals that are stable (relatively) at room temperature but decay at temperatures above 400C. The decay at 750C is found to be zero order while the crystal dehydrates simultaneously. A hydrogen abstraction mechanism is proposed for the spin decay on the basis of the crystal structure and the radical structure. The radical structure was determined from the angular studies of the single crystals. (Diss. Abstr. Int., B)