E.s.r. of spin-trapped radicals in gamma-irradiated polycrystalline DL-alanine. A quantitative determination of radical yield.

The quantitative aspects of determining free radicals in polycrystalline amino acids gamma-irradiated at room temperature and subsequently dissolved in spin-trap solutions were investigated. The deamination radical in DL-alanine was used for detailed studies and 2-methyl-2-nitrosopropane (MNP) was employed as the spin-trap. The spin-trapping efficiency (the number of radicals spin-trapped in solution divided by the number of radicals initially present in the gamma-irradiated solid) was found to be in the range 1 to 10 per cent for aqueous solutions depending on the experimental conditions. The effects of dose, particle size, pH, spin-trap concentration, age of spin-trap solution, MNP monomer to dimer ratio and the presence of organic solvents were investigated. Several reactions were found to decrease the spin-trapping efficiency; radical-radical recombination, the competition between the spin-adduct and the spin-trap for radicals and the reaction of radicals with the MNP dimer. The reaction of intact DL-alanine molecules with deamination radicals to produce H-abstraction radicals which are not spin-trapped does not significantly lower the spin-trapping efficiency. The results obtained with compounds such as glycine, glycylglycine, L-valine and L-proline suggest that the low spin-trapping efficiency found for DL-alanine may be representative of polycrystalline amino acids.