The effect of γ rays upon monohydrated asparagine. A DSC study

Crystalline non-irradiated and irradiated monohydrated asparagine was investigated by means of DSC. The samples were irradiated at room temperature with gamma radiations using a 137Cs source. The exposure doses ranged between 1 and 12 kGy. All samples were scanned in non-sealed pans, from room temperature to a temperature beyond the melting point. The change of registered DSC thermograms for the irradiated samples compared to those of non-irradiated ones and the variation of the parameters associated to dehydration and melting-decomposition with the cumulative dose were analyzed. The study has put in evidence transformations related to the values of characteristic temperatures of peaks and to the thermal effects. The diffusion and desorption of water molecules is hindered by the free radicals formed by irradiation. The most stable free radical species is formed by the extraction of a hydrogen atom from the methylene group of the amino acid chain, done by another hydrogen atom, probably derived from a water molecule.