X-Ray Diffraction using synchrotron radiation and thermal analysis in pure and doped monohydrate L-Asparagine crystals with manganese ions under high temperatures

Full text: Amino acids are important organic molecules, these being the main constituents in the manufacture of proteins by living organisms. When crystallized they may exhibit nonlinear, piezoelectric, ferroelectric optical properties and may serve as biomimetic [1]. The amino acid L-asparagine, for example, is related to the metabolic control of cellular functions in nervous and cerebral tissues. Transition metals exert some functions associated with biological processes, knowledge of the process of interaction between amino acids and transition metals provides a better understanding of the action of transition metals on proteins [2]. The crystals were obtained by slow evaporation and then X-ray diffraction measurements of polycrystals were carried out using synchrotron radiation in the LNLS and thermal analysis. The diffraction patterns found for Mn²⁺ do doped L-asparagine (LAM) do not differ from LAM and at room temperature both pure and doped LAM have orthorhombic structure. At temperatures above 88 ° C the disappearance and the appearance of new peaks in the diffractograms indicate the transition of the structural phase of the LAM crystal from the orthorhombic system to the monoclinic due to the exit of water molecules from the structure. For temperatures above 204 ° C, there is a decrease in peak intensities as due to amorphization. These transitions were also verified for the doped crystal, however with a decrease in the transition temperature to the anhydrous phase and increase to the amorphous phase. Therefore, these differences in the transitions temperatures between the pure and doped crystals may be associated with changes in hydrogen bonds due to the insertion of the Mn²⁺ ions into the LAM chain.References: [1] Boldyreva, E. V, ed. J. C. A. Boeyens and J. F, 2007, pp. 169-194. [2] M.N. Hugues, John Wiley and Sons, London, 1972. (author)