Time and temperature induced phase transformation in L-isoleucine hydrochloride monohydrated crystal

摘要

Semi organic crystals have been intensively studied aiming applications in nonlinear optical (NLO). Such applicability requires crystals with both high quality and thermal stability, which make the full characterization of this material a topic issue. In this paper, single crystals of L-isoleucine hydrochloride monohydrated (L-Ile.H2O.HCl) was synthesized by slow evaporation technique and characterized by thermal analysis and X-ray diffraction (XRD) measurements. XRD results at 298 K showed that the sample crystallize with the orthorhombic structure, and the lattice parameters obtained by Rietveld refinement were a = 5.873(3) angstrom, b = 24.814(4) angstrom, and c = 6.873(5) angstrom. Thermal analysis measurements shows four decomposition stages between 328 -480 K which were associated with loss of water by desolvation, loss crystallization water and decomposition of L-Ile.HCl. XRD measurements as a function of temperature up to 428 K show an irreversible phase transformation. This transformation was obtained after 32 hours keeping the L-Ile.HCl.H2O sample at 413 K. The analysis shows that phase transformation occurs due to water and chlorine losses without destroy the amino acid carbon chain and in the end of transformation only the precursor amino acid remains. L-Ile.HCl.H2O present low thermal stability and the phase transformation is time and temperature dependent.