Pressure-induced phase transitions in DL-glutamic acid monohydrate crystal

• Published in: Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy Molecular and biomolecular spectroscopy, 2020-04, Vol.230, p.118059, Article 118059
• Main Authors: Victor, F.M.S., Rêgo, F.S.C., de Paiva, F.M., dos Santos, A.O., Polian, A., Freire, P.T.C., Lima, J.A., Filho, P.F. Façanha
• Format: Article
• Language: English
• Subjects: Amino acid; DL-glutamic acid monohydrate; High pressure; Phase transition; Physics; Raman spectroscopy
• ISSN: 1386-1425; 1873-3557
• DOI: 10.1016/j.saa.2020.118059

DL-glutamic acid monohydrate crystal was synthesized from an aqueous solution by slow evaporation technique. The crystal was submitted to high-pressure (1 atm–14.3 GPa) to investigate its vibrational behavior and the occurrence of phase transitions. We performed Raman spectroscopy as probe and through the analysis of the spectra we discovered three structural phase transitions. The first one occurs around 0.9 GPa. In this phase transition, glutamic acid molecules suffer modifications in their conformations while water molecules are less affected. The second phase transition at 4.8 GPa involves conformational changes related to CO2−, NH3+ units and the water molecules, while the third one, between 10.9 and 12.4 GPa, involves motions of several parts of the glutamic acid as well as the water molecules. Considering the dynamic of high pressure, the second phase of DL-glutamic acid monohydrate crystal presented a better stability compared with the second phase of its polymorphs α and β L-glutamic acid. In addition, water molecules seem to play important role on this structural stability. All changes are reversible. [Display omitted] •Glutamic acid monohydrate crystal presents three reversible phase transition at high pressure.•Raman spectroscopy proven to be an important tool in the detection of phase transition.•Water molecules play important role on the structural stability of the crystal.