Raman spectroscopy under high pressures and DFT calculations of the amino acid l-glutamine

• Published in: Vibrational spectroscopy Vol. 98; pp. 69 - 76
• Main Authors: Holanda, R.O., Silva, C.B., Silva Filho, J.G., Lima, C.L., Lima, J.A., Freire, P.T.C.
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 01.09.2018; Elsevier BV
• Subjects: Crystal structure; Crystallization; Crystallography; Density functional theory; DFT; Diamond anvil cells; Diamonds; Evaporation; Glutamine; High pressures; l-glutamine; Phase transitions; Pressure; Raman spectra; Raman spectroscopy; Rietveld method; Spectrum analysis; X ray spectra; X-ray diffraction; l-glutamine; High pressures; DFT
• ISSN: 0924-2031; 1873-3697
• DOI: 10.1016/j.vibspec.2018.07.004

l-glutamine crystal was obtained by the slow evaporation method and its crystallographic structure was verified by X-ray diffraction experiments and the Rietveld method. The vibrational modes of l-glutamine were investigated through Raman spectroscopy and the normal modes were obtained using the Density Functional Theory with the B3LYP functional and set of bases 6-31G++(d, p). With such approach, it was possible to make a theoretical-experimental comparison of the results obtained and to furnish a more precise assignment of the normal modes. The crystal was submitted to high pressure conditions and the Raman spectra between 3055 and 40 cm−1 were recorded for pressures up to 6.1 GPa in a diamond anvil cell. This study allowed us to understand that the crystal undergoes a reversible structural phase transition around 4.0 GPa, characterized mainly by spectral changes in the region of the external modes.