Using Raman spectroscopy to understand the origin of the phase transition observed in the crystalline sulfur based amino acid l-methionine

• Published in: Vibrational spectroscopy Vol. 65; pp. 132 - 141
• Main Authors: Lima, José A., Freire, Paulo T.C., Melo, Francisco E.A., Filho, J. Mendes, Fischer, Jennifer, Havenith, Remco W.A., Broer, Ria, Bordallo, Heloisa N.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01-03-2013
• Subjects: Amino acids; Cooling; DFT calculations; Dynamic structural analysis; Intervals; Phase transition; Spectra; Sulfur; Thermal analysis; Unit cell; Vibrational properties; Vibrational properties; DFT calculations; Phase transition
• ISSN: 0924-2031; 1873-3697
• DOI: 10.1016/j.vibspec.2012.12.004

We present the Raman spectra of l-methionine (C5H11NO2S) monocrystals obtained in the spectral region ranging from 3200 to 50cm−1 at temperatures from 20 to 375K. We investigated the dynamics of the different functional groups in l-methionine and related their behaviour to the structural transition previously reported at about 307K. Additionally, on cooling, changes in the intensities of some Raman bands were associated with conformational changes of at least one of the two l-methionine conformers in the monoclinic unit cell in the interval 160–140K. Thermal analysis and DFT calculations provide further support to the interpretation of the Raman results.