Pressure-induced phase transitions inl-alanine, revisited

• Published in: Acta crystallographica. Section B, Structural science Structural science, 2010-08, Vol.66 (4), p.458
• Main Authors: Tumanov, N A, Boldyreva, E V, Kolesov, B A, Kurnosov, A V, Quesada Cabrera, R
• Format: Article
• Language: English
• Subjects: Chemical compounds; Crystal structure; Crystallography; Phase transitions; Pressure
• ISSN: 2052-5192; 2052-5206
• DOI: 10.1107/S010876811001983X

The effect of pressure onl-alanine has been studied by X-ray powder diffraction (up to 12.3 GPa), single-crystal X-ray diffraction, Raman spectroscopy and optical microscopy (up to ∼ 6 GPa). No structural phase transitions have been observed. At ∼ 2 GPa the cell parameters a and b become accidentally equal to each other, but without a change in space-group symmetry. Neither of two transitions reported by others (to a tetragonal phase at ∼ 2 GPa and to a monoclinic phase at ∼ 9 GPa) was observed. The changes in cell parameters were continuous up to the highest measured pressures and the cells remained orthorhombic. Some important changes in the intermolecular interactions occur, which also manifest themselves in the Raman spectra. Two new orthorhombic phases could be crystallized from a MeOH/EtOH/H2O pressure-transmitting mixture in the pressure range 0.8-4.7 GPa, but only if the sample was kept at these pressures for at least 1-2 d. The new phases converted back tol-alanine on decompression. Judging from the Raman spectra and cell parameters, the new phases are most probably notl-alanine but its solvates. [PUBLICATION ABSTRACT]