High-pressure polymorphism in l-threonine between ambient pressure and 22 GPa. Issue 30 (22nd May 2019)

• Record Type: Journal Article
• Authors: Giordano, Nico; Beavers, Christine M.; Kamenev, Konstantin V.; Marshall, William G.; Moggach, Stephen A.; Patterson, Simon D.; Teat, Simon J.; Warren, John E.; Wood, Peter A.; Parsons, Simon
• Is Part Of: CrystEngComm. Volume 21:Issue 30(2019)
• Page Start: 4444
• Page End: 4456
• Publication Date: 2019-05-22
• Subjects: Crystals -- Periodicals; Crystal growth -- Periodicals; Crystallography -- Periodicals; Cristaux -- Périodiques; Cristaux -- Croissance -- Périodiques; Cristallographie -- Périodiques; 548
• DOI: 10.1039/c9ce00388f
• Languages: English
• ISSNs: 1466-8033

Abstract

Abstract : The amino acidl -threonine undergoes three phase transitions between ambient pressure and 22.3 GPa which modify both hydrogen bonding and the molecular conformation. Abstract : The crystal structure ofl -threonine has been studied to a maximum pressure of 22.3 GPa using single-crystal X-ray and neutron powder diffraction. The data have been interpreted in the light of previous Raman spectroscopic data by Holanda et al. ( J. Mol. Struct. (2015), 1092, 160–165) in which it is suggested that three phase transitions occur at ca. 2 GPa, between 8.2 and 9.2 GPa and between 14.0 and 15.5 GPa. In the first two of these transitions the crystal retains its P 21 21 21 symmetry, in the third, although the unit cell dimensions are similar either side of the transition, the space group symmetry drops to P 21 . The ambient pressure form is labelled phase I, with the successive high-pressure forms designated I′, II and III, respectively. Phases I and I′ are very similar, the transition being manifested by a slight rotation of the carboxylate group. Phase II, which was found to form between 8.5 and 9.2 GPa, follows the gradual transformation of a long-range electrostatic contact becoming a hydrogen bond between 2.0 and 8.5 GPa, so that the transformation reflects a change in the way the structure accommodates compression rather than a gross change of structure. Phase III, which was found to form above 18.2 GPa in this work, is characterised by the bifurcation of a hydroxyl group in half of the molecules in the unit cell. Density functional theory (DFT) geometry optimisations were used to validate high-pressure structural models and PIXEL crystal lattice and intermolecular interaction energies are used to explain phase stabilities in terms of the intermolecular interactions.