ζ-Glycine: insight into the mechanism of a polymorphic phase transition

Abstract

Glycine is the simplest and most polymorphic amino acid, with five phases having been structurally characterized at atmospheric or high pressure. A sixth form, the elusive phase, was discovered over a decade ago as a short-lived intermediate which formed as the high-pressure " phase transformed to the form on decompression. However, its structure has remained unsolved. We now report the structure of the phase, which was trapped at 100 K enabling neutron powder diffraction data to be obtained. The structure was solved using the results of a crystal structure prediction procedure based on fully ab initio energy calculations combined with a genetic algorithm for searching phase space. We show that the fate of -glycine depends on its thermal history: although at room temperature it transforms back to the phase, warming the sample from 100 K to room temperature yielded -glycine, the least stable of the known ambientpressure polymorphs.

Structure prediction drives materials discovery

“…A strategy for sampling crystal structures in a reduced configuration space (with only a certain number of space groups and small Z') is powerful for solving crystal structures of molecules in real-life settings, as demonstrated in previous blind tests of organic CSP organized by the Cambridge Crystallographic Data Centre [184]. As a similar example, glycine, the simplest amino acid, is known to have 6 polymorphs; the structure of short-lived metastable ζ-phase could not be solved for more than a decade and was eventually determined via evolutionary CSP [185]. A computational screening of the pharmaceutical compound Dalcetrapib with 10 torsional degrees of freedom led to the discovery of a new form that was successfully synthesized under high pressure [186].…”

High-pressure polymorphism inl-threonine between ambient pressure and 22 GPa

“…4,7 ε-Glycine transforms back to the γ-form via a, sixth, shortlived ζ-polymorph. 8 L-Serine has four high-pressure polymorphs. [9][10][11][12][13][14] The ambient pressure form, L-serine I, transforms to L-serine II and III on rapid compression at ca.…”

Behavior of intermolecular interactions in α-glycine under high pressure

“…high-pressure phase gives another, the third one, high-pressure polymorph before having transformed to α-glycine at ambient pressure. 46,47 In this study, both powder and single-crystal XRD measurements were performed to investigate the high-pressure behavior of deuterated α-glycine. Furthermore, powder neutron diffraction measurements were carried out at high pressure to obtain more accurate positions of hydrogen atoms in the structure, in order to investigate the behavior of the intermolecular hydrogen bonds with compression.…”