Effect of pressure on the crystal structure of alpha-glycylglycine to 4.7 GPa; application of Hirshfeld surfaces to analyse contacts on increasing pressure.
The crystal structure of alpha-glycylglycine (alpha-GLYGLY) has been determined at room temperature at pressures between 1.4 and 4.7 GPa. The structure can be considered to consist of layers. The arrangement of molecules within each layer resembles the antiparallel beta-sheet motif observed in proteins, except that in alpha-GLYGLY the motif is constructed through NH...O hydrogen bonds rather than covalent amide links. Compression of alpha-GLYGLY proceeds via the reduction in void sizes. Voids close in such a way as to decrease the distances of stabilizing interactions such as hydrogen bonds and dipolar contacts. The largest reductions in interaction distances tend to occur for those contacts which are longest at ambient pressure. These longer interactions are formed between the beta-sheet-like layers, and the largest component of the strain tensor lies in the same direction. The N...O distance in one NH...O hydrogen bond measures 2.624 (9) angstroms at 4.7 GPa. This is very short for this kind of interaction and the crystal begins to break up above 5.4 GPa, presumably as the result of a phase transition. The changes that occur have been analysed using Hirshfeld surfaces. Changes in the appearance of these surfaces enable rapid assessment of the structural changes that occur on compression.
School of Chemistry and Centre for Science at Extreme Conditions, The University of Edinburgh, King's Buildings, West Mains Road, Edinburgh EH9 3JJ, Scotland. s.moggach@ed.ac.uk
Stephen A
SA
Moggach
David R
DR
Allan
Simon
S
Parsons
Lindsay
L
Sawyer
D016880:Anisotropy; D018360:Crystallography, X-Ray; D006033:Glycylglycine / Q000737:chemistry*; D006860:Hydrogen Bonding; D006874:Hydrostatic Pressure; D008958:Models, Molecular; D015394:Molecular Structure; D017433:Protein Structure, Secondary; D013696:Temperature
D006033:Glycylglycine