High-pressure structural study of L-alpha-glutamine and the use of Hirshfeld surfaces and graph-set notation to investigate the hydrogen bonding present in the structure up to 4.9 GPa

The crystal structure of L-alpha-glutamine has been elucidated at room temperature at pressures between 0 and 4.9 GPa by using single-crystal high-pressure X-ray diffraction techniques. The structure is primarily stabilized by five N-H center dot center dot center dot O intermolecular interactions, which link molecules in a herringbone-like layer arrangement, giving rise to voids within the solid. The application of pressure on the structure results in a reduction in the size of the voids, as a consequence of the shortening of the N-H center dot center dot center dot O hydrogen bonds, which compress to minimum N center dot center dot center dot O distances of around 2.6 angstrom, without driving the crystal structure to a phase transition. The decrease in the hydrogen-bond distances is due to the necessary stabilization of the structure, which arises from molecules modifying their positions to optimize electrostatic contacts and minimize the occupied space. Hirshfeld surfaces and fingerprint plots have been used to rapidly assess the structural changes that occur on application of pressure.