Crystal structure and Hirshfeld surface analysis of dl-methionine polymorphs (α and β)

Abstract

Hirshfeld surface analysis and two-dimensional (2D) fingerprint plots of dl-methionine polymorphs were investigated using combined crystallographic methods, a possible source to observe the intermolecular interactions in the crystal state of polymorphs. The α and β polymorphs of the dl-methionine were crystallized with the presence and absence of structurally similar additive dl-leucine in pure aqueous solution. Hydrogen bonding between amino acid functionalities is a common structural motif employed in crystal engineering studies. Though the two polymorphs share common structural features, however the conformations of α and β-dl-methionine crystal packing are different from each other. Shape index and Curvedness surfaces indicates p-stacking with different properties in divergent sides of the moieties. Moreover, Fingerprint plot showed carbon contacts with similar contributions to the crystal packing in comparison with those associated to hydrogen bonds. Enrichment ratios for H…H, O…H, S…H and C…H contacts revealed a high propensity for the form in the crystal. While, Hirshfeld surface analysis infers a short contact between carbonyl oxygen and neighbouring aryl hydrogen, as well as carbonyl–carbonyl interaction. In addition, energy-framework calculations are used to analyze and visualize the three dimensional topology of the crystal packing. Also, the electrostatic energy framework is dominant over the dispersion energy framework.