Polymorphism in oxyresveratrol studied by 3D ED.

The polymorphism of oxyresveratrol, a natural extract widely used in traditional Asian medicine, was investigated by means of the most recent structure characterization techniques. A previously unknown anhydrate oxyresveratrol crystal structure was identified for the first time from a submicrometric polyphasic mixture using 3D electron diffraction (3D ED). Additionally, a new polymorph of the dihydrate form of oxyresveratrol was also discovered and structurally studied. Detailed thermal and calorimetry studies revealed their thermal behavior and dehydration path. DFT calculations were also employed to investigate the stability of the rotational conformers involved in the hydrated phases (in both new and already known phases). This research exemplifies how 3D ED combined with cryo-plunging and routine solid-state analysis can elucidate the polymorphism scenario of a nanocrystalline natural compound.