Structural Diversity of Diosgenin Hydrates: Effect of Initial Concentration, Water Volume Fraction, and Solvent on Crystallization

Four hemihydrates (HH-I, HH-II, HH-III, and HH-IV) and two monohydrates (MH-I, MH-II) of diosgenin, a steroid sapogenin, have been prepared. Hydrates HH-I, HH-III, HH-IV, MH-I, and MH-II have been thoroughly characterized by single-crystal X-ray diffraction, powder X-ray diffraction, Fourier transform infrared spectroscopy, thermogravimetry, and differential scanning calorimetry. Although in these cases diosgenin has a similar conformation, hydrogen bonding interactions connect diosgenin and the lattice water molecule into different supermolecular structures. More importantly, three controlling factors, including initial concentration, water volume fraction, and solvent, have been investigated in the crystallization of diosgenin hydrates. The control experiments in ethanol display that as the initial concentration increases, HH-III, HH-I, and HH-II appear in order, and with the increase of water content, HH-I, HH-III, MH-I, and MH-II are obtained correspondingly. When acetone is used as solvent, HH-IV was synthesized. Moreover, we observed that stick-like crystals of HH-III gradually transform to plate-like ones of MH-I in solution at ambient conditions. This transformation is prevented by lowering temperature and is accelerated by adding water.