TOPOGRAPHY OF CYCLODEXTRIN INCLUSION COMPLEXES .30. CRYSTALLINE BETA-CYCLODEXTRIN.12H2O REVERSIBLY DEHYDRATES TO BETA-CYCLODEXTRIN.10.5H2O UNDER AMBIENT CONDITIONS

In contact with mother liquor, crystalline β-cyclodextrin (β-CD) hydrate has composition ∼ β-CD · 12 H2O. If crystals are dried at ambient conditions (18°C, · 50 % humidity), the unit cell volume diminishes ∼ 30 to 50 Å3. X-ray structure analysis of a dry crystal (0.89 Å resolution, 4617 data, R = 0.059) showed the composition β-CD · 10.5 H2O, with ∼ 5.5 water molecules in the β-CD cavity (7 partially and 2 fully occupied sites) and ∼ 5.0 between the β-CD molecules. The positions of the β-CD host and of most of the hydration waters are conserved during dehydration, but the occupancies of the waters in the β-CD cavity diminish. Dry crystals put into solvent re-hydrate to the original form. The mechanism of de- and re-hydration is not evident. © 1992.