Crystal structures of hexakis-(2,6-di-O-methyl)-cyclomaltohexaose (dimethyl-α-cyclodextrin) crystallized from acetone, and crystallized from hot water

X-ray diffraction studies were carried out on hexakis-(2,6-di-O-methyl)-cyclomaltohexaose (dimethyl-α-cyclodextrin, DIMEA) crystallized at room temperature from solutions in pure acetone as the 1:1 inclusion complex, and crystallized from aqueous solution at 80 °C without water of hydration. In both crystal structures, the DIMEA molecules adopt a round shape stabilized by systematic intramolecular O-3H … O-2 hydrogen bonds between neighbouring glucose units, and the DIMEA-cavities are closed at the O-6Me rims by methoxy groups forming van der Waals contacts across the molecular opening. In the DIMEA-acetone complex, the guest molecule is fully included and exhibits excessive thermal motions. In anhydrous DIMEA, the remaining cavity volume is occupied by a methoxy group of a neighbouring DIMEA molecule.