Structure and stability of columnar cyclomaltohexaose (α-cyclodextrin) hydrate Original Research Article

Rapid recrystallization of cyclomaltohexaose (α-cyclodextrin, α-CD) from aqueous solution resulted in formation of the columnar crystal structure of α-CD containing only water as the guest molecule. Complementary water vapor sorption and wide-angle X-ray diffractometry (WAXD) experiments were performed on the α-CD columnar structure to elucidate the crystal structure present at varying sorption levels. Equilibrium isothermal water vapor sorption experiments at 40 °C revealed that the α-CD columnar structure is unstable above a water activity of approximately 0.67. This was confirmed by WAXD diffractograms collected over time, which further revealed that α-CD columnar structure undergoes a phase transformation to the cage structure after approximately 0.25 h at 40 °C and a water activity of 1.0.