Structure and stability of columnar cyclomaltooctaose (γ-cyclodextrin) hydrate

Abstract

Rapid recrystallization of cyclomaltooctaose (γ-cyclodextrin, γ-CD) from aqueous solution resulted in formation of a columnar structure with only water as the guest molecule. Upon vacuum drying at 90 °C for 15 h, γ-CD, which was initially in the columnar structure, became amorphous. Complementary water vapor sorption and wide-angle X-ray diffractometry experiments were performed on columnar γ-CD in its vacuum dried and as-precipitated states to elucidate its stability in humid environments and the crystal structure present at varying sorption levels. These experiments show that both types of γ-CD transform to the cage crystal structure upon exposure to water vapor at 40 °C and with an activity of 1.0. Sorption equilibrium is reached long before the crystal structure transformation is complete, indicating that a significant amount of molecular mobility exists in the various hydrated γ-CD crystal structures.