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

Area of Science:

• Supramolecular Chemistry
• Materials Science

Background:

• Cyclomaltooctaose (gamma-cyclodextrin, gamma-CD) can form various solid-state structures.
• Understanding the structural transitions of gamma-CD in response to environmental factors is crucial for its applications.

Purpose of the Study:

• To investigate the structural stability and transformations of gamma-CD under varying humidity conditions.
• To elucidate the crystal structure evolution of gamma-CD during water vapor sorption.

Main Methods:

• Rapid recrystallization of gamma-CD from aqueous solution.
• Vacuum drying to induce amorphous state.
• Water vapor sorption experiments at controlled temperature and activity.
• Wide-angle X-ray diffractometry (WAXRD) for crystal structure analysis.

Main Results:

• As-precipitated gamma-CD formed a columnar structure with water as the guest molecule.
• Vacuum drying at 90°C for 15h converted columnar gamma-CD to an amorphous state.
• Both columnar and amorphous gamma-CD transformed to a cage crystal structure upon exposure to water vapor at 40°C and activity of 1.0.
• Crystal structure transformation was incomplete even after sorption equilibrium was reached.

Conclusions:

• Gamma-CD exhibits significant structural plasticity in response to water vapor.
• The transformation to a cage crystal structure highlights the dynamic nature of hydrated gamma-CD.
• Substantial molecular mobility exists within the various hydrated gamma-CD crystal structures, even during phase transitions.