Size exclusion effect in binary inclusion compounds of α-cyclodextrin.

Area of Science:

• Supramolecular Chemistry
• Materials Science

Background:

• Alpha-cyclodextrin (aCD) is a cyclic oligosaccharide widely used as a host molecule in host-guest chemistry.
• Understanding the structure-property relationships of aCD is crucial for designing efficient molecular recognition systems.

Purpose of the Study:

• To investigate the size exclusion mechanism of guests by aCD in binary host-guest systems.
• To characterize the phase transitions associated with guest and water inclusion in aCD.
• To determine the thermodynamic parameters governing guest inclusion and hydration in solid aCD.

Main Methods:

• Vapor sorption isotherms of water and volatile organic compounds (VOCs) using dry aCD.
• X-ray powder diffractometry to characterize phase transitions.
• Thermodynamic analysis of sorption data to determine Gibbs energies and clathrate composition.

Main Results:

• A distinct inclusion threshold was observed for both water and VOCs, corresponding to a phase transition in aCD.
• The interaction of aCD with water is similar to that of included organic compounds, suggesting water acts as a mimic.
• Inclusion and hydration Gibbs energies revealed the relative affinities of guests and water for solid aCD, with size exclusion playing a key role.

Conclusions:

• Guest size exclusion is a critical factor in aCD's host-guest interactions, influencing the inclusion of water and organic molecules.
• Water plays a significant role in activating the inclusion of more hydrophobic guests by displacing it.
• The findings provide insights into the suitability of aCD for applications involving water or organic solvents.