α-Cyclodextrin: How Effectively Can Its Hydrophobic Cavity Be Hydrated?

Area of Science:

• Supramolecular Chemistry
• Physical Chemistry

Background:

• Cyclodextrins (CDs) are versatile host molecules forming inclusion complexes.
• The "hydrophobic" cavity of CDs is always occupied by water molecules, even in the absence of other guests.
• Key aspects of cyclodextrin hydration, including water binding sites, stability, and favored binding modes, remain unclear.

Purpose of the Study:

• To elucidate the mechanism of water binding to cyclodextrins.
• To identify preferred water binding sites and assess the stability of water clusters within the cyclodextrin cavity.
• To determine the factors influencing cyclodextrin hydration and water complexation.

Main Methods:

• Experimental measurements using differential scanning calorimetry (DSC) and thermogravimetry (TGA).
• Theoretical calculations employing Density Functional Theory (DFT).
• Evaluation of enthalpies for alpha-cyclodextrin (αCD) hydrate formation.

Main Results:

• Identified key factors governing water binding to αCD, including binding mode (sequential vs. bulk) and hydrogen bond types (water-water vs. water-αCD).
• Assessed the influence of dielectric properties of the medium on the complexation process.
• Determined enthalpies of αCD hydrate formation, providing insights into binding thermodynamics.

Conclusions:

• The study provides a comprehensive understanding of the intimate mechanism of water binding to αCD.
• Key factors controlling cyclodextrin hydration have been disclosed, advancing the field of supramolecular chemistry.
• Results offer valuable insights for designing and utilizing cyclodextrin-based systems in various applications.