Interaction of ionic liquids ions with natural cyclodextrins

Area of Science:

• Supramolecular Chemistry
• Physical Chemistry
• Materials Science

Background:

• Ionic liquids (ILs) are versatile solvents with tunable properties.
• Cyclodextrins (CDs) are host molecules capable of forming inclusion complexes with various guests.
• Understanding IL-CD interactions is crucial for applications in separation, catalysis, and drug delivery.

Purpose of the Study:

• To systematically investigate the binding interactions between natural cyclodextrins (α-, β-, γ-CDs) and 14 hydrophobic ionic liquid moieties.
• To determine the thermodynamic parameters (binding constant, enthalpy, entropy) of inclusion complex formation.
• To elucidate the factors governing the binding affinity and stability of IL-CD complexes.

Main Methods:

• Isothermal titration microcalorimetry (ITC) was employed to quantify binding thermodynamics.
• NMR spectroscopy was used to study the complexation behavior.
• A strategy of using complexation-inactive counterions isolated the effects of individual IL ions.

Main Results:

• Binding constants (K) ranged from 0 to 2 × 10^5, with significant variations in enthalpy (ΔrH°) and entropy (TΔrS°).
• Complexes of perfluorohexyl-containing ions with β-cyclodextrin exhibited among the highest stabilities observed for natural CDs in water.
• Hydrophobic interactions and guest-host size matching were key factors influencing binding affinity.

Conclusions:

• Enthalpy and entropy contributions to complex stability largely compensated each other, consistent with known CD binding behavior.
• The most stable complexes, involving perfluorohexyl groups and β-CD, showed enhanced entropy stabilization due to significant desolvation.
• The findings provide valuable insights into the rational design of IL-CD systems for specific applications.