Encapsulation of ionic liquids inside cucurbiturils.

Area of Science:

• Supramolecular Chemistry
• Host-Guest Chemistry
• Materials Science

Background:

• Cucurbit[n]urils (CBn) are macrocyclic hosts with unique cavity structures.
• Imidazolium-based ionic liquids (ILs) possess amphiphilic properties relevant for molecular recognition.
• Understanding host-guest interactions is crucial for designing novel functional materials.

Purpose of the Study:

• To investigate the complexation of cucurbit[n]urils (CB6-8) with imidazolium-based ionic liquids (ILs) in aqueous solution.
• To elucidate the binding modes and affinities between CBn hosts and IL guests.
• To explore the structural basis of IL recognition by CBn.

Main Methods:

• Nuclear Magnetic Resonance (1H NMR) spectroscopy to probe host-guest interactions.
• Molecular Dynamics (MD) simulations to visualize complex structures and guest conformations.
• Isothermal Titration Calorimetry (ITC) to quantify binding affinities.
• Indicator Displacement Titrations for independent affinity measurements.

Main Results:

• CBn receptors form stable complexes with imidazolium-based ILs in water.
• Complexation involves encapsulation of the IL's hydrophobic alkyl chain within the CBn cavity.
• The imidazolium ring interacts with the carbonyl rim of the CBn.
• CB6 accommodates shorter alkyl chains (up to 5 carbons), while CB7 and CB8 bind longer chains in folded conformations.
• High binding affinities (micromolar range) were observed between ILs and CBn.

Conclusions:

• Cucurbit[n]urils are effective molecular receptors for ionic liquids in aqueous environments.
• The binding mechanism is driven by hydrophobic effects and ion-dipole interactions.
• The size of the CBn cavity dictates the length of the alkyl chain that can be accommodated.
• These findings highlight the potential of CBn-IL complexes in various applications, including separation and sensing.