Hydrogen-bonded host-guest systems are stable in ionic liquids.

Area of Science:

• Supramolecular Chemistry
• Ionic Liquids
• Physical Chemistry

Background:

• Ionic liquids (ILs) are salts with low melting points, characterized by strong dipole-charge interactions.
• Traditional host-guest chemistry relies on hydrogen bonds (H-bonds) and dipole-dipole interactions.
• The behavior of H-bonded systems in ILs is not well understood due to the dominance of electrostatic forces.

Purpose of the Study:

• To investigate the association of H-bonded host-guest systems in ionic liquids.
• To compare binding affinities in ILs versus conventional organic solvents.
• To confirm the occurrence of supramolecular complexation in ILs beyond solvation effects.

Main Methods:

• Titration experiments to determine binding constants (Ka).
• Utilizing four distinct H-bonded host-guest systems.
• Employing force spectroscopy to detect association events.

Main Results:

• H-bonded host-guest systems exhibit smaller, yet comparable, binding constants in ILs compared to organic solvents.
• Force spectroscopy confirmed the association events, ruling out purely (de)solvation contributions.
• Supramolecular complexation is viable in ILs, demonstrating the robustness of H-bonds.

Conclusions:

• Classic H-bonded host-guest supramolecular chemistry is feasible in ionic liquids.
• Strong H-bonds are only moderately influenced by charge-dominated environments.
• The balance of forces in strong H-bonds is not overwhelmingly shifted towards Coulombic interactions.