Hexameric Capsules Studied by Magic Angle Spinning Solid-State NMR Spectroscopy: Identifying Solvent Molecules in...

Area of Science:

• Supramolecular Chemistry
• Materials Science
• Solid-State NMR Spectroscopy

Background:

• Pyrogallol[4]arene hexamers are known for their ability to form self-assembled capsules.
• Understanding the encapsulation behavior and stability of these structures is crucial for potential applications.

Purpose of the Study:

• To investigate the solid-state properties of pyrogallol[4]arene hexamers.
• To characterize the encapsulation of solvent molecules within these hexamers using solid-state NMR.
• To explore the stability and reversibility of the solvent encapsulation process.

Main Methods:

• Production of pyrogallol[4]arene hexamer powders via solvent evaporation.
• Application of magic angle spinning solid-state NMR (MAS ssNMR) for structural and dynamic analysis.
• Utilizing (1)H/(13)C heteronuclear correlation MAS ssNMR to assign signals of encapsulated and external solvent molecules.

Main Results:

• Stable hexameric capsules were formed, selectively encapsulating solvent molecules after evaporation.
• Encapsulation was found to be reversible upon exposure to solvent vapors.
• MAS ssNMR experiments demonstrated that encapsulated solvent molecules occupy distinct sites with varying mobilities.
• The capsules exhibited stability for extended periods (months).

Conclusions:

• The study presents a novel approach for studying solvent encapsulation in pyrogallol[4]arene hexamers in the solid state.
• The findings pave the way for investigating guest exchange, guest affinity, and gas storage capabilities of these supramolecular structures.
• Solid-state NMR is a powerful tool for characterizing host-guest interactions in such systems.