Anion-driven encapsulation of cationic guests inside pyridine[4]arene dimers

Area of Science:

• Supramolecular Chemistry
• Host-Guest Chemistry
• Organic Chemistry

Background:

• Pyridine[4]arenes were presumed to be anion-binding hosts due to their electron-poor pyridine rings.
• Previous research focused on their potential for anion recognition.

Purpose of the Study:

• To investigate the host-guest chemistry of pyridine[4]arenes.
• To determine if pyridine[4]arenes can encapsulate cationic guests.
• To elucidate the driving forces behind guest encapsulation.

Main Methods:

• Gas-phase techniques including Electrospray Ionization Quadrupole Time-of-Flight Mass Spectrometry (ESI-QTOF-MS), Infrared Multiphoton Dissociation (IRMPD), and Differential Mobility Spectrometry - Mass Spectrometry (DT-IMMS).
• Density Functional Theory (DFT) calculations.
• Mass Spectrometry (MS) and Nuclear Magnetic Resonance (NMR) experiments for comparing pyridinearenes and resorcinarenes.

Main Results:

• Demonstrated the encapsulation of tetramethylammonium (Me₄N⁺) cations within a dimeric hydrogen-bonded pyridine[4]arene capsule.
• Confirmed complexation using ESI-QTOF-MS, IRMPD, and DT-IMMS experiments, supported by DFT calculations.
• MS and NMR comparisons revealed distinct host-guest chemistry between pyridinearenes and resorcinarenes.

Conclusions:

• Pyridine[4]arene dimers can encapsulate cationic guests, contrary to previous assumptions.
• The encapsulation of cations within pyridine[4]arene capsules is an anion-driven process.
• Host-guest interactions in pyridinearenes differ significantly from those in classical resorcinarenes.