Triggered exchange of anionic for neutral guests inside a cationic coordination cage

Area of Science:

• Supramolecular Chemistry
• Host-Guest Chemistry
• Coordination Chemistry

Background:

• Molecular encapsulation is crucial for biological signal transduction and enzyme catalysis.
• Controllable host systems are valuable for mimicking natural processes and developing new materials.

Purpose of the Study:

• To design and synthesize an artificial host system capable of controlled molecular encapsulation.
• To investigate the mechanism of guest uptake triggered by external stimuli.
• To compare the binding kinetics and thermodynamics of various guest molecules.

Main Methods:

• Self-assembly of a bis-monodentate ligand with Pd(II) cations to form an interpenetrated double cage.
• X-ray crystallography, Electrospray Ionization Mass Spectrometry (ESI MS), and Nuclear Magnetic Resonance (NMR) techniques for structural and binding analysis.
• Kinetic and thermodynamic studies of guest encapsulation.

Main Results:

• Formation of a pentacationic double cage with three pockets, each initially containing a tetrafluoroborate anion.
• Halide anion activation triggers a conformational change, enabling the central pocket to bind neutral guest molecules.
• The cage transforms into a hexacationic species upon guest encapsulation, expelling the central anion.

Conclusions:

• The developed artificial host system demonstrates controllable molecular encapsulation via external halide anion trigger.
• This system serves as a mimic for biological signal transduction and offers a platform for selective molecular recognition.
• Detailed structural and binding analyses provide insights into the host-guest interactions.