Decoupled Associative and Dissociative Processes in Strong yet Highly Dynamic Host-Guest Complexes

Area of Science:

• Supramolecular chemistry
• Materials science
• Chemical kinetics

Background:

• Kinetics and thermodynamics are crucial for supramolecular systems in sensing and materials.
• Host-guest interactions are vital for water-based materials, sensing, and drug delivery.
• Cucurbit[8]uril (CB[8]) macrocycles form stable complexes with various guests.

Purpose of the Study:

• Investigate binding dynamics of electron-rich aromatics with CB[8] and dimethyl viologen.
• Explore the relationship between guest structure, kinetics, and thermodynamics.
• Demonstrate stimuli-responsive control over complex formation and material properties.

Main Methods:

• Stopped-flow spectrofluorimetry to measure association and dissociation rate constants.
• Synthesis and characterization of hetero-ternary complexes.
• Rheological analysis of hydrogels formed by CB[8] ternary complexes.

Main Results:

• High equilibrium binding constants (Keq up to 10^14 M^-2) were achieved.
• Association rates approached the diffusion limit and were guest-insensitive.
• Dissociation rates varied significantly with guest structure, correlating with thermodynamic selectivity.
• External stimuli (viscosity, pressure) selectively perturbed the associative process.
• Complexes showed increased binding with pressure, leading to pressure-insensitive hydrogels.

Conclusions:

• Decoupling of associative and dissociative processes allows for fine-tuning of kinetic parameters.
• CB[8] ternary complexes offer design flexibility for tailor-made host-guest systems.
• Pressure-insensitive hydrogels have significant implications for material applications.