Binding Interactions between a Ferrocenylguanidinium Guest and Cucurbit[n]uril Hosts

Area of Science:

• Supramolecular Chemistry
• Electrochemistry
• Host-Guest Chemistry

Background:

• Ferrocene derivatives are versatile compounds with applications in various fields.
• Macrocyclic hosts like cucurbiturils are known for their ability to form inclusion complexes.
• Understanding host-guest interactions is crucial for designing novel molecular systems.

Purpose of the Study:

• To investigate the binding interactions between a novel ferrocenylguanidinium derivative (FcG+) and cucurbit[7]uril (CB7) and cucurbit[8]uril (CB8).
• To determine the stoichiometry, stability, and structural characteristics of the formed inclusion complexes.
• To explore the electrochemical consequences of complexation on the ferrocenyl moiety.

Main Methods:

• Nuclear Magnetic Resonance (NMR) spectroscopy to study binding interactions and stoichiometry.
• Electrospray Mass Spectrometry (ESI MS) for complex stoichiometry confirmation.
• NMR competition experiments to determine association equilibrium constants (K).
• Density Functional Theory (DFT) calculations for structural and stoichiometric validation.
• Voltammetric experiments to analyze electrochemical changes upon complexation.

Main Results:

• Stable 1:1 inclusion complexes were formed between FcG+ and both CB7 and CB8.
• Association constants were determined as 3.5 × 10^9 M^-1 for CB7 and 2.5 × 10^8 M^-1 for CB8.
• DFT studies confirmed the 1:1 stoichiometry and inclusion complex formation.
• Complexation induced anodic shifts in the half-wave potentials of FcG+, with CB7 causing a 12 mV shift and CB8 a 32 mV shift.

Conclusions:

• The ferrocenylguanidinium derivative (FcG+) forms robust inclusion complexes with CB7 and CB8, with the ferrocenyl group encapsulated within the host cavity.
• The delocalization of the positive charge within the guanidinium unit influences the electrochemical behavior, mimicking neutral ferrocene derivatives.
• These findings contribute to the understanding of host-guest chemistry involving ferrocene-based guests and cucurbituril hosts.