Recognition of ionic guests by ionic beta-cyclodextrin derivatives.

Area of Science:

• Supramolecular Chemistry
• Physical Chemistry
• Analytical Chemistry

Background:

• Cyclodextrins are widely used host molecules in supramolecular chemistry.
• Understanding host-guest interactions is crucial for designing novel materials and drug delivery systems.
• The influence of charge and substitution patterns on binding affinities requires detailed investigation.

Purpose of the Study:

• To systematically investigate the formation of inclusion compounds between p-substituted tert-butylbenzene derivatives and beta-cyclodextrin derivatives.
• To quantify the binding thermodynamics and stoichiometry of these host-guest complexes.
• To elucidate the contributions of electrostatic and apolar interactions to the overall binding free energy.

Main Methods:

• Isothermal titration calorimetry (ITC) was employed to determine binding constants and stoichiometry.
• ROESY NMR spectroscopy was utilized to ascertain guest orientations within cyclodextrin cavities.
• Coulomb's law and Debye-Hückel-Onsager theory were applied to model electrostatic interactions.

Main Results:

• All investigated inclusion compounds exhibited a 1:1 stoichiometry.
• Binding constants varied significantly, ranging from 10 to 3 x 10(6) M(-1).
• Binding free energies were successfully deconvoluted into apolar and electrostatic components, with electrostatic interactions quantitatively described by theoretical models.

Conclusions:

• The study provides a quantitative understanding of host-guest complexation involving cyclodextrins and substituted aromatic compounds.
• Electrostatic interactions, including ion shielding and protonation states, play a significant role in binding affinity.
• The findings offer valuable insights for the rational design of cyclodextrin-based supramolecular systems.