Binding studies of ions with cyclodextrins using ion-selective electrodes

Area of Science:

• Analytical Chemistry
• Supramolecular Chemistry
• Physical Chemistry

Background:

• Cyclodextrins (CDs) are widely used host molecules in various applications.
• Understanding the binding interactions between organic ions and CDs is crucial for optimizing their use.
• Ion-selective electrodes (ISEs) offer a direct method for monitoring ion activity in solution.

Purpose of the Study:

• To investigate the binding of organic ions to alpha- and beta-cyclodextrins using ion-selective electrodes (ISEs).
• To determine binding parameters, including intrinsic binding constants and the number of binding sites.
• To explore the influence of environmental factors on the binding interactions.

Main Methods:

• Utilized ISEs selective to specific organic ions (chloramine-T, naproxenate, p-nitrophenolate, chlorpromazine).
• Performed titrations of cyclodextrin solutions with the target ions.
• Applied nonlinear fitting of the Scatchard model to experimental data (electrode potential vs. total ion concentration) to calculate binding parameters.

Main Results:

• Identified a single binding site for all tested ion-cyclodextrin pairs.
• Quantified binding constants ranging from 0.67 x 10^3 M^-1 (naproxenate to beta-CD) to 1.27 x 10^4 M^-1 (chlorpromazine to beta-CD) at 25°C.
• Observed nonspecific binding in certain interactions (e.g., chloramine-T to beta-CD).
• Evaluated the impact of pH, temperature, CD concentration, and ionic strength on binding affinity.

Conclusions:

• ISEs provide a reliable method for studying host-guest interactions in supramolecular chemistry.
• Binding affinity is influenced by the size of the guest molecule and the specific cyclodextrin used.
• The study provides thermodynamic insights into the forces governing ion-cyclodextrin complexation.