Complex formation between dodecylpyridinium chloride and multicharged anionic planar substances

Area of Science:

• Supramolecular Chemistry
• Physical Chemistry
• Colloid Science

Background:

• Understanding complex formation between surfactants and planar anionic molecules is crucial for various applications.
• Dodecylpyridinium chloride (DPC) is a common cationic surfactant.
• Azo dyes and sulfonates represent diverse classes of multicharged anionic planar substances.

Purpose of the Study:

• To investigate the complex formation between dodecylpyridinium chloride (DPC) and multicharged anionic planar substances.
• To characterize the binding isotherms and determine binding constants.
• To explore the factors influencing complex formation, including molecular structure and charge.

Main Methods:

• Potentiometric titration using a surfactant-selective electrode.
• Analysis of binding isotherms to identify noncooperative and cooperative binding.
• Multiple regression analysis to correlate binding free energy with partition coefficients and charge.

Main Results:

• Observed n:1 complex formation, where n is the number of anionic charges on the planar molecule.
• Identified two binding types: noncooperative at low DPC concentrations and cooperative at higher concentrations.
• Developed a predictive equation for standard free energy of binding based on partition coefficients and charge.

Conclusions:

• Complex formation is driven by both hydrophobic and electrostatic interactions.
• Binding cooperativity originates from interactions between bound surfactants or complex association.
• These model systems provide valuable insights into ligand binding in biological systems, such as protein local structures.