Moment analysis of intermolecular interactions between plural solute molecules and one ligand molecule by means of high-performance liquid chromatography.

This article focuses on the development and application of a moment analysis method combined with high-performance liquid chromatography (HPLC) to study intermolecular interactions between multiple solute molecules and a single ligand molecule, specifically the inclusion complex formation between dibenzo-15-crown-5 (DB15C5) and metal cations (Na⁺, Ca²⁺, Ba²⁺). Assuming a 2:1 stoichiometry due to the larger diameter of the metal cations relative to the crown ether cavity, the method enables determination of association equilibrium (K_A) and kinetic rate constants (k_a and k_d) from elution peak profiles without requiring immobilization or chemical modification of molecules. Results indicate that size compatibility between the crown ether cavity and metal cation significantly influences complex formation and kinetics, even for 2:1 complexes, while other factors such as solvation effects also affect reactivity. The study demonstrates the moment analysis method as an effective experimental strategy for analyzing chemical equilibria and kinetics of ligand–solute interactions under free-solution conditions.