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

Abstract A moment analysis method was developed by combining moment theory and high-performance liquid chromatography (HPLC) to study intermolecular interactions between plural solute molecules and one ligand molecule from the viewpoints of chemical equilibrium and reaction kinetics. The method was applied to the inclusion complex formation between dibenzo-15-crown-5 (DB15C5) and three metal cations, namely Na+, Ca2+, and Ba2+, as concrete examples, to demonstrate the effectiveness of the method. Because the diameter of the metal cations is probably larger than that of the inner cavity of DB15C5, it was assumed that inclusion complexes with a stoichiometry of 2:1 are formed. Elution peak profiles measured using HPLC were analyzed to determine the association equilibrium constant and the association and dissociation rate constants. Their values were correlated with the ratio of the diameter of the metal cation to that of the inner cavity of crown ether. It was indicated that the size consistency between the inner cavity of the crown ether and metal cation is an important factor for the formation of an inclusion complex between them, even when the stoichiometric ratio is 2:1. It was demonstrated that the moment analysis method is effective as an experimental strategy for studying chemical reactions of one ligand molecule with plural solute ones.