Moment Analysis of Intermolecular Interactions by Using Affinity Capillary Electrophoresis

A moment analysis method was applied to the study of intermolecular interactions between β-cyclodextrin (CD) and trans-2-hexenoic acid (HEXA) or trans-2-octenoic acid (OCTA) from equilibrium and kinetic points of view. The values of first absolute and second central moments of their elution peaks measured by affinity capillary electrophoresis (ACE) were analyzed by using moment equations to determine those of association equilibrium constant and association and dissociation rate constants of the inclusion complex formation. Although OCTA forms more stable complex with β-CD because it is more hydrophobic than HEXA, it seemed that the higher stability of OCTA-β-CD complex is attributed to its smaller value of dissociation rate constant compared with that of HEXA-β-CD one. It was concluded that the moment analysis method using ACE is effective and has some advantageous characteristics for the quantitative analysis of intermolecular interactions. For example, neither immobilization nor fluorescence labelling of solute and/or ligand molecules is required when ACE data are measured. Because the principle of the method for the analysis of intrinsic characteristics of intermolecular interactions is different from those of ordinary methods, it contributes to the study of intermolecular interactions from various perspectives.