Analysis of ion association reactions between monovalent polycyclic aromatic cations and anions in aqueous solution as studied by capillary zone electrophoresis

Ion association reactions between monovalent polycyclic aromatic cations an d anions have been studied through the mobility change in capillary zone el ectrophoresis. When the cationic reagent possessing aromatic moieties was u sed, isomers of aromatic anions were well resolved. Apparent electrophoreti c mobility of the anions decreased with an increase in the concentration of the cationic reagent in the migrating solution; the magnitude of the decre ase was large when bulkier cations were used. The ion association constants obtained by analyzing the mobility change increased with an increase in th e number of aromatic rings of either the pairing cations or the anions. The ion associates formed consist of monovalent cations and anions, and the io n association constant for an ion associate formed between 1-propylbenzo[f] quinolinium ion and pyrene-1-carboxylate ion was in the magnitude of 10(2.7 4) dm(3) mol(-1). Such ion associability was interpreted from the contribut ion of the stacking of aromatic moieties in an aqueous solution, in additio n to the increase in the hydrophobicity.