Pre-micelle and micelle formation of local anesthetic dibucaine hydrochloride

The molecular-aggregate formation of local anesthetic dibucaine hydrochloride (DC·HCl) was investigated from the electrode potential and light scattering measurements of the aqueous solutions. The electrode potential of DC·HCl solutions showed the deviation from Nernstian response at low concentrations below the critical micelle concentration (CMC). We considered the possibility of pre-micelle formation of DC·HCl in the solution and found that dibucaine cation forms a trimer with two chloride ions in the concentration range. On the other hand, the aggregation number of 15 were obtained for DC·HCl micelles in water from the light scattering measurements. Five dibucaine trimers associate cooperatively and form the micelle at concentrations above the CMC. Further, we observed the DC·HCl micelle grow one-dimensional direction like small rod-like micelle in solutions of high ionic strength. The pre-micelle, micelle formation and micellar growth of dibucaine may be attributable to the stacking of dibucaine molecules due to the π electron interaction of an aromatic ring in the molecule.