Incorporation of Micelle-Forming Local Anesthetics into Surface-Adsorbed Films and Micelles of Decylammonium Chloride

Abstract

The incorporation of two micelle-forming local anesthetics, dibucaine hydrochloride (DC·HCl) and tetracaine hydrochloride (TC·HCl), into surface-adsorbed films and micelles formed by decylammonium chloride (DeAC) was studied by measuring the surface tension of aqueous solutions of DeAC−DC·HCl and DeAC−TC·HCl binary mixtures. The quantities of the anesthetics incorporated into the adsorbed film and micelle of DeAC were estimated from the compositions of the anesthetics in the adsorbed film and micelle, which were obtained by thermodynamic analysis of surface tension data. The phase diagrams of surface adsorption and micelle formation constructed on the basis of composition in the molecular aggregates indicated that although significant amounts of both anesthetics were incorporated into the adsorbed film and micelle, larger quantities of DC·HCl than of TC·HCl were present in the hydrophobic environment of the aggregates. The relative ease with which these two anesthetics were incorporated into the model membranes correlates with their observed clinical potency. Interactions between DeAC and the anesthetic molecules in the adsorbed and micellar states were also analyzed by calculating the ideal mixing lines in both states. It was shown that the bulky polar head groups of the anesthetics were more favorable for micelle formation than for surface adsorption by comparing the incorporation of the anesthetics into the adsorbed film with that into the micelle at the critical micelle concentration.

Volume Properties of Decylammonium Chloride and Micelle-Forming Local Anesthetic Mixtures in the Micelle

“…The thinner phase diagram of the DeAC−DC · HCl system than that of the DeAC−TC · HCl system implies that greater quantities of DC · HCl than TC · HCl exist in the mixed micelle. The more hydrophobic DC · HCl than TC · HCl partitions larger quantities into the micelle, and the result correlates with their anesthetic potency . Further, the phase diagrams of both systems showed a slightly distorted shape, especially in the low composition region.…”

“…Although decylammonium and local anesthetic cations are weak electrolytes, we assumed in this study that DeAC and the anesthetics are uni-univalent electrolytes on account of their relatively high p K a values, as described previously. , …”

“…The present paper reports the volume properties of the cationic surfactant decylammonium chloride (DeAC) and a local anesthetic in their mixed micelle from density measurements of aqueous DeAC and anesthetic mixtures. The hydrophobic local anesthetics dibucaine hydrochloride (DC · HCl) and tetracaine hydrochloride (TC · HCl) are selected for this purpose because (i) both anesthetics form micelles in the aqueous solution and this enables us to study the volume of anesthetic in the micelle in the whole range of composition and (ii) the information concerning the miscibilities of the DeAC and DC · HCl and the DeAC and TC · HCl systems in the micellar state has been already reported from surface tension measurements . Volume quantities concerning mixed micelle formation of DeAC and the anesthetic are calculated by applying the thermodynamic equations to the density data.…”

Partitioning of Charged Local Anesthetics into Model Membranes Formed by Cationic Surfactant: Effect of Hydrophobicity of Local Anesthetic Molecules

“…Decylammonium chloride (DeAC) was synthesized and purified by the method reported previously. 27 Their purities were confirmed by elemental analysis, and those of DC‚HCl, TC‚HCl, and DeAC were also checked by observing the absence of a minimum on the surface tension vs concentration curves in the vicinity of the critical micelle concentration. The molecular structures of these anesthetics and surfactant are illustrated in Figure 1.…”

Interactions between Local Anaesthetic Agents and Poly(N-isopropyl acrylamide) through Phase Behavior, Surface Tension, and Adsorption Measurement

“…Analogous to the present results, it was also found that an abrupt transition occurred close to the pK a of these substances. The pH-dependent surface activity is also interesting from the perspective of the mechanisms of the action of local anesthetics (63,64).…”