Counterion complexation of calixarene ligands in monolayers and micellar solutions

Calix[n]arenes and their derivatives are currently the object of several studies, due to their peculiar cavity, that is suitable for very specific and efficient complexation of ions and small organic molecules, with a high degree of efficiency and selectivity, and form host–guest systems in the solid and in the liquid state. Besides some very important applications as ion carriers and cages, they can be used for studying the counterion distribution in micellar aggregates formed by anionic amphiphiles such as alkyl-sulfates. In this paper we report the studies on the complexing properties of a new calixarene derivative, namely the 1,3-dioctyloxy-calix[4]arene-crown-6-ether (CAL), that shows a high selectivity for cesium ions, at the air/water interface and in aqueous micellar solutions of cesium dodecyl sulfate. Langmuir surface pressure (π/A) isotherms were performed in order to study the stability of CAL films and the effect of cesium and potassium ions on the monolayer properties. In addition, small-angle neutron-scattering (SANS) experiments were carried out in order to determine the structure of the micellar system, and the interactions between the ligand and the micellar interface. Our study shows that the charge screening at the micellar interface is the predominant phenomenon that rules over the ion transport across liquid membranes, that is usually performed by macrocyclic ligands.