Counterion complexation of calixarene ligands in monolayers and micellar solutions

Calix[n]arenes and their derivatives are currently the object of several st udies, due to their peculiar cavity, that is suitable for very specific and efficient complexation of ions and small organic molecules, with a high de gree of efficiency and selectivity, and form host-guest systems in the soli d and in the liquid state. Besides some very important applications as ion carriers and cages, they can be used for studying the counterion distributi on in micellar aggregates formed by anionic amphiphiles such as alkyl-sulfa tes. 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/wate r interface and in aqueous micellar solutions of cesium dodecyl sulfate. La ngmuir surface pressure (pi/A) isotherms were performed in order to study t he stability of CAL films and the effect of cesium and potassium ions on th e monolayer properties. In addition, small-angle neutron-scattering (SANS) experiments were carried out in order to determine the structure of the mic ellar system, and the interactions between the ligand and the micellar inte rface. Our study shows that the charge screening at the micellar interface is the predominant phenomenon that rules over the ion transport across liqu id membranes, that is usually performed by macrocyclic ligands. (C) 2000 El sevier Science B.V. All rights reserved.