Interfacial Interactions of Cations with Amphiphilic Dihydroxyphosphonyl-calix-[4]-arene Mesosystems

Abstract

Two novel amphiphilic phosphorylated-calix-[4]-arenes, 5,11,17,23-tetrakis(dihydroxyphosphonyl)-25,26,27,28-tetradecyloxy-calix-[4]-arene and 5,11,17,23-tetrakis(dihydroxyphosphonyl)-25,26,27,28-tetradodecyloxy-calix-[4]-arene, have been synthesized, and their interactions with the cations Na+, K+, Mg2+, and Ca2+ have been measured at varying concentrations of the chloride salts. The systems were studied both at the air−water interface and in aqueous suspension as colloidal nanostructures. In the Langmuir experiments, monolayer expansion and increase in collapse pressure were observed for Na+ at a concentration of 145 mM. For Mg2+, there was monolayer expansion accompanied by the formation of a second phase at a subphase concentration of 30 mM. In contrast, in the case of Ca2+ there is an apparent contraction of the monolayer. The nanostructures were imaged by means of atomic force microscopy in the noncontact mode. As aqueous dispersions, no change in size or stability of the colloidal systems was observed with the monovalent cations; however, for the divalent cations at concentrations above 3 mM for Mg2+ and 3 mM for Ca2+ there is aggregation and flocculation of the dispersions.