PREPARATION AND PROPERTIES OF ORGANIC DISPERSIONS OF MONODISPERSE SILICA RECEPTOR COLLOIDS GRAFTED WITH CALIXARENE DERIVATIVES OR ALKYL CHAINS

We introduce cation-selective receptor colloids consisting of a monodi sperse inorganic silica core grafted with an organic layer containing calixarene receptor molecules. The surface layer is designed to provid e chemical selectivity (toward Cs+) as well as colloidal stability in organic solvents of interest in which silica spheres otherwise may flo cculate. Grafting procedures for commercial- and laboratory-made silic a dispersions are investigated for bis[1-(11-hydroxyundecyl)oxy]calix[ 4]arene-crown-6 (designed and synthesized for this purpose), octadecyl alcohol, and mixtures (''cografting'') of both compounds. Special att ention is given to the nature of the solvent, which markedly influence s grafting densities and colloidal stability during and after grafting procedures. NMR, elemental analysis, and light scattering are used to characterize a variety of carefully purified, grafted silica dispersi ons and to demonstrate, among other things, the presence of calixarene groups on the silica spheres. Preliminary complexation experiments wi th cesium chloride are reported. NMR and electrophoresis indicate that calixarene- silica colloids indeed are receptors for cesium cations.