SELECTIVE COMPLEXATION BY P-TERT-BUTYLCALIX[6]ARENE IN MONOLAYERS AT THE WATER AIR INTERFACE

Calixarene molecules are very powerful ligands for ions and small mole cules and for this reason they have been studied with several techniqu es as models for host-guest systems. In this paper we report the resul ts of a study on the complexation and structural properties of p-tert- butylcalix[6]arene (CAL6) in monolayer at the water-air interface as a function of temperature and subphase composition. The monolayer prope rties of CAL6 films are fully studied by recording the pi/A spreading isotherms and surface potentials and by calculating the related parame ters [limiting area (A(o)), compressibility modulus (C-s(-1)), dipole moment (mu cos theta)]. Changing the temperature (between 20 and 35 de grees C) and the composition of the aqueous subphase (NaCl, KCl, CsCl, guanidinium thiocyanate) produces strong variations on the monolayer parameters, indicating a different selectivity of the CAL6 ligand for the different monovalent cations. In particular, high selectivity in t he case of cesium is found. Surface potential measurements as well as limiting area values, compared to CPK model calculations, are discusse d in relation to the orientation of the cone-shaped molecules at the w ater-air interface.