Synthesis and binding properties of calix[4]arene diamide dicarboxylic acids

Abstract

Calix[4]arenes diametrically substituted at the lower rim with two carboxylic acid and two tertiary amide binding groups were obtained in good yields and their acid–base properties studied in methanol solution. Complexation studies, performed in methanol by potentiometry, show that mononuclear (MLH_z, z  =  0, 1) or dinuclear (M₂L) complexes are formed with alkali metal cations, whereas M_xL₂H_z (x  =  1, 2, z  =  0, 1) species, involving two ligands, are also present with alkaline-earth cations. Both ligands 2 and 3 show a remarkable selectivity for Ca²⁺ and Sr²⁺ among alkali and alkaline-earth metal ions.