SYNTHESIS AND PROPERTIES OF NEW CALIXARENE-BASED DITOPIC RECEPTORS FOR THE SIMULTANEOUS COMPLEXATION OF CATIONS AND CARBOXYLATE ANIONS

Calix[4]arene tetramide mono(thio)urea derivatives 5a,b and 9 are tabl e to solubilize solid sodium salts of different anions in CDCl3 thanks to their ability to complex simultaneously the cation at the lower ri m and the anion at the upper rim. Therefore they behave as ditopic rec eptors. Binding studies in [H-2(6)]DMSO performed only on the thiourea derivatives allowed us to establish that these receptors complex carb oxylates better than spherical anions and that receptor 9 having the t hiourea group directly connected to the aromatic nucleus is more effic ient than 5a, which has a CH2 spacer between the two units; in the lat ter case good selectivity for the acetate anion is observed. Complexat ion of sodium ion by the amide groups at the lower rim causes an incre ase in the anion binding properties of receptor 9 and has little effec t on receptor 5a. This is explained by the effects of the cation encap sulation on the hydrogen bonding ability of the thiourea units in the two receptors.