New upper rim pyridine-bridged calix(4)arenes: synthesis and complexation properties toward neutral molecules and ammonium ions in organic media

A new series of calix(4)arenes, diametrically bridged at the upper rim with pyridino systems, were synthesized. The shape, rigidity and chemical structure of the bridge affected the host-guest complexation characteristics of these systems in solution toward several neural molecules with acidic C-H bonds. Also, selective complexation of methylammonium tosylate in comparison with other ammonium salts was noticed and the strength of this complexation was improved by electron-donor ability of the p-substituent on the pyrimidine moiety of the calixarene host.