Spectroscopic and electrochemical studies of two distal diethyl ester azocalix[4]arene derivatives

Binding properties of two distal diethyl ester azocalix[4]arene derivatives (1–3) with alkali, alkaline earth and transition metal ions were investigated by UV/vis spectroscopy and voltammetry. With respect to the chromogenic and voltammetric behavior of hosts upon metal ion complexation, two distal diethyl ester azocalix[4]arene derivatives (1 and 2) showed a good selectivity toward Ca2+ over many cations. The presence of two proximal hydroxyl groups and two esters in ligands was observed to play an important role in exhibiting cation complexation by extensive control experiments with corresponding azocalix[4]arene derivatives.