Cation Binding Selectivity of Partially Substituted Calix[4]arene Esters (original) (raw)
Partially substituted calix[4]arene ethyl ester derivatives were synthesized as important precursors for new series of non-symmetrical ion and molecule receptors by reacting p-t-butyl calix[4]arene and ethyl bromoacetate. Characteristics of PVC-membrane ion-selective electrodes based on the mono-and di-ester derivatives were compared to those of the well-known calix[4]arene tetraester cationophore. Sodium selectivity is only manifested with the tetraester derivative, whereas the diester complexes potassium and caesium, as well as sodium. Energy-minimized structures for the complexes show the ester groups are involved in sodium complexation for the tetraester and diester derivatives, whereas for the monester, the aryl macrocycle is more important. This provides an excellent example of the critical importance of preorganization on host-guest selectivity, which in turn defines the selectivity of chemical sensors based on such receptors. The influence of this selective ion-binding behavior on the characterization of these derivatives using mass spectroscopy is discussed.
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