Determination of binding constants of various alkali metal cations with p-sulfonatocalix[8]arene by using inclusion equilibrium with thionine dye

Counterion effect on sulfonatocalix[n]arene recognition

Sulfonatocalixarenes, like other ionic receptors, possess counterions that can affect the molecular recognition process. In the present review it is shown that the competitive effect of the alkaline cations frequently used as counterions determines not only the magnitude of the external guest association constant, but also the stoichiometry of the complexes. Experimental evidences are shown about the interaction of the counterions with sulfonatocalixarene, allowing to quantify its association equilibrium constants. The counterions recognition will be a competitive process that must be taken into account when investigating the interaction of calixarenes with an external guests. When the external guest is a neutral molecule it will be possible to form ternary complexes where the counterion shows a competitive and cooperative effect. By increasing the size of the receptor, sulfonatocalix[6] and sulfonatocalix[8]arene, the complexity of the system is increased due to the formation of counterion complexes with stoichiometries 1:1 and 1:2. In the presence of an external guest, the formation of heteroternary complexes with 1:1:1 stoichiometries including a counterion and an organic cation will be possible.

A journey from calix[4]arene to calix[6] and calix[8]arene reveals more than a matter of size. Receptor concentration affects the stability and stoichiometric nature of the complexes

An in-depth study provides the basis for an accurate characterization of supramolecular systems based on p-sulfonatocalix[6,8]arenes.

High affinity of p-sulfonatothiacalix[4]arene with phenanthroline-diium in aqueous solution

The molecular binding behavior of sulfonated calixarenes with phenanthroline-diium guests were systemically investigated. p-Sulfonatothiacalix[4]arene shows a high affinity with phenanthroline-diium guests in the order of magnitude of 105 M⁻¹.