Probing and evaluating transmembrane chloride ion transport in double walled trifluorophenyl/phthalimide extended calix[4]pyrrole-based supramolecular receptors†

Abstract

Therapeutic applications have sparked increased interest in the use of synthetic anion receptors for ion transport across lipid membranes. In this context, the construction of synthetic transmembrane transporters for the physiologically important chloride ion is currently of enormous interest. As a result, considerable effort is being devoted to the design and synthesis of artificial transmembrane chloride ion transporters. However, only inadequate progress has been made in developing macrocyclic chloride ion transporters using the fundamental principles of supramolecular chemistry, and hence this field entails fostering investigations. In this investigation, the synthesis of two new double walled trifluorophenyl/phthalimide extended calix[4]pyrrole (C4P) receptors (3 and 7) has been successfully reported. ¹H-NMR titration and HRMS studies confirmed the 1 : 1 binding stoichiometry of the chloride ion with these receptors in the solution phase (only receptor 3b was studied by ¹H-NMR). Regarding ion transport of 3b and 7, when studied in the HPTS-based vesicular system, 3b showed better activity with an EC₅₀ value of 0.39 μM. The detailed ion transport studies on 3b have revealed that ion transport occurs through the Cl⁻/NO₃⁻ antiport mode.