Squaramide Calix[4]pyrroles for Anion Transport

In this paper we demonstrate the transmembrane chloride transport properties of a series of calix[4]pyrroles appended with squaramide moieties for the first time. The flexibility imparted by the methylene group between the squaramide and macrocycle allowed for changes between 1 : 1 and 1 : 2 (host : guest) binding modes at high chloride concentrations. Electroneutral transport was observed in the substituted compounds compared to the parent calix[4]pyrrole, with an improvement in transport activity when distal electron withdrawing groups were appended. These results highlight the important role of the squaramide in facilitating transmembrane transport for the substituted macrocycles.