Oligoether-strapped calix[4]pyrrole: an ion-pair receptor displaying cation-dependent chloride anion transport

A ditopic ion-pair receptor (1), which has tunable cation- and anion-binding sites, has been synthesized and characterized. Spectroscopic analyses provide support for the conclusion that receptor 1 binds fluoride and chloride anions strongly and forms stable 1:1 complexes ([1?F]? and [1?Cl]?) with appropriately chosen salts of these anions in acetonitrile. When the anion complexes of 1 were treated with alkali metal ions (Li+, Na+, K+, Cs+, as their perchlorate salts), ion-dependent interactions were observed that were found to depend on both the choice of added cation and the initially complexed anion. In the case of [1?F]?, no appreciable interaction with the K+ ion was seen. On the other hand, when this complex was treated with Li+ or Na+ ions, decomplexation of the bound fluoride anion was observed. In contrast to what was seen with Li+, Na+, K+, treating [1?F]? with Cs+ ions gave rise to a stable, host-separated ion-pair complex, [F?1?Cs], which contains the Cs+ ion bound in the cup-like portion of the calix[4]pyrrole. Different complexation behavior was seen in the case of the chloride complex, [1?Cl]?. Here, no appreciable interaction was observed with Na+ or K+. In contrast, treating with Li+ produces a tight ion-pair complex, [1?Li?Cl], in which the cation is bound to the crown moiety. In analogy to what was seen for [1?F]?, treatment of [1?Cl]? with Cs+ ions gives rise to a host-separated ion-pair complex, [Cl?1?Cs], in which the cation is bound to the cup of the calix[4]pyrrole. As inferred from liposomal model membrane transport studies, system 1 can act as an effective carrier for several chloride anion salts of Group?1 cations, operating through both symport (chloride+cation co-transport) and antiport (nitrate-for-chloride exchange) mechanisms. This transport behavior stands in contrast to what is seen for simple octamethylcalix[4]pyrrole, which acts as an effective carrier for cesium chloride but does not operates through a nitrate-for-chloride anion exchange mechanism