Oligoether‐Strapped Calix[4]pyrrole: An Ion‐Pair Receptor Displaying Cation‐Dependent Chloride Anion Transport

Abstract

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.

Calix[4]pyrroles: versatile molecular containers with ion transport, recognition, and molecular switching functions

“…The actual transfer of the Pt(II) centre to AMP was inferred by the appearance of signals corresponding to 9 and a broadening of the AMP proton resonances. The presence of [Pt(OH) 2 …”

“…This system has one anion binding site and two possible cation binding sites. 2 The binding properties of this hybrid calix [4]pyrrole receptor are dependent on the choice of Group I metal counter cations. For example, 1 H NMR spectroscopic studies revealed that the addition of potassium and caesium cations (as the perchlorate salts) to 10% CD 3 OD-CD 3 CN solutions of the preformed TBA + [7ÁF] À complex gives rise to two distinct ion pair complexes ( Fig.…”

“…1 As a class, calix [4]pyrroles have been extensively examined as anion receptors for the last two decades and it is now appreciated that these non-aromatic tetrapyrroles bind a variety of anions including, halides, acetates, phosphates in aprotic media. [2][3][4] More recently, potential applications of calix [4]pyrroles as carriers, species capable of transporting ions across lipophilic membranes, have been reported. [5][6][7][8][9][10] In addition to being relatively easy to synthesise, the ditopic nature of calix [4]pyrrole derivatives allows them to act as receptors and extractants for both anions and cations under appropriately chosen conditions.…”

Anion binding to a tetracopper resorcinarene-based complex

“…These include the calix [4]arene that has cationic ammonium groups for binding (13) and a calix [4]arene with amidourea groups that is a colorimetric anion receptor (14). Along with these are calix [4]pyrroles with etheric handles which show a strong affinity for chloride (15,16), a zinc cyclen calix [4]arene that binds anions (17) and a resorcinarene compound that binds anions through C -H interactions (18).…”

Lithium-selective phosphine oxide-based ditopic receptors show enhanced halide binding upon alkali metal ion coordination

“…1–14 This can be attributed to the increases in selectivity and binding strength observed when ion-pairs are cooperatively targeted over a single ion. 15–17 These receptors have been applied in a number of areas of research such as membrane transport, extraction, salt solubilization and sensing applications.…”