Synthetic K⁺/Cl^–-Selective Symporter across a Phospholipid Membrane

Abstract

Synthetic molecules which selectively transport sodium or potassium chloride across a lipid membrane have been prepared. The salt carriers consist of two heteroditopic binding sites, an anion-binding cavity with three hydrogen bond donors and an azacrown ether for binding an alkali metal cation. The association constants between the carriers and chloride ion have been enhanced by 1 order of the magnitude in the presence of sodium or potassium ion in 10% (v/v) CD3OH/CD3CN, due to the formation of a contact ion-pair between the bound cation and chloride as demonstrated by the single-crystal X-ray structure of a sodium chloride complex. A series of transport experiments have demonstrated that the synthetic molecule functions as a mobile carrier of transporting salts via M(+)/Cl(-) symport. Among alkali metal chlorides, the carrier with an 18-azacrown-6 exhibits a strong selectivity toward potassium chloride, while the carrier with a 15-azacrown-5 displays a moderate selectivity for sodium chloride.

Anion Receptor Chemistry

“…Valkenier et al 87 further utilized their most effective anionophore trans-decalin 172d in the study of anion-transport activity with lucigenin in POPC:cholesterol (7:3) giant Lee et al 89 reported two urea-azacrown ion-pair receptors 177 and 178 as symporters for metal cations and chloride anions. The single-crystal structure of 177$NaCl ( Figure 61B) showed the bound NaCl as a contact ion pair.…”

Anion binding with urea and thiourea derivatives

“…Structure of receptor 50.Membrane transport experiments were also conducted with receptors 51 and 52 in the work of Jeong et al(Fig. 35)[67]. Structures of receptors 51a, 51b, and 52.Receptor 51 has heteroditopic binding sites which enabled the binding of both, a cation and an anion of alkali metal halides, thus forming contact-ion pair.…”

Ion‐Pair Complexation with Dibenzo[21]Crown‐7 and Dibenzo[24]Crown‐8 bis‐Urea Receptors

“…Nevertheless, ion‐pair recognition has attracted a growing interest in supramolecular chemistry and anion/cation recognition. Utilizing ion‐pair receptors in various applications such as salt solubilisation and extraction, membrane transport, catalysis, sensing, and logic gates offers a strong motive to further develop these systems. In spite of the intriguing features of ion‐pair receptors, a surprisingly limited amount of such systems have been developed so far.…”