Ditopic Ion Transport Systems: Anion–π Interactions and Halogen Bonds at Work

Abstract

Single-atom exchange series are introduced to extract the individual contributions of halogen bonds and anion–π interactions to the transport of anions across lipid bilayer membranes (see picture). Known cation binding sites are used for counterion activation of the neutral calix[4]arene transporters. The experimental evidence for anion transport with halogen bonds is unprecedented

Catalysis with Pnictogen, Chalcogen, and Halogen Bonds

“…[25] Chloride binding via pnictogen bonds to 1 was over one order of magnitude stronger than chalcogen bonding to bis(pentafluorophenyl)tellurium 4 (K D = 470 AE 70 mm), which in turn was three times stronger than the known halogen bonding to iodopentafluorobenzene 6 (K D = 1370 AE 30 mm). [22,23] This trend correlates with the increasing molecular polarizability going from main group VII to Vi n row 5inthe periodic table (Table 1). [13] Going one row up in the periodic table,asharp drop in binding ability was observed for all catalysts.H owever, similar trends were measured.…”

Anion−π Interactions with Fluoroarenes

“…Even halogen bonding seems to overrule the interaction between anions and the π-system of electrondeficient arenes. Nevertheless anion−π interactions gained considerable attention in anion-recognition and host−guest chemistry, 163 and due to recent findings their participation in ion transport, 162 …”

“…161 Metrangolo and co-workers reported a series of ditopic calix [4]arene receptors 61a−f ( Figure 70) using anion−π, hydrogen, or halogen bonding for ion transport. 162 Surprisingly, receptor 61a showed the highest transport activity. Computational studies suggest the participation of anion−π interactions in the transport of the anion by 61a.…”

“…Molecular structure of the investigated ion pair receptors 61 for transport studies by Metrangolo, Resnati, Matile, and coworkers. 162 high transport activities and a nice example of the importance and contribution of anion−π interactions in solution.…”

Anion receptor chemistry: highlights from 2008 and 2009

“…107 The benefit of ditopic receptors is that they can co-transport ion pairs thereby avoiding temporary separation of charge. These receptors bind TMA (tetramethylammonium) counter cations in the upper rim of the calix [4]arene, while substitutions at the lower rim allow for anion binding.…”