Anion Transport with Pnictogen Bonds in Direct Comparison with Chalcogen and Halogen Bonds

Abstract

In this communication, we introduce transmembrane anion transport with pnictogen-bonding compounds and compare their characteristics with chalcogen-and halogen-bonding analogs. Tellurium-centered chalcogen bonds are at least as active as antimony-centered pnictogen bonds, whereas iodine-centered halogen bonds are three orders of magnitude less active. Irregular, voltage-dependent single-channel currents, high gating charges, efficient dye leakage and small Hill coefficients support the formation of bulky, membrane-disruptive supramolecular amphiphiles by tris(perfluorophenyl)stibanes that bind anions "too strongly." In contrast, the chalcogen-bonding bis(perfluorophenyl)tellanes do not cause leakage and excel as carriers with nanomolar activity, P(Cl/Na) = 10.4 for anion/cation selectivity and P(Cl/NO3) = 4.5 for anion selectivity. Selectivities are lower with pnictogen-bonding carriers because their membrane-disturbing 3D structure affects also weaker binders (P(Cl/Na) = 2.1, P(Cl/NO3) = 2.5). Their 2D structure, directionality, hydrophobicity and support from proximal anion-π interactions are suggested to contribute to the unique power of chalcogen bonds to transport anions across lipid bilayer membranes. The integration of unorthodox interactions into functional systems is of fundamental importance because it promises access to new activities. 1 Synthetic transport systems 2 have emerged as an attractive tool to assess the functional relevance of such interactions. Realized examples include anion-π interactions in many variations, 1 halogen bonds 3,4 and, more recently, also chalcogen bonds. 5,6 In the following, we elaborate on anion transport with pnictogen bonds in direct comparison to chalcogen and halogen bonds. These so-called s-hole interactions 7,8 originate from highly localized areas of highly positive charge density that appear on heavier and p-block elements. Associated with s* orbitals, the s holes appear at the opposite side of the covalent bonds and deepen with increasing electron deficiency of the atom. As a result, there is one s hole available per atom for halogen bonds, 9 two for chalcogen, 10 three for pnictogen 11,12 and four for tetrel bonds (Figure 1). 7,8 Increasing with polarizability, the depth of the s holes

Redox-controlled chalcogen and pnictogen bonding: the case of a sulfonium/stibonium dication as a preanionophore for chloride anion transport

“…21 Advances in the eld of hydrogen-bond donor anionophores have inspired parallel efforts based on chloridophilic main group compounds. [22][23][24][25][26][27] Owing to their elevated and welldocumented anion affinity, antimony derivatives have drawn attention. In a recent study, Matile and co-workers showed that SbPh(C 6 F 5 ) 2 is an active chloride anion transporter that interacts with the anion via pnictogen-bonding.…”

“…In a recent study, Matile and co-workers showed that SbPh(C 6 F 5 ) 2 is an active chloride anion transporter that interacts with the anion via pnictogen-bonding. 24 Based on the understanding that such interactions are greatly strengthened by oxidation of the antimony center, 28,29 our group concomitantly introduced a family of stibonium cations (C) 30,31 whose anion transport activity is controlled both by the Lewis acidity of the antimony centre and the lipophilic exterior projected by the aryl substituents. 25 Our interest in main group-based anion receptors 32,33 has also led us to consider the use of sulfonium cations for anion capture via chalcogen-bonding, [34][35][36] as in the case of D which forms an isolable uoride anion complex.…”

Development of a Library of Thiophene‐Based Drug‐Like Lego Molecules: Evaluation of Their Anion Binding, Transport Properties, and Cytotoxicity

“…The development of small drug‐like molecules capable of mediating selective transmembrane anion transport remains imperative, and is a field of intensive research . Most of these molecules have been designed by applying knowledge acquired through the development of anion receptors, coupling natural or synthetic platforms with suitable binding units that operate through conventional or unconventional hydrogen bonds, involving halogen‐, chalcogen‐, or pnictogen‐bonding interactions, or even through anion–π interactions . Beyond anion‐binding strength, the anion‐transport ability of a synthetic receptor is also strongly dependent on its ability to partition into the lipid bilayer, that is, its partition coefficient, which can be tuned by the addition of structural motifs with different lipophilicities, such as alkyl chains, aromatic groups, or fluorinated units .…”

Noble Gas Bonding Interactions Involving Xenon Oxides and Fluorides

“…Furthermore, interactions involving aromatic rings (π–π, C–H⋯π, lone pair–π, ion–π) are also commonly used in both fields [ 11 , 12 , 13 , 14 ] being more relevant those involving electron-rich and/or electron-poor π-surfaces, since they exhibit stronger interaction energies. Moreover, other more unconventional interactions are gaining the interest of the scientific community and are increasingly taken into consideration for the construction of molecular receptors and catalysts [ 15 , 16 , 17 , 18 , 19 , 20 ]. These interactions can be divided into σ–hole [ 21 , 22 , 23 , 24 ] and π–hole interactions [ 25 , 26 , 27 , 28 , 29 ] and are nowadays entered into the toolkit supramolecular chemists.…”