Transmembrane Anion Transport Mediated by Halogen Bonds: Using Off-Center Charges

Synthetic anion transporters are promising therapeutic agents designed to emulate the specialized role of certain transmembrane proteins that maintain the ion concentration in cells. In the last few years, besides hydrogen bonds and ion pairs, halogen bonds have also been explored to promote the association between the synthetic molecule and the anion and their subsequent transport. This interaction is due to an anisotropic charge distribution on the halogen, and therefore, modeling halogen bonds is not a trivial task using classical force field methods that typically rely on point-charge models.Herein, a computational protocol capable of dealing with halogen bonds is presented. This protocol takes advantage of the addition of an off-center particle during the charge fitting procedure, and the resulting set of charges can be used along with the classical force field parameters from GAFF or GROMOS 54A7.

Anion Transmembrane Nanochannels from Pore-Forming Helices Constructed by the Dynamic Covalent Reaction of Dihydrazide and Dialdehyde Units

Anion transmembrane nanochannels constructed from dynamic covalent helices (DCHs) are reported. The dynamic covalent structures can be synthesized by one-pot dynamic covalent reactions and helically self-fold into nanotubes through intramolecular hydrogen bonding and π-π interactions. Such helical structures can vertically self-assemble into long nanofibers under π-π stacking and their hollow nanocavities finally form ion permeation pathways across the lipid membranes. Single-channel electrophysiology signals provide solid evidence of DCHs following the channel rather than the carrier mechanism. Owing to the pore-forming capacity of DCHs, nanochannels are able to accelerate the movement of anions across lipid membranes with high transport activity (EC₅₀ =0.08 mol %). Moreover, DCH channels show dehydration energy dependent anion selectivity. This report highlights the importance of such DCHs as general channel scaffolds with economical synthesis and special nanocavities.

Channel Confinement of Aromatic Petrochemicals via Aryl-Perfluoroaryl Interactions With a B←N Host

We report channel confinement properties of an electron-deficient boron host derived from the orthogonal B←N interaction between a boronic ester and trans-pentafluorostilbazole. The boron host forms one-dimensional channels in the crystalline solid state when crystallized with common electron-rich aromatic petrochemicals (i.e., benzene, toluene, o-xylene) to form solvates and a cocrystal with stilbene. Molecular confinement of the electron-rich molecules in the solids is achieved through a combination of aryl-perfluoroaryl interactions (π-πF) and hydrogen bonds.

Fluorinated bisbenzimidazoles: a new class of drug-like anion transporters with chloride-mediated, cell apoptosis-inducing activity

Fluorinated bisbenzimidazoles were synthesized as a new class of drug-like anion transporters with chloride-mediated, cell apoptosis-inducing activity.

Interplay of Lewis acidity, intramolecular O→Sn interactions and selectivity: organotin-functionalized crown ethers as ditopic hosts for sodium and potassium halides

Not only ditopic complexation, but also selectivity has been realized by increasing the Lewis acidity of tin atom in organotin-functionalized crown ethers.

Melittin-induced alterations in morphology and deformability of human red blood cells using quantitative phase imaging techniques

Here, the actions of melittin, the active molecule of apitoxin or bee venom, were investigated on human red blood cells (RBCs) using quantitative phase imaging techniques. High-resolution real-time 3-D refractive index (RI) measurements and dynamic 2-D phase images of individual melittin-bound RBCs enabled in-depth examination of melittin-induced biophysical alterations of the cells. From the measurements, morphological, intracellular, and mechanical alterations of the RBCs were analyzed quantitatively. Furthermore, leakage of haemoglobin (Hb) inside the RBCs at high melittin concentration was also investigated.

Anion Recognition Based on a Combination of Double-Dentate Hydrogen Bond and Double-Side Anion-π Noncovalent Interactions

Anion recognitions between common anions and a novel pincer-like receptor (N,N'-bis(5-fluorobenzoyloxyethyl)urea, BFUR) were theoretically explored, particularly on geometric features of the BFUR@X (X = F^-, Cl^-, Br^-, I^-, CO₃^2-, NO₃^-, and SO₄^2-) systems at a molecular level in this work. Complex structures show that two N-H groups as a claw and two -C₆F₅ rings on BFUR as a pair of tweezers simultaneously interact with captured anions through cooperative double-dentate hydrogen bond and double-side anion-π interactions. The binding energies and thermodynamic information indicate that the recognitions of the seven anions by BFUR in vacuum are enthalpy-driven and entropy-opposed, which occur spontaneously. Although the binding energy ΔE_cp between F^- and BFUR is relatively high (289.30 kJ·mol^-1), ΔE_cp, ΔG, and ΔH of the recognition for CO₃^2- and SO₄^2- are much larger than the cases of F^-, Cl^-, Br^-, I^-, and NO₃^-, suggesting that BFUR is an ideal selective anion receptor for CO₃^2- and SO₄^2-. Additionally, energy decomposition analysis based on localized molecular orbital energy decomposition analysis (LMO-EDA) was performed; electronic properties and behaviors of the present systems were further discussed according to calculations on frontier molecular orbital, UV-vis spectra, total electrostatic potential, and visualized weak interaction regions. The present theoretical exploration of BFUR@X (X = F^-, Cl^-, Br^-, I^-, CO₃^2-, NO₃^-, and SO₄^2-) systems is fundamentally crucial to establish an anion recognition structure-property relationship upon combination of different noncovalent interactions, that is, double-dentate hydrogen bond and double-side anion-π interactions.

Synthesis of a dimeric 3α-hydroxy-7α,12α-diamino-5β-cholan-24-oate conjugate and its derivatives, and the effect of lipophilicity on their anion transport efficacy

A dimeric 3α-hydroxy-7α,12α-diamino-5β-cholan-24-oate conjugate and its derivatives were synthesized, and lipophilicity was found to significantly affect their anion transport efficacy.

Ion pair complexes and anion binding in the solution of a ditopic receptor

The synthesis and crystal structures with alkali halides of a ditopic benzo-15-crown-5 bis-urea receptor have been presented. In addition, the anion binding properties of and its alkali metal complexes in solution are presented. A comprehensive single-crystal X-ray crystallographic study of , all together 13 crystal structures, including the ion pair complexes with NaCl, NaBr, NaI, KF, KCl, KBr, KI, RbF, RbCl, and RbI, give a detailed view of how behaves in the solid-state with different alkali halides depending on the size of the cation and anion. In the solid-state forms a 1 : 1 complex with a sodium cation and the anion is complexed as a contact (NaCl) or a separate ion pair (NaBr, NaI). With larger potassium and rubidium cations assembles into a 2 : 1 complex and forms a separated ion pair complex with the anion. Reflecting the crystal structures the forms a 1 : 1 complex with Na(+) in solution, and a 2 : 1 complex with K(+), which were verified by Job's plot analysis in 4 : 1 CDCl3/dimethyl sulfoxide. The binding strength of the monomeric [·Na](+) and the dimeric [2·K](+) toward chloride, bromide and iodide anions was studied by (1)H NMR titrations in 4 : 1 CDCl3/DMSO, and a clear turn-on effect of the cation complexation compared to the neutral receptor alone (Ka with for Cl(-), Br(-) and I(-) being 832, 174 and 32 M(-1), respectively) was observed. The monomeric [·Na](+) binds chloride 9, bromide 8, and iodide 12 times stronger than , while for the dimeric [2K](+) the corresponding increase in binding is 51 (Cl(-)), 84 (Br(-)), and 22 (I(-)) times with the same stoichiometric ratios as observed for the ion pair complexes in the solid-state.

Highly efficient anion transport mediated by 1,3-bis(benzimidazol-2-yl)benzene derivatives bearing electron-withdrawing substituents

1,3-Bis(benzimidazol-2-yl)benzene exhibits potent anionophoric activity through a process of anion exchange with a minor level of proton/anion symport. Modification of 1,3-bis(benzimidazol-2-yl)benzene with strong electron-withdrawing substituents, such as trifluoromethyl and nitro groups, leads to up to 789-fold increase in the activity. The benzimidazolyl-NH fragments, the relative position and the number of the benzimidazolyl groups on the central phenyl scaffold play an essential role in the transport.

Fluorine substitution effects of halide anion receptors based on the combination of a distinct hydrogen bond and anion–π noncovalent interactions: a theoretical investigation

Fluorine-substitution effects on anion–π interaction were deeply explored, and a more feasible and rational geometric criterion for halide-anion–π contact is established via three inequalities.

Oxacalix[2]arene[2]triazine based ion-pair transporters

Heteracalixaromatics are a new generation of macrocyclic hosts showing a unique structure and versatile recognition properties towards various guests.

QSAR analysis of substituent effects on tambjamine anion transporters

The transmembrane anion transport activity of 43 synthetic molecules based on the structure of marine alkaloid tambjamine were assessed in model phospholipid (POPC) liposomes. The anionophoric activity of these molecules showed a parabolic dependence with lipophilicity, with an optimum range for transport efficiency. Using a quantitative structure-transport activity (QSAR) approach it was possible to rationalize these results and to quantify the contribution of lipophilicity to the transport activity of these derivatives. While the optimal value of log P and the curvature of the parabolic dependence is a property of the membrane (and so similar for the different series of substituents) we found that for relatively simple substituents in certain locations on the tambjamine core, hydrophobic interactions clearly dominate, but for others, more specific interactions are present that change the position of the membrane hydrophobicity parabolic envelope.

Anion binding and transport properties of cyclic 2,6-bis(1,2,3-triazol-1-yl)pyridines

A series of cyclic 2,6-bis-(1,2,3-triazolyl)-pyridine anion receptors with thiourea functionalities were synthesized by click reaction of 2,6-diazidopyridine with protected propargylamine followed by condensation of a bisthiocyanate derivative with a series of diamines. Their chloride binding affinities as well as their transport properties in POPC bilayers were examined. These receptors were found to function as anion carriers, which can mediate both Cl(-)/NO3(-) antiport and H(+)/Cl(-) symport, and the transport activity of these hosts were dominated by their lipophilicity.

Does lipophilicity affect the effectiveness of a transmembrane anion transporter? Insight from squaramido-functionalized bis(choloyl) conjugates

Lipophilicity was found to have little effect on the effectiveness of squaramido-functionalized bis(choloyl) conjugates.

Luminescent probes for the bioimaging of small anionic species in vitro and in vivo

This comprehensive review examines recent developments in the use of fluorescent/luminescent probes for the bioimaging of anionic species. Images in cover art reproduced with permission from ref. 290 and 306.

Metal-free, one-pot conversion of proline derivatives into 2-aryl-3-iodo pyrrolidines by a sequential scission-iodination-arylation process

The metal-free, direct conversion of readily available proline derivatives into 2-aryl-3-iodopyrrolidines is carried out under mild conditions and in good yields, using a sequential radical decarboxylation-oxidation-iodination-arylation reaction. These iodinated pyrrolidines are valuable precursors of other compounds. For instance, they can be cyclized to tricyclic compounds or undergo dehalogenation to 2-aryl-2,5-dihydro-1H-pyrroles, which are iminosugar and 2-arylpyrrole precursors. This process provides a short pathway to a variety of alkaloid and drug analogues of potential pharmaceutical interest.

Transmembrane anion transport and cytotoxicity of synthetic tambjamine analogs

Synthetic tambjamine analogs bearing aromatic enamine moieties are highly efficient transmembrane anion carriers, triggering apoptosis in several cancer cell lines.

2,4,7-Triphenylbenzimidazole: the monomeric unit of supramolecular helical rod-like transmembrane transporters

Supramolecular compact helical rod as transmembrane anion transporter.

Hydrogen bonding effects in anion binding calixarenes

The interplay of anion binding, intra- and intermolecular hydrogen boning patterns in a range of receptors and sensors for chloride anion are discussed.