Aromatic foldamer-derived transmembrane transporters

This review is the first to focus on transmembrane transporters derived from aromatic foldamers, with most studies reported over the past decade. These foldamers have made significant strides in mimicking the essential functions of natural ion channel proteins. With their aromatic backbones rigidified by intramolecular hydrogen bonds or differential repulsive forces, this innovative family of molecules stands out for its structural diversity and functional adaptability. They achieve efficient and selective ion and molecule transport across lipid bilayers via carefully designed helical structures and tunable large cavities. Recent developments in this field highlight the transformative potential of foldamers in therapeutic applications and biomaterial engineering. Key advances include innovative molecular engineering strategies that enable highly selective ion transport by fine-tuning structural and functional attributes. Specific modifications to macrocyclic or helical foldamer structures have allowed precise control over ion selectivity and transport efficiency, with notable selectivity for K+, Li+, H+ and water molecules. Although challenges remain, future directions may focus on more innovative molecular designs, optimizing synthetic methods, improving membrane transport properties, integrating responsive designs that adapt to environmental stimuli, and fostering interdisciplinary collaborations. By emphasizing the pivotal role of aromatic foldamers in modern chemistry, this review aims to inspire further development, offering new molecular toolboxes and strategies to address technological and biological challenges in chemistry, biology, medicine, and materials science.

Redox-Regulated Synthetic Channels: Enabling Reversible Ion Transport by Modulating the Ion-Permeation Pathway

Natural redox-regulated channel proteins often utilize disulfide bonds as redox sensors for adaptive regulation of channel conformations in response to diverse physiological environments. In this study, we developed novel synthetic ion channels capable of reversibly switching their ion-transport capabilities by incorporating multiple disulfide bonds into artificial systems. X-ray structural analysis and electrophysiological experiments demonstrated that these disulfide-bridged molecules possess well-defined tubular cavities and can be efficiently inserted into lipid bilayers to form artificial ion channels. More importantly, the disulfide bonds in these molecules serve as redox-tunable switches to regulate the formation and disruption of ion-permeation pathways, thereby achieving a transition in the transmembrane transport process between the ON and OFF states.

Supramolecular Mechanosensitive Potassium Channel Formed by Fluorinated Amphiphilic Cyclophane

Inspired by mechanosensitive potassium channels found in nature, we developed a fluorinated amphiphilic cyclophane composed of fluorinated rigid aromatic units connected via flexible hydrophilic octa(ethylene glycol) chains. Microscopic and emission spectroscopic studies revealed that the cyclophane could be incorporated into the hydrophobic layer of the lipid bilayer membranes and self-assembled to form a supramolecular transmembrane ion channel. Current recording measurements using cyclophane-containing planer lipid bilayer membranes successfully demonstrated an efficient transmembrane ion transport. We also demonstrated that the ion transport property was sensitive to the mechanical forces applied to the membranes. In addition, ion transport assays using pH-sensitive fluorescence dye revealed that the supramolecular channel possesses potassium ion selectivity. We also performed all-atom hybrid quantum-mechanical/molecular mechanical simulations to assess the channel structures at atomic resolution and the mechanism of selective potassium ion transport. This research demonstrated the first example of a synthetic mechanosensitive potassium channel, which would open a new door to sensing and manipulating biologically important processes and purification of key materials in industries.

Bis(cholyl)-based chloride channels with oxalamide and hydrazide selectivity filters

We report the development of supramolecular bis(cholyl) ion channels by using oxalamide and hydrazide as selectivity filters. The hydrazide system displayed superior chloride transport activity than oxalamide via the formation...

Spiro-based diamond-type nanogrids (DGs) via two ways: 'A1B1'/'A2 + B2' type gridization of vertical spiro-based fluorenol synthons

Regular or well-defined nanogrids with atomically precise extension sites offer an opportunity for covalent nano-architectures as well as frameworks. Previously, we discovered organic nanogrids based on the 2,7-linkage of fluorene via Friedel-Crafts gridization. However, the regularity of nanogrids is not always based on the actual molecular backbone, which leads to ineffective linkage for the more regular complex nanogrids such as nano-windows. Herein, we report the introduction of spirobifluorene, which has more orthogonal shapes, to fix the backbone of nanogridons with regards to the diarylfluorenes. The diamond-type nanogridons (DGs) obtained as a result have the potential feature of cross extension, which is different from their ladder-type counterparts, although they both have four well-defined extension sites. In order to screen efficient monogridon modules, we designed two types of DGs (spiro[fluorene-9,8'-indeno[2,1-b]thiophene] (SFIT)-based DGs-1 and spirobifluorene-based DGs-2) and compared their synthetic routes. The results show that the Friedel-Crafts (F-C) gridization of the A₁B₁ synthon (A₁B₁ mode) offers DGs-1 in 44-50% yields, while the F-C gridization of A₂ + B₂ synthons (A₂ + B₂ mode) is more efficient and gives DGs-2 in 64% yield. Furthermore, unlike in the A₁B₁ mode, the dehydroxylated byproduct and linear polymers were not observed in the A₂ + B₂ mode.

Utilizing an Amino Acid Scaffold to Construct Heteroditopic Receptors Capable of Interacting with Salts under Interfacial Conditions

A 4-nitro-L-phenylalanine scaffold was used to construct effective ion pair receptors capable of binding anions in an enhanced manner with the assistance of alkali metal cations. A benzocrown ether was linked to a receptor platform via the amide function so as to support the squaramide function in anion binding and to allow all three NHs to act simultaneously. The binding properties of the receptors were determined using UV-vis, ¹H NMR, 2D NMR, and DOSY spectroscopy in MeCN and in the solid state by X-ray measurements. Ion pair receptor 2 was found to interact with the most strongly with salts, and the removal of its key structural elements was shown to hinder the receptor action. The amide proton was recognized to switch from having involvement in an intramolecular hydrogen bond to interacting with anions upon complexation. Apart from carboxylates, which promote deprotonation, and other monovalent salts creating 1:1 complexes with the receptor, more complex equilibria were established upon the complexation of 2 with sulfates. Receptor 2 was shown to be capable of the extraction of ion pairs from the aqueous to organic phase and of the cation-enhanced transport chloride and sulfate anions across a bulk chloroform membrane. These features may open the door for its use in regulating ion concertation under interfacial conditions and acting as a potential drug to treat channelopathies.

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.

Advances in anion transport and supramolecular medicinal chemistry

Advances in anion transport by synthetic supramolecular systems are discussed in this article. Developments in the design of discrete molecular carriers for anions and supramolecular anion channels are reviewed followed by an overview of the use of these systems in biological systems as putative treatments for diseases such as cystic fibrosis and cancer.

Effect of charge status on the ion transport and antimicrobial activity of synthetic channels

The charge status of channels formed by pillararene–gramicidin hybrid molecules has a significant impact on their trans-membrane transport properties, membrane-association abilities and antimicrobial activities.

Acylhydrazone functionalized benzimidazole-based metallogel for the efficient detection and separation of Cr3

Chromium(iii) is a kind of microelement and can be converted to the more toxic chromium(vi), which is a carcinogen, by redox cycling. Thus, the development of novel materials for the detection and removal of Cr³⁺ is a very important issue. A novel metallogel chemosensor (BMG-Fe) based on functionalized benzimidazole (BM) and Fe³⁺ was constructed, which could fluorescently detect and separate Cr³⁺. The detection limit of BMG-Fe for Cr³⁺ is 2.62 × 10^-8 M, and it exhibited high sensitivity and selectivity for Cr³⁺. Meanwhile, the absorbing percentage of BMG-Fe for Cr³⁺ is 96.36%, indicating a high separation rate. Interestingly, the sensitivity and ingestion capacity of BMG-Fe for Cr³⁺ are better than that of the simple organogel (BMG). So, the metallogel BMG-Fe could be utilized for the efficient removal of heavy metal ions from waste water.

Lone pair–π vs. σ-hole–π interactions in bromine head-containing oxacalix[2]arene[2]triazines

New bromine head-containing oxacalix[2]arene[2]triazines were synthesized. Owing to the bromine head and complementary V-shaped cavity, the solid state structure showed an intriguing and unique 1D-supramolecular chain-like self-assembly.

One-pot formation of hydrazide macrocycles with modified cavities: an example of pH-sensitive unimolecular cation channels

The number and position of carboxyls in the channel have a significant impact on the membrane-incorporation ability, ion selectivity and NH₄⁺ transport activity of the macrocyclic channels.