Highly Selective Artificial Potassium Ion Channels Constructed from Pore‐Containing Helical Oligomers

A biomimetic ion channel shortens the QT interval of type 2 long QT syndrome through efficient transmembrane transport of potassium ions

Potassium ion transport across myocardial cell membrane is essential for type 2 long QT syndrome (LQT2). However, the dysfunction of potassium ion transport due to genetic mutations limits the therapeutic effect in treating LQT2. Biomimetic ion channels that selectively and efficiently transport potassium ions across the cellular membranes are promising for the treatment of LQT2. To corroborate this, we synthesized a series of foldamer-based ion channels with different side chains, and found a biomimetic ion channel of K+ (BICK) with the highest transport activity among them. The selected BICK can restore potassium ion transport and increase transmembrane potassium ion current, thus shortening phase 3 of action potential (AP) repolarization and QT interval in LQT2. Moreover, BICK does not affect heart rate and cardiac rhythm in treating LQT2 model induced by E4031 in isolated heart as well as in guinea pigs. By restoring ion transmembrane transport tactic, biomimetic ion channels, such as BICK, will show great potential in treating diseases related to ion transport blockade. STATEMENT OF SIGNIFICANCE: Type 2 long QT syndrome (LQT2) is a disease caused by K+ transport disorder, which can cause malignant arrhythmia and even death. There is currently no radical cure, so it is critical to explore ways to improve K+ transmembrane transport. In this study, we report that a small-molecule biomimetic ion channel BICK can efficiently simulate natural K+ channel proteins on the cardiomyocyte and cure E4031-induced LQT2 in guinea pig by restoring K+ transport function for the first time. This study found that the potassium transmembrane transport by BICK significantly reduced the QT interval, which provides a conceptually new strategy for the treatment of LQT2 disease.

Efficient Sodium Transmembrane Permeation through Helically Folded Nanopores with Natural Channel-Like Ion Selectivity

The selective transmembrane permeation of sodium ions achieved by biomimetic chemistry shows great potential to solve the problem of sodium ion transport blockade in diseases, but its implementation faces enormous difficulties. Herein, we design and synthesize a series of helically folded nanopores by employing a quinoline-oxadiazole structural sequence to finely replicate the pentahydrate structure of sodium ions. Surprisingly, these nanopores are capable of achieving sodium transmembrane permeation with ion selectivity at the level of natural sodium channels, as observed in rationally designed nanopores (M1-M5) with Na+/K+ ion selectivity ratio of up to 20.4. Moreover, slight structural variations in nanopore structures can switch ion transport modes between the channel and carrier. We found that, compared to the carrier mode, the channel mode not only transports ions faster but also has higher ion selectivity during transmembrane conduction, clearly illustrating that the trade-off phenomenon between ion selectivity and transport activity does not occur between the two transport modes of channel and carrier. At the same time, we also found that the spatial position and numbers of coordination sites are crucial for the sodium ion selectivity of the nanopores. Moreover, carrier M1 reported in this work is totally superior to the commercial Na+ carrier ETH2120, especially in terms of Na+/K+ ion selectivity, thus being a potentially practical Na+ carrier. Our study provides a new paradigm on the rational design of sodium-specific synthetic nanopores, which will open up the possibility for the application of artificial sodium-specific transmembrane permeation in biomedicine and disease treatment.

Non-Covalently Stapled H+ /Cl- Ion Channels Activatable by Visible Light for Targeted Anticancer Therapy

The development of stimuli-responsive artificial H+ /Cl- ion channels, capable of specifically disturbing the intracellular ion homeostasis of cancer cells, presents an intriguing opportunity for achieving high selectivity in cancer therapy. Herein, we describe a novel family of non-covalently stapled self-assembled artificial channels activatable by biocompatible visible light at 442 nm, which enables the co-transport of H+ /Cl- across the membrane with H+ /Cl- transport selectivity of 6.0. Upon photoirradiation of the caged C4F-L for 10 min, 90 % of ion transport efficiency can be restored, giving rise to a 10.5-fold enhancement in cytotoxicity against human colorectal cancer cells (IC50 =8.5 μM). The mechanism underlying cancer cell death mediated by the H+ /Cl- channels involves the activation of the caspase 9 apoptosis pathway as well as the scarcely reported disruption of the autophagic processes. In the absence of photoirradiation, C4F-L exhibits minimal toxicity towards normal intestine cells, even at a concentration of 200 μM.

In vivo therapy of osteosarcoma using anion transporters-based supramolecular drugs

BACKGROUND

Osteosarcoma represents a serious clinical challenge due to its widespread genomic alterations, tendency for drug resistance and distant metastasis. New treatment methods are urgently needed to address those treatment difficulties in osteosarcoma to improve patient prognoses. In recent years, small-molecule based anion transporter have emerged as innovative and promising therapeutic compound with various biomedical applications. However, due to a lack of efficient delivery methods, using ion transporters as therapeutic drugs in vivo remains a major challenge.

RESULT

Herein, we developed self-assembled supramolecular drugs based on small-molecule anion transporters, which exhibited potent therapeutic effect towards osteosarcoma both in vitro and in vivo. The anion transporters can disrupt intracellular ion homeostasis, inhibit proliferation, migration, epithelial-mesenchymal transition process, and lead to osteosarcoma cell death. RNA sequencing, western blot and flow cytometry indicated reprogramming of HOS cells and induced cell death through multiple pathways. These pathways included activation of endoplasmic reticulum stress, autophagy, apoptosis and cell cycle arrest, which avoided the development of drug resistance in osteosarcoma cells. Functionalized with osteosarcoma targeting peptide, the assembled supramolecular drug showed excellent targeted anticancer therapy against subcutaneous xenograft tumor and lung metastasis models. Besides good tumor targeting capability and anti-drug resistance, the efficacy of the assembly was also attributed to its ability to regulate the tumor immune microenvironment in vivo.

CONCLUSIONS

In summary, we have demonstrated for the first time that small-molecule anion transporters are capable of killing osteosarcoma cells through multiple pathways. The assemblies, OTP-BP-L, show excellent targeting and therapeutic effect towards osteosarcoma tumors. Furthermore, the supramolecular drug shows a strong ability to regulate the tumor immune microenvironment in vivo. This work not only demonstrated the biomedical value of small-molecule anion transporters in vivo, but also provided an innovative approach for the treatment of osteosarcoma.

Artificial transmembrane potassium transporters: designs, functions, mechanisms and applications

Potassium channels represent the most prevalent class of ion channels, exerting regulatory control over numerous vital biological processes, including muscle contraction, neurotransmitter release, cell proliferation, and apoptosis. The seamless integration of astonishing functions into a sophisticated structure, as seen in these protein channels, inspires the chemical community to develop artificial versions, gearing toward simplifying their structure while replicating their key functions. In particular, over the past ten years or so, a number of elegant artificial potassium transporters have emerged, demonstrating high selectivity, high transport efficiency or unprecedented transport mechanisms. In this review, we will provide a detailed exposition of these artificial potassium transporters that are derived from a single molecular backbone or self-assembled from multiple components, with their respective structural designs, channel functions, transport mechanisms and biomedical applications thoroughly reviewed.

Molecular Sensing and Manipulation of Protein Oligomerization in Membrane Nanotubes with Bolaamphiphilic Foldamers

Adaptive and reversible self-assembly of supramolecular protein structures is a fundamental characteristic of dynamic living matter. However, the quantitative detection and assessment of the emergence of mesoscale protein complexes from small and dynamic oligomeric precursors remains highly challenging. Here, we present a novel approach utilizing a short membrane nanotube (sNT) pulled from a planar membrane reservoir as nanotemplates for molecular reconstruction, manipulation, and sensing of protein oligomerization and self-assembly at the mesoscale. The sNT reports changes in membrane shape and rigidity caused by membrane-bound proteins as variations of the ionic conductivity of the sNT lumen. To confine oligomerization to the sNT, we have designed and synthesized rigid oligoamide foldamer tapes (ROFTs). Charged ROFTs incorporate into the planar and sNT membranes, mediate protein binding to the membranes, and, driven by the luminal electric field, shuttle the bound proteins between the sNT and planar membranes. Using Annexin-V (AnV) as a prototype, we show that the sNT detects AnV oligomers shuttled into the nanotube by ROFTs. Accumulation of AnV on the sNT induces its self-assembly into a curved lattice, restricting the sNT geometry and inhibiting the material uptake from the reservoir during the sNT extension, leading to the sNT fission. By comparing the spontaneous and ROFT-mediated entry of AnV into the sNT, we reveal how intricate membrane curvature sensing by small AnV oligomers controls the lattice self-assembly. These results establish sNT-ROFT as a powerful tool for molecular reconstruction and functional analyses of protein oligomerization and self-assembly, with broad application to various membrane processes.

Sulfur-Containing Foldamer-Based Artificial Lithium Channels

Unlike many other biologically relevant ions (Na+ , K+ , Ca2+ , Cl- , etc) and protons, whose cellular concentrations are closely regulated by highly selective channel proteins, Li+ ion is unusual in that its concentration is well tolerated over many orders of magnitude and that no lithium-specific channel proteins have so far been identified. While one naturally evolved primary pathway for Li+ ions to traverse across the cell membrane is through sodium channels by competing with Na+ ions, highly sought-after artificial lithium-transporting channels remain a major challenge to develop. Here we show that sulfur-containing organic nanotubes derived from intramolecularly H-bonded helically folded aromatic foldamers of 3.6 Å in hollow cavity diameter could facilitate highly selective and efficient transmembrane transport of Li+ ions, with high transport selectivity factors of 15.3 and 19.9 over Na+ and K+ ions, respectively.

Highly Selective Transmembrane Transport of Exogenous Lithium Ions through Rationally Designed Supramolecular Channels

Lithium ions have been applied in the clinic in the treatment of psychiatric disorders. In this work, we report artificial supramolecular lithium channels composed of pore-containing small aromatic molecules. By adjusting the lumen size and coordination numbers, we found that one of the supramolecular channels developed shows unprecedented transmembrane transport of exogenous lithium ions with a Li⁺ /Na⁺ selectivity ratio of 23.0, which is in the same level of that of natural Na⁺ channels. Furthermore, four coordination sites inside channels are found to be the basic requirement for ion transport function. Importantly, this artificial lithium channel displays very low transport of physiological Na⁺ , K⁺ , Mg²⁺ , and Ca²⁺ ions. This highly selective Li⁺ channel may become an important tool for studying the physiological role of intracellular lithium ions, especially in the treatment of psychiatric disorders.

Self-Assembly of Helical Nanofibrous Chiral Covalent Organic Frameworks

Despite significant progress on the design and synthesis of covalent organic frameworks (COFs), precise control over microstructures of such materials remains challenging. Herein, two chiral COFs with well-defined one-handed double-helical nanofibrous morphologies were constructed via an unprecedented template-free method, capitalizing on the diastereoselective formation of aminal linkages. Detailed time-dependent experiments reveal the spontaneous transformation of initial rod-like aggregates into the double-helical microstructures. We have further demonstrated that the helical chirality and circular dichroism signal can be facilely inversed by simply adjusting the amount of acetic acid during synthesis. Moreover, by transferring chirality to achiral fluorescent molecular adsorbents, the helical COF nanostructures can effectively induce circularly polarized luminescence with the highest luminescent asymmetric factor (g_lum ) up to ≈0.01.

Mixed Matrix Membrane with Penetrating Subnanochannels: A Versatile Nanofluidic Platform for Selective Metal Ion Conduction

Biological ion channels penetrated through cell membrane form unique transport pathways for selective ionic conductance. Replicating the success of ion selectivity with mixed matrix membranes (MMMs) will enable new separation technologies but remains challenging. Herein, we report a soft substrate-assisted solution casting method to develop MMMs with penetrating subnanochannels for selective metal ion conduction. The MMMs are composed of penetrating Prussian white (PW) microcubes with subnanochannels in dense polyimide (PI) matrices, achieving selective monovalent metal ion conduction. The ion selectivity of K⁺ /Mg²⁺ is up to 14.0, and the ion conductance of K⁺ can reach 45.5 μS with the testing diameter of 5 mm, which can be further improved by increasing the testing area. Given the diversity of nanoporous materials and polymer matrices, we expect that the MMMs with penetrating subnanochannels could be developed into a versatile nanofluidic platform for various emerging applications.

Formation of supramolecular channels by reversible unwinding-rewinding of bis(indole) double helix via ion coordination

Stimulus-responsive reversible transformation between two structural conformers is an essential process in many biological systems. An example of such a process is the conversion of amyloid-β peptide into β-sheet-rich oligomers, which leads to the accumulation of insoluble amyloid in the brain, in Alzheimer's disease. To reverse this unique structural shift and prevent amyloid accumulation, β-sheet breakers are used. Herein, we report a series of bis(indole)-based biofunctional molecules, which form a stable double helix structure in the solid and solution state. In presence of chloride anion, the double helical structure unwinds to form an anion-coordinated supramolecular polymeric channel, which in turn rewinds upon the addition of Ag⁺ salts. Moreover, the formation of the anion-induced supramolecular ion channel results in efficient ion transport across lipid bilayer membranes with excellent chloride selectivity. This work demonstrates anion-cation-assisted stimulus-responsive unwinding and rewinding of artificial double-helix systems, paving way for smart materials with better biomedical applications.

Cholesterol-stabilized membrane-active nanopores with anticancer activities

Cholesterol-enhanced pore formation is one evolutionary means cholesterol-free bacterial cells utilize to specifically target cholesterol-rich eukaryotic cells, thus escaping the toxicity these membrane-lytic pores might have brought onto themselves. Here, we present a class of artificial cholesterol-dependent nanopores, manifesting nanopore formation sensitivity, up-regulated by cholesterol of up to 50 mol% (relative to the lipid molecules). The high modularity in the amphiphilic molecular backbone enables a facile tuning of pore size and consequently channel activity. Possessing a nano-sized cavity of ~ 1.6 nm in diameter, our most active channel Ch-C1 can transport nanometer-sized molecules as large as 5(6)-carboxyfluorescein and display potent anticancer activity (IC₅₀ = 3.8 µM) toward human hepatocellular carcinomas, with high selectivity index values of 12.5 and >130 against normal human liver and kidney cells, respectively.

Bacterial cells utilize cholesterol-enhanced pore formation to specifically target eukaryotic cells. Here, the authors present a class of bio-inspired, cholesterol-enhanced nanopores which display anticancer activities in vitro.

Ion Channels and Transporters as Therapeutic Agents: From Biomolecules to Supramolecular Medicinal Chemistry

Ion channels and transporters typically consist of biomolecules that play key roles in a large variety of physiological and pathological processes. Traditional therapies include many ion-channel blockers, and some activators, although the exact biochemical pathways and mechanisms that regulate ion homeostasis are yet to be fully elucidated. An emerging area of research with great innovative potential in biomedicine pertains the design and development of synthetic ion channels and transporters, which may provide unexplored therapeutic opportunities. However, most studies in this challenging and multidisciplinary area are still at a fundamental level. In this review, we discuss the progress that has been made over the last five years on ion channels and transporters, touching upon biomolecules and synthetic supramolecules that are relevant to biological use. We conclude with the identification of therapeutic opportunities for future exploration.

Unimolecular Helix-Based Transmembrane Nanochannel with a Smallest Luminal Cavity of 1 Å Expressing High Proton Selectivity and Transport Activity

Natural protein channels have evolved with exquisite structures to transport ions selectively and rapidly. Learning from nature to construct biomimetic artificial channels is always challenging. Herein we present a unimolecular transmembrane proton channel by quinoline-derived helix, which exhibited highly selective and ultrafast proton transport behaviors. This helix-based channel possesses a small luminal cavity of 1 Å in diameter, which could efficiently reject the permeation of cations, anions or water molecules but only permits the translocation of protons owing to the size effect. The proton flow rate exceeded 10⁷ H⁺ s^-1 channel^-1 and reached the same magnitude with gramicidin A. Mechanism investigation revealed that the directionally arrayed NH-chain inside the synthetic channel played a pivotal role during the proton flux. This work not only presented a helix-based channel with the smallest observable nanopore, but also unveiled an unexplored pathway for realizing efficient transport of protons via the consecutive NH-chain.

Current status and future directions of self-assembled block copolymer membranes for molecular separations

One of the most efficient and promising separation alternatives to thermal methods such as distillation is the use of polymeric membranes that separate mixtures based on molecular size or chemical affinity. Self-assembled block copolymer membranes have gained considerable attention within the membrane field due to precise control over nanoscale structure, pore size, and chemical versatility. Despite the rapid progress and excitement, a significant hurdle in using block copolymer membranes for nanometer and sub-nanometer separations such as nanofiltration and reverse osmosis is the lower limit on domain size features. Strategies such as polymer post-functionalization, self-assembly of oligomers, liquid crystals, and random copolymers, or incorporation of artificial/natural channels within block copolymer materials are future directions with the potential to overcome current limitations with respect to separation size.

Supramolecular helices from helical building blocks via head-to-tail intermolecular interactions

Supramolecular helices from helical building blocks represent an emerging analogue of the α-helix. In cases where the helicity of the helical building block is well propagated, the head-to-tail intermolecular interactions that lead to the helix could be enhanced to promote the formation and the stability of the supramolecular helix, wherein homochiral elongation dominates and functional helical channel structures could also be generated. This feature article outlines the supramolecular helices built from helical building blocks, i.e., helical aromatic foldamers and helical short peptides that are held together by intermolecular π-π stacking, hydrogen/halogen/chalcogen bonding, metal coordination, dynamic covalent bonding and solvophobic interactions, with emphasis on the influence of efficient propagation of helicity during assembly, favouring homochirality and channel functions.

Crystal Packing-Guided Construction of Hetero-Oligomeric Peptidic Ensembles as Synthetic 3-in-1 Transporters

Strategies to generate heteromeric peptidic ensembles via a social self-sorting process are limited. Herein, we report a crystal packing-inspired social self-sorting strategy broadly applicable to diverse types of H-bonded peptidic frameworks. Specifically, a crystal structure of H-bonded alkyl chain-appended monopeptides reveals an inter-chain separation distance of 4.8 Å dictated by the H-bonded amide groups, which is larger than 4.1 Å separation distance desired by the tightly packed straight alkyl chains. This incompatibility results in loosely packed alkyl chains, prompting us to investigate and validate the feasibility of applying bulky tert-butyl groups, modified with an anion-binding group, to alternatively interpenetrate the straight alkyl chains, modified with a crown ether group. Structurally, this social self-sorting approach generates highly stable hetero-oligomeric ensembles, having alternated anion- and cation-binding units vertically aligned to the same side. Functionally, these hetero-oligomeric ensembles promote transmembrane transport of cations, anions and more interestingly zwitterionic species such as amino acids.

Nanomachine-Assisted Ion Transport Across Membranes: From Mechanism to Rational Design and Applications

Assisting ion transport across membranes by means of sophisticated molecular machines has promising applications in the treatment of diseases induced by dysregulated ion transport. To develop such nanoscale devices imbued with specific functions, rational de novo design, upstream from costly syntheses, is eminently desirable but would require the atomic detail of the translocation mechanism, which is still largely missing. We have explored the full ion capture-transport-release process over an aggregate simulation time of 60 μs, employing leading-edge enhanced-sampling algorithms to disentangle with unprecedented detail the mechanism that underlies ion transport mediated by a membrane-spanning [2]rotaxane composed of an ion carrier linked to a wheel threaded onto an axle. Beyond validating the reliability of our methodology through careful examination of the clockwork of a documented nanomachine, we put forth an original pH-controlled nano-object that can assist transient unidirectional ion transport across membranes.

Foldamer-Based Potassium Channels with High Ion Selectivity and Transport Activity

Small molecules that independently perform natural channel-like functions show greatly potential in the treatment of human diseases. Taking advantage of aromatic helical scaffolds, we develop a kind of foldamer-based ion channels with lumen size varying from 3.8 to 2.3 Å through a sequence substitution strategy. Our results clearly elucidate the importance of channel size in ion transport selectivity in molecular detail, eventually leading to the discoveries of the best artificial K⁺ channel by far and a rare sodium-preferential channel as well. High K⁺ selectivity and transport activity together make foldamers promising in therapeutic applications.

Helical polymer self-assembly and chiral nanostructure formation

This review surveys recent progress towards robust chiral nanostructure fabrication techniques using synthetic helical polymers, the unique inferred properties that these materials possess, and their intricate connection to natural, biological chirality.

Regulation of Lipid Bilayer Ion Permeability by Antibacterial Polymethyloxazoline-Polyethyleneimine Copolymers

Amphiphilic antimicrobial polymers display activity against the outer bacterial cell membrane, triggering various physiological effects. We investigated the regulation of ion transport across the lipid bilayer to understand differences in biological activity for a series of amphiphilic polymethyloxazoline - polyethyleneimine copolymers. The results confirmed that the tested structures were able to increase the permeability of the lipid bilayer (LB) membrane or its rupture. Black lipid membrane (BLM) experiments show that the triggered conductance profile and its character is strongly correlated with the polymer structure and zeta potential. The polymer exhibiting the highest antimicrobial activity promotes ion transport by using a unique mechanism and step-like characteristics with well-defined discreet openings and closings. The molecule was incorporated into the membrane in a reproducible way, and the observed channel-like activity could be responsible for the antibacterial activity of this molecule.

Switchable foldamer ion channels with antibacterial activity

Synthetic ion channels may have applications in treating channelopathies and as new classes of antibiotics, particularly if ion flow through the channels can be controlled. Here we describe triazole-capped octameric α-aminoisobutyric acid (Aib) foldamers that "switch on" ion channel activity in phospholipid bilayers upon copper(ii) chloride addition; activity is "switched off" upon copper(ii) extraction. X-ray crystallography showed that CuCl₂ complexation gave chloro-bridged foldamer dimers, with hydrogen bonds between dimers producing channels within the crystal structure. These interactions suggest a pathway for foldamer self-assembly into membrane ion channels. The copper(ii)-foldamer complexes showed antibacterial activity against B. megaterium strain DSM319 that was similar to the peptaibol antibiotic alamethicin, but with 90% lower hemolytic activity.

Hybrid Helical Polymer Nanochannels Constructed by Combining Aromatic Amide and Pyridine-Oxadiazole Structural Sequences

An effective method is reported to synthesize aromatic helical polymer nanochannels by combining both the well-studied aromatic amide helical codons with pyridine-oxadiazole helical codons into helical structure sequences. With this strategy, a type of helical polymer nanochannel that shows structure-directed transmembrane transport functions is synthesized. Although such nanochannels show relatively weak selectivity for the transportation of alkali metal ions, accessible chemical mutation of helical structure sequences will provide a great chance for the design of desired channel property. The straightforward preparation of well-established pyridine-oxadiazole helical structure will significantly promote the synthesis of this kind of aromatic helical polymer nanochannels. With the development of aromatic amide foldamers, moreover, a number of "monomers" will be available for the preparation of helical polymer nanochannels.

Highly Efficient Exclusion of Alkali Metal Ions via Electrostatic Repulsion Inside Positively Charged Channels

Understanding of the structure-function relationships of natural protein channels remains a challenging task because of their unattainable physiological functions in terms of selectivity. To achieve this, a synthetic system of chemically modified channels has been constructed based on helical polymer scaffolds. Here, we report a type of positively charged channels in which multiple quaternary ammonium groups are covalently modified on the lumen surface of helical polymer while the helical conformation is intact. Compared to unmodified channels, the existence of multiple charged groups in the cavity not only makes the lumen size narrower but also essentially changes the channel properties without obstructing channel structure. Our study indicates that positively charged channels preferentially transport anions with size-dependent selectivity, whereas alkali metal ions are almost completely suppressed by electrostatic repulsion. As a consequence, a specific artificial channel with high Cl^-/Na⁺ selectivity ratio of 41:1 is obtained.

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.

Enhancing K+ transport activity and selectivity of synthetic K+ channels via electron-donating effects

Electron-withdrawing groups enhance ion transport activity by 160% and selectivity by >50%, leading to high K⁺/Na⁺ selectivity of 14.0.

Pyridine/Oxadiazole-Based Helical Foldamer Ion Channels with Exceptionally High K+ /Na+ Selectivity

Protein channels are characterized by high transport selectivity, which is essential for maintaining cellular function. Efforts to reproduce such high selectivity over the past four decades have not been very successful. We report a novel series of aromatic foldamer-based polymeric channels where the backbone is stabilized by differential electrostatic repulsions among heteroatoms helically arrayed along the helical backbone. Nanotubes averaging 2.3 and 2.7 nm in length mediate highly efficient transport of K⁺ ions as a consequence of hydrophilic electron-rich hollow cavities that are 3 Å in diameter. Exceptionally high K⁺ and Na⁺ selectivity values of 16.3 and 12.6, respectively, are achieved.

Helical supramolecular polymer nanotubes with wide lumen for glucose transport: towards the development of functional membrane-spanning channels

The manipulation of strong noncovalent interactions provides a concise and versatile strategy for constructing highly ordered supramolecular structures. By using a shape-persistent building block consisting of phenanthroline derivatives and two quadruply hydrogen-bonding AADD moieties, a type of precise helical supramolecular polymer (HSP) nanotube has been developed. The helical conformation of the supramolecular polymers has been proved via various techniques, showing significantly expanded topologies of supramolecular polymers. From the production of new topological structures of supramolecular polymers, predictable properties and functions have arisen. In this study, the helical folding of supramolecular polymers gave rise to the generation of specific wide lumen structures that can be directly visualized via TEM, and the resulting HSP nanotubes can puncture the lipid bilayer membrane to facilitate the transportation of glucose.

Helical supramolecular polymers with a wide lumen structure can puncture the lipid bilayer membrane to facilitate the transport of glucose.

Structure Elucidation of Helical Aromatic Foldamer-Protein Complexes with Large Contact Surface Areas

The development of large synthetic ligands could be useful to target the sizeable surface areas involved in protein-protein interactions. Herein, we present long helical aromatic oligoamide foldamers bearing proteinogenic side chains that cover up to 450 Ų of the human carbonic anhydrase II (HCA) surface. The foldamers are composed of aminoquinolinecarboxylic acids bearing proteinogenic side chains and of more flexible aminomethyl-pyridinecarboxylic acids that enhance helix handedness dynamics. Crystal structures of HCA-foldamer complexes were obtained with a 9- and a 14-mer both showing extensive protein-foldamer hydrophobic contacts. In addition, foldamer-foldamer interactions seem to be prevalent in the crystal packing, leading to the peculiar formation of an HCA superhelix wound around a rod of stacked foldamers. Solution studies confirm the positioning of the foldamer at the protein surface as well as a dimerization of the complexes.

Biomimetic hybrid membranes: incorporation of transport proteins/peptides into polymer supports

Molecular sensing, water purification and desalination, drug delivery, and DNA sequencing are some striking applications of biomimetic hybrid membranes. These devices take advantage of biomolecules, which have gained excellence in their specificity and efficiency during billions of years, and of artificial materials that load the purified biological molecules and provide technological properties, such as robustness, scalability, and suitable nanofeatures to confine the biomolecules. Recent methodological advances allow more precise control of polymer membranes that support the biomacromolecules, and are expected to improve the design of the next generation of membranes as well as their applicability. In the first section of this review we explain the biological relevance of membranes, membrane proteins, and the classification used for the latter. After this, we critically analyse the different approaches employed for the production of highly selective hybrid membranes, focusing on novel materials made of self-assembled block copolymers and nanostructured polymers. Finally, a summary of the advantages and disadvantages of the different methodologies is presented and the main characteristics of biomimetic hybrid membranes are highlighted.

Artificial K+ Channels Formed by Pillararene-Cyclodextrin Hybrid Molecules: Tuning Cation Selectivity and Generating Membrane Potential

A class of artificial K⁺ channels formed by pillararene-cyclodextrin hybrid molecules have been designed and synthesized. These channels efficiently inserted into lipid bilayers and displayed high selectivity for K⁺ over Na⁺ in fluorescence and electrophysiological experiments. The cation transport selectivity of the artificial channels is tunable by varying the length of the linkers between pillararene and cyclodexrin. The shortest channel showed specific transmembrane transport preference for K⁺ over all alkali metal ions (selective sequence: K⁺ > Cs⁺ > Rb⁺ > Na⁺ > Li⁺ ), and is rarely observed for artificial K⁺ channels. The high selectivity of this artificial channel for K⁺ over Na⁺ ensures specific transmembrane translocation of K⁺ , and generated stable membrane potential across lipid bilayers.

Hyperfast Water Transport through Biomimetic Nanochannels from Peptide-Attached (pR)-pillar[5]arene

Synthetic water channels offer great promise to replace natural aquaporins (AQPs) for making new-generation biomimetic membranes for water treatment. However, the water permeability of the current synthetic water channels is still far below that of AQPs. Here, peptide-attached (pR)-pillar[5]arene (pR-PH) channels are reported to mimic the high permeability of AQPs. It is demonstrated that the pR-PH channels with an open pore can transport water smoothly and efficiently. The pR-PH channels are competitive with AQPs in terms of water permeability and are much superior to diastereomer peptide-attached (pS)-pillar[5]arene (pS-PH) and other reported synthetic water channels. The exceptional water-transport properties of the pR-PH channels are further demonstrated in a composite polymeric membrane that incorporates the nanochannels into the top selective layer. This membrane gives a significantly improved water flux while retaining high salt rejection. The results establish a tangible foundation for developing highly efficient artificial water channel-based biomimetic membrane for water purification applications.

Single-stranded DNA designed lipophilic G-quadruplexes as transmembrane channels for switchable potassium transport

G-quadruplex single-stranded DNA was modified lipophilically and developed as a biomimetic ion channel for selective and switchable K⁺ transport.

Crystal structure of a protein–aromatic foldamer composite: macromolecular chiral resolution

A protein–foldamer crystal structure illustrates protein assembly by a sulfonated aromatic oligoamide, and chiral resolution of the foldamer helix handedness.

Structure-Driven Selection of Adaptive Transmembrane Na+ Carriers or K+ Channels

Self-assembled alkyl-ureido-benzo-15-crown-5-ethers are selective ionophores for K⁺ cations, which are preferred to Na⁺ cations. The transport mechanism is determined by the optimal coordination rather than classical dimensional compatibility between the crown ether hole and the cation diameter. Herein, we demonstrate that systematic changes of the structure lead to unexpected modifications in the cation-transport activity and suffice to produce adaptive selection. We show that the main contribution to performance arises from optimal constraints on the conformational freedom, which are determined by the binding macrocycles, the nature of the hydrogen-bonding groups, and the hydrophobic tails. Simple changes to the flexible 15-crown-5-ether lead to selective carriers for Na⁺ . Hydrophobic stabilization of the channels through mutual interactions between lipids and variable hydrophobic tails appears to be an important cause of increased activity. Oppositely, restricted translocation is achieved when constrained hydrogen-bonded macrocyclic relays are less dynamic in a pore superstructure.