Supramolecular Mechanosensitive Potassium Channel Formed by Fluorinated Amphiphilic Cyclophane

Fluorinated Conjugated Microporous Polymers Based on Pillar[n]arenes for Removal of Water Pollutants and Their Cation Selective Adsorption

Organic dyes are widely used in many applications. However, the leakage of organic dyes into the natural environment has become a severe and worldwide problem owing to their high toxicity and nonbiodegradability. Therefore, the development of effective removal technologies for organic dyes is required. In this article, we report the synthesis and adsorption properties of highly fluorinated conjugated microporous polymers based on pillar[n]arenes. The polymers exhibited large Brunauer-Emmett-Teller surface areas of up to 1063 m2 g-1 and selective adsorptive removal of cationic organic dyes from aqueous solutions. Comparison with the nonfluorinated polymers indicated that the adsorption mechanism mainly relies on the fluorine-cation electrostatic interaction. The maximum adsorption capacity reached 313 mg g-1 for crystal violet, which is higher than those of conventional adsorbents. Additionally, the fluorinated polymers could function as proton channels when they were embedded into lipid membranes.

Engineered Reactive Oxygen Species (ROS)-Responsive Artificial H+/Cl- Ion Channels for Targeted Cancer Treatment

Reactive oxygen species (ROS)-responsive ion channels regulate the ion flow across the membranes in response to alterations in the cellular redox state, playing a crucial role in cellular adaptation to oxidative stress. Despite their significance, replicating ROS-responsive functionality in artificial ion channels remains elusive. In this study, we introduce a novel class of artificial H+/Cl- ion channels activatable by elevated ROS levels in cancer cells. ROS-induced decaging of the phenylboronate group triggers the rapid release of the channel-forming units, leading to self-assembly of the H-bonded cascades facilitating the synergistic transport of H+ and Cl- ions, with H+/Cl- ion transport selectivity of 7.7. Upon activation, ROS-C-Cl exhibits significant apoptotic activity against human breast cancer cells, achieving an IC50 of 2.8 μM, comparable to that of paclitaxel. Exploiting the intrinsic oxidative microenvironment of cancer cells, along with the enhanced oxidative stress arising from H+/Cl- co-transport, ROS-C-Cl demonstrates exceptional selectivity in targeting cancer cells with a selectivity index of 10.2 over normal breast cells, outperforming that of paclitaxel by 19.4 folds.

G-quadruplex-Based Artificial Transmembrane Channels Induce Cancer Cell Apoptosis by Perturbing Potassium Ion Homeostasis

Transmembrane ion transport modality has received a widespread attention due to its apoptotic activation toward anticancer cell activities. In this study, G-quadruplex-based potassium-specific transmembrane channels have been developed to facilitate the intracellular K+ efflux, which perturbs the cellular ion homeostasis thereby inducing cancer cell apoptosis. Cholesterol-tag, a lipophilic anchor moiety, serves as a rudiment for the G-quadruplex immobilization onto the membrane, while G-quadruplex channel structure as a transport module permits ion binding and migration along the channels. A c-Myc sequence tagged with two-cholesterol is designed as a representative lipophilic G-quadruplex, which forms intramolecular parallel G-quadruplex with three stacks of G-quartets (Ch2-Para3). Fluorescence transport assay demonstrates Ch2-Para3 a high transport activity (EC50 = 10.9 × 10-6 m) and an ion selectivity (K+/Na+ selectivity ratio of 84). Ch2-Para3 mediated K+ efflux in cancer cells is revealed to purge cancer cells through K+ efflux-mediated cell apoptosis, which is confirmed by monitoring the changes in membrane potential of mitochondria, leakage of cytochrome c, reactive oxygen species yield, as well as activation of a family of caspases. The lipophilic G-quadruplex exhibits obvious antitumor activity in vivo without systemic toxicity. This study provides a functional scheme aimed at generating DNA-based selective artificial membrane channels for the purpose of regulating cellular processes and inducing cell apoptosis, which shows a great promising for anticancer therapy in the future.

Nanohoops in membranes: confined supramolecular spaces within phospholipid bilayer membranes

Nanohoops, an exciting class of fluorophores with supramolecular binding abilities, have the potential to become innovative tools within biological imaging and sensing. Given the biological importance of cell membranes, incorporation of macrocyclic materials with the dual capability of fluorescence emission and supramolecular complexation would be particularly interesting. A series of different-sized nanohoops-ethylene glycol-decorated [n]cyclo-para-pyrenylenes (CPYs) (n = 4-8)-were synthesised via an alternate synthetic route which implements a stannylation-based precursor, producing purer material than the previous borylation approach, enabling the growth of single-crystals of the Pt-macrocycle. Reductive elimination of these single-crystals achieved significantly higher selectivity and yields towards smaller ring-sized nanohoops (n = 4-6). The supramolecular binding capabilities of these CPYs were then explored through host-guest studies with a series of polycyclic (aromatic)hydrocarbons, revealing the importance of molecular size, shape, and CH-π contacts for efficient binding. CPYs were incorporated within the hydrophobic layer of lipid bilayer membranes, as confirmed by microscopic imaging and emission spectroscopy, which also demonstrated the size-preferential incorporation of the five-fold nanohoop. Molecular dynamics simulations revealed the position and orientation within the membrane, as well as the unique non-covalent threading interaction between nanohoop and phospholipid.

Using Nanoscale Passports To Understand and Unlock Ion Channels as Gatekeepers of the Cell

Natural ion channels are proteins embedded in the cell membrane that control many aspects of cell and human physiology by acting as gatekeepers, regulating the flow of ions in and out of cells. Advances in nanotechnology have influenced the methods for studying ion channels in vitro, as well as ways to unlock the delivery of therapeutics by modulating them in vivo. This review provides an overview of nanotechnology-enabled approaches for ion channel research with a focus on the synthesis and applications of synthetic ion channels. Further, the uses of nanotechnology for therapeutic applications are critically analyzed. Finally, we provide an outlook on the opportunities and challenges at the intersection of nanotechnology and ion channels. This work highlights the key role of nanoscale interactions in the operation and modulation of ion channels, which may prompt insights into nanotechnology-enabled mechanisms to study and exploit these systems in the near future.

Core-Alkynylated Fluorescent Flippers: Altered Ultrafast Photophysics to Track Thick Membranes

Fluorescent flippers have been introduced as small-molecule probes to image membrane tension in living systems. This study describes the design, synthesis, spectroscopic and imaging properties of flippers that are elongated by one and two alkynes inserted between the push and the pull dithienothiophene domains. The resulting mechanophores combine characteristics of flippers, reporting on physical compression in the ground state, and molecular rotors, reporting on torsional motion in the excited state, to take their photophysics to new level of sophistication. Intensity ratios in broadened excitation bands from differently twisted conformers of core-alkynylated flippers thus report on mechanical compression. Lifetime boosts from ultrafast excited-state planarization and lifetime drops from competitive intersystem crossing into triplet states report on viscosity. In standard lipid bilayer membranes, core-alkynylated flippers are too long for one leaflet and tilt or extend into disordered interleaflet space, which preserves rotor-like torsional disorder and thus weak, blue-shifted fluorescence. Flipper-like planarization occurs only in highly ordered membranes of matching leaflet thickness, where they light up and selectively report on these thick membranes with red-shifted, sharpened excitation maxima, high intensity and long lifetime.

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.

Recent advances of droplet-based microfluidics for engineering artificial cells

Artificial cells, synthetic cells, or minimal cells are microengineered cell-like structures that mimic the biological functions of cells. Artificial cells are typically biological or polymeric membranes where biologically active components, including proteins, genes, and enzymes, are encapsulated. The goal of engineering artificial cells is to build a living cell with the least amount of parts and complexity. Artificial cells hold great potential for several applications, including membrane protein interactions, gene expression, biomaterials, and drug development. It is critical to generate robust, stable artificial cells using high throughput, easy-to-control, and flexible techniques. Recently, droplet-based microfluidic techniques have shown great potential for the synthesis of vesicles and artificial cells. Here, we summarized the recent advances in droplet-based microfluidic techniques for the fabrication of vesicles and artificial cells. We first reviewed the different types of droplet-based microfluidic devices, including flow-focusing, T-junction, and coflowing. Next, we discussed the formation of multi-compartmental vesicles and artificial cells based on droplet-based microfluidics. The applications of artificial cells for studying gene expression dynamics, artificial cell-cell communications, and mechanobiology are highlighted and discussed. Finally, the current challenges and future outlook of droplet-based microfluidic methods for engineering artificial cells are discussed. This review will provide insights into scientific research in synthetic biology, microfluidic devices, membrane interactions, and mechanobiology.

Transient control of lytic activity via a non-equilibrium chemical reaction system

The development of artificial non-equilibrium chemical reaction systems has recently attracted considerable attention as a new type of biomimetic. However, due to the lack of bioorthogonality, such reaction systems could not be linked to the regulation of any biological phenomena. Here, we have newly designed a non-equilibrium reaction system based on olefin metathesis to produce the Triton X-mimetic non-ionic amphiphile as a kinetic product. Using phospholipid vesicles encapsulating fluorescent dyes and red blood cells as cell models, we demonstrate that the developed chemical reaction system is applicable for transient control of the resulting lytic activity.

Lipid vesicle-based molecular robots

A molecular robot, which is a system comprised of one or more molecular machines and computers, can execute sophisticated tasks in many fields that span from nanomedicine to green nanotechnology. The core parts of molecular robots are fairly consistent from system to system and always include (i) a body to encapsulate molecular machines, (ii) sensors to capture signals, (iii) computers to make decisions, and (iv) actuators to perform tasks. This review aims to provide an overview of approaches and considerations to develop molecular robots. We first introduce the basic technologies required for constructing the core parts of molecular robots, describe the recent progress towards achieving higher functionality, and subsequently discuss the current challenges and outlook. We also highlight the applications of molecular robots in sensing biomarkers, signal communications with living cells, and conversion of energy. Although molecular robots are still in their infancy, they will unquestionably initiate massive change in biomedical and environmental technology in the not too distant future.

Beyond Natural Channel Proteins: Recent Advances in Fluorinated Nanochannels

Inspired by the structures and functions of natural channel proteins that selectively permeate ions and molecules across biological membranes, synthetic molecules capable of self-assembling into supramolecular nanotubes within the hydrophobic layer of the membranes have been designed and their material permeation properties have been studied. More recently, synthetic chemists have ventured to incorporate fluorine atoms, elements rarely found in natural proteins, into the structure of synthetic channels and discovered anomalous transmembrane material permeation properties. In this Perspective, the author provides a brief overview of recent advances in the development of fluorinated nanochannels and possible directions for the future.

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.

Modular Gating of Ion Transport by Postsynthetic Charge Transfer Complexation in a Metal-Organic Framework

Nature's design of biological ion channels that demonstrates efficient gating and selectivity brings to light a very promising model to mimic and design for achieving selective and tunable ion transport. Functionalized nanopores that permit modulation of the pore wall charges are a compelling approach to gain control over the ion transport mechanism through the pores. This makes way for employing a noncovalent supramolecular approach for attaining charge reversal of the MOF pore walls using donor-acceptor pairs that can demonstrate strong charge transfer interactions. Herein, robust Zr4+-based mesoporous MOF-808 was postsynthetically modified into an anion-selective nanochannel (MOF-808-MV) by modification with dicationic viologen-based motifs. Charge modulation and even reversal of the MOF-808-MV pore walls were then explored taking advantage of strong charge transfer interactions between the grafted dicationic viologen acceptor moieties and anionic, π-electron-rich donor guest molecules such as pyranine (PYR) and tetrathiafulvalene tetrabenzoic acid (TTF-TA). Tunability of the MOF pore charge from positive to neutral to negative was achieved via simple methodologies such as diffusion control in case of guest molecule like PYR and by pH modulation for pH-responsive guest like TTF-TA. This results in a concomitant modulation in the selectivity of the nanochannel, rendering it from anion-selective to ambipolar to cation-selective. Furthermore, as a real-time application of this ion channel, Na+ ion conductivity (σ = 3.5 × 10-5 S cm-1) was studied at ambient temperature.

G-Quadruplex-Filtered Selective Ion-to-Ion Current Amplification for Non-Invasive Ion Monitoring in Real Time

Living cells efflux intracellular ions for maintaining cellular life, so intravital measurements of specific ion signals are of significant importance for studying cellular functions and pharmacokinetics. In this work, de novo synthesis of artificial K+ -selective membrane and its integration with polyelectrolyte hydrogel-based open-junction ionic diode (OJID) is demonstrated, achieving a real-time K+ -selective ion-to-ion current amplification in complex bioenvironments. By mimicking biological K+ channels and nerve impulse transmitters, in-line K+ -binding G-quartets are introduced across freestanding lipid bilayers by G-specific hexylation of monolithic G-quadruplex, and the pre-filtered K+ flow is directly converted to amplified ionic currents by the OJID with a fast response time at 100 ms intervals. By the synergistic combination of charge repulsion, sieving, and ion recognition, the synthetic membrane allows K+ transport exclusively without water leakage; it is 250× and 17× more permeable toward K+ than monovalent anion, Cl- , and polyatomic cation, N-methyl-d-glucamine+ , respectively. The molecular recognition-mediated ion channeling provides a 500% larger signal for K+ as compared to Li+ (0.6× smaller than K+ ) despite the same valence. Using the miniaturized device, non-invasive, direct, and real-time K+ efflux monitoring from living cell spheroids is achieved with minimal crosstalk, specifically in identifying osmotic shock-induced necrosis and drug-antidote dynamics.

Chemically Fueled Communication Along a Scaffolded Nanoscale Array of Squaramides

Relaying conformational change over several nanometers is central to the function of allosterically regulated proteins. Replicating this mechanism artificially would provide important communication tools, but requires nanometer-sized molecules that reversibly switch between defined shapes in response to signaling molecules. In this work, 1.8 nm long rigid rod oligo(phenylene-ethynylene)s are scaffolds for switchable multi-squaramide hydrogen-bond relays. Each relay can adopt either a parallel or an antiparallel orientation relative to the scaffold; the preferred orientation is dictated by a director group at one end. An amine director responded to proton signals, with acid-base cycles producing multiple reversible changes in relay orientation that were reported by a terminal NH, which is 1.8 nm distant. Moreover, a chemical fuel acted as a dissipative signal. As the fuel was consumed, the relay reverted to its original orientation, illustrating how information from out-of-equilibrium molecular signals can be communicated to a distant site.

Structure Activity Relationships for Reversible O2 Chemisorption by the Solid Phases of Co(salen) and Co(3F-salen)

The potential of solid-state materials comprising Co(salen) units for concentrating dioxygen from air was recognized over 80 years ago. While the chemisorptive mechanism at the molecular level is largely understood, the bulk crystalline phase plays important, yet unidentified roles. We have reverse crystal-engineered these materials and can for the first time describe the nanostructuring requisite for achieving reversible O₂ chemisorption by Co(3R-salen) R = H or F, the simplest and most effective of the many known derivatives of Co(salen). Of the six phases of Co(salen) identified, α-ζ: α = ESACIO, β = VEXLIU, γ, δ, ε, and ζ (this work), only γ, δ, ε, and ζ are capable of reversible O₂ binding. Class I materials (phases γ, δ, and ε) are obtained by desorption (40-80 °C, atmospheric pressure) of the co-crystallized solvent from Co(salen)·(solv), solv = CHCl₃, CH₂Cl₂, or 1.5 C₆H₆. The oxy forms comprise between 1:5 and 1:3 O₂:[Co] stoichiometries. Class II materials achieve an apparent maximum of 1:2 O₂:Co(salen) stoichiometries. The precursors for the Class II materials comprise [Co(3R-salen)(L)·(H₂O)_x], R = H, L = pyridine, and x = 0; R = F, L = H₂O, and x = 0; R = F, L = pyridine, and x = 0; R = F, L = piperidine, and x = 1. Activation of these depends on the desorption of the apical ligand (L) that templates channels through the crystalline compounds with the Co(3R-salen) molecules interlocked in a Flemish bond brick pattern. The 3F-salen system produces F-lined channels proposed to facilitate O₂ transport through the materials through repulsive interactions with the guest O₂. We postulate that a moisture dependence of the activity of the Co(3F-salen) series is due to a highly specific binding pocket for locking in water via bifurcated hydrogen bonding to the two coordinated phenolato O atoms and the two ortho F atoms.

Label-free quantification of passive membrane permeability of cyclic peptides across lipid bilayers: penetration speed of cyclosporin A across lipid bilayers

Cyclic peptides that passively penetrate cell membranes are under active investigation in drug discovery research. PAMPA (Parallel Artificial Membrane Permeability Assay) and Caco-2 assay are mainly used for permeability measurements in these studies. However, permeability rates across the artificial membrane and the cell monolayer used for these assays are intrinsically different from the ones across pure lipid bilayers. There are also membrane permeability assays for peptides using reconstructed lipid bilayers, but they require labeling for detection, and the absolute membrane permeability of the natural peptides themselves could not be determined. Here, we constructed a lipid bilayer permeability assay and realized the first label-free measurements of the lipid bilayer permeability of cyclic peptides. Quantitative permeability values across lipid bilayers were determined for model cyclic hexapeptides and an important natural product, cyclosporin A (CsA). The obtained quantitative permeability values will provide new and advanced knowledge about the passive permeability of cyclic peptides.

A Chiral 19F NMR Reporter of Foldamer Conformation in Bilayers

Understanding and controlling peptide foldamer conformation in phospholipid bilayers is a key step toward their use as molecular information relays in membranes. To this end, a new 19F "reporter" tag has been developed and attached to dynamic peptide foldamers. The (R)-1-(trifluoromethyl)ethylamido ((R)-TFEA) reporter was attached to the C-terminus of α-amino-iso-butyric acid (Aib) foldamers. Crystallography confirmed that the foldamers adopted 310 helical conformations. Variable temperature (VT) NMR spectroscopy in organic solvents showed that the (R)-TFEA reporter had an intrinsic preference for P helicity, but the overall screw-sense was dominated by a chiral "controller" at the N-terminus. The 19F NMR chemical shift of the CF3 resonance was correlated with the ability of different N-terminal groups to induce either an M or a P helix in solution. In bilayers, a similar correlation was found. Solution 19F NMR spectroscopy on small unilamellar vesicle (SUV) suspensions containing the same family of (R)-TFEA-labeled foldamers showed broadened but resolvable 19F resonances, with each chemical shift mirroring their relative positions in organic solvents. These studies showed that foldamer conformational preferences are the same in phospholipid bilayers as in organic solvents and also revealed that phospholipid chirality has little influence on conformation.