Nanotubular Structures Research Articles

One-step synthesis of iron and nitrogen co-doped porous biochar for efficient removal of tetracycline from water: Adsorption performance and fixed-bed column

Here, Fe/N co-doped porous biochars (FeNKBCs) were obtained by grinding corncob, CH3COOK, FeCl3·6H2O, and C3H6N6 via one-step synthesis and were applied to remove antibiotics from wastewater. Notably, CH3COOK had an excellent porous activation ability. The developed nanotubular structure of Fe1N2KBC had a high pore volume (Vtotal) (1.2131 cm3/g) and specific surface areas (SSA) (2083.54 m2/g), which showed outstanding sorption abilities for TC (764.35 mg/g), OTC (560.82 mg/g), SMX (291.45 mg/g), and SMT (354.65 mg/g). The adsorption process of TC was controlled by chemisorption. Moreover, Fe1N2KBC has an excellent dynamic adsorption performance (620.14 mg/g) in a fixed-bed column. The properties of SSA, Vtotal, and the content of graphite N and Fe–N were positively correlated with TC adsorption capacity. The high performance of TC removal was related to π-π stacking, pore-filling, hydrogen bond, and electrostatic interaction. Fe1N2KBC possessed stable sorption amounts in pH 2–12 and actual water, and well reuse performance. The results of this work present an effective preparation method of Fe/N porous biochar for TC-contaminated water remediation.

Inactivation of influenza virus as representative of enveloped RNA viruses on photocatalytically active nanoparticle and nanotubular TiO2 surfaces

The recent pandemic showed us that there is a strong demand for standardized methods to evaluate the antiviral activity of different materials using enveloped RNA viruses (e.g. SARS-CoV-2, influenza virus). Virucidal activity can be achieved as a result of photoexcitation of a TiO2 photocatalyst under UV illumination. All standardized methods evaluating the virucidal activity of photocatalytic surfaces use bacteriophage Q-beta, a representative of small non-enveloped viruses. This work was thus devoted to the evaluation of the virucidal efficiency of photocatalytically active nanostructured TiO2 surfaces (nanotubular and nanoparticle) to inactivate the influenza virus with particular interest paid to the methodology of virucidal testing and the influence of the surface nanostructure (porosity). Two different TiO2 nanostructures were used in this study, namely nanoparticle and nanotubular structures. A significant decrease in the amount of viral RNA and titre was obtained after rinsing, because the virus was retained on the surface of the nanostructured TiO2 during exposure in the dark. The decrease can be understood as an additional effect of the surface porosity on the TiO2 virucidal activity after UV illumination. However, this fact was taken into account in the calculation of virucidal activity due to UV light. Both nanostructured TiO2 coatings have comparable porosity and thickness, but the photocatalytic activity (to oxidatively degrade aqueous pollutants) is higher for the nanoparticle than for the nanotubular surface. On the other hand, the virucidal activity is much higher for the nanotubular surface. This can be explained by the uniform and open structure of nanotubes resulting in a lower amount of virus being retained on the surface under dark conditions and the high surface area of the nanotubes.

Elevating Energy Density in Li-Ion Batteries through Electrospun Nanotubular Titania-Polymer Interfaces

The introduction of new anode materials holds the potential to address critical safety concerns associated with current commercialized options in Li-ion batteries. Graphite, while widely used, poses challenges due to its low charging potential, which contributes to the growth of dendrites and safety risks. In contrast, titania-based materials present an appealing solution. Their higher operational potential not only curbs dendrite formation but also prevents the formation of a thick solid electrolyte interface (SEI). Furthermore, the limited volume expansion during lithiation significantly enhances their safety profile, differentiating them from graphite-based anodes such as those incorporating silicon.In this new study, titania-based nanotubular structures were created for high-energy Li-ion batteries using a novel electrospinning technique. Titania-based nanotubes were synthesized, modified for optimal charge transfer, and combined with a self-standing electrode through electrospinning with PVDF. The effects of various thermal treatment conditions on Li-ion diffusion were explored using electrochemical methods. The best charge transfer kinetics were observed in the sample treated for 10 hours. After optimizing the electrospinning process, a fully embedded nanotube fibrous structure was achieved, confirmed by electron microscopy. The use of a polymeric network removed the need for metallic current collectors, boosting energy density by 14%. These electrospun electrodes show great promise for high-energy applications.This work was supported by the M-era.Net 2019 call project “LiBASED Li-ion BAttery-SupErcapacitor Hybrid Device”. The research was co-funded by the Turkish Scientific and Technological Research Council (TUBITAK) with project number 119N758.

Surface Properties of Ti65Zr Alloy Modified with TiZr Oxide and Hydroxyapatite.

Titanium-zirconium dioxide nanostructures loaded by hydroxyapatite were produced on the surface of Ti65Zr alloy. The alloy was treated by anodization with the subsequent immersion in calcium glycerophosphate (CG) solutions. The resulting surfaces present TiO2-ZrO2 nanotubular (TiZr-NT) structures enriched with hydroxyapatite (HAP). The nanotube texture is expected to enhance the surface's corrosion resistance and promote integration with bone tissue in dental implants. The TiZr-NT structure had a diameter of 73 ± 2.2 nm and a length of 10.1 ± 0.5 μm. The most favorable result for the growth of HAP in Hanks' balanced salt solution (Hanks' BSS) was obtained at a CG concentration of 0.5 g/L. Samples soaked in CG at a concentration of 0.5 g/L demonstrated in a decrease of the contact angles to 25.2°; after 3 days of exposure to Hanks' BSS, the contact angles further reduced to 18.5°. The corrosion studies also showed that the TiZr-NT structure soaked in the CG = 0.5 g/L solution exhibited the best corrosion stability.

Luminescence in Anion-Deficient Hafnia Nanotubes.

Hafnia-based nanostructures and other high-k dielectrics are promising wide-gap materials for developing new opto- and nanoelectronic devices. They possess a unique combination of physical and chemical properties, such as insensitivity to electrical and optical degradation, radiation damage stability, a high specific surface area, and an increased concentration of the appropriate active electron-hole centers. The present paper aims to investigate the structural, optical, and luminescent properties of anodized non-stoichiometric HfO2 nanotubes. As-grown amorphous hafnia nanotubes and nanotubes annealed at 700 °C with a monoclinic crystal lattice served as samples. It has been shown that the bandgap Eg for direct allowed transitions amounts to 5.65 ± 0.05 eV for amorphous and 5.51 ± 0.05 eV for monoclinic nanotubes. For the first time, we have studied the features of intrinsic cathodoluminescence and photoluminescence in the obtained nanotubular HfO2 structures with an atomic deficiency in the anion sublattice at temperatures of 10 and 300 K. A broad emission band with a maximum of 2.3-2.4 eV has been revealed. We have also conducted an analysis of the kinetic dependencies of the observed photoluminescence for synthesized HfO2 samples in the millisecond range at room temperature. It showed that there are several types of optically active capture and emission centers based on vacancy states in the O3f and O4f positions with different coordination numbers and a varied number of localized charge carriers (V0, V-, and V2-). The uncovered regularities can be used to optimize the functional characteristics of developed-surface luminescent media based on nanotubular and nanoporous modifications of hafnia.

Pyro-piezoelectric effect of BaTiO3 bio-nanocarrier for osteomyelitis therapy

Implant-related osteomyelitis harms patients’ health and lives. Non-invasive treatments triggered by external physical stimuli have been brought into focus in antibiosis. Herein, a therapeutic strategy through coupling piezoelectricity and pyroelectricity of BaTiO3 nanotubes (BNT) by synchronous treatments of ultrasound (US) and near-infrared light (NIR) is applied to kill bacteria in an osteomyelitis model. NIR or US treatment reduces spontaneous polarization of BNT, inducing pyroelectric/piezoelectric field and energy band tilting. Compared with single treatment, their synergistic effect further enhances charge transfer and electron-hole pair separation, improving the pyro-piezoelectric catalysis and thus the yield of reactive oxygen species (ROS); meanwhile, the tilting of energy bands induces an irreversible conductive circuit from bacteria to BNT, resulting in membrane electron loss and the disrupted bacterial metabolic balance. As a result, 99.8% of bacteria are killed under the pyro-piezoelectric therapy of BNT. Additionally, BNT with nanotubular structure acts as nanocarriers to load and release bone morphogenetic protein-2 (BMP-2), improving bone regeneration obviously after antibacterial therapy. This study provides a promising pyro-piezoelectric therapy by BMP-2 loaded BaTiO3 nanotubes for antibiosis and bone regeneration in treating osteomyelitis. It also brings new insight for developing pyro-piezoelectric sensors to deal with tissue infection.

Bioinspired Nanotubes by Soft‐template Electropolymerization from Fully Conjugated Monomers

AbstractBioinspired by the strong water‐adhesive forces of gecko foot or rose petals, here, nanotubular structures are prepared by soft‐template electropolymerization. Water is mixed to a solvent of low water‐solubility to form a micellar solution in the presence of tetrabutylammonium perchlorate as the electrolyte and surfactant. As the monomer, a benzene is trifunctionalized with various thiophene and carbazole moieties. The monomers are fully conjugated to favor the deposition compared to polymerization, as confirmed by cyclic voltammetry experiments. The surface nanostructures (nanotubes, nano‐ribbons, coral‐like structures) are highly dependent on the monomer and the water content but less on the deposition method. The maximum water contact angle is 158.1° accompanied with strong water adhesive force. These surfaces are highly interesting for applications in water‐harvesting systems or in sensing platforms.

Lotus-root-like multichannel nanotubes of IrO2–ZnO for electrocatalysis of pH-universal oxygen evolution reaction: A simple strategy to control the structure and crystallinity

A series of IrO2-ZnO composite oxide nanomaterials (IrO2-ZnO-x) were synthesized by electrospinning and subsequent calcination process using an electrospinning solution composed of Ir/Zn metal precursors and blended polymers of PVP/PVDF at different mixing ratios (PVDF wt% out of total polymer is denoted as x = 0, 17, 33, 50, 100). The fine structure and crystallinity of the produced IrO2-ZnO-x materials were tuned simply depending on the polymer mixing ratio: As PVDF content increased in a polymer blend, IrO2-ZnO-x (x = 0, 17, 33, 50) changed the structure from wire-in-tubes to nanofibers and then to lotus-root-like multichannel nanotubes with a greater degree of amorphization via better alloying between Ir and Zn elements. IrO2-ZnO-33, exhibiting a lotus-root-like multichannel nanotubular structure with very porous surface morphology and low crystallinity, showed the best OER activity and long-term durable stability for 24 h in a wide range of pH solutions among a series of IrO2-ZnO-x, outperforming commercial Ir/C and a counterpart containing only Ir element. IrO2-ZnO-33 synthesized with an optimal polymer-blending ratio boosted up the electrocatalytic activity toward OER, which was ascribed to (1) enlarged surface area from its unique structure, (2) increased defects along with the greater amount of oxygen vacancies in the amorphous phase, and (3) the synergistic effect between Ir and Zn. This study presents a straightforward strategy to control the structure and crystallinity of nanocatalysts using a blend of properly selected two different polymers.

Ceria tubular nanoarchitecture antioxidants achieve sustainable fuel cell devices via tuning the oxophilicity of Pt catalytic surfaces and radical scavenging

The durability of polymer electrolyte membrane fuel cells (PEMFCs) crucially depends on the use of antioxidants to prevent electrocatalyst degradation. Here, we report for the first time, by in situ X-ray absorption and H2O2 electrochemistry, that ceria significantly weakens the Pt-surface oxophilicity, which determines oxygen reduction (ORR) activity and durability, within the PEMFC cathode. Ceria mitigates catalyst disintegration and improves ORR durability by Pt oxophilicity reduction and its inherent radical scavenging behavior. We also found that the antioxidation efficacy of ceria could be finely tuned through nanostructuring. Among various ceria nanostructures, tubular ceria nanoarchitectures (CeOx NT), designed to have the largest surface area and abundant oxygen vacancies, enable the most potent interaction between Pt and Ce without direct chemical contact with Pt. The nanotubular structure confers superior multifunctional antioxidant therapeutic efficacy to Pt/C catalyst in PEMFCs, resulting in outstanding durability that retains 94% of initial performance after 100-hour tests.

Degree-based topological indices of boron nanotubes

In the past two decades, boron nanotubes have received significant attention from researchers and scientists due to their wide-ranging applications in electronics, nanodevices, optical engineering, nanobiotechnology, and cosmetics. These nanotubular structures composed of boron present exceptional electrical and mechanical properties, making them highly potential nanomaterials. In this article, we study the molecular structure of significant classes of boron nanotubes, namely, trihexagonal boron nanotubes, triangular boron nanotubes, and boron-α nanotubes. Furthermore, we calculate various topological indices for these nanotubes, including the augmented Zagreb index, Sombor index, reduced Sombor index, sum-connectivity index, and arithmetic–geometric index. These indices hold substantial importance in assessing the physical, chemical, and biological characteristics of boron nanotubes.

The Effects of Anodization Conditions on TiO2 Nanotubes Features Obtained Using Aqueous Electrolytes with Xanthan Gum

Titanium surfaces were anodized to create nanotube structures utilizing an aqueous electrolyte made of xanthan gum (XG) and sodium fluoride. The purpose of employing this type of anodizing solution was to investigate the impact of XG addition on the morphology and organization of nanotubes. As far as we know, this is the first time that TiO2 nanotubes, made using aqueous electrolytes with XG as an additive, have been reported. The organization of the nanotubes was measured using the regularity ratio (RR) from the fast Fourier transformation (FFT) pictures. Contrary to the nanotubes formed in aqueous solutions without XG, the addition of XG to the aqueous electrolyte improved the nanotube organization, with no effect on packability. Based on the findings of this experimental work, organized and homogeneous nanotubular structures might be produced utilizing an inexpensive and non-toxic aqueous electrolyte.

Synergistically enhanced electrochemical performance using N-rich multilayered carbon nanofibers

N-rich multilayered carbon nanofibers with hollow channels (PPMPN) are fabricated to fully utilize the mesopores, micropores, and nitrogen-functional groups of carbon nanofibers (CNFs) for superior electrochemical properties. Among all composites, the PPMPN(10) exhibits high specific surface area (570 m2g−1) with mesopore volume fraction (42%) and rich surface functionalities (∼7.25at% nitrogen and ∼ 16.1at% oxygen), helping to improveelectrochemical performance. The performance of the symmetric supercapacitor of the PPMPN was significantly improved in terms of its specific capacitance of 189 Fg−1 at 1 mAcm−2, good retention of 80% (when the current density is increased from 1 to 20 mAcm−2), energy density of 23.5 Whkg−1 at a power density of 400 Wkg−1, and cycling stability of 94% for 10,000 cycles. The top layer plays a role in charge storage/transport by increasing electrical conductivity due to N-functional groups. The intermediate layer with tubular 1D nanostructures enhances the diffusion of electrolyte ions even at higher current densities. The bottom layer composed of numerous micropores serves as a charge storage layer. Therefore, in the multilayer CNF, the micropores/mesopores and N-functional properties of each layer do not interfere with each other, and the advantages of the factors of each layer are maximized in the electrochemical properties.

BAGSPl of mesoporous Ag/ZnO nanostructures for visible light mediated photocatalytic removal of ciprofloxacin from water; a morphological perspective

Presence of antibiotics like ciprofloxacin (CIPRO) in drinking water resources has become a serious concern worldwide. Persistent existence of CIPRO in water environment leads to higher antimicrobial resistance by aiding the development of new and virulent bacterial strains. With the help of semiconductor based photocatalysts along with suitable metal doping, here we present, the successful synthesis of ZnO and Ag/ZnO nanocomposites derived from biosource for the active degradation of CIPRO from water through visible radiation. ‘Bio-source assisted green synthesis’ (BAGS) strategy has been followed using plantain-banana Musa balbisiana pseudostem (MBP) fibers for the successful replication of ZnO and Ag/ZnO mesoporous tubular-structured nanocomposites (NCs). Mesoporous morphological structures have been achieved in all three-weight percentages (wt%) of Ag/ZnO NCs (2, 5 and 10 wt%). The as-obtained bare and Ag/ZnO mesoporous tubular nanostructures are studied via XRD, UV-VIS, FT-IR, SEM and BET techniques. Out of three wt%, 5Ag/ZnO NCs better performed in the photocatalytic degradation of CIPRO under visible illumination (∼76%). Crystallite size, morphology and enhanced surface area have played crucial role in their photocatalytic mechanism. 5Ag/ZnO NCs are highly effective in CIPRO degradation even after five repeat cycles. Through LC-MS intermediate analysis, quinolone moiety-based pathway for CIPRO degradation is proposed. These bioderived NCs would pave a sustainable pathway for visible photocatalysis of emerging organic pollutants.

Hydrothermal Synthesis of a Technical Lignin-Based Nanotube for the Efficient and Selective Removal of Cr(VI) from Aqueous Solution.

Aminated lignin (AL) was obtained by modifying technical lignin (TL) with the Mannich reaction, and aminated lignin-based titanate nanotubes (AL-TiNTs) were successfully prepared based on the AL by a facile hydrothermal synthesis method. The characterization of AL-TiNTs showed that a Ti-O bond was introduced into the AL, and the layered and nanotubular structure was formed in the fabrication of the nanotubes. Results showed that the specific surface area increased significantly from 5.9 m2/g (TL) to 188.51 m2/g (AL-TiNTs), indicating the successful modification of TL. The AL-TiNTs quickly adsorbed 86.22% of Cr(VI) in 10 min, with 99.80% removal efficiency after equilibration. Under visible light, AL-TiNTs adsorbed and reduced Cr(VI) in one step, the Cr(III) production rate was 29.76%, and the amount of total chromium (Cr) removal by AL-TiNTs was 90.0 mg/g. AL-TiNTs showed excellent adsorption capacities of Zn2+ (63.78 mg/g), Cd2+ (59.20 mg/g), and Cu2+ (66.35 mg/g). After four cycles, the adsorption capacity of AL-TiNTs still exceeded 40 mg/g. AL-TiNTs showed a high Cr(VI) removal efficiency of 95.86% in simulated wastewater, suggesting a promising practical application in heavy metal removal from wastewater.

CO2-Derived Nanocarbons with Controlled Morphology and High Specific Capacitance.

The conversion of CO2 to nanocarbons addresses a dual goal of harmful CO2 elimination from the atmosphere along with the production of valuable nanocarbon materials. In the present study, a simple one-step metallothermic CO2 reduction to nanocarbons was performed at 675 °C with the usage of a Mg reductant. The latter was employed alone and in its mixture with ferrocene, which was found to control the morphology of the produced nanocarbons. Scanning electron microscopy (SEM) analysis reveals a gradual increase in the amount of nanoparticles with different shapes and a decrease in tubular nanostructures with the increase of ferrocene content in the mixture. A possible mechanism for such morphological alterations is discussed. Transmission electron microscopy (TEM) analysis elucidates that the nanotubes and nanoparticles gain mainly amorphous structures, while sheet- and cloud-like morphologies also present in the materials possess significantly improved crystallinity. As a result, the overall crystallinity was preserved constant for all of the samples, which was confirmed by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) techniques. Finally, electrochemical tests demonstrated that the prepared nanocarbons retained high specific capacitance values in the range of 200-310 F/g (at 0.1 V/s), which can be explained by the measured high specific surface area (650-810 m2/g), total pore volume (1.20-1.55 cm3/g), and the degree of crystallinity. The obtained results demonstrate the suitability of ferrocene for managing the nanocarbons' morphology and open perspectives for the preparation of efficient "green" nanocarbon materials for energy storage applications and beyond.

Hetero-dimeric covalent-organic pillars with aliphatic linkers

Penta-bridged covalent bis-pillar[5]arenes have garnered significant attention recently as single-molecule nanotubular structures. In this study, we synthesized hetero-dimeric covalent-organic pillars (hetero-COPs) by coupling penta-aldehyde and penta-amine pillar[5]arene derivatives. NMR spectroscopic, mass spectrometric, and X-ray crystallographic analyses confirmed the formation of a pair of directionally asymmetrical hetero-COPs with an overall length of 1.8 nm. Furthermore, we observed social chiral sorting during the [1 + 1] imine condensation process of these macrocyclic building blocks. Although the synthetic efficiency requires further improvement, our findings provide valuable insights into the design of directional nanotubes based on bis-pillar[5]arene.

Flexibility Analysis of DNA Nanotubes with Prescribed Circumferences and Their Pearl-Necklace Assemblies with Gold Nanoclusters.

DNA has been demonstrated as a powerful platform for the construction of inorganic nanoparticles (NPs) into complex three-dimensional assemblies. Despite extensive research, the physical fundamental details of DNA nanostructures and their assemblies with NPs remain obscure. Here, we report the identification and quantification of the assembly details of programmable DNA nanotubes with monodisperse circumferences of a 4, 5, 6, 7, 8, or 10 DNA helix and their pearl-necklace-like assemblies with ultrasmall gold nanoparticles, Au25 nanoclusters (AuNCs), liganded by -S(CH2)nNH3+ (n = 3, 6, 11). The flexibilities of DNA nanotubes, analyzed via statistical polymer physics analysis through atomic force microscopy (AFM), demonstrate that ∼2.8 power exponentially increased with the DNA helix number. Moreover, the short-length liganded AuS(CH2)3NH3+ NCs were observed to be able to form pearl-necklace-like DNA-AuNC assemblies stiffened than neat DNA nanotubes, while long-length liganded AuS(CH2)6NH3+ and AuS(CH2)11NH3+ NCs could fragment DNA nanotubular structures, indicating that DNA-AuNC assembling can be precisely manipulated by customizing the hydrophobic domains of the AuNC nanointerfaces. We prove the advantages of polymer science concepts in unraveling useful intrinsic information on physical fundamental details of DNA-AuNC assembling, which facilitates DNA-metal nanocomposite construction.

Doped halloysite nanotubes as a nanocontainer for the fabrication of ciprofloxacin hydrochloride loaded 3D printed scaffolds

Burn injuries are considered to be the most catastrophic form of skin injury, with a slight risk of mortality. This type of injury has a significant negative impact on both individuals and health care system. The hollow nano-tubular structures of doped halloysite nanotubes (DHNTs) facilitate in loading a wide variety of active molecules and make a potential nanocarrier for the delivery of drugs. Coincidentally, the high mechanical strength, good biocompatibility, and hemostasis properties of DHNTs offer a new platform for the fabrication of scaffolds to promote faster wound healing activity. Ciprofloxacin hydrochloride (Cip HCl) was chosen as the model drug to control the bacterial proliferation at the site of injury. Therefore, the present study was aimed to design a customized drug loaded nano-polymeric scaffolds by three dimensional (3D) printing techniques for tissue engineered applications in pharmaceutical sciences. Cip HCl loaded DHNTs coated poly vinyl alcohol pellets were extruded for the preparation of filaments by the hot melt extrusion process, and the prepared filaments were further processed for the fabrication of 3D printed scaffolds by fused deposit modelling (FDM) technique. The pellets were free-flowing with a coating efficiency of 60.23 – 82.65%. Scaffold 1 (S1) presented an excellent porous structure, while scaffold 2 (S2) revealed a slight porous structure with the porosity of 60%. The average pore diameter for both scaffolds ranged from 50.82 ± 23 to 93.06 ± 52 μm. S1 expressed a conventional release pattern of 73.35% ± 0.02 within 2 h of the time profile, S2 evidenced an inaugural burst release of 42.84% ± 0.05 at 2 h, followed by a sustained release of 85.54% ± 0.17 up to 12 h. Thus the FDM technique proves to be an ideal approach for the design of drug nanofiller coated polymeric 3D scaffolds for personalized drug delivery systems in the arena of tissue engineering and pharmaceutical sciences.

Covalently Linked Hexakis(m-Phenylene Ethynylene) Macrocycles as Molecular Nanotubes.

The construction of nanotubular structures with non-deformable inner pores is of both fundamental and practical significance. Herein we report a strategy for creating molecular nanotubes with defined lengths. Macrocyclic (MC) units based on shape-persistent hexakis(m-phenylene ethynylene) (m-PE) macrocycle MC-1, which are known to stack into hydrogen-bonded tubular assemblies, are tethered by oligo(β-alanine) linkers to give tubular stacks MC-2 and MC-4 that have two and four MC units, respectively. The covalently linked MC units in MC-2 and MC-4 undergo face-to-face stacking through intramolecular non-covalent interactions that further results in the helical stacks of these compounds. Oligomer MC-4 can form potassium and proton channels across lipid bilayers, with the channels being open continuously for over 60 seconds, which is among the longest open durations for synthetic ion channels and indicates that the thermodynamic stability of the self-assembling channels can be drastically enhanced by reducing the number of molecular components involved. This study demonstrates that covalently tethering shape-persistent macrocyclic units is a feasible and reliable approach for building molecular nanotubes that otherwise are difficult to create de novo. The extraordinarily long lifetimes of the ion channels formed by MC-2 and MC-4 suggest the likelihood of constructing the next-generation synthetic ion channels with unprecedented stability.

Covalently Linked Hexakis(m‐Phenylene Ethynylene) Macrocycles as Molecular Nanotubes

AbstractThe construction of nanotubular structures with non‐deformable inner pores is of both fundamental and practical significance. Herein we report a strategy for creating molecular nanotubes with defined lengths. Macrocyclic (MC) units based on shape‐persistent hexakis(m‐phenylene ethynylene) (m‐PE) macrocycle MC‐1, which are known to stack into hydrogen‐bonded tubular assemblies, are tethered by oligo(β‐alanine) linkers to give tubular stacks MC‐2 and MC‐4 that have two and four MC units, respectively. The covalently linked MC units in MC‐2 and MC‐4 undergo face‐to‐face stacking through intramolecular non‐covalent interactions that further results in the helical stacks of these compounds. Oligomer MC‐4 can form potassium and proton channels across lipid bilayers, with the channels being open continuously for over 60 seconds, which is among the longest open durations for synthetic ion channels and indicates that the thermodynamic stability of the self‐assembling channels can be drastically enhanced by reducing the number of molecular components involved. This study demonstrates that covalently tethering shape‐persistent macrocyclic units is a feasible and reliable approach for building molecular nanotubes that otherwise are difficult to create de novo. The extraordinarily long lifetimes of the ion channels formed by MC‐2 and MC‐4 suggest the likelihood of constructing the next‐generation synthetic ion channels with unprecedented stability.