Self-assembled Nanotubes Research Articles

Self-assembled chiral phosphorus nanotubes from phosphorene: a molecular dynamics study

Phosphorous nanotubes with predefined chiralities would be important in electronic devices. Here, we provide a novel and feasible approach for the fine controlled synthesis of chiral phosphorus nanotubes from phosphorene nanoribbons, theoretically.

Controlling the length of self-assembled nanotubes by sonication followed by polymer wrapping.

This work demonstrates that sonication, followed by polymer-wrapping, is an effective strategy to modulate the length of self-assembled nanotubes. The length distributions of the nanotubes were controlled by varying the amplitude of sonication. Wrapping the nanotubes with ionic polymers suspended the propensity of the nanotube fragments to re-assemble over time into their elongated precursors.

Templated J-Aggregate Nanotubes for the Detection of Dopamine

J-aggregates of dye molecules are a unique supramolecular structure, which shows great promise in photoelectric devices due to its remarkable optical and transport properties. In this paper, we report the templated formation of J-aggregate nanotubes by the adsorption of 3,3’-diethylthiacarbocyanine iodide on the self-assembled nanotubes of lithocholic acid. The optical and electronic properties of the templated J-aggregate nanotubes are studied. A sensor platform is fabricated by depositing the J-aggregate nanotubes on interdigitated gold electrodes for the detection of dopamine (DA). We find that the current change of the J-aggregate nanotube-based sensor platform in response to DA is linear in the concentration range from 10 nM to 70 nM, giving the detection limit of 0.27 nM.

High Resolution Piezoresponse Force Microscopy Study of Self-Assembled Peptide Nanotubes

ABSTRACT Peptide nanotubes based on short dipeptide diphenylalanine (FF) attract a lot of attention due to their unique physical properties ranging from strong piezoelectricity to extraordinary mechanical rigidity. In this work, we present the results of high-resolution Piezoresponse Force Microscopy (PFM) measurements in FF microtubes prepared from the solution. First in-situ temperature measurements show that the effective shear piezoelectric coefficient d15 (proportional to axial polarization) significantly decreases (to about half of the initial value) under heating up to 100 oC. The piezoresponse becomes inhomogeneous over the surface being higher in the center of the tubes. Further, PFM study of a composite consisting of FF microtubes and reduced graphene oxide (rGO) was performed. We show that piezoelectric properties of peptide microtubes are significantly modified and radial (vertical) piezoresponse appears in the presence of rGO as confirmed via PFM analysis. The results are rationalized in terms of molecular approach in which π – π molecular interaction between rGO and dipeptide is responsible for the appearance of radial component of polarization in such hybrid structures.

Self-assembling DNA nanotubes to connect molecular landmarks

Within cells, nanostructures are often organized using local assembly rules that produce long-range order. Because these rules can take into account the cell's current structure and state, they can enable complexes, organelles or cytoskeletal structures to assemble around existing cellular components to form architectures. Although many methods for self-assembling biomolecular nanostructures have been developed, few can be programmed to assemble structures whose form depends on the identity and organization of structures already present in the environment. Here, we demonstrate that DNA nanotubes can grow to connect pairs of molecular landmarks with different separation distances and relative orientations. DNA tile nanotubes nucleate at these landmarks and grow while their free ends diffuse. The nanotubes can then join end to end to form stable connections, with unconnected nanotubes selectively melted away. Connections form between landmark pairs separated by 1-10 µm in more than 75% of cases and can span a surface or three dimensions. This point-to-point assembly process illustrates how self-assembly kinetics can be designed to produce structures with a desired physical property rather than a specific shape.

Multifunctionality of cement based composite with electrostatic self-assembled CNT/NCB composite filler

In this paper, electrostatic self-assembled carbon nanotube (CNT)/nanocarbon black (NCB) composite is employed as filler for developing multifunctional cement-based composites. The performances of the composites with different content of filler are investigated. The electrochemical impedance spectroscopy and equivalent circuit are used to explore the conductive and mechanical mechanisms of the composites. Experimental results indicate that the compressive strength and elasticity modulus of the composites sharply decrease when the filler content exceeds 0.77vol.%. The percolation threshold zone of the electrical conductivity of the composites ranges from 0.39vol.% to 1.52vol.%. The piezoresistive properties of the composites with 2.40vol.% filler are stable and sensitive, and the maximum fractional change of electrical resistivity is 25.4% when the stress amplitude is 10MPa. The composites feature sensitive and linear thermal resistance effect when the filler content is 0.77vol.%. Electromagnetic shielding effectiveness of the composites with 2.40vol.% filler at 18GHz is 5.0dB, which is 2.2 times of that of the control samples. The composites exhibit high absorbing electromagnetic wave performances in the frequency range of 2–18GHz, and the minimum reflectivity reaches −23.08dB with 0.77vol.% filler.

Solid-state NMR and FTIR investigations of standard and nanotubular polyanilines

The standard emeraldine base (EB) form of polyaniline and the product obtained by the oxidative polymerization of aniline using a pH-stat method at a constant pH of 2.5 are investigated. The morphology of the pH-stat product was examined using scanning electron microscopy and transmission electron microscopy. The prevalence of self-assembled nanotubes in the pH-stat product is confirmed. The structural differences between the EB and pH-stat products are revealed by FTIR and solid-state NMR experiments. On the basis of these investigations, the presence and the role of the oligomeric material in the formation of nanotubes is confirmed.

Two-Dimensional Alignment of Self-Assembled Organic Nanotubes through Langmuir-Blodgett Technique.

A C3-symmetric molecule was found to form organic nanotubes through supramolecular gel formation in organic solvents. These nanotubes can be dispersed in toluene without destroying the tubular nanostructures. Using the dispersions of these organic nanotubes as "spreading solutions", Langmuir-spreading films of these nanotubes were formed. Through repeated compression and expansion cycles, the nanotubes can be aligned to a certain extent. The formed Langmuir films could be subsequently transferred to a solid substrate, and the well-aligned nanotube films were constructed by Langmuir-Blodgett film deposition technique. Interestingly, many guests including polymers, water-soluble or oil-soluble organic molecules can be encapsulated into the nanotubes and further spread on a water subphase. Through elaborate control, large-scale parallel alignment of self-assembled organic nanotubes encapsulated by guests was also realized. This study implies that 2D hierarchical alignment of one-dimensional organic nanostructures can be realized using a simple method.

Synthesis of self-assembled rectangular-shaped polyaniline nanotubes and their physical characteristics

Abstract We reports synthesis of polyaniline (PANI) nanotubes with a rectangular cross-sectional shape by simply changing both molar ratio of organic dopant acid to monomer and reaction time. The PANI nanotubes were fabricated with a controlled rectangular pore structure by an in-situ chemical oxidation polymerization process in the absence of surfactant and template. Morphology of citric acid (CA)-doped PANI was observed via scanning electron microscopy and transmission electron microscopy. Fourier transform infrared spectroscopy and X-ray diffraction confirmed chemical structure and hydrogen bonding between amine group of PANI and hydroxyl and carboxyl group of CA, is the driving force for this self-assembly.

Glucose derivatives substitution and cyclic peptide diameter effects on the stability of the self-assembled cyclic peptide nanotubes; a joint QM/MD study

Dynamical behavior and the stability of eighteen nanostructures composed of cyclic peptide (CP) with the general structure of the cyclo(CO(CH2)n=4, 6, 10COCyst), in the gas phase, water and chloroform were investigated during 50ns molecular dynamic (MD) simulations. CP dimers and cyclic peptide nanotubes (CPNTs) are more stable in chloroform than water and this stability is reversely correlated with the ring size of the CP units. Also the effect of glucose derivatives substitution, d-glucose (S1) and N-methyl-d-glucamine (S2), on the stability and other physicochemical properties of the CP dimers and CPNTs were evaluated. These substitutions increase the inner-subunits hydrogen bonds (H-bond) which in turn increase the stability of these structures. Moreover, the S2 substitution in comparison to the S1 makes dimers and CPNTs more stable. Gibbs free energy analysis based on the MM-PBSA and MM-GBSA calculations confirmed that substitutions affect the stability of the studied nanostructures, considerably and an increase in the length of the CPNT units reduces their stability. Quantum chemistry calculations on the dimer structures using the density functional theory (DFT) and DFT-D3 methods were performed. Based on the DFT-D3 calculations, it was revealed that the dispersion interactions play a key role in the dimerization process. The ring size increment, elevates the dispersion interaction energy which is accordance with the MD results. H-bond formation between the CO and NH groups of the CP units inside the dimers have been analyzed by using the quantum theory of atoms in molecules and natural bond orbital description. Finally, through these analyses, the electrostatic interaction between the mentioned groups have been evaluated.

Room-Temperature Micron-Scale Exciton Migration in a Stabilized Emissive Molecular Aggregate.

We report 1.6 ± 1 μm exciton transport in self-assembled supramolecular light-harvesting nanotubes (LHNs) assembled from amphiphillic cyanine dyes. We stabilize LHNs in a sucrose glass matrix, greatly reducing light and oxidative damage and allowing the observation of exciton-exciton annihilation signatures under weak excitation flux. Fitting to a one-dimensional diffusion model, we find an average exciton diffusion constant of 55 ± 20 cm2/s, among the highest measured for an organic system. We develop a simple model that uses cryogenic measurements of static and dynamic energetic disorder to estimate a diffusion constant of 32 cm2/s, in agreement with experiment. We ascribe large exciton diffusion lengths to low static and dynamic energetic disorder in LHNs. We argue that matrix-stabilized LHNS represent an excellent model system to study coherent excitonic transport.

Photoactivation of Noncovalently Assembled Peptide Ligands on Carbon Nanotubes Enables the Dynamic Regulation of Stem Cell Differentiation.

Stimuli-responsive hybrid materials that combine the dynamic nature self-assembled organic nanostructures, unique photophysical properties of inorganic materials, and molecular recognition capability of biopolymers can provide sophisticated nanoarchitectures with unprecedented functions. In this report, infrared (IR)-responsive self-assembled peptide-carbon nanotube (CNT) hybrids that enable the spatiotemporal control of bioactive ligand multivalency and subsequent human neural stem cell (hNSC) differentiation are reported. The switching between the ligand presented and hidden states was controlled via IR-induced photothermal heating of CNTs, followed by the shrinkage of the thermoresponsive dendrimers that exhibited lower critical solution temperature (LCST) behavior. The control of the ligand spacing via molecular coassembly and IR-triggered ligand presentation promoted the sequential events of integrin receptor clustering and the differentiation of hNSCs into electrophysiologically functional neurons. Therefore, the combination of our nanohybrid with biomaterial scaffolds may be able to further improve effectiveness, durability, and functionality of the nanohybrid systems for spatiotemporal control of stem cell differentiation. Moreover, these responsive hybrids with remote-controllable functions can be developed as therapeutics for the treatment of neuronal disorders and as materials for the smart control of cell function.

Water-driven stabilization of diphenylalanine nanotube structures

L,L-diphenylalanine has been employed in the formation of self-assembled peptide nanotubes with great potential for the development of biosensors, molecular carriers, and optoelectronic devices. They are usually formed in an aqueous solution, and it is well known that water remains confined inside the structure. However, the role played by water in the overall stability of the nanotube is still unknown at the microscopic level. In this work, we investigate the stability of peptide structures after assembly due to the interaction with water molecules. We demonstrate, using molecular dynamics based on density functional tight-binding techniques, that water is fundamental in keeping the nanotube structure. It interacts with the nanotube walls as well as with other water molecules via hydrogen bonds keeping the structure stable. We identify and quantify the interaction between water and the relevant groups, and, upon increasing the solvent concentration, we show there is a transition region where there is a competition between the formation of water/water hydrogen bonds, and steric effects.

Self-Assembled Heterojunction Carbon Nanotubes Synergizing with Photoimmobilized IGF-1 Inhibit Cellular Senescence.

Synthesis of artificial and functional structures for bone tissue engineering has been well recognized but the associated cell senescence issue remains much less concerned so far. In this work, surface-modified polycaprolactone-polylactic acid scaffolds using self-assembled heterojunction carbon nanotubes (sh-CNTs) combined with insulin-like growth factor-1 are synthesized and a series of structural and biological characterizations are carried out, with particular attention to cell senescence mechanism. It is revealed that the modified scaffolds can up-regulate the expressions of alkaline phosphates and bone morphogenetic proteins while down-regulate the expressions of senescence-related proteins in mesenchymal stem cells, demonstrating the highly preferred anti-senescence functionality of the sh-CNTs modified scaffolds in bone tissue engineering. Furthermore, it is also found that with sh-CNTs, scaffolds can accelerate bone healing with extremely low toxicity in vivo.

Synergistic effects of carboxylic acid-functionalized carbon nanotube and nafion/silica nanofiber on electrical actuation efficiency of shape memory polymer nanocomposite

Synergistic effects of self-assembled carboxylic acid-functionalized carbon nanotube (CNT) and nafion/silica nanofiber on the electro-activated shape recovery behavior of shape memory polymer (SMP) nanocomposite were investigated. Carboxylic acid-functionalized CNTs were self-assembled onto the carbon fiber mat to enhance their bonding reliability and achieve efficient electrical actuation for SMP matrix. Nafion/silica nanofibers were electrospun onto surfaces of the carbon fiber mat to prevent electrically resistive heat dissipation. The combination of electrically/thermally conductive CNTs and thermally resistive nafion/silica nanofibers results in improvement for both electrically induced shape recovery and actuation efficiency in the SMP nanocomposite.

Interface Storage and Diffusion in Titania-Based Na-Ion Battery Negative Electrodes

Ordered, nanostructured transition metal oxides are currently in the spotlight of battery research. To exploit, however, the full potential of self-assembled titania nanotube layers in Na-ion battery technology we need to close the gap in knowledge about the underlying storage mechanisms as well as ion dynamics. For this purpose, amorphous TiO2 nanotubes (70-130 nm in diameter, 4.5 – 17 µm in length) were fabricated by anodization, i.e., electrochemical oxidation. The electrochemical behaviour with respect to sodium insertion was studied by cyclic voltammetry and galvanostatic cycling with potential limitation. It turned out that the nanotubes are very resilient to cycling, some being able to withstand more than 300 charge-discharge cycles without significant loss of capacity. Compared to classical insertion reactions, the mechanism of reversible electrochemical storage of Na+ in the nanotubes seems to differ significantly. There is strong evidence that a large amount of the Na+ ions is stored on the surface or in the surface-influenced regions while only a smaller fraction is inserted in the walls of the tubes. The interfacial Na+ storage is governed by a faradaic adsorption phenomena, which is essentially different from the (pseudo-)capacitive model hitherto used in the literature. The finding that, in the case of sodium, interfacial storage is more important than ion insertion into the crystal lattice is supported by the very low Na+ diffusion coefficients determined at various electrode potentials (in the order of 4 · 10-20 - 10-21 cm2/s). This dominant interfacial storage mechanism may explain the high specific capacity and the very good cycling performance recently reported for some nanostructured titania phases as well as for other nanosized titanate materials. Figure A. Chemical diffusion coefficient of Na+ into amorphous TiO2 at room temperature (23 ±1°C) after subtracting the interfacial storage contributions for different sample types. Figure B. Pseudo-capacitance values corresponding to the interfacial storage of Na+ ions on various nanotube layers plotted as a function of the electrode potential. Figure 1

Joint defect- and variation-aware logic mapping of multi-outputs crossbar-based nanoarchitectures

Nanotechnology-based manufacturing, relying on self-assembly of nanotubes or nanowires, has shown promising potentials for future nanoscale circuit designs. However, high defect density and extreme process variations for crossbar-based nanoarchitectures are expected to be fundamental design challenges. Consequently, defect and variation issues must be considered in logic mapping on nanoscale crossbars. In this paper, we establish a mathematical model for the simultaneous variation and defect-aware logic mapping of multi-outputs crossbar arrays. We model this problem using a new sub-weighted-graph isomorphism problem and propose a greedy algorithm for the variation- and defect-aware logic mapping. Based on Monte-Carlo simulation, we compare the proposed technique with other logic mapping techniques such as, variation-unaware and exhaustive search mapping in terms of accuracy as well as runtime. Results show that the effectiveness of our new mapping technique in variation and defect tolerance as well as run time improvement.

Diphenylalanine peptide nanotubes self-assembled on functionalized metal surfaces for potential application in drug-eluting stent.

This study focuses on the potential of diphenylalanine self-assembled peptide nanotubes (FF Nts) for delivery of flufenamic acid (FA) from metal implants. Self-assembly of FF Nts was studied in solution and on surfaces of glass, silicone and gold substrates. FA was loaded inside the shell of FF Nts and subsequently FF/FA Nts were attached to gold surfaces. The substrate were characterized by Field Emission Scanning Electron Microscopy (FESEM), fluorescence microscopy, confocal microscopy, and UV-vis spectroscopy. Release of FA from FF Nts were investigated by immersing coated metal substrates in phosphate-buffered saline for 12 days. Self-assembly of FF in water and solvent resulted in formation of nanotubes, which efficiently loaded 98% of FA with concentration of 20 µg/mL. FESEM images confirmed successful attachment of FF/FA Nts to functionalized gold substrates. In vitro release studies indicated using FF Nts has prolonged the release rate of FA for several days. Biocompatibility studied confirmed more than 50% of the cells were alive in concentration of 250-1000 µg/mL of FF Nts thus suggesting the potential of peptide based self-assemble nanostructures as an alternate system for polymer coating in drugs eluting stents. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 104A: 2280-2290, 2016.

Structural and optical properties of self-assembled polypyrrole nanotubes

Polypyrrole (PPy) nanotubes doped with camphorsulfonic acid (CSA) have been synthesized using self-assembly polymerization method. The average diameter of the resulting PPy nanotubes has been controlled by varying the dopant/monomer molar ratio. Formation mechanism of PPy nanotubes has been discussed at length. The formation of PPy nanotubes has been confirmed from the high resolution transmission electron microscopy (HRTEM) studies. FTIR studies depict that the “effective conjugation length” of PPy nanotubes increases with increasing CSA/Py molar ratio. UV-vis studies reveal the formation of polaron and bipolaron bands within the band gap of neural PPy, confirming the doping of PPy nanotubes with CSA. The optical band gap energy decreases with increasing CSA/Py ratio and also the thermal stability of PPy nanotubes gets enhanced with increasing dopant/monomer molar ratio.

Polypeptoid self-assembles into nanotubes

A study shows that diblock copolymers made from peptide analogs called peptoids can stack together in a novel way to form crystalline nanotubes. Ronald N. Zuckermann of Lawrence Berkeley National Laboratory and coworkers created the new class of nanotubes by synthesizing diblock copolymers containing same-sized blocks of hydrophilic (ethyleneoxy side-chain) and hydrophobic (decyl side-chain) poly(N-substituted glycines). The peptoid chains form rings that stack vertically, with the hydrophilic and hydrophobic blocks aligning with one another, by a not-yet-understood mechanism, to form nanotubes with amphiphilic interior and exterior surfaces (Proc. Natl. Acad. Sci. USA 2016, DOI: 10.1073/pnas.1517169113). Self-assembling nanotubes have been prepared before by mechanisms involving hydrogen bonding, electrostatic, or π-π interactions. But the new ones do not form via any of those mechanisms. The researchers hope to learn how they do form, as well as determine their atomic-resolution structure, cross-link th...