Lipid nanotubes and microtubes: experimental evidence for unsymmetrical monolayer membrane formation from unsymmetrical bolaamphiphiles

Unsymmetrical bolaamphiphiles, omega- [N-beta-D-glucopyranosylcarbamoyl] alkanoic acids, with even-numbered oligomethylene chains (12, 14, 16, 18, and 20 carbons) self-assembled in water to form lipid nano- and microtubes. The tubular assemblies were separated by centrifugation and examined by transmission electron microscopy, X-ray diffraction, and Fourier transform infrared spectroscopy to study the molecular packing within the tubular membranes. The nanotubes encapsulated the staining reagent phosphotungstate, which revealed them to be hollow cylinders up to several hundred micrometers long with 30-43-nm outer diameters and 14-29-nm inner diameters. By comparing the membrane stacking periodicity obtained from powder X-ray diffraction analysis of the dehydrated tubes with the molecular packing within single crystals, we found that the nanotubes consist of an unsymmetrical monolayer lipid membrane (MLM) in which the molecules are packed in a parallel fashion. This suggests that the inner surface of the nanotubes is covered with carboxy headgroups and the outer surface with 1-glucosamide headgroups. The inner diameters of the lipid nanotubes could be controlled in the range 17.7-22.2 nm in steps of approximately 1.5 nm/two carbons by varying the oligomethylene spacer length. The microtubes had three types of molecular arrangements. The first type was a symmetrical MLM in which the molecules were packed in an antiparallel fashion. The other two types had unsymmetrical MLM stacking with head-to-head and head-to-tail motifs. Increasing the number of oligomethylene spacers stabilized the unsymmetrical MLM structure in both nano- and microtubes.     

Self-assembly of Peptide nanotubes in an organic solvent

The self-assembly of a modified fragment of the amyloid beta peptide, based on sequence Abeta(16-20), KLVFF, extended to give AAKLVFF is studied in methanol. Self-assembly into peptide nanotubes is observed, as confirmed by electron microscopy and small-angle X-ray scattering. The secondary structure of the peptide is probed by FTIR and circular dichroism, and UV/visible spectroscopy provides evidence for the important role of aromatic interactions between phenylalanine residues in driving beta-sheet self-assembly. The beta-sheets wrap helically to form the nanotubes, the nanotube wall comprising four wrapped beta-sheets. At higher concentration, the peptide nanotubes form a nematic phase that exhibits spontaneous flow alignment as observed by small-angle neutron scattering.     

Sol–gel template synthesis and characterization of VO2 nanotube arrays

In this paper, we report on the obtention of highly ordered VO₂ nanotube arrays synthesized by the simple sol?Cgel template method. Techniques of transmission electron microscopy, X-ray powder diffraction, X-ray photoelectron spectroscopy, Raman spectroscopy were used to characterize the morphology and structure of the as-synthesized nanotube arrays. It is found that the size of the as-obtained nanotubes has the dimension of 180?C220?nm in outer diameter, 110?C140?nm in inner diameter and up to 10???m in length. The results show that as-synthesized sample is assigned to VO₂ (B) phase in expected V/O ratio with V existing in the +4 oxidation state.     

Low-temperature catalytic preparation of multi-wall MoS_2 nanotubes

Since the first report on inorganic fullerene-like WS2 polyhedra and nanotubes by Tenne et al.[1] in 1992, this kind of nanostructural materials have become extensive research topics owing to their unique electronic structures. WS2 and MoS2 nanomaterials have shown potential applications in the fields of scanning probe microscopy[2], solid-state lubrication[3], heterogeneous catalysis[4], and electrochemical hydrogen storage[5]. Up to now, a great deal of progress has been achieved in the st…     

Self-assembled nanotubes and helical tapes from diacetylene nonionic amphiphiles. Structural studies before and after polymerization

We synthesized new amphiphiles comprised of a single diacetylenic chain and an oligoethylenoxide polar chain linked by an amide bond. In aqueous medium, they are not soluble at room temperature but form weak gels. Electron microscopy studies have shown that they self-assemble into helical tapes or nanotubes with lengths of several micrometers, and inner and outer diameters of 50 ± 1 and 59 ± 1 nm, respectively. The wall has a thickness of 10 ± 1 nm for both kinds of objects and has an amphiphile bilayer structure. The hydrophobic chains are ordered, and the amide groups are linked with each other by H-bonds. The dissociation of the tubes is a first-order transition with an enthalpy of ca. 40 kJ mol(-1). The nanotubes were photopolymerized to yield purple solutions consisting of helical tapes and almost flat ribbons. The polymers exhibit irreversible thermochromism upon heating.     

Continuous Production of Carbon Nanotubes by Using Moving Bed Reactor

Since the discovery in 19911, carbon nanotubes have been the subject of intensive research due to their extraordinary mechanical and electronic properties2-7. However, lack of sufficient amount of materials limited the study of the fundamental properties and development of more practical applications. It is highly desirable to have large quantities of pure nanotubes. To date, few methods have been developed for the production of high-quality tubes which can adapted to industrial production …     

Pushing the size limits in the replication of nanopores in anodized aluminum oxide via the layer-by-layer deposition of polyelectrolytes

We report on the successful replication of the smallest pores in anodized aluminum oxide (AAO) via the layer-by-layer (LBL) deposition of polyelectrolytes to date to yield free-standing, open nanotubes with inner and outer diameters (±2σ) down to 37 ± 4 and 52 ± 19 nm, respectively. This work is based on the fabrication of defined arrays of highly regular nanopores by anodic oxidation of aluminum. Pores with pore diameters between 53 ± 9 and 356 ± 14 nm and interpore distances between 110 ± 3 and 500 ± 17 nm were obtained using an optimized two-step anodization procedure. 3-(Ethoxydimethylsilyl)propylamine-coated pores were replicated by alternating LBL deposition of poly(styrenesulfonate) and poly(allylamine). The detrimental adsorption of polyelectrolyte on the top surface of the template that typically results in partial pore blocking was eliminated by controlling the surface energy of the top surface via deposition of an ultrathin gold layer. The thickness of the deposited LBL multilayer assembly at the pore orifice agreed to within the experimental error with the thicknesses measured by variable angle spectroscopic ellipsometry and atomic force microscopy (AFM) for layers assembled on flat substrates. The selective dissolution of the alumina template afforded free-standing, open polymer nanotubes that were stable without any cross-linking procedure. The nanotubes thus obtained possessed mean outer diameters as small as 52 nm, limited by the size of the AAO template.     

单晶CaSO4纳米管的制备——非片状结构化合物形成纳米管的新途径

以Ti-O-Ti油酸偶合体作为结构引导生长剂,采用溶剂热技术成功地制备了单晶无水硫酸钙纳米管,并通过XRD、X射线能谱(EDX)、TEM、选区电子衍射(CBED)对CaSO₄纳米管进行了表征.其晶格常数与JCPDS标准卡单斜相CaSO₄晶体数值一致,属P3m1(164)空间群.纳米管呈均匀的直管形,直径约为30nm,内径约为10nm,长度达到3.0μm.并对硫酸钙纳米管的形成机理进行了浅析,提出了非片状结构的离子晶体,通过结构引导生长剂诱导生长成为片状结构,在溶剂热条件下弯曲、旋转、卷拢形成纳米管的新方法.     

Synthesis of vanadium oxide nanotubes via an ultrasonic method

Vanadium oxide nanotubes were synthesized using V₂O₅ powder as the precursor and hexadecylamine as the structure-directing template using a sol-gel reaction method followed by a one-step hydrothermal treatment. The effect of ultrasonics on the formation of nanotubes is reported. The structure and morphology of the nanotubes were investigated by X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. The inner and outer diameters of the nanotubes varied from 20 to 40 nm and 80 to 100 nm, respectively. The nanotubes measured several micrometers in length.     

Synthesis and characterization of ultrahigh crystalline TiO2 nanotubes

Ultrahigh crystalline TiO2 nanotubes were synthesized by hydrogen peroxide treatment of very low crystalline titania nanotubes (TiNT-as prepared), which were prepared with synthesized TiO2 nanoparticles by hydrothermal methods in an aqueous NaOH solution. Thus, prepared ultrahigh crystalline TiO2 nanotubes (TiNT-H2O2) showed comparable crystallinity with high crystalline TiO2 nanoparticles. The details of nanotubular structures were elucidated by high resolution-transmission electron microscopy (HR-TEM), field emission-scanning electron microscopy (FE-SEM), energy-dispersive X-ray analysis in transmission electron microscopy (TEM-EDX), X-ray diffraction (XRD), photoluminescence (PL), and BET surface area. TiNT-H2O2 was found to be a multiwalled anatase phase only with an average outer diameter of approximately 8 nm and an inner diameter of approximately 5 nm and grown along the [001] direction to 500-700 nm long with an interlayer fringe distance of ca. 0.78 nm. The photocatalytic activity of TiNT-H2O2 was about 2-fold higher than those of TiNT-as prepared, synthesized TiO2 nanoparticles, and TiO2-P25 (Degussa) in the photocatalytic oxidation of trimethylamine gas under UV irradiation.     

Low-temperature catalytic preparation of multi-wall MoS<Subscript>2</Subscript> nanotubes

In the catalytic reduction atmosphere of H₂+CH₄+C₄H₄S, the ball-milled precursor (NH₄)₂MoS₄ is heated to 300°C for decomposition. The as-synthesized product is characterized by XRD, SEM, HRTEM, EDX, and BET. The results show that multi-wall MoS₂ nanotubes are obtained. The length of the nanotubes is around 3–5 μm. The diameters of the nanotubes are homogeneous, with an inner diameter of ∼15 nm, an outer diameter of ∼30 nm, and an interlayer (002) d-spacing of 0.63 nm. This catalytic thermal reaction occurring at low temperatures is important for the large-scale preparation of similar transition-metal disulfide nanotubes.     

Synthesis and mechanism of polyaniline nanotubes with rectangular cross section via in situ polymerization

Polyaniline (PANI) nanotubes with rectangular cross section, which had 90–500 nm in outer diameter and 30–400 nm in inner diameter, were synthesized via a self‐assembly process in the presence of chiral acid (1S)‐(+)‐10‐camphorsulfonic (D‐CSA) and non‐chiral hydrochloric acid (HCl) coordinating with sodium dodecylbenzenesulfonate (SDBS), respectively. By using SEM, TEM, OM, FTIR, and WAXD, the as‐prepared PANI nanotubes with diversified morphologies were also characterized so as to investigate the formation mechanism of such tubular nanostructures with square cross sections. The results showed that the bilayer‐lamellar micelles formed by anilinium cations and CSA anions acted as the primary templates in the formation of the flat oligomer flakes, and the flakes finally united together to form rectangular nanotubes initiated by the reaction of the active centers on their edges. This study sheds light on the formation process of the PANI nanotubes with rectangular holes and outer contours and may be instructive to the controllable growth of certain nanostructures with unique morphologies. Copyright © 2011 John Wiley & Sons, Ltd.     

碳包覆Na2Ti6O13纳米管的电化学性能研究

以金红石型TiO2和NaOH为原料,由水热反应制备Na2Ti6O13纳米管.然后,在含有0.1 mol.L-1NaOH的葡萄糖水溶液中反应4 h制得碳包覆的Na2Ti6O13纳米管.X射线衍射(XRD)、扫描电子显微镜(SEM)和透射电子显微镜(TEM)等分析表明,该碳包覆Na2Ti6O13纳米管外径约14～19 nm,内径约2～5 nm,长度为数百纳米,有一层厚度约为2 nm的碳层包覆在纳米管外壁.以其作为锂离子电池负极材料,恒电流充放电测试表明,在50 mA.g-1电流密度下首周可逆容量达到161 mAh.g-1,循环100周后容量保持在147 mAh.g-1.相比于Na2Ti6O13纳米管,提高了20%以上.电流密度升至1600 mA.g-1充放电,碳包覆Na2Ti6O13纳米管可逆容量仍有70 mAh.g-1左右,远高于Na2Ti6O13纳米管,表现出良好的倍率性能.     

SiOx纳米管的制备及其发光特性

Amorphous SiOx nanotubes with homogeneous diameters were fabricated in large-scale on silicon substrate by thermal evaporation method, with liquid gallium as medium. The average diameter of tubes is about 80 nm and the length is more than 10 1m, with small ratio between the inner and outer diameter of the tube. The silicon element in the substrate and the residual oxygen element in reaction chamber were first dissolved into liquid Ga. Then the SiOx precipitated from the surface of gallium droplet, forming the nanotube structure with Ga droplet being the center. The room temperature photoluminescence measurements under excitation at 260 nm show that the SiOx nanotubes has a strong blue emission at 453 nm with two shoulders at 410 and 480 nm respectively, which may be related to oxygen defects. The preparation method improved the traditional complicated method and also provided a new way to fabricate SiOx nanotubes in large quantity.     

The Synthesis and Photocatalytic Properties of TiO2 Nanotube Array by Starch‐Modified Anodic Oxidation

In this study, the characterization and photocatalytic activity of TiO₂ nanotube arrays prepared by anodization process with starch addition were investigated in detail. The results suggested that the optimum mass fraction of starch added in anodization process was 0.1%, with which TiO₂ nanotube arrays owning good tubular structure were synthesized. The tube length and average inner diameter of nanotubes were approximately 4 μm and 30 nm, respectively. Through the characterization of TiO₂ nanotube arrays by energy dispersive spectrometer, scanning electron microscopy, transmission electron microscopy, X‐ray diffraction, Fourier Transform Infrared (FTIR) spectroscopy, it was found that the as‐prepared nanotubes possessed well uniformed and higher photodegradation responsive than the pure TiO₂. Moreover, it was expected that the as‐prepared nanotubes exhibited good photocatalytic activity for the degradation of RhB under UV‐light irradiation, which could be ascribed to their good morphology, enhanced UV‐light absorption property and electron transmission ability during the photocatalytic reaction. In addition, the nanotubes were not significantly regenerated during the cycling runs experiment. Overall, this study could provide a principle method to synthesize TiO₂ nanotube arrays with enhanced photocatalytic activity by anodization process with starch addition for environmental purification.     

Photoinduced Morphological Transformations of Soft Nanotubes

In water, synthetic amphiphiles composed of a photoresponsive azobenzene moiety and an oligoglycine hydrogen‐bonding moiety selectively self‐assembled into nanotubes with solid bilayer membranes. The nanotubes underwent morphological transformations induced by photoisomerization of the azobenzene moiety within the membranes, and the nature of the transformation depended on the number of glycine residues in the oligoglycine moiety (i.e., on the strength of intermolecular hydrogen bonding). Upon UV‐light irradiation of nanotubes prepared from amphiphiles with the diglycine residue, trans‐to‐cis isomerization induced a transformation from nanotubes (inner diameter (i.d.) 7 nm), several hundreds of nanometers to several tens of micrometers in length, to imperfect nanorings (i.d. 21–38 nm). The cis‐to‐trans isomerization induced by continuous visible‐light irradiation resulted in the stacking of the imperfect nanorings to form nanotubes with an i.d. of 25 nm and an average length of 310 nm, which were never formed by a self‐assembly process. Time‐lapse fluorescence microscopy enabled us to visualize the transformation of nanotubes with an i.d. of 20 nm (self‐assembled from amphiphiles with the monoglycine residue) to cylindrical nanofibers with an i.d. of 1 nm; shrinkage of the hollow cylinders started at the two open ends with simultaneous elongation in the direction of the long axis.     

Template Synthesis and Magnetic Behavior of FeNi Alloy Nanotube Arrays

"FeNi nanotubes were successfully prepared in pores of anodic aluminium oxide templates by the wetting template method. By varying the deposition conditions and the parameters of the templates, the lengths and the outer as well as the inner diameters of the tubes can be tailored. The FeNi nanotubes and their arrays were characterized by transmission and scanning electron microscopy. Macroscopic magnetic measurements show the FeNi nanotube arrays to have obvious anisotropy, and the easy axis is parallel to the nanotube axis. The magnetic moment distributions in the tube walls and the magnetization reversal mechanism are discussed. Magnetic moments of the FeNi nanotube preferentially lie in the nanotube wall, but the distribution is spatially isotropic. These magnetic behaviours are due to the unique shape of the nanotube."     

Substrate-supported lipid nanotube arrays

This Communication describes the self-assembly of phospholipids into lipid nanotubes inside nanoporous anodic aluminum oxide substrate. Orientations of the lipid molecules in such lipid nanoscale structures were verified by high-resolution spin labeling EPR at 95 GHz. The static order parameter of lipids in such nanotube arrays was determined from low-temperature EPR spectra and was found to be exceptionally high, Sstatic approximately 0.9. We propose that substrate-supported lipid nanotube arrays have potential for building robust biochips and biosensors in which rigid nanoporous substrates protect the bilayer surface from contamination. The total bilayer surface in the lipid nanotube arrays is much greater than that in the planar substrate-supported membranes. The lipid nanotube arrays seem to be suitable for developing patterned lipid deposition and could be potentially used for patterning of membrane-associated molecules.     

Molecular dynamics simulation of the spontaneous formation of a small DPPC vesicle in water in atomistic detail

Molecular dynamics simulations have been used to study the spontaneous aggregation of a concentrated solution of dipalmitoylphosphatidylcholine (DPPC) molecules in water into a small vesicle. The molecules were represented in atomistic detail. Starting from a DPPC solution in water, an oblong vesicle with a long axis of 15 nm and short axes of 10 nm was formed spontaneously. After 90 ns of simulation, the vesicle contained a number of water pores. Water pores were shown to facilitate exchange of lipids between inner and outer leaflets. Lipid tails were shown to be less ordered in the inner leaflet of the vesicle, as compared to those in the outer leaflet of the vesicle and an equilibrated lamellar bilayer.     

Anodic growth of highly ordered TiO2 nanotube arrays to 134 microm in length

Described is the fabrication of self-aligned highly ordered TiO(2) nanotube arrays by potentiostatic anodization of Ti foil having lengths up to 134 mum, representing well over an order of magnitude increase in length thus far reported. We have achieved the very long nanotube arrays in fluoride ion containing baths in combination with a variety of nonaqueous organic polar electrolytes including dimethyl sulfoxide, formamide, ethylene glycol, and N-methylformamide. Depending on the anodization voltage, pore diameters of the resulting nanotube arrays range from 20 to 150 nm. Our longest nanotube arrays yield a roughness factor of 4750 and length-to-width (outer diameter) aspect ratio of approximately 835. The as-prepared nanotubes are amorphous but crystallize with annealing at elevated temperatures. In initial measurements, 45 mum long nanotube-array samples, 550 degrees C annealed, under UV illumination show a remarkable water photoelectrolysis photoconversion efficiency of 16.25%.