Phospholipid tubelets

A novel electron microscopy specimen protocol shows that the presumed phospholipid bilayer membrane ribbons that wind helically to form the cylinders known as "tubules" are actually flattened tubes. These flattened tubes are alternatively found with a helical twist about the tube's long axis or occasionally flat with no winding or twist. Flat, cylindrically wound and axially twisted segments are routinely found along a single tube's length, and at the helically wound and axially twisted segment junctions, the chiral sense of the structure often, but not always, changes chiral sense.     

Modulating artificial membrane morphology: pH-induced chromatic transition and nanostructural transformation of a bolaamphiphilic conjugated polymer from blue helical ribbons to red nanofibers.

Design and characterization of helical ribbon assemblies of a bolaamphiphilic conjugated polymer and their color-coded transformation into nanofibers are described. An L-glutamic acid modified bolaamphiphilic diacetylene lipid was synthesized and self-assembled into right-handed helical ribbons with micron scale length and nano scale thickness under mild conditions. The ribbon structures were further stabilized by polymerizing well-aligned diacetylene units to form bisfunctional polydiacetylenes (PDAs). Transitions from flat sheets to helical ribbons and tubes were observed by transmission electron microscopy. The helical ribbons appear to originate from the rupture of flat sheets along domain edges and the peeling off between stacked lipid layers. These results point to the applicability of chiral packing theory in bolaamphiphilic supramolecular assemblies. Contact mode atomic force microscopy observations revealed that high order existed in the surface packing arrangement. Hexagonal and pseudorectangular packings were observed in flat and twisted regions of the ribbons, respectively, suggesting a correlation between microscopic morphologies and nanoscopic packing arrangements. The tricarboxylate functionalities of the bolaamphiphilic lipid provide a handle for the manipulation of the bisfunctional PDAs' morphology. Increasing solution pH caused the fraying of helical ribbons into nanofibers accompanied by a sharp blue-to-red chromatic transition. A dramatic change in circular dichroism spectra was observed during this process, suggesting the loss of chirality in packing. A model is proposed to account for the pH-induced morphological change and chromatic transition. The color-coded transition between two distinct microstructures would be useful in the design of sensors and other "smart" nanomaterials requiring defined molecular templates.     

Tunable self-assembled peptide amphiphile nanostructures

Peptide amphiphiles are capable of self-assembly into a diverse array of nanostructures including ribbons, tubes, and vesicles. However, the ability to select the morphology of the resulting structure is not well developed. We examined the influence of systematic changes in the number and type of hydrophobic and hydrophilic amino acids on the self-assembly of amphiphilic peptides. Variations in the morphology of self-assembled peptides of the form X(6)K(n) (X = alanine, valine, or leucine; K = lysine; n = 1-5) are investigated using a combination of transmission electron microscopy and dynamic light scattering measurements. The secondary structures of the peptides are determined using circular dichroism. Self-assembly is controlled through a combination of interactions between the hydrophobic segments of the peptide molecules and repulsive forces between the charged segments. Increasing the hydrophobicity of the peptide by changing X to a more lipophilic amino acid or decreasing the number of hydrophilic amino acids transforms the self-assembled nanostructures from vesicles to tubes and ribbons. Changes in the hydrophobicity of the peptides are reflected in changes in the critical micelle concentration observed using pyrene probe fluorescence analysis. Self-assembled materials formed from cationic peptide amphiphiles of this type display promise as carriers for insoluble molecules or negatively charged nucleic acids in drug or gene delivery applications.     

Molybdenum dichalcogenide nanotube arrays for hydrogen-evolution-reaction catalysis: Synergistic effects of sulfur and selenium in a core-shell tube wall

The present work shows the growth and conversion of self-organized anodic Mo-oxide nanotube arrays to core-shell structures consisting of a conducting molybdenum sub-oxide core and a shell of Mo-Se/S – this structure is then investigated for electrochemical hydrogen evolution catalysis. To form the core-shell tubes, we first anneal MoO₃ nanotube arrays under vacuum conditions, to induce reduction to MoO₂. Subsequently these oxide tubes are thermally sulfurized and selenized resulting in dichalcogenide@sub-oxide structures. Under optimized conditions, the mixed dichalcogenide (selenized and sulfurized) tube walls on the conductive oxide core lead to a synergistic beneficial effect for the electrocatalytic H₂ generation from H₂SO₄ solution.     

Nanoribbon‐Structured Organo Zinc Phosphite Polymorphs with White‐Light Photoluminescence

The first neutral organo zinc phosphites composed of 2.8 nm‐wide ribbons were obtained in pure phases and exhibit near‐white‐light photoluminescence (PL). By using the “mesitylene strategy”, interesting polymorphism in the system of NTHU‐14 was discovered. The S‐shaped ribbons are arranged into R and L arrays, resulting in RLR and RRR stacking for two polymorphs. π–π interactions exist within each array and hydrogen bonding between adjacent arrays. Besides a common ligand‐based emission band at 410 nm, the PL curves of polymorphs 14‐α and 14‐β are distinctly different: 14‐α gave a defect‐based emission at 565 nm, whereas 14‐β primarily shows a π‐excimer‐based emission at 535 nm. Electron paramagnetic resonance (EPR) data disclosed that radical species exist in the reaction and that the two phases were growing from different environments. Based on these results, the origin of the 565 nm band can be ascribed to lattice defects, and one possible cause of 14‐β not showing noticeable yellow emission is identified.     

Effect of alcohol-water exchange and surface scanning on nanobubbles and the attraction between hydrophobic surfaces

4-(4′-Butoxyphenyl)phenyl-β-O-d-glucoside was synthesized as a low-molecular-mass gelator. It was able to immobilize a variety of aqueous and organic solvents in large amounts through the formation of three-dimensional self-assembled fibrillar networks. The morphologies of the aggregates depended on the nature of solvent where they were formed. Planar ribbons were observed in water, while helical ribbons were dominant in toluene and sheets in CHCl₃. The xerogel from water exhibited a lamellar structure with a d-spacing of 2.45 nm as demonstrated by 1D-WAXD, indicating a bilayer structure interdigitated with butoxy tails, whereas the xerogel from CHCl₃ or toluene yielded a lamellar structure with a d-spacing of 3.05 nm, implying a bilayer structure interdigitated with glycosyl heads. Increasing the content of 1,4-dioxane in water caused a gradual transformation from planar to twisted ribbons and then tubes.     

Spatial organization and patterning of palladium nanoparticles on a self-assembled helical ribbon lipid

A cholesterol derivative forms self-assembled helical ribbons in organic solvent, and treatment of this helical ribbon lipid as a template with Pd(Ac)2 provides helically-patterned arrays of palladium nanoparticles followed by reduction.     

Effect of the initial state of carbon nanotubes on their ability to be dispersed in polar solvents upon liquid-phase oxidative treatments

Effect of the structural defectiveness of carbon nanotubes on the influence exerted on these nanotubes by their liquid-phase treatments with oxidizing agents (hydrogen peroxide, concentrated nitric acid, and its mixture with sulfuric acid) was studied. It was found that this factor affects changes in the structure of oxidized carbon nanotubes, their hydrophilicity, high-quality arrays of these tubes, and their ability to form stable dispersions in water, ethanol, isopropanol, and acetone.     

Studies of the morphology of emulsion-grade polytetrafluoroethylene

Two types of emulsion-grade polytetrafluoroethylene particles have been studied. We refer to these as ribbons and rods. The ribbons consist of very thin ribbons or lamellae folded upon themselves a number of times. In typical emulsion-grade material prepared at Allied Chemical, the unraveled ribbon measures about 3.25 μ in length, 0.25 μ in width, and 60Å in thickness. The folded ribbons, which form the particles, are about 0.5 μ long and 0.25 μ wide. Electron diffraction shows that the ribbons are single crystals with the chain axis parallel to the long axis of the ribbons thus forming extended chain crystals. This extended-chain packing is consistent with the observed cleavage or fibrillation of the ribbons and with the molecular weight. The rods are formed in low–yield polymerizations. Electron diffraction also shows that the rods are single crystals with the chain axis parallel to the long axis of the rods. Striations parallel to the long axis are believed to result from stacking of parallel segments. Considerable bending of the long axis of rods is observed.     

Photoisomerization of azobenzene derivatives in nanostructured silica

A series of derivatized azobenzene molecules are synthesized such that one of the phenyl groups can be chemically bonded to mesostructured silica and the other, derivatized with dendrons, is free to undergo large-amplitude light-driven motion. The silica frameworks on which the motion takes place are either 150 nm thick films containing ordered hexagonal arrays of tubes (inner diameter about 2 nm) containing the bonded azobenzenes, or particles (about 500 nm in diameter) containing the same ordered arrays of functionalized tubes. The photoisomerization yields and the rate constants for the thermal cis to trans back-reaction of the azobenzenes in the tubes are measured and compared to those of the molecules in solution. The rate constants decrease with increasing size of the dendrons. Fluorescence spectra of the cis and trans isomers in the pores show that the photoisomerization in the nanostructured materials is selectively driven by specific wavelengths of light and is reversible.     

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.     

Spontaneous formation of cluster array of gold particles by convective self-assembly

Cluster arrays composed of metal nanoparticles are promising for application in sensing devices because of their interesting surface plasmon characteristics. Herein, we report the spontaneous formation of cluster arrays of gold colloids on flat substrates by vertical-deposition convective self-assembly. In this technique, under controlled temperature, a hydrophilic substrate is vertically immersed in a colloid suspension. Cluster arrays form when the particle concentration is extremely low (in the order of 10(-6)-10(-8) v/v). These arrays are arranged in a hierarchically ordered structure, where the particles form clusters that are deposited at a certain separation distance from each other, to form "dotted" lines that are in turn aligned with a constant spacing. The size of the cluster can be controlled by varying the particle concentration and temperature while an equal separation distance is maintained between the lines formed by the clusters. Our technique thus demonstrates a one-step, template-free fabrication method for cluster arrays. In addition, through the direct observation of the assembly process, the spacing between the dotted lines is found to result from the "stick-and-slip" behavior of the meniscus tip, which is entirely different from the formation processes observed for the striped patterns, which we reported previously at higher particle concentrations. The difference in the meniscus behavior possibly comes from the difference in colloidal morphology at the meniscus tip. These results demonstrate the self-regulating characteristics of the convective self-assembly process to produce colloidal patterns, whose structure depends on particle concentration and temperature.     

Unraveling the mechanism of nanotube formation by chiral self-assembly of amphiphiles

The self-assembly of nanotubes from chiral amphiphiles and peptide mimics is still poorly understood. Here, we present the first complete path to nanotubes by chiral self-assembly studied with C(12)-β(12) (N-α-lauryl-lysyl-aminolauryl-lysyl-amide), a molecule designed to have unique hybrid architecture. Using the technique of direct-imaging cryo-transmission electron microscopy (cryo-TEM), we show the time-evolution from micelles of C(12)-β(12) to closed nanotubes, passing through several types of one-dimensional (1-D) intermediates such as elongated fibrils, twisted ribbons, and coiled helical ribbons. Scattering and diffraction techniques confirm that the fundamental unit is a monolayer lamella of C(12)-β(12), with the hydrophobic tails in the gel state and β-sheet arrangement. The lamellae are held together by a combination of hydrophobic interactions, and two sets of hydrogen-bonding networks, supporting C(12)-β(12) monomers assembly into fibrils and associating fibrils into ribbons. We further show that neither the "growing width" model nor the "closing pitch" model accurately describe the process of nanotube formation, and both ribbon width and pitch grow with maturation. Additionally, our data exclusively indicate that twisted ribbons are the precursors for coiled ribbons, and the latter structures give rise to nanotubes, and we show chirality is a key requirement for nanotube formation.     

Structural and vibrational study of a new organic hydrogen sulfate

This paper presents a structural and vibrational study of a new compound, namely, monohydrate 1,5-pentanediammonium hydrogen sulfate (NH3(CH2)5NH3(HSO4)2.H2O). The X-ray crystal structure shows that this compound crystallizes in the monoclinic system, space group P2(1)/c, with the lattice parameters a=9.2250(2)A, b=7.7540(4)A, c=20.8520(1)A, beta=116.23(3) degrees, V=1337.97(10)A3, and Z=4. From the structural investigations, it is found that the studied compound is built by infinite anionic ribbons parallel to the "a" axis. These ribbons form tunnels in which organic cations are inserted. Infrared (IR) spectrum of the compound in the 300-4000 cm(-1) spectral region is reported. A tentative assignment of the observed bands, supported by a molecular orbital semi-empirical calculation, is given.     

Molybdenum disulfide nanowires and nanoribbons by electrochemical/chemical synthesis

Molybdenum disulfide nanowires and nanoribbons have been synthesized by a two-step, electrochemical/chemical synthetic method. In the first step, MoO(x) wires (a mixture of MoO(2) and MoO(3)) were electrodeposited size-selectively by electrochemical step-edge decoration on a highly oriented pyrolytic graphite (HOPG) surface. Then, MoO(x) precursor wires were converted to MoS(2) by exposure to H(2)S either at 500-700 degrees C, producing "low-temperature" or LT MoS(2) nanowires that were predominantly 2H phase, or above 800 degrees C producing "high-temperature" or HT MoS(2) ribbons that were predominantly 3R phase. The majority of these MoS(2) wires and ribbons were more than 50 microm in length and were organized into parallel arrays containing hundreds of wires or ribbons. MoS(2) nanostructures were characterized by X-ray photoelectron spectroscopy, scanning and transmission electron microscopy, selected area electron diffraction, X-ray diffraction, UV-visible absorption spectrometry, and Raman spectroscopy. HT and LT MoS(2) nanowires were structurally distinct: LT MoS(2) wires were hemicylindrical in shape and nearly identical in diameter to the MoO(x) precursor wires from which they were derived. LT MoS(2) wires were polycrystalline, and the internal structure consisted of many interwoven, multilayer strands of MoS(2); HT MoS(2) ribbons were 50-800 nm in width and 3-100 nm thick, composed of planar crystallites of 3R-MoS(2). These layers grew in van der Waals contact with the HOPG surface so that the c-axis of the 3R-MoS(2) unit cell was oriented perpendicular to the plane of the graphite surface. Arrays of MoS(2) wires and ribbons could be cleanly separated from the HOPG surface and transferred to glass for electrical and optical characterization. Optical absorption measurements of HT MoS(2) nanoribbons reveal a direct gap near 1.95 eV and two exciton peaks, A1 and B1, characteristic of 3R-MoS(2). These exciton peaks shifted to higher energy by up to 80 meV as the wire thickness was decreased to 7 nm (eleven MoS(2) layers). The energy shifts were proportional to 1/ L( parallel)(2), and the effective masses were calculated. Current versus voltage curves for both LT and HT MoS(2) nanostructures were probed as a function of temperature from -33 degrees C to 47 degrees C. Conduction was ohmic and mainly governed by the grain boundaries residing along the wires. The thermal activation barrier was found to be related to the degree of order of the crystallites and can be tuned from 126 meV for LT nanowires to 26 meV for HT nanoribbons.     

Progress in the direct structural characterization of fibrous amphiphilic supramolecular assemblies in solution by transmission electron microscopic techniques

The self-assembly of amphiphilic molecules into fibrous structures has been the subject of numerous studies over past decades due to various current and promising technical applications. Although very different in their head group chemistry many natural as well as synthetic amphiphilic compounds derived from carbohydrates, carbocyanine dyes, or amino acids tend to form fibrous structures by molecular self-assembly in water predominantly twisted ribbons or tubes. Often a transition between these assembly structures is observed, which is a phenomenon already theoretically approached by Wolfgang Helfrich and still focus point in current research. With the development of suitable sample preparation and electron optical imaging techniques, cryogenic transmission electron microscopy (cryo-TEM) in combination with three-dimensional (3D) reconstruction techniques has become a particular popular direct characterization technique for supramolecular assemblies in general. Here we review the recent progress in deriving precise structural information from cryo-TEM data of particularly fibrous structures preferably in three dimensions.     

氢气在单壁碳纳米管束的吸附的密度泛函研究

作者利用密度泛函理论（DFT）计算了氢气在单壁碳纳米管束（SWNTs)中管内 和管间的吸附。考察了温度,孔径以及压力对吸附的分子数密度,重量百分比,单 位体积储存能力以及超额吸附量的影响。DFT计算发现,较大的孔径有利于氢气在 SWNTs中的吸附且氢气在管隙中的吸附不可忽略。计算表明在77 K和6 MPa时,氢气 在2.719 mm的SWNTs的总的吸附的重量百分比分别可达到13.2 wt%,这约是美国能 源部（DOE）目标值的两倍,而单位体积储存能力在DOE目标值附近,而在300 K和 6 MPa时,氢气在2.719 nm的SWNTs的总的吸附的重量百分比仅为1.5 wt%。通过实 验结果与计算结果的比较表明,密度泛函理论的计算结果支持SWNTs有较高的吸附 储氢能力的实验结论。     

Uniform micro-sized alpha- and beta-Si3N4 thin ribbons grown by a high-temperature thermal-decomposition/nitridation route

Uniform micro-sized alpha- and beta-Si(3)N(4) thin ribbons have been achieved by a high-temperature thermal-decomposition/nitridation route. As-grown ribbons were characterized by using powder X-ray diffraction, scanning electron microscopy, transmission electron microscopy, energy-dispersive X-ray spectroscopy, electron energy loss spectroscopy, and cathodoluminescence. These alpha- and beta-Si(3)N(4) ribbons are structurally uniform micro-sized single crystals, and have a width of approximately 2-3 microns, a thickness of approximately 20-60 nm, and a length, that ranges from several hundreds of microns to the order of millimeters. A room-temperature cathodoluminescence spectrum recorded from these ribbons shows one intensive blue emission peak at approximately 433 nm. The growth for the new ribbon form of this material is believed to be dominated by a vapor-solid process.     

Aligned MoOx/MoS2 Core–Shell Nanotubular Structures with a High Density of Reactive Sites Based on Self‐Ordered Anodic Molybdenum Oxide Nanotubes

The present work demonstrates the self‐organized formation of anodic molybdenum oxide nanotube arrays. The amorphous tubes can be crystallized to MoO₂ or MoO₃ and be converted fully or partially into molybdenum sulfide. Vertically aligned MoO_x/MoS₂ nanotubes can be formed when, under optimized conditions, defined MoS₂ sheets form in a layer by layer arrangement that provide a high density of reactive stacking misalignments (defects). These core–shell nanotube arrays consist of a conductive suboxide core and a functional high defect density MoS₂ coating. Such structures are highly promising for applications in electrocatalysis (hydrogen evolution) or ion insertion devices.     

A novel strategy for in situ maskless synthesis of biochips： Self-driving micro-fluid porous type printing （SMPTP）

A novel maskless technique,self-driving micro-fluid porous type printing(SMPTP),was reported to in situ synthesize oligonucleotide arrays on glass slide,which has the merits of low cost,high quality and simple craft.In SMPTP for fabricating gene- chips,porous fiber tubes with a number of nanometric or micron channels functioned as“active letters”and were assembled in designed patterns,which are identical to the distribution of monomers in each layer of the array,and four patterns were needed for each layer.By means of capillarity,the synthesis solution was automatically taken into porous tubes assembled in a printing plate and reached the surface.An oligonucleotide array of 160 features with four different 15-mer probes was in situ synthesized using this technique.The four specific oligonucleotide probes,including the matched and the mismatched by the fluorescent target sequence,gave obviously different hybridization fluorescent signals.