Self-assembling structures of long-chain phenyl glucoside influenced by the introduction of double bonds

Four long-chain phenyl glucoside amphiphiles possessing a saturated or unsaturated long alkyl chain group as the self-assembling unit of a highly organized molecular architecture were synthesized. Their self-assembling properties were investigated by EF-TEM, SEM, CD, FT-IR, and XRD. Compound 2 possessing one double bond in the lipophilic portion showed twisted helical fibers, which formed a bilayered structure with a 3.59 nm period, while compound 3 showed the helical ribbons and left-handed nanotubular structures with 150-200 nm inner diameters and ca. 20 nm of wall. Very interestingly, compound 4 possessing three double bonds showed a nanotubular structure with ca. 70 nm of inner diameter through a helical ribbon, which formed a loose bilayered structure with 4.62 nm. These results indicate that self-assembling properties strongly depend on the number of cis double bonds.     

Self-assembling structures of long-chain sugar-based amphiphiles influenced by the introduction of double bonds

Nine phenyl glucoside or galactoside amphiphiles possessing a saturated or unsaturated long alkyl-chain group as the self-assembling unit of a highly organized molecular architecture were synthesized. Their self-assembly properties were investigated by using energy-filtering TEM (EF-TEM), SEM, CD, XRD, and FT-IR techniques. Compound 2, possessing one cis double bond in the lipophilic portion, exhibited twisted helical fibers, which formed a bilayered structure with a 3.59 nm period, while 3 exhibited helical ribbons and left-handed nanotubular structures with 150-200 nm inner diameters and a wall thickness of approximately 20 nm. Very interestingly, 4, possessing three cis double bonds, exhibited a nanotubular structure with an inner diameter of approximately 70 nm and a d spacing value of 4.62 nm. On the other hand, 7, possessing two trans double bonds in the lipophilic region, exhibited crystal- or plate-like structures, which formed a bilayer structure with a d spacing value of 3.93 nm. These results indicate that the self-assembly properties are strongly dependent on the type of double bond. Furthermore, 8 and 9, with the galactopyranose moiety, revealed helical ribbon and well-defined double helical fiber structures, respectively. These findings support the view that the orientation of the intermolecular hydrogen-bonding interaction between the sugar moieties plays a critical role in producing the nanotubular structures. According to CD and powder XRD experiments, the relatively strong intermolecular hydrogen-bonding interaction of the glucopyranoside moiety in 3 and 4 provided a highly ordered chiral packing structure. Even though these compounds formed a weak hydrophobic interaction between lipophilic groups, it led to the formation of the nanotubular structure.     

A new motif in the formation of peptide nanotubes: the crystallographic signature

Terminally protected acyclic tripeptides Boc-Tyr(1)-Val(2)-Tyr(3)-OMe 1 and Boc-Tyr(1)-Ile(2)-Tyr(3)-OMe 2 self-assemble into nanotubes in crystals through various noncovalent interactions with an average internal diameter of 5 A (0.5 nm), and the tubular ensemble is developed through the hydrogen-bonded side chains of tyrosine residues. The inside of the hollow nanotubular structures is hydrophilic; however, no solvent molecules have been crystallographically detected. [structure: see text]     

A Stable Microporous Mixed‐Metal Metal–Organic Framework with Highly Active Cu2+ Sites for Efficient Cross‐Dehydrogenative Coupling Reactions

Two metalloporphyrin octacarboxylates were used to link copper(II) nodes for the formation of two novel porous mixed‐metal metal–organic frameworks (M′MOFs) containing nanopore cages (2.1 nm in diameter) or nanotubular channels (1.5 nm in diameter). The highly active Cu²⁺ sites on the nanotubular surfaces of the stable porous M′MOF ZJU‐22 , stabilized by three‐connected nets, lead to the superior catalytic activity for the cross‐dehydrogenative coupling (CDC) reaction.     

Giant macrocycles composed of thiophene, acetylene, and ethylene building blocks

Fully conjugated giant macrocyclic oligothiophenes with 60pi, 90pi,120pi, 150pi, and 180pi frames (1, 2, 3, 4 and 5) have been designed, and their butyl-substituted derivatives (1a, 2a, 3a, 4a, and 5a) have been synthesized using modified Sonogashira and McMurry coupling reactions as key steps. The 60-180pi systems 1-5 are circular with 1.8-6 nm inner cavities and 3.3-7.5 nm outside molecular diameters. Compound 1a containing ten 3,4-dibutyl-2,5-thienylene, eight ethynylene, and two vinylene units has been converted into macrocyclic oligo(3,4-dibutyl-2,5-thienylene-ethynylene) 6a using bromination/dehydrobromination procedure. Giant macrocycles 1a-6a exhibit a red shift of their absorption spectra and a fairly strong fluorescence with a large Stokes shift as compared to a linear conjugated counterpart having five thiophene rings. Compounds 1a-6a exhibit multistep reversible redox behaviors with fairly low first oxidation potentials, reflecting their cyclic conjugation. Furthermore, chemical oxidation of 1a-6a with FeCl3 shows drastic changes of spectroscopic properties due to intramolecular and intermolecular pi-pi interactions. Doping of 1a-3a with iodine forms semiconductor due to its pi-donor properties and pi-pi stacking ability. X-ray analysis of 1a confirmed a round, planar structure with nanoscale inner cavity, and revealed host ability for alkanes and unique packing structure. Interestingly, 2a and 3a self-aggregate in the solid state to form "molecular wires," which are about 200 nm thick and more than 1 mm long. The internal structures of fibrous aggregates have been investigated by optical microscope, scanning electron microscopy, atomic force microscopy, and X-ray diffraction analyses.     

Self-organized nanotubular TiO2 matrix as support for dispersed Pt/Ru nanoparticles: Enhancement of the electrocatalytic oxidation of methanol

We explore oxidative electrocatalytic properties of a system consisting of bimetallic Pt/Ru nanoparticles dispersed over a nanotubular self-organized TiO₂ matrix. The nanotubular TiO₂ layers consist of individual tubes of 100 nm diameter, 500 nm length and 15 nm wall thickness. This nanotubular TiO₂ support provides a high surface area and it significantly enhances the electrocatalytic activity of Pt/Ru for methanol oxidation (relative to the performance of Pt/Ru at the same loading but immobilized on a conventional compact TiO₂ support). Annealed to anatase, the TiO₂ nanotubular support exhibits even higher enhancement effect during electrooxidation of methanol than when used in the “as-formed” amorphous structure. The overall electrocatalytic activity of the system can be further increased by illumination with UV-light (wavelength 325 nm).     

Composition of gas hydrates of CHClF2, CCl2F2 and SF6

Gas hydrates are forms of ice stabilized by the presence of molecules of gas occupying cavities in the solid water lattice. There are two common forms: structure I and structure II. The mean free diameters of the two types of cavities in structure I are about 5.0 and 5.8 angstroms. Very small gas molecules such as Xe or H₂S can occupy both. In the past it has been considered that gas molecules of larger diameter than 5.0 angstroms could not occupy the smaller cavities. It has now been shown through measurement of hydration numbers of CHClF₂ (diameter about 5.4 angstroms) under various pressures at 0°, that some of the small cavities are filled. This state of affairs also exists for CH₃Br. In structure II, the mean diameters of the two types of cavities are about 5.0 and 6.6 angstroms. Hydration numbers of SF₆ (diameter about 5.8 angstroms) and CCl₂F₂ (about 6.2 angstromsm) show that nearly all of the large cavities but essentially none of the small cavities are occupied.     

Coordination polymers of La(III) as bunched infinite nanotubes and their conversion into an open-framework structure

Pyridine-2,6-dicarboxylic acid (pdcH2) reacts with LaCl3 x 7H2O under hydrothermal conditions followed by evaporation at room temperature to give a metal-organic framework structure of the empirical formula, [La(pdc)(H2O)4] x Cl (1), in the form of infinitely long bunched nanotubes. The chloride ions and water molecules occupy the tubular as well as the inter-tubular spaces. When La(NO3)3 x 7H2O is used in place of LaCl3 x 6H2O, a similar structure is formed with the empirical formula, [La(pdc)(H2O)4] x NO3 (2), where water molecules and the nitrate anions occupy the voids as in the case of 1. When an aqueous solution of AgNO3 is added to an aqueous solution of 1, the Cl- ions are replaced completely by NO3- ions to form 2; thus, the tubular structure is conserved. However, when AgBF4 is used in place of AgNO3, the tubular structure breaks down, and a new 3-D MOF structure, [La(pdc)(pdcH)(H2O)2] x 4H2O (3), is formed where the cavities are occupied by hexameric and dimeric water clusters. Structure 3 is also formed as the sole product when La(OAc)3 x xH2O is treated with pyridine-2,6-dicarboxylic acid following the method adopted for 1 and 2. Formation of the tubular structure depends on the molar ratio of the ligand and the metal. When higher than 1 equiv of the metal is taken, a linear coordination polymer, [La2(pdc)3(H2O)6] x 2H2O (4), is formed. This study provides the first nanotubular structure of a pure lanthanide metal.     

十二烷基硫酸钠为模板制备ZnO纳米管新方法的研究

自从1991年日本科学家Iijim a发现碳纳米管以来,在纳米管制备和理论方面的研究引起了广泛的关注[1]。管状、线状、棒状、带状、针状等一维纳米结构已成为世界各国研究人员关注的焦点[2￣6]。究其原因在于其特殊的物理性质,对于纳米领域的基础研究有新的启发作用,这些一维纳米结     

Anodic formation of high aspect ratio, self-ordered Nb2O5 nanotubes

In the present work, we demonstrate the feasibility to form an aligned Nb(2)O(5) nanotube layer by self-organizing anodization of Nb in a NH(4)F-glycerol electrolyte. In order to achieve a nanotubular rather than a nanoporous layer, careful optimization of the anodization electrolyte is required. We show that only in a narrow window of electrolyte parameters highly aligned nanotubes of 50 nm inner diameter and several micrometres in length can be formed.     

A Structurally Variable Porous Organic Salt Based on a Multidirectional Supramolecular Cluster

A porous organic salt (POS) composed of 2‐sulfophenyl anthracene (2‐SPA) and triphenylmetylamine (TPMA) forms five types of porous crystals, POS‐a–e, by recognizing subtle differences in the molecular structure of incorporated guest molecules. This structurally variable POS was hierarchically designed on the basis of a supramolecular cluster with a directionally flexible linker formed by the organic salt. X‐ray crystallographic analysis reveals that the salt forms six conformers attributable to rocking and rotational motions of the phenylene group in 2‐SPA. The clusters form POS crystals through different porous networks according to the conformers. The POS crystals show a wide range of fluorescence spectra that are responsive to differences in the molecular and electronic structure of the guest molecule. This remarkable behavior has potential application in sensitive chemical sensors that are responsive to slight differences in molecular structures.     

Synthesis and characterization of hybrid organic/inorganic nanotubes of the imogolite type and their behaviour towards methane adsorption

Imogolite-like nanotubes have been synthesised in which SiCH(3) groups have been introduced in place of the SiOH groups that naturally occur at the inner surface of imogolite, an alumino-silicate with formula (OH)(3)Al(2)O(3)SiOH, forming nanotubes with inner and outer diameter of 1.0 and 2.0 nm, respectively. The new nanotubular material, composition (OH)(3)Al(2)O(3)SiCH(3), has both larger pores and higher specific surface area than unmodified imogolite: it forms as hollow cylinders 3.0 nm wide and several microns long, with a specific surface area of ca. 800 m(2) g(-1) and intriguing surface properties, due to hydrophobic groups inside the nanotubes and hydrophilic Al(OH)Al groups at their outer surface. Adsorption of methane at 30 °C has been studied in the pressure range between 5 and 35 bar on both the new material and unmodified imogolite: it resulted that the new material adsorption capacity is about 2.5 times larger than that of imogolite, in agreement with both its larger pore volume and the presence of a methylated surface. On account of these properties and of its novelty, the studied material has several potential technical applications, e.g. in the fields of gas chromatography and gas separation.     

Mesoporous nanotubes of iron phosphate: synthesis, characterization, and catalytic property

Iron phosphate nanotubes with mesoporous walls are solvothermally synthesized using sodium dodecyl sulfate (SDS) as a template. With different template concentrations, various shapes of nanosized iron phosphates can be obtained. When the concentration of SDS is set at the transition regions between the lamellar and the hexagonal mesophases, according to its phase diagram, the coassembly of iron phosphate precursor and SDS forms a flake-type mesoporous iron phosphate. Otherwise, nanoparticles or bulky sheets of iron phosphates are obtained. The followed solvothermal treatments on the mesoporous iron phosphate flakes produce iron phosphate nanotubes with mesoporous walls. The removal of the surfactant by acetate exchange and heat treatment results in the clean mesoporous nanotubes of iron phosphate with diameters of 50-400 nm and lengths of several microns. The nanotubular and mesoporous iron phosphate possesses a specific surface area of 232 m2/g and a bimodal distribution of pore sizes, corresponding to the size of mesopores in the walls and the diameter of the nanotubes, respectively. The novel nanotubular iron phosphate with composite meso-macroporous structure, in favor of the diffusion of reactive molecules, has been tested for direct hydroxylation of benzene with hydrogen peroxide and has shown better catalytic performance compared with the conventional particulate mesoporous iron phosphate.     

Direct Visualization and Semi‐Quantitative Analysis of Payload Loading in the Case of Gold Nanocages

Upon incubation with Au nanocages, pyrrole (Py) molecules can enter the cavities by diffusing through the porous walls and then be polymerized to generate a polypyrrole (PPy) coating on the inner surface. The thicknesses of the PPy coating can serve as a direct indicator for the amount of Py molecules that diffuse into the cavity. Py molecules are able to diffuse into the cavities throughout the polymerization process, while a prolonged incubation time increases the amount of Py accumulated on both inner and outer surfaces of the nanocages. Furthermore, it is demonstrated that the dimensions of the cavity and the size of the pores in the wall are not critical parameters in determining the loading efficiency, as they do not affect the thickness of the PPy coating on the inner surface. These findings offer direct evidence to support the applications of Au nanocages as carriers for drug delivery and controlled release.     

Evolution of the vibrational spectrum of ammonia from single molecule to bulk

Ammonia clusters (NH3)n (n=2-10(4)) have been assembled inside helium droplets and studied via infrared laser spectroscopy. The studied spectral range of 3100-3500 cm(-1) covers the nu1 and nu3 fundamental stretching bands as well as the 2nu4 overtone of the bend of ammonia molecules. The results show strong coupling of the 2nu4 overtone with the fundamental vibrations for all cluster sizes except dimers. The intensity of the nu3 band relative to the total intensity in the spectrum increases from about 30% to about 80% upon increase of the average cluster size from n=5 to n=10(4). We attributed this effect to the concomitant decrease in the fraction of the surface molecules. The results indicate that ammonia clusters obtained in He droplets have a compact structure and that inner molecules in the clusters have similar hydrogen-bonded coordination as in the crystalline form of ammonia. This surprising result is ascribed to a directionality of the hydrogen bond, which guides the low temperature growth of the cluster in He droplets.     

Electronic state of small and large cavities for methane hydrate

It is well known that methane hydrate is aggregates of small and large hydrogen bonded water cavities (composed of 12 pentagonal faces of 20 water molecules, and 12 pentagonal and two hexagonal faces of 24 water molecules, respectively) where one methane molecule is encaged. We calculated the methane molecule in vacuum, the small and large cavities by ab initio MO method to clarify the electronic state. The proton of methane in the cavities is shown to form the weak hydrogen bond (O...H[bond]C) between methane and four water molecules, and the H-bond lengths and energies in the small and large cavities were estimated as (0.293 nm, 6.8 kJ/mol) and (0.309 nm, 5.2 kJ/mol), respectively. The calculated values of symmetric C[bond]H stretching frequencies and (13)C-NMR chemical shieldings of the methane in the two cluster cavities show good agreement with the experimental ones observed by Sum et al. and Ripmeester and coworker, respectively.     

Conjugated macrocycles: concepts and applications

One of the most important objectives in materials, chemical, and physical sciences is the creation of large conjugated macrocycles with well-defined shapes, since such molecules are not only theoretically and experimentally interesting but also have potential applications in nanotechnology. Fully unsaturated macrocycles are regarded as models for infinitely conjugated π systems with inner cavities, and exhibit unusual optical and magnetic behavior. Macrocycles have interior and exterior sites, and site-specific substitution at both or either site can afford attractive structures, such as 1D, 2D, and 3D supramolecular nanostructures. These nanostructures could be controlled through the use of π-extended large macrocycles by a bottom-up strategy. Numerous shape-persistent π-conjugated macrocycles have been synthesized, but only a few are on the nanoscale. This Review focuses on nanosized π-conjugated macrocycles (>1 nm diameter) and giant macrocycles (>2 nm diameter), and summarizes their syntheses and properties.     

Complex clover cross-sectioned nanotubules exist in the structure of the first uranium borate phosphate

An actinide borate phosphate was prepared via a high temperature solid-state reaction. This phase exhibits unprecedented complex inorganic nanotubular fragments with an external diameter of ~2 × 2 nm. The nanotubular aggregates are based on borate tubes where the exterior of the tubes is decorated with UO(2)(PO(4))(3) moieties to form a complex shape with a cross-section similar to the clover cross.     

Unusually Strong Dipole–Dipole and Dipole–Quadrupole Interactions in a Nanoporous Solid. Crystal Structure and Related Properties of (VO)3[M(CN)6]2·nH2O (M = Fe,Co)

In porous Prussian blue (PB) analogues, the partially naked central metal atoms found at the cavities surface are responsible for many of their physical properties, among them the adsorption potentials. In the as‐synthesized PB analogues, such metal sites stabilize water molecules inside the cavity through coordination bond formation. The filling of the cavity volume is completed with water molecules linked to the coordinated ones through hydrogen bonds formation. Vanadyl‐based PB analogue shows quite different features. The metal(V) at the cavities surface has saturated its coordination sphere with the O atom of the vanadyl ion (V=O). In this material, the V=O group preserves enough strong dipole moment to stabilize adsorbed species at the cavity through dipole–dipole and dipole–quadrupole interactions. This contribution reports the preparation, crystal structure and properties for (VO)₃[M(CN)₆]₂ · nH₂O (M = Fe, Co). According to the refined crystal structure, IR spectra and TG data, six water molecules remain stabilized inside the cavities through a strong dipole–dipole coupling with the vanadyl group. The cavity contains additional water molecules interacting through hydrogen bond bridges with the water molecules coupled to the V=O group. The vanadyl ion is free of hydrogen bonding interactions with the water molecules. The recorded adsorption isotherms for N₂, CO₂ and H₂, three molecules with only quadrupole moment, reveal presence of relative strong adsorption forces due to dipole‐quadrupole interactions.     

水热法制备铂掺杂二氧化钛及其可见光催化性能

以纳米管钛酸为前驱体,采用水热法制备了Pt掺杂TiO2样品.水热反应过程中,纳米管钛酸表面羟基与氯铂酸发生酸碱中和反应,导致反应后pH值升高;在130°C开始纳米管钛酸晶体结构由正交晶系转变为锐钛矿相TiO2.表面化学组成分析表明,掺杂的Pt主要以+2价形式存在.以丙烯为模型污染物,评价样品的可见光(λ≥420nm)光催化活性.结果表明,Pt-TiO2具有明显的可见光光催化降解丙烯的活性,其中160°C水热处理制得的Pt-TiO2活性最高.最后讨论了低温水热法Pt掺杂的形成机理及Pt-TiO2具有可见光响应的原因.