Redox‐Controlled Helical Self‐Assembly of a Polyoxometalate Complex

Polyoxometalate (POM) complex (DODA)₂[Mo₆O₁₉] with a symmetrical linear structure was prepared conveniently by replacing the tetrabutylammonium (TBA) counterions of Lindquist‐type cluster (TBA)₂[Mo₆O₁₉] with cationic surfactant dioctadecyldimethylammonium (DODA). A helical self‐assembled structure of the complex was formed in dichloromethane/propanol. The dynamically reversible transformation between helical and spherical assemblies on alternate UV irradiation and H₂O₂ oxidation was characterized by SEM, TEM, and UV/Vis studies. The redox‐controlled morphology change is modulated by variation of the electrostatic interactions between the inorganic polyanion and the organic cation DODA through controlling the redox properties of the POM component, as shown by the XRD, X‐ray photoelectron spectroscopic, and ¹H NMR measurements. The strategy applied herein is a unique example of targeted smart and helical assembly of POM complexes.     

新型侧链聚硅氧烷高分子液晶作毛细管柱气相色谱固定液的研究

 以合成的新型胆甾酯类侧链聚硅氧烷高分子液晶作固定液 ,涂渍在弹性石英毛细管柱上 ,获得了具有较高的柱效和选择性、良好的热稳定性、适于分离多种异构体混合物的毛细管柱。     

Self-assembly of organic-inorganic hybrid amphiphilic surfactants with large polyoxometalates as polar head groups

Mn-Anderson-C6 and Mn-Anderson-C16, A type of inorganic-organic hybrid molecules containing a large anionic polyoxometalate (POM) cluster and two C6 and C16 alkyl chains, respectively, demonstrate amphiphilic surfactant behavior in the mixed solvents of acetonitrile and water. The amphiphilic hybrid molecules can slowly assemble into membrane-like vesicles by using the POM clusters as polar head groups, as studied by laser light scattering and TEM techniques. The hollow vesicles have a typical bilayer structure with the hydrophilic Mn-Anderson cluster facing outside and long hydrophobic alkyl chains staying inside to form the solvent-phobic layer. Due to the rigidity of the POM polar heads, the two alkyl tails have to bend significantly for the vesicle formation, which makes the vesicle formation more difficult compared to some conventional surfactants. This is the first example of using hydrophilic POM macroions as polar head groups for a surfactant system.     

Sorting the assemblies of unsymmetrically covalently functionalized mn-anderson polyoxometalate clusters with mass spectrometry

The unsymmetrical Mn-Anderson polyoxometalate cluster, [N(C4H9)4]3[MnMo6O18(C4H6O3NO2)(C4H6O3NH2)] (1; N(C4H9)4(+) = TBA(+)), has been prepared and characterized by X-ray crystallography and electrospray ionization mass spectrometry (ESI-MS). Covalent functionalization of compound 1 leads to the controlled assemblies of unsymmetrical alkoxopolyoxometalate clusters of compounds 2-5, which can be directly observed in solution as revealed by ESI-MS studies.     

ATRP法在纳米SiO2表面接枝PBA及其对POM的改性

本论文研究了原子转移自由基聚合法(ATRP)在纳米二氧化硅(SiO2)表面接枝聚丙烯酸丁酯(PBA)以及其对聚甲醛（POM）进行改性。红外光谱（FTIR）、透射电镜(TEM)及凝胶渗透色谱（GPC）等测试表明：采用ATRP法可制备均匀分散的SiO2-g-PBA纳米复合粒子。力学性能、扫描电子显微镜（SEM）及透射电子显微镜（TEM）等测试表明：纳米SiO2在POM中团聚明显,而SiO2-g-PBA纳米复合粒子POM中分散均匀,导致POM/SiO2-g-PBA纳米复合材料的缺口冲击强度明显高于POM及POM/SiO复合材料,当SiO2-g-PBA纳米复合粒子的质量分数为2%时,POM/SiO2-g-PBA复合材料的冲击强度是POM的8倍多,同时拉伸强度有一定的增加。     

Inorganic-organic hybrid vesicles with counterion- and pH-controlled fluorescent properties

Two inorganic-organic hybrid clusters with one or two covalently linked pyrene fluorescent probes, [(n-C(4)H(9))(4)N](2)[V(6)O(13){(OCH(2))(3)C(NH(CO)CH(2)CH(2)CH(2)C(16)H(9))}{(OCH(2))(3)C-(NH(2))}] ((TBA(+))(2)1) and [(n-C(4)H(9))(4)N](2)[V(6)O(13){(OCH(2))(3)C(NH(CO)CH(2)CH(2)CH(2)C(16)H(9))}(2)] ((TBA(+))(2)2), respectively, are synthesized from Lindqvist type polyoxometalates (POMs). The incorporation of pyrene into POMs results in amphiphilic hybrid molecules and simultaneously offers a great opportunity to study the interaction between hybrid clusters and their counterions. 2D-NOESY NMR and fluorescence techniques have been used to study the role of counterions such as tetrabutyl ammonium (TBA) in the vesicle formation of the hybrid clusters. The TBA(+) ions not only screen the electrostatic repulsions between the POM head groups but also are involved in the hydrophobic region of the vesicular structure where they interrupt the formation of pyrene excimers that greatly perturbs the luminescence signal from the vesicle solution. By replacing the TBA(+) counterions with protons, the new vesicles demonstrate interesting pH-dependent fluorescence properties.     

Ultralong cadmium hydroxide nanowires: synthesis, characterization, and transformation into CdO nanostrands

Ultralong Cd(OH)2 nanowires were fabricated by a hydrothermal method from Cd(CH3COO)2 x H2O (0.01 mol/L) and C6H12N4 (0.015 mol/L) aqueous solution at 95 degrees C for 16 h without using any templates and were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), transmission electron microscopy (TEM), selected area electron diffraction (SAED), and high-resolution transmission electron microscopy (HRTEM). The length of the nanowires reached several micrometers, giving an aspect ratio of a few thousands. The formation mechanism of the nanowires is attributed to the oriented attachment of small particles. The growth method for the 1D nanostructure presented here offers an excellent tool for the design of other advanced materials with anisotropic properties. The Cd(OH)2 nanowires efficiently captured negatively charged dye, and the adsorbed dye molecules can be released after the addition of EDTA. The Cd(OH)2 nanowires as template compounds were further transformed into CdO semiconductor nanomaterials with similar morphology by calcination under 350 degrees C in air for 3 h.     

氧化还原对Lindqvist型多金属氧簇复合物自组装的动态调控

Dynamic regulation of self-assembly is of vital importance in chemistry, biology and material science thanks to its great potential for development of smart materials and devices. Polyoxometalates (POMs) are a class of functional inorganic nanoclusters, which has become one of the excellent building blocks for supramolecular self-assemblies, especially when covalently or non-covalently modified by organic species. As typical stimuli-responsive functional clusters, the POMs could be photochemically or electrochemically reduced to mixed-valence states, of which the structural integrity remains even after encountering stepwise multi-electron redox process. The intriguing photochromism of the POMs in different states exhibits distinct photophysical properties, which motivates us to exploit the dynamic self-assemblies of POM-based complexes. The divalent Lindqvist-type hexamolybdate cluster [Mo₆O₁₉]^2- is one of the least negative-charged POMs, which is the ideal building blocks to construct novel assembly structures. Based on this motivation, herein, a single chain surfactant-encapsulated polyoxometalate (POM) complex (ODTA)₂[Mo₆O₁₉] was prepared by simple counterion replacement of Lindqvist-type (TBA)₂[Mo₆O₁₉] with octadecyltrimethylammonium (ODTA) in acetonitrile solution. The structure of the POM complex was confirmed by ¹H nuclear magnetic resonance (NMR), Fourier transform infrared (FT-IR) spectroscopy, thermogravimetric analysis (TGA) and elemental analysis. The solution of complex (ODTA)₂[Mo₆O₁₉] in the mixed solvents of acetonitrile and isopropanol with the volume ration of 4 to 1 exhibited reversible photochromism upon alternate UV light irradiation and air exposure. Upon UV light irradiation, the light yellow transparent solution of (ODTA)₂[Mo₆O₁₉] turned into blue quickly. The new broad absorption band appearing at ca.751 nm assigned to the Mo^V → Mo^VI intervalence charge-transfer (IVCT) transition, indicated the formation of reduced POM, as revealed by UV-Vis absorption spectra. After exposed to air, the blue solution was bleached. The alternate photochromism could be conducted for multiple cycles. Helical self-assembled morphology of (ODTA)₂[Mo₆O₁₉] was formed in acetonitrile/isopropanol, characterized by scanning electron microscope (SEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD) methods. More interestingly, morphology transformation of the complex from helical strips to spherical assemblies occurred accompanied by photochromism occurrence. The morphology evolution during the photochromism process experienced from shortened helical strips through sea urchin-like aggregates to spherical assemblies. Most significantly, the helical assemblies could be recovered again after air oxidation, implying the reversible morphology transformation driven by redox stimulus. The redox-modulated reversible self-assembly is driven by the variation of electrostatic attraction between organic cations and inorganic anions as well as the electrostatic repulsion between inorganic ionic clusters, proved by X-ray photoelectron spectroscopy (XPS) and ¹H NMR spectra. The results will contribute to better understanding the mechanism of dynamic assemblies and inspire the precise fabrication of advanced smart materials.     

Synthesis of diamondoid lanthanide-polyoxometalate solids as tunable photoluminescent materials

The reaction between polyoxometalate (POM) [TBA](12)[WZn{Zn(H(2)O)}(2)(ZnW(9)O(34))(2)] (TBA = tetrabutyl ammonium) and lanthanide (Ln) nitrate (Ln = La, Eu and Tb) in a mixed solvent of CH(3)CN and DMF yielded three noncentrosymmetric diamondoid Ln-POM solid materials, {[Ln(2)(DMF)(8)(H(2)O)(6)][ZnW(12)O(40)]}·4DMF (Ln-POM; Ln = La, Eu and Tb). In these compounds, the {ZnW(12)O(40)} unit, transferred from the metastable [WZn{Zn(H(2)O)}(2)(ZnW(9)O(34))(2)] cluster, acts as a tetradentate ligand to connect with four Ln nodes, while the Ln ion links up two {ZnW(12)O(40)} units. These compounds generated interesting luminescence emissions that are dependent on the Ln ions and their ratios. White light emission was obtained by a doped approach with a rational ratio of the Eu(3+) and Tb(3+) ions.     

Surfactant-free hydrothermal synthesis of highly tetragonal barium titanate nanowires: a structural investigation

Barium titanate nanowires synthesized with a surfactant-free hydrothermal method have been characterized by various techniques such as transmission electron microscopy (TEM), scanning electron microscopy (SEM), synchrotron X-ray diffraction, X-ray photoelectron spectroscopy (XPS), and Raman spectroscopy. The TEM and SEM analyses show the uniform cylindrical nanowires. The Rietveld refinement with synchrotron X-ray powder diffraction showed that the lattice parameters of cubic and tetragonal phases were a (= b = c) = 4.0134 A and a (= b) = 3.9998 A, c = 4.0303 A, respectively. The final weighted R-factor, R(wp), was 6.75% and the goodness of fit indicator was 1.30. The mass fraction of tetragonal and cubic phases based on the refined scale factor for the two phases were 98.4% and 1.6%, respectively, which clearly show the nanowires are tetragonal. The XPS analysis has shown that as-obtained BaTiO3 nanowires were phase pure. The Raman spectra confirm the tetragonal phase of the BaTiO3 nanowires. The dielectric constant measurement shows the shift in the transition temperature (Tc = 105 degrees C) compared to the bulk transition temperature (Tc = 132 degrees C). The dielectric constant at Tc was 174 measured at 1 kHz frequency.     

Anion modules: building blocks of supramolecular assemblies by combination with π-conjugated anion receptors

Dipyrrolyldiketone boron complexes, as π-conjugated acyclic anion receptors, act as building subunits of various assemblies through noncovalent interactions in the form of receptor-anion complexes. Instead of, or in addition to, the modification of receptor structures, the introduction of anion modules as building blocks for the assemblies was found to be useful in forming various soft materials. Gallic carboxylate derivatives 3-n (n = 16, 18, 20), as tetrabutylammonium (TBA) salts, form receptor-anion-module complexes that can be used to fabricate supramolecular assemblies. Combinations of aliphatic anion modules 3-n and receptors 1a,b along with a TBA cation afforded products with mesophases, which were indicated by differential scanning calorimetry and polarized optical microscopy. X-ray diffraction measurements of the solid states and mesophases of 1a·3-n·TBA and 1b·3-n·TBA revealed highly ordered structures including lamellar structures, which could be modulated by the lengths of the alkyl chains of the modules. Functional materials exhibiting electrical conductivity were fabricated by using combinations of anionic building blocks that form assemblies by themselves and π-conjugated acyclic receptors.     

Preparation and characterization of polyoxymethylene‐copolymer/hydroxyapatite nanocomposites for long‐term bone implants

In this work, new polyoxymethylene (POM)/hydroxyapatite (HAp) nanocomposites for long‐term bone implants have been obtained via extrusion and injection molding processes and characterized by differential scanning calorimetry (DSC), temperature‐modulated DSC (TMDSC), scanning electron microscopy (SEM), transmission electron microscopy (TEM), wide‐angle X‐ray diffraction (WAXD), Fourier transform infrared spectroscopy (FTIR), thermogravimetry (TG), and tensile mechanical and in vitro stability tests. Based on the DSC results, it was found that the degree of crystallinity increases for POM/0.5% HAp sample and decreases for POM/1.0% HAp and POM/2.5% HAp. SEM and TEM observations for POM/HAp nanocomposites indicated that the dispersion of HAp in the polymer matrix was uniform and the diameter of the HAp particles was less than 100 nm for most of them. Young's modulus increases with increasing HAp concentration, whereby elongation at break decreases. On the contrary, HAp concentration does not have a significant influence on the tensile strength. TG results show that for POM/0.5% HAp, POM/1.0% HAp, and POM/2.5% HAp, thermal stability slightly increases in comparison to pure POM, whereas for POM/5.0 HAp and POM/10.0% HAp, lower thermal stability was observed. In vitro data reveal that with an increase of HAp content, bioactivity of nanocomposites increases; a good in vitro chemical stability of POM and POM nanocomposites was confirmed. Copyright © 2011 John Wiley & Sons, Ltd.     

The Influence of Concentration on the Morphology of Fibres Self‐assembled by Ferrocenyl Surfacant and Methyl Orange

Ionic self‐assembly, the combination of the building blocks with opposite charge by electrostatic association, has many merits, such as simple, cheap and easy to get, flexible reversible and wide range of applications. In this paper, fibres were synthesized by combining surfactant N, N‐dimethylferrocenylmethyl hexadecyl‐ammonium bromide (Fc16AB) and fluorescent dye methyl orange (MO) using ionic self‐assembly techniques. The morphology of self‐assemblies with different concentration are measured and characterized by optical microscopy (OM), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results show that the concentration of Fc16AB and MO has great effects on the morphology of obtained microfibers.     

Strategic design and refinement of Lewis acid-base catalysis by rare-earth-metal-containing polyoxometalates

Efficient polyoxometalate (POM)-based Lewis acid-base catalysts of the rare-earth-metal-containing POMs (TBA(6)RE-POM, RE = Y(3+), Nd(3+), Eu(3+), Gd(3+), Tb(3+), or Dy(3+)) were designed and synthesized by reactions of TBA(4)H(4)[γ-SiW(10)O(36)] (TBA = tetra-n-butylammonium) with RE(acac)(3) (acac = acetylacetonato). TBA(6)RE-POM consisted of two silicotungstate units pillared by two rare-earth-metal cations. Nucleophilic oxygen-enriched surfaces of negatively charged POMs and the incorporated rare-earth-metal cations could work as Lewis bases and Lewis acids, respectively. Consequently, cyanosilylation of carbonyl compounds with trimethylsilyl cyanide ((TMS)CN) was efficiently promoted in the presence of the rare-earth-metal-containing POMs via the simultaneous activation of coupling partners on the same POM molecules. POMs with larger metal cations showed higher catalytic activities for cyanosilylation because of the higher activation ability of C═O bonds (higher Lewis acidities) and sterically less hindered Lewis acid sites. Among the POM catalysts examined, the neodymium-containing POM showed remarkable catalytic performance for cyanosilylation of various kinds of structurally diverse ketones and aldehydes, giving the corresponding cyanohydrin trimethylsilyl ethers in high yields (13 substrates, 94-99%). In particular, the turnover frequency (714,000 h(-1)) and the turnover number (23,800) for the cyanosilylation of n-hexanal were of the highest level among those of previously reported catalysts.     

Design and analysis of chain and network structures from organic derivatives of polyoxometalate clusters

Polyoxometalate (POM) clusters derivatized with aniline groups exhibit distinct interactions with counterions and with each other. These interactions lead to the assembly of the clusters into chains and networks upon crystallization. Two cluster types were examined, [W(6)O(25)H(AsC(6)H(4)-4-NH(2))(2)](5-) and [Mo(12)O(46)(AsC(6)H(4)-4-NH(2))(4)](4-). The X-ray crystal structures were solved for the mixed salts containing [C(NH(2))(3)](+)/Na(+), Ag(+)/H(+), or Cu(2+)/H(+) as counterions. The X-ray crystal structures reveal that the POM clusters are linked together by hydrogen bonds or POM-metal ion-POM linkages. The roles of the counterions, solvents, and organic groups in the formation of specific crystalline architectures are discussed. Strongly interacting counterions form bonds to the oxo ligands of the POM and connect them into tetrameric units and/or into one-dimensional chains. The hydrogen bonding strength of the solvent influences the formation of hydrogen bonds between the aniline groups and oxo ligands of the cluster. The aniline groups played differing roles in the final structures: they were either nonbonding, bonded to a counterion, or involved in hydrogen bonding. Depending on the bonding interactions, the architecture of the cluster salts may be significantly altered.     

Synthesis of siloxane‐containing benzoxazine and its synergistic effect on flame retardancy of polyoxymethylene

A type of trialkoxysilane‐containing naphtholoxazine compound (Naph‐boz) was successfully synthesized and combined with ammonium polyphosphate/melamine (APP/ME) as an intumescent flame retardant (IFR) to improve the flame‐retardant efficiency of polyoxymethylene (POM). The Underwriters Laboratories 94 (UL94) vertical burning test, limiting oxygen index (LOI), cone calorimeter, thermogravimetric analysis (TGA), scanning electron microscopy (SEM), and Raman spectral analysis were used to study the flame‐retardant properties and related mechanism. The results showed that the formulation with 20 wt.% of APP, 6 wt.% of ME, and 4 wt.% of Naph‐boz passed UL94 V‐1 rating, and the LOI value was improved to 40.3%. Compared with pure POM, the IFR with Naph‐boz had greater reduction in peak heat release rate (lower 74.9%) and total heat release (lower 40.2%). SEM images showed that compact and reinforcing charred layer was formed during the POM/IFR/4Naph‐boz samples combustion, which was beneficial at reducing and maintaining low combustion parameters throughout the cone calorimeter test. The synergistic flame‐retardant effect between Naph‐boz and APP/ME was considered as the reason for the improvement in flame retardancy POM. Furthermore, because of the Naph‐boz was conducive to the compatibility between the flame retardants and matrix, the notched Izod impact strength of POM/IFR/4Naph‐boz composite was higher than that of POM/IFR system.     

Synthesis of DL-alanine hollow tubes and core-shell mesostructures

Three double hydrophilic block copolymers were used as crystal-growth modifiers of DL-alanine to generate amorphous precursor nanoparticles that undergo subsequent mesoscopic transformation to core-shell mesostructures and hollow tubes with quadratic cross-sections. The growth sequence can be stopped at various stages so that a series of intermediates between amorphous core- and crystalline-shell particles and tubes can be obtained. Time-dependent conductivity, TEM, SEM, and environmental scanning electron microscopy (ESEM) measurements were used to obtain a better understanding of the crystallization process, and a formation mechanism for the generation of the tubes is proposed. Na2SO4, NaCl, and NaNO3 as salts differ in their influence on the crystallization behavior of alanine by changing the solubility of alanine and by decreasing the stability of the intermediate particles. Core-shell mesostructures that formed in the dissolution-recrystallization process were captured as the transformation rate was decreased by the addition of copolymers or salts. Hollow tubes with quadratic cross-sections are the final product of the transformation process.     

PS colloidal particles stabilized by graphene oxide

Exfoliated graphene oxide (GO) sheets with hydrophilic functional groups on the surface were prepared by the oxidation of graphite. Because of the hydrophilic groups on the sheets and the hydrophobic carbon surface, GO sheets were located at the oil-water interface and could be used as a stabilizer in Pickering emulsions. After the Pickering emulsion polymerization of styrene, PS colloidal particles with GO sheets on the surface were prepared. The size of the GO sheets exerts an important influence on the preparation of PS colloidal particles. Small GO sheets located at the liquid-liquid interface and GO-stabilized PS colloidal particles were prepared; however, for large GO sheets, smaller PS colloidal particles prepared on the GO surface were observed. Transmission electron microscopy (TEM), scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS) were used to characterize the structure and morphology of the colloidal particles. TEM, SEM, and XPS results all suggest the successful preparation of GO-stabilized PS colloidal particles.     

PTC‐Promoted Japp–Klingmann Reaction for the Synthesis of Indole Derivatives

Abstract

Indole derivatives have been efficiently synthesized from ethyl 2‐phenylhydrazono‐5‐phthalimido‐pentanoate and its derivatives, which were obtained by Japp–Klingmann reaction under phase‐transfer catalytic (PTC) conditions. Several different phase‐transfer catalysts were investigated and dimethyldioctadecyl ammonium chloride (DMDOA) was found to promote this reaction efficiently. Using DMDOA as the PTC, aryl hydrazones were obtained in yields of 90%. The pure aryl hydrazones were then efficiently cyclized to indole derivatives in yields of more than 80%.     

Preparation and Magnetic Property of La0.7Sr0.3MnO3 Nanorod by Combination Sol-Gel with Molten Salt

La0.7Sr0.3MnO3（LSMO） nanorods were synthesized by a method combining sol-gel with molten salts at 950 ℃ for 10 h, which employed KCl＋NaCl（mass ratio 4：1） as eutectic molten salts. The morphologies and magnetic properties of the resulting LSMO nanorods were investigated by X-ray diffraction（XRD）, scanning electron microscopy（SEM）, transmission electron microscopy（TEM）, and vibrating sample magnetometer（VSM） measurements. It was found that the obtained perovskite manganite LSMO was a uniform nanorod with a diameter of about 50 nm and a length of longer than 500 rim. The Curie temperature（To） of the LSMO nanorod used here was 262 K, much lower than that of bulky single crystal LSMO（360 K）. The low Curie temperature might be a result of the great disorder near the grain boundary, which could be observed clearly from the TEM picture.