A new three-connected metal-organic coordination polymer with helical motifs: synthesis,crystal structure and photoluminescence

An interesting metal-organic network with helical motifs, {[Zn₂(mpdc)₂(bpy)(H₂O)₂]?·?2H₂O} (1, mpdc?=?2,6-dimethyl pyrdine-3,5-dicarboxylate), was synthesized under hydrothermal conditions, and characterized. Single-crystal X-ray structural analysis indicates that the title compound crystallizes in a monoclinic lattice, P2(1)/c with a?=?7.811(2), b?=?12.324(3), c?=?15.794(4)A, β?=?98.206(4)°, Z?=?2, V?=?1504.8(7)?ų, D _c?=?1.704?Mg?m^?3, F(000)?=?816, R ₁?=?0.0379, wR ₂?=?0.0807. In the structure of 1 the helical strands composed of [Zn(mpdc)(H₂O)] array in an interlacing fashion, and trap solvated water molecules to assemble a novel supramolecular network. Compound 1 exhibits strong photoluminescence in the solid state at room temperature.     

Translation of helical chirality from polymer into monomer: supramolecular polymerization of a chirality-memory molecule with an asymmetric Pd(II) complex

A chirality-memorizing saddle-shaped porphyrin (1_2H) with 3,5-dipyridylphenyl side arms at the opposite meso positions underwent supramolecular polymerization in CH₂Cl₂ with a chiral Pd(II) complex of 2,2′-bis(diphenylphosphino)-1,1′-binaphthyl (Pd^II(BINAP)), forming a ladder-shaped polymer (3_2H) with a prevailing one-handed helical chirality. When this polymer was poured into AcOH containing 1,3-bis(diphenylphosphino)propane (DPPP) as a decomplexing agent, 3_2H was depolymerized in a stereochemically retentive way to give optically active 1_2H, hydrogen-bonded with AcOH. Although a cyclodimeric reference of 3_2H, formed from 2_2H having two 3-pyridylphenyl meso substituents in conjunction with Pd^II(BINAP), behaved similar to 3_2H, the translation efficiency of helical chirality was lower than that in the case with 3_2H.     

Acrylation of polyvinylsilazane with allyl bromide for an UV photosensitive inorganic polymer

A novel inorganic polymer resin with high photosensitivity was prepared by grafting acrylate functional groups onto the backbone of polyvinylsilazane through a reaction with methyl-2-(bromo-methyl)acrylate via the highly efficient electrophilic substitution of allyl bromide. The as-modified polymer was characterized by ¹H NMR and 2D-¹H-¹H NMR (COSY) methods to determine the reaction mechanism. Differential photocalorimetry, FT-IR spectroscopy and TGA were used to examine its properties. The modified polyvinylsilazane is a promising inorganic polymer photoresist with a high UV sensitivity and a 55% ceramic yield, which is useful for fabricating non-oxide ceramic microstructures using mold free photocuring shaping processes.     

Morphological evolution of Cu2O nanocrystals in an acid solution: stability of different crystal planes

The morphological evolution of uniform Cu(2)O nanocrystals with different morphologies in a weak acetic acid solution (pH = 3.5) has been studied for cubic, octahedral, rhombic dodecahedral, {100} truncated octahedral, and {110} truncated octahedral nanocrystals. Cu(2)O nanocrystals undergo oxidative dissolution in weak acid solution, but their morphological changes depend on the exposed crystal planes. We found that the stability of Cu(2)O crystal planes in weak acid solution follows the order of {100} ? {111} > {110} and determines how the morphology of Cu(2)O nanocrystals evolves. The stable {100} crystal planes remain, and new {100} facets form at the expense of the less stable {111} and {110} crystal planes on the surface of Cu(2)O nanocrystals. Density functional theory calculations reveal that the Cu-O bond on Cu(2)O(100) surface has the shortest bond length. These results clearly exemplify that the morphology of inorganic crystals will evolve with the change of local chemical environment, shedding light on fundamentally understanding the morphological evolution of natural minerals and providing novel insights into the geomimetic synthesis of inorganic materials in the laboratory.     

A novel method for encapsulation of a liquid crystal in monodisperse micron-sized polymer particles

Liquid crystals (LCs) encapsulated in monodisperse micron-sized polymer particles were prepared to control the size and size distribution of LC droplets in polymer-dispersed LCs. The poly(methyl methacrylate) (PMMA) seed particles were swollen with the mixture of liquid crystal, monomers (methyl methacrylate and styrene) and initiator by using a diffusion-controlled swelling method. A single LC domain was produced by the phase separation between PMMA and LC through polymerization. The optical microscopy and scanning electron microscopy showed that the particles are highly monodisperse with core–shell structure. Moreover, monodisperse LC core domains were confirmed from polarized optical microscope observations. The final particle morphology was influenced by the cross-linking of the seed particle. When linear PMMA particles, which are not cross-linked, were used as a seed, the microcapsules were distorted after annealing for a few days; however, in the case of cross-linked PMMA particles, the core–shell structure was sustained stably after annealing. Received: 22 November 2000 Accepted: 12 March 2001     

Osmotically driven crystal morphogenesis: a general approach to the fabrication of micrometer-scale tubular architectures based on polyoxometalates

The process of osmotically driven crystal morphogenesis of polyoxometalate (POM)-based crystals is investigated, whereby the transformation results in the growth of micrometer-scale tubes 10-100 μm in diameter and many thousands of micrometers long. This process initiates when the crystals are immersed in aqueous solutions containing large cations and is governed by the solubility of the parent POM crystal. Evidence is presented that indicates the process is general to all types of POMs, with solubility of the parent crystal being the deciding parameter. A modular approach is adopted since different POM precursor crystals can form tubular architectures with a range of large cationic species, producing an ion-exchanged material that combines the large added cations and the large POM-based anions. It is also shown that the process of morphogenesis is electrostatically driven by the aggregation of anionic metal oxides with the dissolved cations. This leads to the formation of a semi-permeable membrane around the crystal. The osmotically driven ingress of water leads to an increase in pressure, and ultimately rupture of the membrane occurs, allowing a saturated solution of the POM to escape and leading to the formation of a "self-growing" microtube in the presence of the cation. It is demonstrated that the growth process is sustained by the osmotic pressure within the membrane surrounding the parent crystal, as tube growth ceases whenever this pressure is relieved. Not only is the potential of the modular approach revealed by the fact that the microtubes retain the properties of their component parts, but it is also possible to control the direction of growth and tube diameter. In addition, the solubility limits of tube growth are explored and translated into a predictive methodology for the fabrication of tubular architectures with predefined physical properties, opening the way for real applications.     

A generic approach for preparing core-shell carbon-metal oxide nanofibers: morphological evolution and its mechanism

Carbon-SnO(2) core-shell hybrid nanofibers were prepared via single-spinneret electrospinning and subsequent heat treatment. The Kirkendall effect during the heat treatment is found to be responsible for the formation of core-shell morphology. The route is proven to be generic for fabrication of carbon-metal oxide or carbon-metal core-shell nanofibers, and corresponding nanotubes.     

Acyclic diene metathesis: a versatile tool for the construction of defined polymer architectures

Two decades have passed since the metathesis polymerisation of α,ω-dienes was successfully demonstrated by the group of Wagener and the term acyclic diene metathesis (ADMET) polymerisation was coined. Since then, the advances of metathesis chemistry have allowed to expand the scope of this versatile polymerisation reaction that nowadays finds applications in different fields, such as polymer, material, or medicinal chemistry. This critical review provides an insight into the historical aspects of ADMET and a detailed overview of the work done to date applying this versatile polymerisation reaction (221 references).     

Photoinduced anisotropy and photoalignment of nematic liquid crystals by a novel polymer liquid crystal with a coumarin-containing side group

A new type of photo-crosslinkable methacrylate polymer liquid crystal (PLC) with a coumarincontaining mesogenic side group was synthesized and applied as the photoalignment layer for low molecular mass nematic liquid crystals. Linearly polarized ultraviolet light was directed onto a thin film of PLC under various exposure conditions. When a film was irradiated at room temperature, a small negative optical anisotropy was generated due to angular-selective photo-crosslinking. In contrast, when the film was exposed near the clearing temperature of the PLC, the induced anisotropy was positive due to thermally enhanced photoinduced reorientation of the side groups. The aggregation of the mesogenic groups was also observed when the irradiation was carried out in the liquid crystalline temperature range of the PLC. The LC alignment on the photoreacted film was greatly dependent on these irradiation conditions. It was made clear that the LC alignment was regulated by the interaction among the LC, the photo-crosslinked side groups and the remaining mesogenic side groups, and that the aggregated mesogenic groups inhibited the LC alignment.     

Photoinduced anisotropy and photoalignment of nematic liquid crystals by a novel polymer liquid crystal with a coumarin-containing side group

A new type of photo-crosslinkable methacrylate polymer liquid crystal (PLC) with a coumarincontaining mesogenic side group was synthesized and applied as the photoalignment layer for low molecular mass nematic liquid crystals. Linearly polarized ultraviolet light was directed onto a thin film of PLC under various exposure conditions. When a film was irradiated at room temperature, a small negative optical anisotropy was generated due to angular-selective photo-crosslinking. In contrast, when the film was exposed near the clearing temperature of the PLC, the induced anisotropy was positive due to thermally enhanced photoinduced reorientation of the side groups. The aggregation of the mesogenic groups was also observed when the irradiation was carried out in the liquid crystalline temperature range of the PLC. The LC alignment on the photoreacted film was greatly dependent on these irradiation conditions. It was made clear that the LC alignment was regulated by the interaction among the LC, the photo-crosslinked side groups and the remaining mesogenic side groups, and that the aggregated mesogenic groups inhibited the LC alignment.     

Dendrimer/inorganic nanomaterial composites: Tailoring preparation,properties,functions,and applications of inorganic nanomaterials with dendritic architectures

Inorganic nanomaterials have a variety of fascinating properties and a wide range of promising applications.However,they often suffer from instability and poor processibility.To solve it,dendrimers,a special family of macromolecules having a unique three-dimensional architecture,provide one of the excellent solutions.In addition,the site-selective functionalization of the specific elements in the dendritic structure endows the nanohybrid system new functions and applications.Inspired by such ideas,a variety...     

Hydrothermal syntheses and crystal structure of a novel one-dimensional Pb(II) coordination polymer with chenodeoxycholic acid ligand

A novel 1D chain-like coordination polymer, {[Pb(CDCA)₂(DMF)] · DMF · 2H₂O]} _n (I) (HCDCA = chenodeoxycholic acid, DMF = dimethyl formamide), has been synthesized by hydrothermal method and characterized by single crystal X-ray diffraction, IR spectroscopy, and elemental analysis (CIF file CCDC no. 996098). X-ray diffraction analyses indicated that I displays distorted octahedral metal centers with secondary building units [Pb(CDCA)₂(DMF)] bridged by a pair of μ²-COO^?-bridges. In the crystal, interchain O-H?O hydrogen bonds are present and assemble the neighboring 1D chain into a (4,4) sql type three-dimensional (3D) supramolecular topological network.     

Conformation of a polymer chain in solution: an exact density expansion approach

The conformation of a polymer chain in solution is intrinsically coupled to the thermodynamic and structural properties of the solvent. Here we study such solvent effects in a system consisting of a flexible interaction-site n-mer chain immersed in a monomeric solvent. Chain conformation is described with a set of intramolecular site-site probability functions. We derive an exact density expansion for these intramolecular probability functions and give a diagrammatic representation of the terms contributing at each order of the expansion. The expansion is tested for a short hard-sphere chain (n=3 or 4) with site diameter sigma in a hard-sphere solvent with solvent diameter D. In comparison with Monte Carlo simulation results for 0.2< or =D/sigma< or =100, the expansion (taken to second order) is found to be quantitatively accurate for low to moderate solvent volume fractions for all size ratios. Average chain dimensions are predicted accurately up to liquidlike solvent densities. The hard-sphere chains are compressed with both increasing solvent density and decreasing solvent size. For small solvent (D相似文献   

Using flowerlike polymer–copper nanostructure composite and novel organic–inorganic hybrid material to construct an amperometric biosensor for hydrogen peroxide

A new type of amperometric hydrogen peroxide biosensor was fabricated by entrapping horseradish peroxidase (HRP) in the organic–inorganic hybrid material composed of zirconia–chitosan sol–gel and Au nanoparticles (ZrO₂–CS–AuNPs). The sensitivity of the biosensor was enhanced by a flowerlike polymer–copper nanostructure composite (pPA–FCu) which was prepared from co-electrodeposition of CuSO₄ solution and 2,6-pyridinediamine solution. Several techniques, including UV–vis absorption spectroscopy, scanning electron microscopy, cyclic voltammetry, chronoamperometry and electrochemical impedance spectroscopy were employed to characterize the assembly process and performance of the biosensor. The results showed that this pPA–FCu nanostructure not only had excellent redox electrochemical activity, but also had good catalytic efficiency for hydrogen peroxide. Also the ZrO₂–CS–AuNPs had good film forming ability, high stability and good retention of bioactivity of the immobilized enzyme. The resulting biosensors showed a linear range from 7.80 × 10^?7 to 3.7 × 10^?3 mol L^?1, with a detection limit of 3.2 × 10^?7 mol L^?1 (S/N = 3) under optimized experimental conditions. The apparent Michaelis–Menten constant was determined to be 0.32 mM, showing good affinity. In addition, the biosensor which exhibits good analytical performance, acceptable stability and good selectivity, has potential for practical applications.     

Synthesis,properties and crystal structure of a novel organic–inorganic hybrid constructed from tungstophosphoric acid and benzotriazole

A novel compound, (C₆H₅N₃)₈[PW₁₂O₄₀]·2H₂O, was prepared and characterized by elemental analysis, i.r., ¹H-n.m.r., u.v., c.v. and single crystal X-ray diffraction. An X-ray crystallographic study showed that the crystal was constructed by electrostatic attraction and hydrogen bonds between tungstophosphoric acid and the benzotriazole cation. The benzotriazole and water molecules are arranged in good order to form a large hole in the structure, the polyoxometalates occupying the cavities. The catalytic behavior of the title compound in the context of oxidation of benzaldehyde to benzoic acid, using H₂O₂ as oxidant in a liquid–solid biphase system, was investigated.     

Dipicolylglycyl-phenylalanine zinc(II): a metallopeptide with a built-in conformational switch and its homochiral helical coordination polymer

The peptide-zinc complex [(Dpg-Phe)Zn]2+ (Dpg = N,N-dipicolylglycine; Phe = phenylalanine) reversibly forms a homochiral P-helical coordination polymer upon switching the pH from mildly basic to mildly acidic.     

Molecular chairs, zippers, zigzag and helical chains: chemical enumeration of supramolecular isomerism based on a predesigned metal-organic building-block

A predesigned metal-organic building-block [Cu(I)(2-pytz)](2-Hpytz = 3,5-di-2-pyridyl-1,2,4-triazole) has been successfully used to synthesize four genuine supramolecular isomers.     

Synthesis and crystal structure of a novel three-dimensional inorganic open-framework: Cd8(OH)8(SO4)4

The title compound Cd₈(OH)₈(SO₄)₄ (1) obtained under hydrothermal conditions by reacting Cd(OH)₂ with 4-aminobenzenesulfonic acid in an aqueous ethanol solution was confirmed by single-crystal X-ray diffraction. Crystal data: P2₁/c with a?=?6.8984(4), b?=?7.5640(4), c?=?11.3919(5)?Å, β?=?119.763(2)°, V?=?516.01(5)?ų, H₈Cd₈O₂₄S₄, M _r ?=?1419.50, Z?=?1, D _c ?=?4.568?Mg?m^?3, μ?=?8.595?mm^?1, F(000)?=?648, R?=?0.023, wR?=?0.060 for 1208 observed reflections [I?>?2σ(I?)]. The crystal structure of complex 1 forms a three-dimensional (3-D) framework.