One-step synthesis of palladium/SBA-15 nanocomposites and its catalytic application

Well-dispersed palladium nanoparticles in mesoporous SBA- 15 SiO2 were prepared in a facile one-step approach during sol-gel route under reductive atmosphere. X-ray diffraction (XRD) results indicate that as-synthesized nanocomposites basically remain ordered two-dimensional hexagonal mesostructure while transmission electron microscopy (TEM) study exhibits a well dispersion of palladium nanoparticles within the mesoporous SBA-15 channels. The size of Pd nanoparticles is approximately in the range of 5-10nm. However, the resulting nanocomposites exhibit a highly catalytic activity and reused ability at least after five recycles without ligand in air for both the Suzuki and Heck coupling reactions.

Sugars-grafted aliphatic biodegradable poly(L-lactide-co-carbonate)s by click reaction and their specific interaction with lectin molecules

A novel biodegradable aliphatic poly(L-lactide-co-carbonate) bearing pendant acetylene groups was successfully prepared by ring-opening copolymerization of L-lactide (LA) with 5-methyl-5-propargyloxycarbonyl-1,3-dioxan-2-one (PC) in the presence of benzyl alcohol as initiator with ZnEt2 as catalyst in bulk at 100 degrees C and subsequently used for grafting 2-azidoethyl beta-D-glucopyranoside and 2-azidoethyl beta-lactoside by the typical "click reaction," that is Cu(I)-catalyzed cycloaddition of azide and alkyne. The density of acetylene groups in the copolymer can be tailored by the molar ratio of PC to LA during the copolymerization. The aliphatic copolymers grafted with sugars showed low cytotoxicity to L929 cells, improved hydrophilic properties and specific recognition and binding ability with lectins, that is Concanavalin A (Con A) and Ricinus communis agglutinin (RCA). Therefore, this kind of sugar-grafted copolymer could be a good candidate in variety of biomedical applications.

RGD peptide grafted biodegradable amphiphilic triblock copolymer poly(glutamic acid)-b-poly(L-lactide)-b-poly(glutamic acid): Synthesis and self-assembly

A novel amphiphilic biodegradable triblock copolymer (PGL-PLA-PGL) with polylactide (PLA) as hydrophobic middle block and poly(glutamic acid) (PGL) as hydrophilic lateral blocks was successfully synthesized by ring-opening polymerization (ROP) Of L-lactide (LA) and N-carboxy anhydride (NCA) consecutively and by subsequent catalytic hydrogenation. The results of cell experiment of PGL-PLA-PGL suggested that PGL could improve biocompatibility of polyester obviously. The copolymer could form micelles of spindly shape easily in aqueous solution. The pendant carboxyl groups of the triblock copolymer were further activated with N-hydroxysuccinimide and combined with a cell-adhesive peptide GRGI)SY Incorporation of the oligopeptide further enhanced the hydrophilicity and led to formation of spherical micelles. PGL-PLAPGL showed better cell adhesion and spreading ability than pure PLA and the GRGDSY-containing copolymer exhibited even further improvement in cell adhesion and spreading ability, indicating that the copolymer could find a promising application in drug delivery or tissue engineering.

Synthesis and characterization of novel poly(ester carbonate)s based on pentaerythritol

Novel poly(ester carbonate)s were synthesized by the ring-opening polymerization Of L-lactide and functionalized carbonate monomer 9-phenyl-2,4,8,10-tetraoxaspiro[5,5]undecan-3-one derived from pentaerythritol with diethyl zinc as an initiator. H-1 NMR analysis revealed that the carbonate content in the copolymer was almost equal to that in the feed. DSC results indicated that T-g of the copolymer increased with increasing carbonate content in the copolymer. Moreover, the protecting benzylidene groups in the copolymer poly(L-lactide-co-9-phenyl-2,4,8,10-tetraoxaspiro[5,5]undecan-3-one) were removed by hydrogenation with palladium hydroxide on activated charcoal as a catalyst to give a functional copolymer, poly(L-lactide-co-2,2-dihydroxylmethyl-propylene carbonate), containing pendant primary hydroxyl groups. Complete deprotection was confirmed by H-1 NMR and FTIR spectroscopy. The in vitro degradation rate of the deprotected copolymers was faster than that of the protected copolymers in the presence of proteinase K. The cell morphology and viability on a copolymer film evaluated with ECV-304 cells showed that poly(ester carbonate)s derived from pentaerythritol are good biocompatible materials suitable for biomedical applications.

Liquid crystal properties of a mesogenic polyacetylene, poly(11-[(4 '-heptoxy-4-biphenylyl)carbonyloxy]-1-undecyne)

The liquid crystalline properties of a mesogenic poly(1-alkyne) and the corresponding monomer were studied using transmission electron microscopy, X-ray diffraction, polarizing optical microscopy and differential scanning calorimetry. The monomer exhibits a monotropic smectic A phase and a metastable crystalline phase. The rigid polymer backbones do not prevent the mesogenic moieties from packing into smectic A and B phases in the temperature ranges 127.6 - 74.1degreesC and 74.1degreesC - room temperature, respectively, on cooling from the isotropic melt.

An ionic liquid based on a cyclic guanidinium cation is an efficient medium for the selective oxidation of benzyl alcohols

A novel room temperature ionic liquid (RTIL) has been prepared containing a cyclic hexaalkylguanidinium cation. The selective oxidation of a series of substituted benzyl alcohols has been carried out in it, with sodium hypochlorite as the oxidant. The RTIL acts as both phase transfer catalyst (PTC) and solvent. The ionic liquid could be recycled after extraction of the benzaldehyde product with ether.

A new route to control product selectivity in the oxidative dehydrogenation of cyclohexane and cyclohexene

The product selectivity can be controlled by adding acetic acid in feed over vanadium phosphate (VPO) in gas phase oxidative dehydrogenation (ODH), in which cyclohexane and cyclohexene are oxidized to cyclohexene and 1,3-cyclohexadiene (1,3-CHD), respectively, at almost 100% selectivity. This approach is also an efficient method to capture the very unstable intermediates in the mechanism study.

Synthesis of a novel structural triblock copolymer of poly(gamma-benzyl-L-glutamic acid)-b-poly(ethylene oxide)-b-poly(epsilon-caprolactone)

A novel structural triblock copolymer of poly(gamma-benzyl-L-glutamic acid)-b-poly(ethylene oxide)-b-poly(epsilon-caprolactone) (PBLG-PEO-PCL) was synthesized by a new approach in the following three steps: (1) sequential anionic ring opening polymerization (ROP) of ethylene oxide and epsilon-caprolactone with an acetonitrile/potassium naphthalene initiator system to obtain a diblock copolymer CN-PEO-PCL with a cyano end-group; (2) conversion of the CN end-group into NH2 end-group by hydrogenation to obtain NH2-PEO-PCL; (3) ROP of gamma-benzyl-L-glutamate-N-carboxyanhydrides (Bz-L-GluNCA) with NH2-PEO-PCL as macroinitiator to obtain the target triblock copolymer. The structures from CN-PEO precursor to the triblock copolymers were confirmed by FT-IR and H-1 NMR spectroscopy, and their molecular weights were measured by gel permeation chromatography. The monomer of Bz-L-GluNCA can react almost quantitatively with the amino end-groups of NH2-PEO-PCL macroinitiator by ROP.

Biodegradable amphiphilic triblock copolymer bearing pendant glucose residues: Preparation and specific interaction with Concanavalin A molecules

A novel biodegradable amphiphilic block copolymer PLGG-PEG-PLGG bearing pendant glucose residues is successfully prepared by the coupling reaction of 3-(2-aminoethylthio) propyl-R-D-glucopyranoside with the pendant carboxyl groups of PLGG-PEG-PLGG in the presence of N,N'-carbonyldiimidazole. The polymer PLGG-PEG-PLGG, i.e., poly {(lactic acid)-co-[(glycolic acid)-alt-(L-glutamic acid)]}-block-poly(ethylene glycol)-block-poly{( lactic acid)-co-[( glycolic acid)-alt-(L-glutamic acid)]}, is prepared by ring-opening copolymerization of L-lactide (LLA) with (3s)-benzoxylcarbonylethylmorpholine-2,5-dione (BEMD) in the presence of dihydroxyl PEG with molecular weight of 2000 as macroinitiator and Sn(Oct)(2) as catalyst, and then by catalytic hydrogenation. The glucose-grafted copolymer shows a lower degree of cytotoxicity to ECV-304 cells and improved specific recognition and binding with Concanavalin A (Con A). Therefore, this kind of glucose-grafted copolymer may find biomedical applications.

Synthesis and characterization of RGD peptide grafted poly(ethylene glycol)-b-poly(L-lactide)-b-poly(L-glutamic acid) triblock copolymer

Advances in tissue engineering require biofunctional scaffolds that can provide not only physical support for cells but also chemical and biological cues needed in forming functional tissues. To achieve this goal, a novel RGD peptide grafted poly(ethylene glycol)-b-poly(L-lactide)-b-poly(L-glutamic acid) (PEG-PLA-PGL/RGD) was synthesized in four steps (1) to prepare diblock copolymer PEG-PLA-OH and to convert its -OH end group into -NH2 (to obtain PEG-PLA-NH2), (2) to prepare triblock copolymer PEG-PLA-PBGL by ring-opening polymerization of NCA (N-carboxyanhydride) derived from benzyl glutamate with diblock copolymer PEG-PLA-NH2 as macroinitiator, (3) to remove the protective benzyl groups by catalytic hydrogenation of PEGPLA-PBGL to obtain PEG-PLA-PGL, and (4) to react RGD (arginine-glycine-(aspartic amide)) with the carboxyl groups of the PEG-PLA-PGL. The structures of PEG-PLA-PGL/RGD and its precursors were confirmed by H-1 NMR, FT-IR, amino acid analysis, and XPS analysis. Addition of 5 wt % PEG-PLA-PGL/RGD into a PLGA matrix significantly improved the surface wettability of the blend films and the adhesion and proliferation behavior of human chondrocytes and 3T3 cells on the blend films. Therefore, the novel RGD-grafted triblock copolymer is expected to find application in cell or tissue engineering.

Developments and applications of supported liquid phase catalysts

Supported liquid phase catalyst (SLPC) is one of effectively heterogenized homogeneous catalysts using organometallic complexes as active components, which are dissolved in a small quantity of liquid phase dispersed in the form of isle or film on the surface of supports. The SLPC has successfully been applied for several chemical transformations and this article will review recent results with respect to the preparation and catalytic performance, the applicability to continuous flow operations, and the capability of multifunctional catalysis.

Fabrication of self-assembled palladium nanosheets using layered organic/inorganic hybrid as the template

In this paper, a simple route to the fabrication of palladium nanosheets is described. The interaction of palladium chloride (PdCl2) and n-octylamine salt resulted in the formation of a quasi-perovskite-type composite with a layered structure on a molecular scale. This composite can be employed as a template for preparing ultrathin Pd nanosheets when a {PdCl4}(2-) network is reduced in situ by hydrogen in toluene. The x-ray diffraction results indicate that the resulting Pd nanosheets are highly ordered, and they are confined inside the organic matrix as evidenced by high resolution transmission electron microscopy. These Pd nanosheets can be reorganized into layered structures in non-polarized organic solvent when the ordered structure is destroyed. This method of preparing Pd nanosheets is expected to be applicable to other layered organic/inorganic perovskite systems for obtaining the corresponding metal nanosheets.

Catalytic properties of silica/silver nanocomposites

The catalytic properties of silver nanoparticles supported on silica and the relation between catalytic activity of silver particles and the support (silica) size are investigated in the present article. The silver nanoparticles with 4 nm diameters were synthesized and were attached to silica spheres with sizes of 40, 78, 105 nm, respectively. The reduction of Rhodamine 6G (R6G) by NaBH4 was designed by using the SiO2/Ag core-shell nanocomposites as catalysts. The experimental results demonstrated that the catalytic activity of silica/silver nanoparticles depends on not only the concentration of catalysts (silver) but also the support silica size. Silver particles supported on small SiO2 spheres (similar to 40 nm) show high catalytic activity. Moreover, by making a comparison between the UV-vis spectra of the catalyst before and after the catalytic reaction, we found that the position of surface plasma resonance (SPR) peak of Ag nanoparticles changes little. The above results suggested that the size and morphology of silver particles were probably kept unchanged after the reduction of R6G and also implied that the catalytic activity of silver particles was hardly lost during the catalytic reaction.

Kinetic and electrochemical properties of icosahedral quasicrystalline Ti45Zr35Ni17Cu3 powder

Kinetic and electrochemical properties of icosahedral quasicrystalline Ti45Zr35Ni17Cu3 alloy powder as negative electrode material of Ni-MH battery have been investigated at different temperatures. The calculated results show that the apparent activation enthalpy of the charge-transfer reaction is 43.89 kJ mol(-1), and the activation energy of hydrogen diffusion is 21.03 kJ mol(-1). The exchange current density and the diffusion coefficient of hydrogen in the bulky electrode increase with increasing temperature, indicating that increasing temperature is beneficial to charge-transfer reaction and hydrogen diffusion. As a result, the maximum discharge capacity, activation property and high-rate dischargeability are greatly improved with increasing temperature. However, the charge retention and the cycling stability degrade with the increase of the temperature.