Segmented All-Platinum Nanowires with Controlled Morphology through Manipulation of the Local Electrolyte Distribution in Fluidic Nanochannels during Electrodeposition

Synthesis of segmented all-Pt nanowires is achieved by a template-assisted method. The combination of a suitably chosen electrolyte/template system with pulse-reverse electrodeposition allows the formation of well-defined segments linked to nanowires. Manipulation of the morphology is obtained by controlling the electrokinetie effects on the local electrolyte distribution inside the nanochannels during the nanowire growth process, allowing a deviation from the continuously cylindrical geometry given by the nanoporous template. The length of the segments can be adjusted as a function of the cathodic pulse duration. Applying constant pulses leads to segments with homogeneous shape and dimensions along most of the total wire length. X-ray diffraction demonstrates that the preferred crystallite orientation of the polycrystalline wires varies with the average segment length. The results are explained considering transitions in texture formation with increasing thickness of the electrodeposit. A mechanism of segment formation is proposed based on structural characterizations. Nanowires with controlled segmented morphology are of great technological importance, because of the possibility to precisely control their substructure as a means of tuning their electrical, thermal, and optical properties. The concept we present in this work for electrodeposited platinum and track-etched polycarbonate membranes can be applied to other selected materials as well as templates and constitutes a general method to controlled nanostructuring and synthesis of shape controlled nanostructures.

Capillary zone electrophoresis investigation of the interaction between heparin and granulocyte-colony stimulating factor

The interaction between standard heparin, low-molecular-weight heparin (LMWH), and granulocyte-colony stimulating factor (G-CSF) was studied by capillary zone electrophoresis. Both qualitative and quantitative characterizations of the heparin-protein binding were determined. The binding constants of the two different groups of heparins with G-CSF, calculated from the Scatchard plot by regression, were 4.805 x 10(5) m(-1) and 4.579 x 10(5) m(-1), respectively. The two binding constants measured are of the same order of magnitude at 10(5) m(-1), indicating that LMWH contains most of the functional groups bound to G-CSF by standard heparin.

Development of functionalized terbium fluorescent nanoparticles for antibody labeling and time-resolved fluoroimmunoassay application

Silica-based functionalized terbium fluorescent nanoparticles were prepared, characterized and developed as a fluorescence probe for antibody labeling and time-resolved fluoroimmunoassay. The nanoparticles were prepared in a water-in-oil (W/O) microemulsion containing a strongly fluorescent Tb3+ chelate. N,N.N-1,N-1-12,6-bis(3'-aminomethyl-1'-pyrazolyl)phenylpyridine] tetrakis(acetate)-Tb3+ (BPTA-Tb3+), Triton X-100, octanol, and cyclohexane by controlling copolymerization of tetraethyl orthosilicate (TEOS) and 3-[2-(2- aminoethylamino)-ethylamino]propyl-trimethoxysilane (AEPS) with ammonia water. The characterizations by transmission electron microscopy and fluorometric quantum methods show that the nanoparticles are spherical and uniform in size, 45 +/- 3 nm in diameter, strongly fluorescent with fluorescence yield of 10% and a long fluorescence lifetime of 2.0 ms. The amino groups directly introduced to the nanoparticle's surface by using AEPS in the preparation made the surface modification and bioconjugation of the nanoparticles easier. The nanoparticle-labeled anti-human alpha-fetoprotein antibody was prepared and used for time-resolved fluoroimmunoassay of (x-fetoprotein (AFP) in human serum samples. The assay response is linear from 0.10 ng ml(-1) to about 100 ng ml(-1) with the detection limit of 0.10 ng ml(-1). The coefficient variations (CVs) of the method are less than 9.0%. and the recoveries are in the range of 84-98% for human serum sample measurements. (C) 2004 Elsevier B.V. All rights reserved.

Effect of support on chromium based catalysts for the oxidative dehydrogenation of C2H6 with CO2 to C2H4

The oxidative dehydrogenation of ethane (ODE) with CO2 to C2H4 has been studied over a series of Cr-based catalysts using SiO2, Al2O3, (MCM-41 zeolite) MCM-41, MgO and Silicate-2 (Si-2) as the supports. TPR, NH3-TPD, and EPR characterizations of catalysts were carried out to investigate the reduction property of Cr species on different supports, the acidities of catalysts and Cr species of 6Cr/SiO2 catalysts, respectively.

Amphiphilic Core-Shell Nanocarriers Based On Hyperbranched Poly(ester amide)-star-PCL: Synthesis, Characterization, and Potential as Efficient Phase Transfer Agent

Amphiphilic biodegradable star-shaped polymer was conveniently prepared by the Sn(Oct)(2)-catalyzed ring opening polymerization of c-caprolactone (CL) with hyperbranched poly(ester amide) (PEA) as a macroinitiator. Various monomer/initiator ratios were employed to vary the length of the PCL arms. H-1 NMR and FTIR characterizations showed the successful synthesis of star polymer with high initiation efficiency. SEC analysis using triple detectors, RI, light scattering, and viscosity confirmed the controlled manner of polymerization and the star architecture.

Pd nanoparticles supported on WO3/C hybrid material as catalyst for oxygen reduction reaction

Pd nanoparticles supported on WO3/C hybrid material have been developed as the catalyst for the oxygen reduction reaction (ORR) in direct methanol fuel cells. The resultant Pd-WO3/C catalyst has an ORR activity comparable to the commercial Pt/C catalyst and a higher activity than the Pd/C catalyst prepared with the same method. Based on the physical and electrochemical characterizations, the improvement in the catalytic performance may be attributed to the small particle sizes and uniform dispersion of Pd on the WO3/C, the strong interaction between Pd and WO3 and the formation of hydrogen tungsten bronze which effectively promote the direct 4-electron pathway of the ORR at Pd.

Novel Hybrid Electrocatalyst with Enhanced Performance in Alkaline Media: Hollow Au/Pd Core/Shell Nanostructures with a Raspberry Surface

In this paper, a hollow Au/Pd core/shell nanostructure with a raspberry surface was developed for methanol, ethanol, and formic acid oxidation in alkaline media. The results showed that it possessed better electrocatalyst performance than hollow Au nanospheres or Pd nanoparticles. The nanostructure was fabricated via a two-step method. Hollow Au nanospheres were first synthesized by a galvanic replacement reaction, and then they were coated with a layer of Pd grains. Several characterizations such as transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), and X-ray photoelectron spectroscopy (XPS) were used to investigate the prepared nanostructures.

High activity PtRu/C catalysts synthesized by a modified impregnation method for methanol electro-oxidation

A modified impregnation method was used to prepare highly dispersive carbon-supported PtRu catalyst (PtRu/C). Two modifications to the conventional impregnation method were performed: one was to precipitate the precursors ((NH4)(2)PtCl6 and Ru(OH)(3)) on the carbon support before metal reduction: the other was to add a buffer into the synthetic solution to stabilize the pH. The prepared catalyst showed a much higher activity for methanol electro-oxidation than a catalyst prepared by the conventional impregnation method. even higher than that of current commercially available, state-of-the-art catalysts. The morphology of the prepared catalyst was characterized using TEM and XRD measurements to determine particle sizes, alloying degree, and lattice parameters. Electrochemical methods were also used to ascertain the electrochemical active surface area and the specific activity of the catalyst.

Facile synthesis of PtRu/C electrocatalyst with high activity and high loading for passive direct methanol fuel cell by synergetic effect of ultrasonic radiation and mechanical stirring

The PtRu/C electrocatalyst with high loading (PtRu of 60 wt%) was prepared by synergetic effect of ultrasonic radiation and mechanical stirring. Physicochemical characterizations show that the size of PtRu particles of as-prepared PtRu/C catalyst is only several nanometers (2-4 nm), and the PtRu nanoparticles were homogeneously dispersed on carbon surface. Electrochemistry and single passive direct methanol fuel cell (DMFC) tests indicate that the as-prepared PtRu/C electrocatalyst possessed larger electrochemical active surface (EAS) area and enhanced electrocatalytic activity for methanol oxidation reaction (MOR). The enhancement could be attributed to the synergetic effect of ultrasound radiation and mechanical stirring, which can avoid excess concentration of partial solution and provide a uniform environment for the nucleation and growth of metal particles simultaneously hindering the agglomeration of PtRu particles on carbon surface.

Synthesis and Characterization of Hyperbranched Poly(ether amide)s with Thermoresponsive Property and Unexpected Strong Blue Photoluminescence

A facile and efficient strategy for the syntheses of novel hyperbranched poly(ether amide)s (HPEA) from multihydroxyl primary amines and (meth)acryloyl chloride has been developed. The chemical structures of the HPEAs were confirmed by IR and NMR spectra. Analyses of SEC (size exclusion chromatography) and viscosity characterizations revealed the highly branched structures of the polymers obtained. The resultant hyperbranched polymers contain abundant hydroxyl groups. The thermoresponsive property was obtained from in situ surface modification of abundant OH end groups with N-isopropylacrylamide (NIPAAm). The study oil temperature-dependent characteristics has revealed that NIPAAm-g-HPEA exhibits an adjustable lower critical solution temperature (LCST) of about 34-42 degrees C depending on the grafting degree. More interestingly, the work provided an interesting phenomenon where the HPEA backbones exhibited strong blue photoluminescence.

Why [6,6]- and 1,2-Benzal-3-N-4-O-Cyclic Phenylimidate C-60 Undergo Electrochemically Induced Retro-Addition Reactions while 1,4-Dibenzyl-2,3-Cyclic Phenylimidate C-60 Does Not? C-H center dot center dot center dot X (X = N, O) Intramolecular Interactions in Organofullerenes

The electrochemical properties of a series of structurally related fullerooxazoles, [6,6] cyclic phenylimidate C-60 (1), 1,2-benzal-3-N-4-O-cyclic phenylimidate C-60 (2), and 1,4-dibenzyl-2,3-cyclic phenylimidate C-60 (3), are described, and the spectroscopic characterizations of their anionic species are reported. The results show that compounds I and 2 undergo retro-cycloaddition reactions that lead to the formation of C-60 and C61HPh, respectively, upon two-electron-transfer reduction. However, compound 3 demonstrates much more electrochemical stability as no retro-cycloaddition reaction occurs under similar conditions. Natural bond orbital (NBO) calculations on charge distribution show there is no significant difference among the dianions of 1, 2, and 3, indicating that the electrochemical stability of 3 is unlikely to be caused by the charge distribution difference of the dianions of three compounds. Examination on the crystal structure of compound 3 reveals close contacts of the C-H group with the heteroatoms (N and O) of cyclic phenylimidate, suggesting the existence of C-H center dot center dot center dot X (X = N, O) intramolecular hydrogen bonding among the addends, which is further confirmed by NBO analysis.

Formation of Fullerooxazoles from C61HPh3-: The Regioselectivity of Heteroatom Additions

The formation of fullerooxazoles from C61HPh3- has been examined in benzonitrile (PhCN), m-methoxybenzonitrile (m-OCH3PhCN), m-tolunitrile (m-CH3PhCN), and o-tolunitrile (o-CH3PhCN), where cis-1 bisadducts wit h Ph-, m-OCH3Ph-, m-CH3Ph-, and o-CH3Ph-substituted cyclic imidate next to the phenylmethano are formed its evidenced by various characterizations. Interestingly, only regioisomers 2a-d with the oxygen atom bonded to C4/C5 and the nitrogen atom bonded to C3/C6 are generated its demonstrated by heteronuclear multiple bond coherence (HMBC) NMR, while the alternative regioisomers 3a-d, which have the oxygen and nitrogen atoms at C3/C6 and C4/C5, respectively, are not formed from the reactions, even though the DFT (density functional theory) calculations have predicted that the energy differences between the two types of regioisomers are very small, with regioisomers 3a-d actually having lower energies than 2a-d The results are rationalized by the charge distributions Of C61HPh3-, where computational calculations have shown that the negative charges on C4 and C5 are greater than those on C3 and C6, indicating that the exhibited site selectivity of heteroatoms is a result of the charge-directed addition process

Preparation of TiO2, CeO2, and ZrO2 hierarchical structures in "one-pot" reactions

In this paper, a novel template of carbon foam is used in building hierarchical structures of TiO2, CeO2, and ZrO2. They had multiscale morphologies, from nanowalls, nanoparticles to layer nanostructures. Oil a hundred-micron scale, the product was a sponge-like material constructed by nanowalls. On a hundred-nanometer scale, the electron microscope images showed that the nanowalls were porous and assembled by polycrystalline nanoparticles. Meanwhile, on one nanometer scale, many nanoparticles exhibited layer nanostructures with about 1.1 run of thickness and spacing. In mechanism section, the process analysis and characterizations suggested that the hierarchical structures were the combined result of two templates in a "one-pot" reaction. The mesoporous nanowalls were derived from carbon foams, while the layer nanostructures were the replicas of graphite sheets. The method has potential utilizations in preparation of various adsorbent and catalyst.

Surface plasmon resonance and electrochemistry characterization of layer-by-layer self-assembled DNA and Zr4+ thin films, and their interaction with cytochrome c

Through electrostatic layer-by-layer (LbL) assembly, negatively charged calf thymus double stranded DNA (CTds-DNA), and positively charged Zr4+ ions were alternately deposited on gold substrate modified with chemisorbed cysteamine. Thus-prepared three-dimensional DNA networks were characterized by surface plasmon resonance (SPR) spectroscopy, X-ray photoelectron spectroscopy (XPS) and infrared reflection-absorption spectroscopy (IR-RAS). SPR spectroscopy indicates that the effective thickness of DNA monolayer in the (DNA/Zr4+), bilayer was 1.5 +/- 0.1 nm, which corresponds to the surface coverage of 79% of its full packed monolayer. At the same time, a linear increase of film thickness with increasing number of layers was also confirmed by SPR characterizations. The data of XPS and IR-RAS show that Zr4+ ions interact with both the phosphate groups and nitrogenous bases of DNA and load into the framework of DNA. Furthermore, the interactions between this composite film and heme protein cytochrome c (Cyt c) were investigated by SPR spectroscopy and electrochemistry.

Surface plasmon resonance and electrochemistry characterization of layer-by-layer self-assembled DNA and Zr4+ thin films, and their interaction with cytochrome c

Through electrostatic layer-by-layer (LbL) assembly, negatively charged calf thymus double stranded DNA (CTds-DNA), and positively charged Zr4+ ions were alternately deposited on gold substrate modified with chemisorbed cysteamine. Thus-prepared three-dimensional DNA networks were characterized by surface plasmon resonance (SPR) spectroscopy, X-ray photoelectron spectroscopy (XPS) and infrared reflection-absorption spectroscopy (IR-RAS). SPR spectroscopy indicates that the effective thickness of DNA monolayer in the (DNA/Zr4+), bilayer was 1.5 +/- 0.1 nm, which corresponds to the surface coverage of 79% of its full packed monolayer. At the same time, a linear increase of film thickness with increasing number of layers was also confirmed by SPR characterizations. The data of XPS and IR-RAS show that Zr4+ ions interact with both the phosphate groups and nitrogenous bases of DNA and load into the framework of DNA. Furthermore, the interactions between this composite film and heme protein cytochrome c (Cyt c) were investigated by SPR spectroscopy and electrochemistry. Compared with the adsorption of Cyt c on DNA monolayer, this composite multilayer film can obviously enhance the amount of immobilized Cyt c confirmed by SPR reflectivity-incident angle (R-theta) curves.