Coverage effects on the adsorption of sulfur on Co(0 0 0 1): A DFT study

The adsorption of sulfur on Co(0 0 0 1) was studied using density functional theory calculations at coverage from 0.11 ML to 1.0 ML. Calculated results indicate that atomic S favors in hollow sites with bond S–Co dominated at lower coverage and at higher coverage the strong adsorbate S–S interaction leads to the formation of S₂ species. It was shown that the adsorption energy generally increases (gets weaker) with the coverage in a near linear fashion for the most stable configurations. In addition, modification of the surface electronic properties has been discussed and some discrepancy are found between our calculations and the findings of O adsorption on Au(1 1 1) and Pt(1 1 1) surfaces.     

Direct Electrochemistry of Myoglobin in a Nafion‐Ionic Liquid Composite Film Modified Carbon Ionic Liquid Electrode

In this paper two kinds of ionic liquids (ILs) were used for the construction of a myoglobin (Mb) electrochemical biosensor. Firstly a hydrophilic ionic liquid of 1‐ethyl‐3‐methylimidazolium tetrafluoroborate (EMIMBF₄) was used as binder to prepare a carbon ionic liquid electrode (CILE), then a Nafion and hydrophobic ionic liquid of 1‐butyl‐3‐methylimidazolium hexafluorophosphate (BMIMPF₆) composite film was applied on the surface of the CILE. The direct electrochemistry of Mb in the Nafion‐BMIMPF₆/CILE was achieved with the cathodic and anodic peak potentials located at ?0.345 V and ?0.213 V (vs. SCE). The formal potential (E°′) was located at ?0.279 V, which was the characteristic of Mb Fe^III/Fe^II redox couples. The electrochemical behaviors of Mb in the Nafion‐ionic liquid composite film modified CILE were carefully investigated. The Mb modified electrode showed good electrocatalytic behaviors to the reduction of trichloroacetic acid (TCA) and NaNO₂. Based on the Nafion‐BMIMPF₆/Mb/CILE, a new third generation reagentless biosensor was constructed.     

A Novel Hydrogen Peroxide Biosensor Based on the Synergistic Effect of Gold‐Platinum Alloy Nanoparticles/Polyaniline Nanotube/Chitosan Nanocomposite Membrane

Based on the immobilization of horseradish peroxidase (HRP) in chitosan(CS) on a glassy carbon electrode (GCE) modified with the Au‐Pt alloy nanoparticles (NPs) / polyaniline nanotube (nanoPAN) nanocomposite film, a novel hydrogen peroxide biosensor was constructed. The modified processes of GCE were monitored by cyclic voltammetry and electrochemical impedance spectroscopy. Au‐PtNPs/nanoPAN/CS had a better synergistic electrochemical effect than did AuNPs/nanoPAN/CS or PtNPs/nanoPAN/CS. The amperometric response of the biosensor towards H₂O₂ was investigated by successively adding aliquots of H₂O₂ to a continuous stirring phosphate buffer solution under the optimized conditions. Because Au‐PtNPs have unique catalytic properties and good biocompatibility, and especially Au‐PtNPs and nanoPAN have synergistic augmentation for facilitating electron‐transfer, the biosensor displayed a fast response time (<2 s) and broad linear response to H₂O₂ in the range from 1.0 to 2200 μmol L^?1 with a relatively low detection limit of 0.5 μmol L^?1 at 3 times the background noise. Moreover, the biosensor can be applied in practical analysis and exhibited high sensitivity, good reproducibility, and long‐term stability.     

Improvement of electrochemical properties of LiFePO4/C cathode materials by chlorine doping

The olivine-type cathode materials of LiFePO₄ were prepared via solid-state reaction under argon atmosphere and doped by chlorine to improve their electrochemical performances. The crystal structure, morphology, and electrochemical properties of the prepared samples were investigated using thermogravimetry–differential scanning calorimetry, X-ray diffraction, Fourier transform infrared, scanning electron microscopy, cyclic voltammetry, and charge–discharge cycle measurements. The result showed that the electrochemical performance of LiFePO₄ had been improved by chlorine doping, and the effect of chlorine in lattice was discussed. The heavily doped samples show better electrochemical performance in relative high rates.     

Highly Sensitive Determination of microRNA Using Target‐Primed and Branched Rolling‐Circle Amplification

One‐nucleotide differences in microRNAs (miRNAs) can be discriminated in an assay based on a branched rolling‐circle amplification (BRCA) reaction and fluorescence quantification. With the proposed method miRNA can be detected at concentrations as low as 10 fM , and the miRNA in a total RNA sample of a few nanograms can be determined.

     

Absolute configuration of new cytotoxic and other bioactive trichothecene macrolides

Three new cytotoxic 10,13-cyclotrichothecane-derived macrolides, myrothecines A-C (1-3), were characterized from the extracts of two Myrothecium roridum strains, IFB-E009 and IFB-E012, isolated as endophytic fungi found on the traditional Chinese medicinal plants Trachelospermum jasminoides and Artemisia annua, respectively. The absolute configuration of myrothecines A-C was elucidated by a combination of spectral techniques (UV, IR, MS, circular dichroism (CD), (1)H and (13)C NMR, DEPT, (1)H-(1)H COSY, NOESY, HMQC, and HMBC spectrascopic analyses), Mosher's ester analysis, and single-crystal X-ray diffraction. The absolute configuration of the reported bioactive analogue, mytoxin B was established by correlating its spectral data with that of known absolute configurational structures. Furthermore, the significance in endophytism (or symbiosis) and biocatabolism, highlighted by production of those macrolides by the endophytic strains, is discussed in brief.     

Syntheses, photophysical properties, and application of through-bond energy-transfer cassettes for biotechnology

We have designed fluorescent "through-bond energy-transfer cassettes" that can harvest energy of a relatively short wavelength (e.g., 490 nm), and emit it at appreciably longer wavelengths without significant loss of intensity. Probes of this type could be particularly useful in biotechnology for multiplexing experiments in which several different outputs are to be observed from a single excitation source. Cassettes 1-4 were designed, prepared, and studied as model systems to achieve this end. They were synthesized through convergent routes that feature coupling of specially prepared fluorescein- and rhodamine-derived fragments. The four cassettes were shown to emit strongly, with highly efficient energy transfer. Their emission maxima cover a broad range of wavelengths (broader than the four dye cassettes currently used for most high-throughput DNA sequencing), and they exhibit faster energy-transfer rates than a similar through-space energy-transfer cassette. Specifically, energy-transfer rates in these cassettes is around 6-7 ps, in contrast to a similar through-space energy-transfer system shown to have a decay time of around 35 ps. Moreover, the cassettes are considerably more stable to photobleaching than fluorescein, even though they each contain fluorescein-derived donors. This was confirmed by bulk fluorescent measurements, and in single-molecule-detection studies. Modification of a commercial automated DNA-sequencing apparatus to detect the emissions of these four energy-transfer cassettes enabled single-color dye-primer sequencing.     

Fabrication, characterization, and formation mechanism of hollow spindle-like hematite via a solvothermal process

As a novel hollow nanostructure, hollow spindle-like hematite with uniform size and morphology was solvothermally synthesized. These hollow polycrystalline particles with the length of 220-300 nm, the width of 70-100 nm, and the wall thickness of ca. 18 nm were characterized by TEM, FE-SEM, XRD, FT-IR, TGA, M?ssbauer spectrum, and XPS methods. It was found that these hollow-structured particles were transformed from their original solid spindle particles. During the hollow structure formation process, the interiors of solid particles were preferentially dissolved while the retained exteriors were protected by coordinated sulfate ions. The formation mechanism was proposed as a coordination-assisted dissolution process occurred in a reverse microemulsion system.     

Benzoporphyrins via an olefin ring-closure metathesis methodology

A new route to benzoporphyrins is reported in which readily available vicinal dibromoporphyrins are bis-allylated using the Suzuki reaction, cyclized by way of olefin metathesis and finally oxidized to give mono-, di-, or tri-benzoporphyrins.     

Stepwise formation and characterization of covalently linked multiporphyrin-imide architectures on Si(100)

A major challenge in molecular electronics and related fields entails the fabrication of elaborate molecular architectures on electroactive surfaces to yield hybrid molecular/semiconductor systems. A method has been developed for the stepwise synthesis of oligomers of porphyrins linked covalently via imide units. A triallyl-porphyrin bearing an amino group serves as the base unit on Si(100), and the alternating use of a dianhydride (3,3',4,4'-biphenyltetracarboxylic dianhydride) and a porphyrin-diamine for reaction enables the rapid and simple buildup of oligomers composed of 2-5 porphyrins. The properties of these porphyrin "multad" films on Si(100) were interrogated using a variety of techniques. The charge densities of the redox-active porphyrin oligomers were determined via electrochemical methods. The stepwise growth was evaluated in detail via Fourier transform infrared (FTIR) spectroscopy and by selected X-ray photoelectron spectroscopic (XPS) studies. The morphology was probed via AFM methods. Finally, the thickness was evaluated by using a combination of ellipsometry and AFM height profiling, accompanied by selected XPS studies. Collectively, these studies demonstrate that high charge density, ultrathin, multiporphyrin films of relatively well-controlled thickness can be grown in a stepwise fashion using the imide-forming reaction. The increased charge densities afforded by the porphyrin multads may prove important for the fabrication of molecular-based information-storage devices. This bottom-up process for construction of surface-tethered molecular architectures complements the top-down lithographic approach for construction of functional devices with nanoscale dimensions.