Cationic Dye Modified Sawdust as Electrode Modifier for Electrochemical Detection of Anions

Because of its chemical properties, sawdust displays poor anionic exchange capacity. Here we demonstrate that sawdust modification with methylene blue (MB) dye represents an interesting and facile alternative to render this natural biomaterial capable to accumulate anionic species. MB adsorption onto sawdust was monitored by cyclic voltammetry and experimental parameters carefully optimized. Under the ideal experimental conditions (composition of accumulation and desorption solution, accumulation and desorption time and the nature of the electrolytic solution), the adsorbed MB showed poor mobility, which results in the absence of the characteristic electrochemical signal of MB. The ability of the material to accumulate anionic species was thus evaluated using Fe(CN)₆^3? as a model anions. The slow Fe(CN)₆^3?/4? system recorded onto the electrode modified by pristine sawdust (P/SFE) become fast and reversible after immobilization of MB onto P/SFE (MB/SFE). Electrochemical impedance spectroscopy confirms this result through the spectacular decrease of charge transfer resistance after MB adsorption (from 83 kΩ on P/SFE to 637 Ω on MB/SFE). MB/SFE was applied to the electroanalysis of nitrites and a sensitivity of 7.4 μA mM^?1 was obtained. Although this sensitivity was less important compared to that obtained on glassy carbon electrode (9.4 μA mM^?1), the dye modified electrode displays by far the best reproducibility even at higher nitrite concentration.     

High-sensitivity miniaturized immunoassays for tumor necrosis factor alpha using microfluidic systems

We use microfluidic chips to detect the biologically important cytokine tumor necrosis factor alpha (TNF- alpha) with picomolar sensitivity using sub-microliter volumes of samples and reagents. The chips comprise a number of independent capillary systems (CSs), each of which is composed of a filling port, an appended microchannel, and a capillary pump. Each CS fills spontaneously by capillary forces and includes a self-regulating mechanism that prevents adventitious drainage of the microchannels. Thus, interactive control of the flow in each CS is easily achieved via collective control of the evaporation in all CSs by means of two Peltier elements that can independently heat and cool. Long incubation times are crucial for high sensitivity assays and can be conveniently obtained by adjusting the evaporation rate to have low flow rates of approximately 30 nL min(-1). The assay is a sandwich fluorescence immunoassay and takes place on the surface of a poly(dimethylsiloxane)(PDMS) slab placed across the microchannels. We precoat PDMS with capture antibodies (Abs), localize the capture of analyte molecules using a chip, then bind the captured analyte molecules with fluorescently-tagged detection Abs using a second chip. The assay results in a mosaic of fluorescence signals on the PDMS surface which are measured using a fluorescence scanner. We show that PDMS is a compatible material for high sensitivity fluorescence assays, provided that detection antibodies with long excitation wavelength fluorophores ( > or =580 nm) are employed. The chip design, long incubation times, proper choice of fluorophores, and optimization of the detection Ab concentration all combine to achieve high-sensitivity assays. This is exemplified by an experiment with 170 assay sites, occupying an area of approximately 0.6 mm(2) on PDMS to detect TNF-alpha in 600 nL of a dendritic cell (DC) culture medium with a sensitivity of approximately 20 pg mL(-1)(1.14 pM).     

Catechol-Coordinated Framework Film-based Micro-Supercapacitors with AC Line Filtering Performance

Coordination polymer frameworks (CPFs) have broad applications due to their excellent features, including stable structure, intrinsic porosity, and others. However, preparation of thin-film CPFs for energy storage and conversion remains a challenge because of poor compatibility between conductive substrates and CPFs and crucial conditions for thin-film preparation. In this work, a CPF film was prepared by the coordination of the anisotropic four-armed ligand and Cu^II at the liquid–liquid interface. Such film-based micro-supercapacitors (MSCs) are fabricated through high-energy scribing and electrolytes soaking. As-fabricated MSCs displayed high volumetric specific capacitance of 121.45 F cm⁻³. Besides, the volumetric energy density of MSCs reached 52.6 mWh cm⁻³, which exceeds the electrochemical performance of most reported CPF-based MSCs. Especially, the device exhibited alternating current (AC) line filtering performance (−84.2° at 120 Hz) and a short resistance capacitance (RC) constant of 0.08 ms. This work not only provides a new CPF for MSCs with AC line filtering performance but also paves the way for thin-film CPFs preparation with versatile applications.     

Molecular control of macroscopic cubic, columnar, and lamellar organizations in luminescent lanthanide-containing thermotropic liquid crystals

The connection of lipophilic gallic acid derivatives at the 5,5'- or 6,6'-positions of the rigid 2,6-bis(1-ethyl-benzimidazol-2-yl)pyridine core provides two pro-mesogenic tridentate ligands L10 and L12, whose molecular shapes, anisometries, and directional intermolecular pi-stacking can be tuned. X-ray diffraction data in the crystalline state, combined with solution 1H NMR measurements, show that complexation with trivalent lanthanides, Ln(III), produces the neutral hemi-disklike complexes [Ln(Li)(NO3)3] (i = 10, 12), which dimerize to give the rodlike bimetallic complexes [Ln2(Li)2(NO3)6] at lower temperature. The relevant thermodynamic parameters for the latter process depend on the nature of the ligand, the size of the metal ion, and the strength of the intermolecular interactions involved in the condensed phase. These three-dimensional models obtained for the complexes in the crystals and in solution are eventually confronted with small-angle XRD profiles recorded in the intermediate thermotropic liquid crystalline phase, in which the rigidity of the packed polyaromatic cores is maintained, while the alkyl chains are molten. According to the specific geometries and nuclearities of the molecular complexes, three types of mesophases (lamellar, columnar, and cubic) can be induced, which provides a direct correlation between the microscopic arrangements and the macroscopic ordering in lanthanide-containing metallomesogens.     

The combination of liquid chromatography/tandem mass spectrometry and chip-based infusion for improved screening and characterization of drug metabolites

An approach has been developed for drug metabolism studies of non-radiolabeled compounds using on-line liquid chromatography/tandem mass spectrometry (LC/MS/MS) combined with chip-based infusion following fraction collection. The potential of this approach, which improves the data quality compared with only LC/MS analysis, has been investigated for the analysis of in vitro metabolites of tolcapone and talinolol, two compounds with well-characterized metabolism. The information-dependent LC/MS/MS analysis enables the characterization of the major metabolites while the chip-based infusion is used to obtain good product ion spectra for lower level metabolites, to generate complementary MS information on potential metabolites detected in the LC/MS trace, or to screen for unexpected metabolites. Fractions from the chromatographic analysis are collected in 20 second steps, into a 96-well plate. The fractions of interest can be re-analyzed with chip-based infusion on a variety of mass spectrometers including triple quadrupole linear ion trap (QqLIT or Q TRAP) and QqTOF systems. Acquiring data for several minutes using multi-channel acquisition (MCA), or signal averaging while infusing the fractions at approximately 200 nL/min, permits about a 50 times gain in sensitivity (signal-to-noise) in MS/MS mode. A 5-10 microL sample fraction can be infused for more than 30 min allowing the time to perform various MS experiments such as MS(n), precursor ion or neutral loss scans and accurate mass measurement, all in either positive or negative mode. Through fraction collection and infusion, a significant gain in data quality is obtained along with a time-saving benefit, because the original sample needs neither to be re-analyzed by re-injection nor to be pre-concentrated. Therefore, a novel hydroxylated talinolol metabolite could be characterized with only one injection.     

Synthesis and reactions of N-heterocyclic carbene boranes

Boranes are widely used Lewis acids and N-heterocyclic carbenes (NHCs) are popular Lewis bases, so it is remarkable how little was known about their derived complexes until recently. NHC-boranes are typically readily accessible and many are so stable that they can be treated like organic compounds rather than complexes. They do not exhibit "borane chemistry", but instead are proving to have a rich chemistry of their own as reactants, as reagents, as initiators, and as catalysts. They have significant potential for use in organic synthesis and in polymer chemistry. They can be used to easily make unusual complexes with a broad spectrum of functional groups not usually seen in organoboron chemistry. Many of their reactions occur through new classes of reactive intermediates including borenium cations, boryl radicals, and even boryl anions. This Review provides comprehensive coverage of the synthesis, characterization, and reactions of NHC-boranes.     

Capillary soft valves for microfluidics

Capillary-driven microfluidics are simple to use and provide the opportunity to perform fast biological assays with nanogram quantities of reagents and microliters of sample. Here we describe capillary soft valves (CSVs) as a simple-to-implement and -actuate approach for stopping liquids in capillary-driven microfluidics. CSVs are inserted between wettable microstructures and work to block liquids owing to a capillary pressure barrier of a few kPa. This barrier is suppressed by pressing down the soft cover of the CSV using, for example, the tip of a pen. CSVs comprise a hard layer (in silicon or polymer) with wettable microstructures and a soft cover made of poly(dimethylsiloxane) (PDMS) here. CSVs have a footprint as small as 0.6 mm(2). We illustrate how these valves work in the context of detecting DNA analytes. Specifically, a dsDNA target (997 bp PCR product, non-purified) was detected at concentrations of 20 and 200 nM in a sample volume of 0.7 μL and within 10 min. The assay includes melting of the dsDNA at 95 °C, annealing of a 30-base biotinylated probe at 50 °C, and intercalation of a fluorescent dye into the re-hybridized dsDNA at 25 °C. Actuation of the CSV allows the DNA target-probe-dye complexes to flow over 100 μm wide, streptavidin receptor lines. This work suggests that CSVs can fulfil the requirements set by complex assays, in which elevated temperatures and reaction with probes, dyes and capture species are needed. CSVs therefore greatly complement capillary-driven microfluidics without adding significant design, fabrication and actuation issues.     

Synthesis of azide‐functionalized nanoparticles by microemulsion polymerization and surface modification by click chemistry in aqueous medium

Stable translucent aqueous suspensions of azide‐functionalized cross‐linked nanoparticles (NPs), with diameters in the 15–20 nm range, were prepared using two synthetic approaches. Copolymerization of azidomethylstyrene (VBN₃), styrene, and divinylbenzene in various oil‐in‐water microemulsions led to NPs with modulable azide contents (0.53–0.78 mmol/g) and surface over volume distributions. Surface modifications of reactive NPs bearing chlorobenzyl groups, produced by microemulsion copolymerization of vinylbenzylchloride, with sodium azide led to azido‐coated NPs with high densities of peripheral groups (0.13–0.45 mmol/g). It is shown that the nature of the surfactant used for the preparation of the microemulsion has an impact on the incorporation of VBN₃ in the polymer particles as well as on the surface reaction yield. The azide‐functionalized NPs were used as clickable polymeric scaffolds for the grafting of sparingly water‐soluble dansyl and fluorescein derivatives through copper(I)‐catalyzed azide‐alkyne cycloaddition in water in the presence of surfactants as solubilizing agents to produce fluorescent NPs. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Random End‐Switching Configurational Bias Monte Carlo for Long Chain Molecules

Summary: The exponential attrition of configurational bias Monte Carlo for long chains can be reduced to almost quadratic by a simple modification of the basic move. Each trial move begins on the side of the remaining sub chain opposite to the cut location. This type of move is akin to large‐scale reptation and in the limit of one‐segment cut is reptation. The extension is shown to require the same Rosenbluth weighting scheme as the original algorithm. Several examples are used to demonstrate the reliability and the improved performance of the proposed method.

     

A Versatile Iron‐Catalyzed Protocol for the One‐Pot Synthesis of Isoxazoles or Isoxazolines from the Same Propargylic Alcohols

The use N‐sulfonyl‐protected hydroxylamines as bi‐nucleophiles in iron‐catalyzed propargylic substitutions allows the selective one‐pot synthesis of four classes of substituted isoxazoles or isoxazolines from the same propargylic alcohols (21 examples) by simply tuning the nature of the base. By using an iron(III) catalyst and a base such as triethylamine (3 equiv), isoxazoles 3 are obtained in good isolated yields (56–95%), whereas N‐sulfonyl‐protected isoxazolines 6 are selectively obtained (77–93% yield) by using iron and gold catalysts in the presence of a catalytic amount of pyridine (10 mol%).