Polyaniline-Supported Zinc Oxide (ZnO) Nanoparticles: An Active and Stable Heterogeneous Catalyst for the Friedel–Crafts Acylation Reaction

We report herein the synthesis of zinc oxide (ZnO) nanoparticles incorporating a polyaniline (PANI) matrix in aqueous medium and its catalytic performance toward Friedel–Crafts acylation reactions. The acylation reactions demonstrate that polyaniline/nano-ZnO composites are very active catalysts and are able to activate the reactant at ambient temperature. The obtained nanocatalyst was characterized by Fourier transform–infrared, scanning electron microscopy, transmission electron microscopy, Brunauer–Emmett–Teller, X-ray diffraction, and particle-size analysis techniques. The catalyst was reusable for five cycles without appreciable loss in activity.     

Highly sensitive methanol chemical sensor based on undoped silver oxide nanoparticles prepared by a solution method

We have prepared silver oxide nanoparticles (NPs) by a simple solution method using reducing agents in alkaline medium. The resulting NPs were characterized by UV–vis and FT-IR spectroscopy, X-ray powder diffraction, and field-emission scanning electron microscopy. They were deposited on a glassy carbon electrode to give a sensor with a fast response towards methanol in liquid phase. The sensor also displays good sensitivity and long-term stability, and enhanced electrochemical response. The calibration plot is linear (r ²?=?0.8294) over the 0.12?mM to 0.12?M methanol concentration range. The sensitivity is ~2.65?μAcm^?2?mM^?1, and the detection limit is 36.0?μM (at a SNR of 3). We also discuss possible future prospective uses of this metal oxide semiconductor nanomaterial in terms of chemical sensing.

Simultaneous determination of five commercial cationic dyes in stream waters using diatomite solid-phase extractant and multivariate calibration

A simple spectrophotometric method was developed for the simultaneous determination of five commercial cationic dyes at 2.0?8.5 μg L^?1 level after using diatomite as solid-phase extractant. The method is based on preconcentration of the five dyes on natural diatomite solid-phase extractant and on multivariate calibration using partial least squares method (PLS-1). Compared with commonly used chromatographic or electrophoretic methods the developed method is simple and sensitive. With enrichment factors between 89 and 96, diatomite outperformed zeolite and activated carbon for dyes preconcentration. Before preconcentration and using PLS-1 method, the cationic dyes were simultaneously analyzed with linear ranges of 0.18–4.5, 0.32–5.0, 0.23–4.5, 0.45–8.0 and 0.82–12.0 mg L^?1 for crystal violet, malachite green, methylene blue, safranine O, and thioflavin T, respectively. The detection limits of dyes were estimated using Lorber’s method and found to be within the range 43–245 μg L^?1. The proposed SPE/PLS-1 method was applied to spiked stream water samples with good accuracy (79–91%) and precision (RSD 1.8–7.3%) but with slightly lower enrichment factors (80–92).     

Density functional study on the functionalization of BN nanotubes with nitramide

Chemical functionalization of a boron nitride nanotube (BNNT) with nitramide molecule (H₂NNO₂) has been investigated using density functional theory. It was found that the molecule prefers to be adsorbed and dissociated on a diagonal B-N bond of the tube surface so that the -NH₂ and -NO₂ groups are attached on B and N atoms, releasing energy of 0.50 eV. The results show that the functionalized BNNT is more soluble than the pristine one which may render the chemical modification process to be an effective way for purification of the BNNTs. Depending on the cleavage behavior of nitramide on the tube, HOMO/LUMO gap of the system can be either decreased or increased while the chemically modified BNNT is still a semiconductor. Furthermore, the chemical functionalization results in hindered field emission in the tube by raising the potential barrier of the electron emission.     

Pt(II)-promoted [2 + 3] cycloaddition of azide to cyanopyridines: convenient tool toward heterometallic structures

The [2 + 3] cycloaddition reactions (which are greatly accelerated by microwave irradiation) of the di(azido)platinum(II) compounds cis-[Pt(N(3))(2)(PPh(3))(2)] (1) with cyanopyridines NCR (2) (R = 4-, 3-, and 2-NC(5)H(4)) give the corresponding bis(pyridyltetrazolato) complexes trans-[Pt(N(4)CR)(2)(PPh(3))(2)] (3) [R = 4-NC(5)H(4) (3a), 3-NC(5)H(4) (3b), and 2-NC(5)H(4) (3c)]. Compound 3c has been characterized as the N(1)N(2)-bonded isomer in the solid state by X-ray crystallography and represents the first bis(tetrazolato) complex of this kind. Complexes 3a and 3b have been used as metallaligands to generate heteronuclear coordination polymers in the presence of copper nitrate. A one-dimensional supramolecular architecture was obtained as the exclusive product, {trans-[Pt(2)(N(4)CR)(4)(PPh(3))(4)Cu](n)(NO(3))(2n).nH(2)O (4.nH(2)O) (R = 4-NC(5)H(4)), when 3a was employed, whereas with 3b the heteronuclear square complex trans-[Pt(N(4)CR)(2)(PPh(3))(2)Cu(NO(3))(2)(H(2)O)](2) (5) (R = 3-NC(5)H(4)), composed of Pt/Cu ions, was obtained. All the isolated complexes were characterized by IR, elemental, and (for 3b, 3c, 4, and 5) X-ray structural analyses. Complexes 3 were additionally characterized by (1)H, (13)C, and (31)P {(1)H} NMR spectroscopies.     

The suppression of selected acoustic frequencies in MRI

A study is made of certain dominant frequencies in the acoustic noise spectrum of the magnetic resonance imaging system. Motivated by both spring and string ideas, we investigate whether the contributions to the sound from certain frequencies can be canceled by the appropriate gradient pulse sequence design. From both simulations and experiments, vibrations resulting from an impulsive force associated with a ramping up of a gradient pulse are shown to be cancelled immediately upon the application of another impulsive force coming from the subsequent appropriately timed ramping down of that pulse. A general approach to suppression of multiple-frequency contributions involving a series of gradient pulses with variable timings is given for the cancellations between pairs of impulsive forces. Various examples are confirmed through string simulations, MRI experiments, and linear response theory. This also provides a foundation to explain some results in previous papers on this subject. The method suggests that a variety of pulse profiles and timing combinations can be used to attenuate important contributions to the acoustic spectrum.     

Bioactivities and structural studies of withanolides fromWithania somnifera

Four bioactive withanolides withalactone (1), withaoxylactone (2), quresimine-A (4-hydroxy, 3-methoxy-5, 6-epoxy-(22R)-witha-24-enolide) (3) and quresindne-B (4, 27 dihydroxy-3-methoxy-5, 6-epoxy-(22R)-witha-24-enolide (4) have been isolated from the herbs of Withania somnifera, Dunal (Solanaceae). The elucidation of their structures is based on extensive spectroscopic studies, such as¹H-NMR, COSY-45°, HMBC, HMQC HOHAHA, E.I., FAB (+ ve), and HR MS, etc.Published in Khimiya Geterotsiklicheskikh Soedinenii, No. 9, pp. 1200–1213, September, 1995.     

Effect of molecular binding to a semiconductor on metal/molecule/semiconductor junction behavior

Diodes made by (indirectly) evaporating Au on a monolayer of molecules that are adsorbed chemically onto GaAs, via either disulfide or dicarboxylate groups, show roughly linear but opposite dependence of their effective barrier height on the dipole moment of the molecules. We explain this by Au-molecule (electrical) interactions not only with the exposed end groups of the molecule but also with its binding groups. We arrive at this conclusion by characterizing the interface by in situ UPS-XPS, ex situ XPS, TOF-SIMS, and Kelvin probe measurements, by scanning microscopy of the surfaces, and by current-voltage measurements of the devices. While there is a very limited interaction of Au with the dicarboxylic binding groups, there is a much stronger interaction with the disulfide groups. We suggest that these very different interactions lead to different (growth) morphologies of the evaporated gold layer, resulting in opposite effects of the molecular dipole on the junction barrier height.     

Cytotoxic effect and electrophysiological study on human MRC-5 fibroblasts of R-irniine, a natural alkylpyrrolidine alkaloid

R-irniine is a natural 2-alkylpyrrolidine alkaloid extracted from Arisarum vulgare Targ., a species belonging to the Araceae family known in Morocco for its toxicity. Cytotoxic and electrophysiological studies of this compound on human MRC-5 fibroblasts were carried out. Cytotoxic potential of R-irniine was detected on MRC-5 fibroblasts at 40 microg/mL. We carried out the electrophysiological study of this compound on MRC-5 cells by using the technique of patch-clamp in "Whole cell" configuration. R-irniine showed no effect on the outward potassium current of the MRC-5 fibroblasts.