Silica-supported 1,3-dichloro-5,5-dimethylhydantoin(DCH) as a useful reagent for microwave-assisted aromatization of 1,3,5-trisubstituted pyrazolines under solvent-free conditions

1,3,5-Trisubstituted pyrazolines are rapidly and conveniently oxidized to their corresponding pyrazoles by 1,3-dichloro-5,5- dimethylhydantoin(DCH) in solution and solvent-free conditions under microwave irradiation.The presence of silica gel as a supporting agent is shown to be effective in reducing the reaction times and increasing the yields.     

Fe3O4@silica‐MCM‐41@DABCO: A novel magnetically reusable nanostructured catalyst for clean in situ synthesis of substituted 2‐aminodihydropyrano[3,2‐b]pyran‐3‐cyano

DABCO (1,4‐diazabicyclo[2.2.2]octane)‐modified magnetite with silica‐MCM‐41 shell (Fe₃O₄@silica‐MCM‐41@DABCO) as an effective, magnetic and novel heterogeneous reusable nanocatalyst was synthesized and analysed using various techniques. Evaluation of the catalytic activity of this nanocatalyst was performed in the clean synthesis of substituted 2‐aminodihydropyrano[3,2‐b]pyran‐3‐cyano in high yields via in situ reaction of azido kojic acid, malononitrile and various aldehydes.     

Ultrasound-assisted temperature-controlled ionic-liquid dispersive liquid-phase microextraction method for simultaneous determination of anethole,estragole, and para-anisaldehyde in different plant extracts and human urine: a comparative study

In this study, the performances of four ionic-liquid-based microextraction methods, ionic-liquid-based dispersive liquid–liquid microextraction (IL-DLLME), ionic-liquid-based ultrasound-assisted emulsification microextraction (IL-USA-ME), temperature-controlled ionic-liquid dispersive liquid-phase microextraction (TC-IL-DLME), and ultrasound-assisted temperature-controlled ionic-liquid dispersive liquid-phase microextraction (USA-TC-IL-DLME), were investigated for extraction of three bioactive compounds (anethole, estragole, and anisaldehyde) from different plant extracts and human urine. Anethole and estragole were chosen because they can alter cellular processes positively or negatively, and an efficient method is needed for their extraction and sensitive determination in the samples mentioned. Because there is no previous report on the separation of anethole and estragole (structural isomers), first, simultaneous gradient elution and flow programming were used. The microextraction methods were then applied and compared for analysis of these compounds in plant extracts and human urine by use of high-performance liquid chromatography (HPLC). The effect of conditions on extraction efficiency was studied and under the optimum conditions, the best enrichment factors (58–64), limits of detection (14–18 ng mL^?1), limits of quantification (47–60 ng mL^?1), and recovery (94.4–101.7 %) were obtained by use of USA-TC-IL-DLME. The optimized conditions were used to determine anethole, estragole, and para-anisaldehyde in fennel, anise, and tarragon extracts and in human urine.     

A fully discrete Galerkin method for Abel-type integral equations

In this paper, we present a Galerkin method for Abel-type integral equation with a general class of kernel. Stability and quasi-optimal convergence estimates are derived in fractional-order Sobolev norms. The fully-discrete Galerkin method is defined by employing simple tensor-Gauss quadrature. We develop a corresponding perturbation analysis which allows to keep the number of quadrature points small. Numerical experiments have been performed which illustrate the sharpness of the theoretical estimates and the sensitivity of the solution with respect to some parameters in the equation.     

Novel nanocomposite membranes based on polybenzimidazole and Fe<Subscript>2</Subscript>TiO<Subscript>5</Subscript> nanoparticles for proton exchange membrane fuel cells

In this work, Fe₂TiO₅ nanoparticles were used for improving the proton conductivity, and water and acid uptake of polybenzimidazole (PBI)-based proton exchange membranes. The nanocomposite membranes have been prepared using different amounts of Fe₂TiO₅ nanoparticles and dispersed into a PBI membrane with the solution-casting method. The prepared membranes were then physico-chemically and electrochemically characterized for use as electrolytes in high-temperature PEMFCs. The PBI/Fe₂TiO₅ membranes (PFT) showed a higher acid uptake and proton conductivity compared with the pure PBI membranes. The highest acid uptake (156 %) and proton conductivity (78 mS/cm at 180 °C) were observed for the PBI nanocomposite membranes containing 4 wt% of Fe₂TiO₅ nanoparticles (PFT₄). The PFT₄ composite membrane showed 380 mW/cm² power density and 760 mA/cm² current density in 0.5 V at 180 °C at dry condition. The above results indicated that the PFT₄ nanocomposite membranes could be utilized as proton exchange membranes for high-temperature fuel cells.     

Influence of dose on particle size of colloidal silver nanoparticles synthesized by gamma radiation

Colloidal silver nanoparticles were synthesized by γ-irradiation-induced reduction method of an aqueous solution containing silver nitrate as a precursor in various concentrations between 7.40×10^?4 and 1.84×10^?3 M, polyvinyl pyrrolidone for capping colloidal nanoparticles, isopropanol as radical scavenger of hydroxyl radicals and deionised water as a solvent. The irradiations were carried out in a ⁶⁰Co γ source chamber at doses up to 70 kGy. The optical absorption spectra were measured using UV–vis spectrophotometer and used to study the particle distribution and electronic structure of silver nanoparticles. As the radiation dose increases from 10 to 70 kGy, the absorption intensity increases with increasing dose. The absorption peak λ_max blue shifted from 410 to 403 nm correspond to the increase of absorption conduction electron energy from 3.02 to 3.08 eV, indicating the particle size decreases with increasing dose. The particle size was determined by photon cross correlation spectroscopy and the results showed that the particle diameter decreases exponentially with the increase of dose. The transmission electron microscopy images were taken at doses of 20 and 60 kGy and the results confirmed that as the dose increases the diameter of colloidal silver nanoparticle decreases and the particle distribution increases.     

Electrogenerated base-promoted synthesis of tetrahydrobenzo[b]pyran derivatives

An efficient and convenient synthesis of tetrahydrobenzo[b]pyrans is described, using an electrogenerated base of the anion of malononitrile in a one-pot, three component condensation of an aromatic aldehyde, an active methylene compound and dimedone. The reaction is carried out at room temperature in acetonitrile with the use of a sacrificial magnesium anode in a single-compartment cell.     

A Straightforward Method for the Synthesis of Functionalized Trisubstituted Alkenes through Na2S/Al2O3 Catalyzed Knoevenagel Condensation

Na₂S/Al₂O₃ catalyzed the Knoevenagel condensation between an aldehyde and an active methylene compound to yield various trisubstituted alkenes.     

Direct analysis of air filter samples for alpha-emitting isotopes

The traditional method for determination, of alpha-emitting isotopes on air filters has been to process the samples by radiochemical methods. However, this method is too slow for incidents involving radioactive materials where the determination of personnel dose is urgent. A method is developed to directly analyze the air filters taken from personal and area air monitors. The site knowledge is used in combination with alpha-spectral information to identify isotopes. A mathematical function is developed to estimate the activity for each isotope. The strengths and weaknesses of the method are discussed.