Fast synthesis of optically active polyamides containing <Emphasis Type="SmallCaps">l</Emphasis>-methionine linkages in ionic liquid via a microwave-assisted process

Several optically active aromatic polyamides have been synthesized via direct polycondensation of chiral diacid monomer 1 containing l-methionine moiety with diverse aromatic diamines 2a–2h in a green medium, namely 1,3-dipropylimidazolium bromide as a room temperature ionic liquid. In order to evaluate the advantages of microwave promotion of these polymerization reactions, we compared microwave irradiation (method I) with conventional oil bath heating (method II) by means of reaction rates, conversions, and inherent viscosities. The inherent viscosities of resulting polymers were ranging between 0.47–0.65 and 0.35–0.57 dL/g in methods I and II, respectively. These polymers were characterized by means of ¹H-NMR, FT-IR, elemental, organosolubility, differential scanning calorimetry, and thermal gravimetric analysis techniques. The obtained polymers show thermal stability up to 273 °C under nitrogen atmosphere and good solubility in polar organic solvents. Polymerization reactions proceeded in higher yields and moderate inherent viscosities under microwave irradiation conditions besides the dramatically shorter reaction times and achieving the more pure products.     

ZnS nanoparticles incorporated in polyaniline composite: Preparation and optical characterization

Hybrid polyaniline based composites incorporating zinc sulfide nanoparticles have been synthesized by using chemical oxidation technique. Morphological and optical properties of the nanocomposite were characterized by scanning electron microscopy, Fourier transform infrared and UV–Vis spectroscopy measurement. The results were compared with pure polyaniline. The characteristic FTIR peaks of polyaniline were found to shift to lower wave-number in nanocomposite. The band gap of nanocomposites increases and the refractive index of the nanocomposites decreases with increasing content of ZnS nanoparticles. These results showed the interaction between ZnS nanoparticles and polyaniline.     

Optimization of process conditions for biodiesel production over CaO–Al<Subscript>2</Subscript>O<Subscript>3</Subscript>/ZrO<Subscript>2</Subscript> catalyst using response surface methodology

CaO–Al₂O₃/ZrO₂ mixed oxide catalyst was prepared using free-solvent method. The catalyst was characterized using X-ray diffraction, BET surface area, acidity index (obtained by titration method), and scanning electron microscopy (SEM). With calcium aluminate and calcium zirconate been successfully formed, the mix exhibited small crystal size, high acidity, and large surface area, pore size, and pore volume, making it a catalyst of choice for biodiesel production. The activity of catalyst was evaluated in the course of esterification of oleic acid as well as transesterification of waste cooking oil (WCO) into biodiesel. Based on a four-variable central composite design (CCD), response surface methodology (RSM) was used to optimize effective variables on oleic acid conversion. The optimum yield of 94.68% was obtained at the following set of optimum conditions: reaction temperature of 120 °C, methanol/oleic acid molar ratio of 15.64, catalyst concentration of 2.94 wt%, and reaction time of 4 h; the result was in excellent agreement with the predicted values. Furthermore, under the optimum conditions, the catalyst succeeded to convert 93.48% of WCO into biodiesel.     

Relationships between linear and nonlinear shear response of polymer nano-composites

Rheological analysis was used to understand the structure?Cproperty relations of polymer nano-composites based on ethylene vinyl acetate. Two geometrically different nano-particles (sphere of CaCO₃ and platelet of montmorillonite) having the same energetic attractions with ethylene vinyl acetate were studied for concentrations between 2.5 and 15 wt%. Three phenomena were studied: the appearance of a solid-like behavior in the linear viscoelastic domain, the limits of linear viscoelasticity, and the presence of stress overshoot in step shear tests. In particular, stress overshoot was investigated based on the tube concept of polymeric chains. Also, differences related to nano-particle geometry (platelet vs. spherical) were investigated based on a filler-network mechanism. Due to higher physical contacting probability, platelet particles can better interact and create a network structure, which dominates the rheological response. On the other hand, although spherical particles can limit the motion of polymeric chains under flow, a strong physical network was not formed. For platelets, scaling behavior was well described by fractal model which considers direct aggregation, and such scaling was not observed for spherical particles. The filler-network mechanism was validated by image analysis.     

Improved visibility graph fractality with application for the diagnosis of Autism Spectrum Disorder

Recently, the visibility graph (VG) algorithm was proposed for mapping a time series to a graph to study complexity and fractality of the time series through investigation of the complexity of its graph. The visibility graph algorithm converts a fractal time series to a scale-free graph. VG has been used for the investigation of fractality in the dynamic behavior of both artificial and natural complex systems. However, robustness and performance of the power of scale-freeness of VG (PSVG) as an effective method for measuring fractality has not been investigated. Since noise is unavoidable in real life time series, the robustness of a fractality measure is of paramount importance. To improve the accuracy and robustness of PSVG to noise for measurement of fractality of time series in biological time-series, an improved PSVG is presented in this paper. The proposed method is evaluated using two examples: a synthetic benchmark time series and a complicated real life Electroencephalograms (EEG)-based diagnostic problem, that is distinguishing autistic children from non-autistic children. It is shown that the proposed improved PSVG is less sensitive to noise and therefore more robust compared with PSVG. Further, it is shown that using improved PSVG in the wavelet-chaos neural network model of Adeli and c-workers in place of the Katz fractality dimension results in a more accurate diagnosis of autism, a complicated neurological and psychiatric disorder.     

Heck-type reaction of aryldiazonium silica sulfates

Abstract  

Aryldiazonium silica sulfates were employed as new and efficient reagents for Heck-type arylation reactions with styrene and methyl acrylate. The reactions were carried out in an organic solvent, in the presence of Pd(OAc)₂ as precatalyst without use of base and free ligand. The trans isomers of desired products, methyl cinnamates and stilbenes, were obtained with full conversion. Use of a catalytic amount of Pd(OAc)₂ produced the corresponding products in short reaction times and excellent yields.     

Polysulfone/pyrene membranes: a new microwell assay platform for bioapplications

The use of PSU‐Py prepared by click chemistry as a platform in membrane‐bottom microwell plates for oxidase and hydrolase/oxidase‐based enzyme assays is studied. For the GOx assay, the postulated fluorescence mechanism is based on the consumption of glucose by dissolved oxygen and GOx in the microwell plates covered with the PSU‐Py membrane. For the AG‐GOx assay, maltose is used as AG substrate and hydrolyzed to glucose which is then oxidized by the GOx activity. It is shown that the PSU‐Py membrane acts as a fluorescence indicator of the enzymatic reactions, and both GOx and AG/GOx enzyme assays are successfully applied for glucose, maltose and acorbose analysis in the range 0.125–2.0 × 10^?3 M glucose, 0.05–0.5 × 10^?3 M maltose, and 0.0125–0.1 mg · mL^?1 acorbose, respectively.

     

Laminar convective heat transfer of non-Newtonian nanofluids with constant wall temperature

Nanofluids are obtained by dispersing homogeneously nanoparticles into a base fluid. Nanofluids often exhibit higher heat transfer rate in comparison with the base fluid. In the present study, forced convection heat transfer under laminar flow conditions was investigated experimentally for three types of non-Newtonian nanofluids in a circular tube with constant wall temperature. CMC solution was used as the base fluid and γ-Al₂O₃, TiO₂ and CuO nanoparticles were homogeneously dispersed to create nanodispersions of different concentrations. Nanofluids as well as the base fluid show shear thinning (pseudoplastic) rheological behavior. Results show that the presence of nanoparticles increases the convective heat transfer of the nanodispersions in comparison with the base fluid. The convective heat transfer enhancement is more significant when both the Peclet number and the nanoparticle concentration are increased. The increase in convective heat transfer is higher than the increase caused by the augmentation of the effective thermal conductivity.     

Trace Level Determination of Hydrogen Peroxide at a Carbon Ceramic Electrode Modified with Copper Oxide Nanostructures

An electrochemical sensor was developed for determination of hydrogen peroxide based on nanocopper oxides modified carbon sol‐gel or carbon ceramic electrode (CCE). The modified electrode was prepared by electrodeposition of metallic copper on the CCE surface and derivatized in situ to copper oxides nanostructures and characterized by scanning electron microscopy (SEM) and X‐ray diffraction (XRD) techniques. The modified electrode responded linearly to the hydrogen peroxide (H₂O₂) concentration over the range 0.78–193.98 µmol L^?1 with a detection limit of 71 nmol L^?1 (S/N=3) and the sensitivity of 0.697 A mol^?1 L cm^?2. This electrode was used as selective amperometric sensor for determination of H₂O₂ contents in hair coloring creams.     

Amperometric determination of L-tyrosine by an enzymeless sensor based on a carbon ceramic electrode modified with copper oxide nanoparticles

We report on the electrochemical formation of copper oxide nanoparticles (CuO-NPs) at a carbon ceramic electrode (CCE) as a highly-porous substrate. A copper film was deposited on the surface of the CCE and derivatized in situ to give CuO-NPs by potential cycling between ?0.8 and 0.35?V in strongly alkaline solution. The electrode was characterized by scanning electron microscopy and cyclic voltammetry. The CuO-NPs exhibited excellent electrocatalytic activity toward the oxidation of L-tyrosine (L-Tyr) in responding linearly in the 2 to 1,350???M concentration range, an associated detection limit (S/N?=?3) of 160?nM, and a sensitivity of 0.61?A?M^?1?cm^?2.