Synthesis and characterization of Ni(II) complexes bearing of 2‐(1H–benzimidazol‐2‐yl)‐phenol derivatives as highly active catalysts for ethylene oligomerization

Novel Ni(II) complexes of 2‐(1H–benzimidazol‐2‐yl)‐phenol derivatives (HL_x: x  =  1–5; C1–C5 ) have been synthesized and characterized. In the mononuclear complexes, the ligands were coordinated as bidentate, via one imine nitrogen and the phenolate oxygen atoms. The structures of the compounds were confirmed on the basis of FT‐IR, UV–Vis, ¹H‐, ¹³C–NMR, inductively coupled plasma and elemental analyses (C, H and N). The purity of these compounds was ascertained by melting point (m.p.) and thin‐layer chromatography. The geometry optimization and vibrational frequency calculations of the compounds were performed using Gaussian 09 program with B3LYP/TZVP level of theory. All Ni(II) complexes were activated with diethylaluminum chloride (Et₂AlCl), so that C2 showed the highest activity [6600 kg mol^?1 (Ni) h^?1], where the ligand contains a chlorine substituent. Oligomers obtained from the complexes consist mainly of dimer and trimer, and also exhibit high selectivity for linear 1‐butene and 1‐hexene. Both the steric and electronic effects of coordinative ligands affect the catalytic activity and the properties of the catalytic products.     

Direct ultrasonic-assisted synthesis of sphere-like nanocrystals of spinel Co3O4 and Mn3O4

A simple sonochemical method was developed to synthesize uniform sphere-like or cubic Co(3)O(4) and Mn(3)O(4) nanocrystals by using acetate salts and sodium hydroxide or tetramethylammonium hydroxide (TMAH) as precursors. Influence of some parameters such as time of reaction, alkali salts, and power of the ultrasound and the molar ratio of the starting materials on the size, morphology and degree of crystallinity of the products was studied. Powder X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), FTIR spectroscopy, Thermal gravimetry analysis and differential thermal analysis (TGA/DTA) were used to characterize the nanocrystals.     

Design and construction of a home-made and cheaper argon arc lamp

The authors report on the design and construction of an argon arc lamp which provides noticeably a cheaper instrument for laser and medical applications. Cesium-doped tungsten and pure tungsten rods were used, respectively, for the lamp cathode and anode. To seal the glassy tube, a 50–50 Fe–Ni alloy was successfully used as a medium to attach the tungsten electrodes to the borosilicate glass tube. Starting voltage of the lamp versus the gas pressure, operation voltage–current diagram at various gas pressures, and lamp spectrum in the various pressures were measured. A comparison was made with krypton arc lamp. The lamp operation was satisfactory without any crack or fracture during lightening operation. The results showed that the lamp-lightening threshold voltage depends linearly on the pressure and arc length in such a way that there is an increase in the voltage by raising these two parameters. We have also observed that by increasing the argon pressure, there is a shifting in emission spectrum from the ultraviolet to the visible region. Comparison with krypton arc lamp indicated that argon lamp needs a higher threshold lightening voltage.     

Size and shape-dependent melting mechanism of Pd nanoparticles

Molecular dynamics simulation was employed to understand the thermodynamic behavior of cuboctahedron (cub) and icosahedron (ico) nanoparticles with 2–20 number of full shells. The original embedded atom method (EAM) was compared to the more recent highly optimized version as inter-atomic potential. The thermal stability of clusters were probed using potential energy and specific heat capacity as well as structure analysis by radial distribution function (G(r)) and common neighbor analysis (CNA), simultaneously, to make a comprehensive picture of the solid-state and melting transitions. The result shows ico is the only stable shape of small clusters (Pd₅₅–Pd₃₀₉ using original EAM and Pd₅₅ using optimized version) those are melting uniformly due to their small diameter. An exception is cub Pd₃₀₉ modeled via optimized EAM that transforms to ico at elevated temperatures. A similar cub to ico transition was predicted by original EAM for Pd₉₂₃–Pd₂₀₇₅ clusters, while for the larger clusters both cub and ico are stable up to the melting point. As detected by \(G(r)\) and CNA, moderate and large cub clusters were showing surface melting by nucleation of the liquid phase at (100) planes and growth of liquid phase at the surface before inward growth. While diagonal (one corner to another) melting was dominating over ico clusters owing to their partitioned structure, which retarded the growth of the liquid phase. The large ico clusters, using optimized EAM, presented a combination of surface and diagonal melting due to the simultaneous diagonal melting started from different corners. Finally, the melting temperature as well as latent heat of fusion were calculated and compared with the available models and previous studies, which showed, unlike the present result, the models failed to predict size-dependent motif cross-over.     

Effects of arachidonic acid concentration on prostaglandin biosynthesis and feasibility of semibatch processes

The reaction characteristics of prostaglandin E2 biosynthesis by PGH-synthase and PGE2 isomerase and the substrate dependency of this biosynthesis were studied. The activity of PG-synthases was blocked by the inhibitory action of one or more byproducts, probably resulting from the action of PGH-synthase. This inhibitory action then appeared to be partly reversible, indicating that the substrate and the inhibitor compete for the catalytic sites. According to these findings, the feasibility of a successful semibatch biosynthesis was investigated. A combination of the substrate concentration reducing procedure and the semibatch process resulted in an about 3.5-fold higher increase in the total amount of PGE2 formed in comparison with the batch results obtained at the substrate concentration of 1.0 mg/cm3. Since the cost of enzyme is a governing factor in this biosynthesis, development of semibatch biosynthesis of PGE2 becomes a matter of economic importance.     

An efficient four-component reaction for the synthesis of chromeno[4,3-<Emphasis Type="Italic">b</Emphasis>]quinolone derivatives

Chromenoquinolines have been prepared via an efficient one-pot, multi-component reaction of 4-hydroxy coumarin, aqueous ammonia, dimedone and different aldehydes.     

One‐Pot Synthesis of Cu2O/ZnO Nanoparticles at Present of Folic Acid to Improve UV‐Protective Effect of Cotton Fabrics

In this study, the effect of using folic acid on the in situ synthesis process of nanostructures has been investigated. Folic acid, as a biotemplate for synthesis of Cu₂O/ZnO, was used to improve the reducing and stabilizing the ability of cotton fabric and avoid agglomeration of the particles. Scanning electron microscopy images revealed that using folic acid caused the formation of particles with smaller sizes on the cotton fabric and X‐ray diffraction confirmed the same crystalline pattern of nanoparticles in comparison with the previous synthesis process. The effect of using this biotemplate on different properties of treated fabrics including UV‐protection effect, hydrophilicity, crease recovery angle, softness, thickness and mechanical properties has been evaluated. The folic acid had a great influence on UV‐protection effect, in synthesis procedure, decreasing the droplet absorption time, bending length and improving the wrinkle resistance and mechanical properties. Interestingly, the higher tensile strength of the treated cotton fabrics proved the incorporation of nanoparticles into the cotton fibers. An in situ, green and rapid method can be provided by using folic acid for the synthesis of the nanostructures with controlled size.     

A glassy carbon electrode modified with carbon nanotubes and reduced graphene oxide decorated with platinum-gold nanoparticles for voltammetric aptasensing of urea

This article reports on a novel aptamer-based platform for the quantitation of urea by using an aptamer with high affinity and selectivity for urea. The surface of a glassy carbon electrode (GCE) was modified by drop casting a cocktail consisting of carbon nanotubes and reduced graphene oxide (rGO) decorated with platinum-gold nanoparticles. The urea aptamer was then immobilized on the nanocomposite via covalent conjugation. Cyclic voltammetry and electrochemical impedance spectroscopy were employed to trace the modification of the GCE. Binding of urea caused the aptamer to be folded, and this result in an inhibition of the interfacial charge transfer rate when using hexacyanoferrate as an electrochemical redox probe. The change in redox current was quantified by differential pulse voltammetry, typically at a working voltage of 0.22 V vs. Ag/AgCl. The assay has a 1.9 pM detection limit, and the response is linear up to 150 nM concentration of urea. The superior selectivity and affinity of aptamer-modified GCE makes it a most useful tool for analysis of urea present in very low concentrations.

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Graphical abstract Schematic representation of different steps of aptasensor fabrication.

     

Cu(II)-β-cyclodextrin-catalyzed synthesis of spiro[indoline-3,4′-pyrano[3,2-c]chromene]-3′-carbonitrile derivatives

Cu(II)-β-cyclodextrin-catalyzed synthesis of spiro[indoline-3,4′-pyrano[3,2-c]chromene]-3′-carbonitriles through the reaction of isatin derivatives, 4-hydroxycoumarin, and malononitrile in ethanol at room temperature.