Selective aerobic photocatalytic oxidation of benzyl alcohol over spherical structured WO<Subscript>3</Subscript>/TiO<Subscript>2</Subscript> nanocomposite under visible light irradiation

TiO₂/WO₃ nanocomposite with nanodisk morphology was prepared and successfully used as a photocatalyst. The nanocomposite was obtained via sonochemical and hydrothermal methods, using pomegranate juice as a capping agent. The products were characterized by FE-SEM imaging, BET, EDAX spectroscopy, X-ray diffraction, DRS, and FT-IR spectroscopy. TiO₂/WO₃ nanocomposite showed high sensitivity to absorb visible light in compared to TiO₂. In an optimized condition, the yield of the aerobic photocatalytic oxidation of benzyl alcohol derivatives reached to 65% for the TiO₂/WO₃ nanocomposite, while the conversion percent of the derivatives was less than 8% and 50% on the TiO₂ and WO₃ nanoparticles, respectively. Experimental results were supported by density functional theory (DFT) calculations. The DFT results in several solvents of different dielectric constants, confirmed the strong dependence of light absorption and photocatalytic activity to adsorption energy of the substrates on the surface of the nanoparticles (E_ad). In addition, the theoretical results showed an inverse correlation between the adsorption energy of benzyl alcohol and its conversion percent, accordance to the experimental trend.

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Effect of low-salinity water on asphaltene precipitation

The effect of low-salinity (1000 to 5000?ppm) and intermediate-salinity (5000 to 40000?ppm) water (MgSO₄, MgCl₂, Na₂SO₄, CaCl₂, NaCl and KCl) on asphaltene precipitation was investigated in this work. The results revealed that all brines intensify the amount of asphaltene precipitation. All cases exhibited initial downward trend followed by the upward trend for the amount of asphaltene precipitation with increasing the brine concentration. A similar trend was also observed for Interfacial Tension (IFT) between crude oil and brine in this study. IFT was tested for MgSO₄, MgCl₂, Na₂SO₄, CaCl₂, NaCl and KCl brines with concentrations of 1000 to 40000?ppm. Finally, experimental results showed that an increase in volume of all brines in the mixture (brine +oil) led to increase and decrease of the asphaltene precipitation in low and intermediate salinity regions, respectively.     

Synthesis and photocatalytic activity assessing of the TiO<Subscript>2</Subscript> nanocomposites modified by some lanthanide ions and tin-derivative sandwich-type polyoxometalates

New nanocomposites containing sandwich-type polyoxometalate of [(PW₉O₃₄)₂(HOSn^IVOH)₃]^12? (P₂W₁₈Sn₃) loaded onto Ln-doped TiO₂ (Nd, Sm, Dy, Tb) nanoparticles were synthesized and their catalytic activities were assessed. The Ln–TiO₂ nanoparticles and Ln–TiO₂/P₂W₁₈Sn₃ nanocomposites were characterized by Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction, field emission scanning electron microscope, energy dispersive analysis of X-rays spectra and diffuse reflectance spectra. The photocatalytic efficiency of the Ln–TiO₂ and Ln–TiO₂/P₂W₁₈Sn₃ were examined in the photodegradation of methyl orange and methylene blue solutions. It was revealed through different characterization techniques that the P₂W₁₈Sn₃ was successfully loaded on the lanthanide-doped anatase phase TiO₂ nanoparticles and the particles diameter were relatively 20–30 nanometers. It was revealed that doping by the lanthanide ions followed by loading of polyoxometalates improves the photocatalytic performance of TiO₂ effectively. The effects of operational parameters and the kinetics of photocatalytic degradation under UV light were discussed. The prepared nanocomposites were stable and could be easily separated from the reaction system.     

Synthesis, characterization, spectroscopic and thermodynamic studies of charge transfer interaction of a new water-soluble cobalt(II) Schiff base complex with imidazole derivatives

The water-soluble cobalt(II) tetradentate Schiff base complex [Co(II)L](ClO4)(2), L: (N,N'-bis(5-[(triphenylphosphonium)-methyl]salicylidine)-o-phenylenediamineperchlorate has been synthesized and characterized. This complex forms charge transfer (CT) complexes with imidazole and 1-methylimidazole. The formation constant, molar absorptivity (epsilon'), and thermodynamic parameters for charge transfer complexes formation of cobalt(II) Schiff base complexes with imidazole derivatives were determined by using UV-vis spectrophotometric method in aqueous solutions at constant ionic strength (I=0.2mol dm(-3) KNO3) at pH 6.0 and various temperatures between 292 and 315K.     

Facile synthesis of heterocycles via 2-picolinium bromide and antimicrobial activities of the products

The 2-picolinium N-ylide 4, generated in situ from the N-acylmethyl-2-picolinium bromide 3, underwent cycloaddition to N-phenylmaleimide or carbon disulfide to give the corresponding cycloadducts 6 and 8, respectively similar reactions of compound 3 with some electron-deficient alkenes in the presence of MnO(2) yielded the products 11 and 12. In addition, reaction of 4 with arylidene cyanothioacetamide andmalononitrile derivatives afforded the thiophene and aniline derivatives 15 and 17, respectively. Heating of picolinium bromide 3 with triethylamine in benzene furnished 2-(2-thienyl)indolizine (18). The structures of the isolated products were confirmed by elemental analysis as well as by (1)H- and (13)C-NMR, IR, and MS data. Both the stereochemistry and the regioselectivity of the studied reactions are discussed. The biological activity of the newly synthesized compounds was examined and showed promising results.     

Sonochemical syntheses of xanthene derivatives using zeolite-supported transition metal catalysts in aqueous media

An efficient green method for the syntheses of biologically active xanthene derivatives by use of zeolite-supported transition metal catalysts is described. A Fe-Cu/ZSM-5 heterogeneous catalyst has the highest activity in the one-pot syntheses with a wide range of aldehydes and cyclic 1,3-diketones, under ultrasonic irradiation in water at ambient temperatures. The three-component condensation in the presence of supported metal catalysts is operationally simple, requires no expensive or toxic reagents, and gives high yields in short reaction times.     

Determination of the stability constant and thermodynamic parameters between Tl<Superscript>+</Superscript>, Ag<Superscript>+</Superscript> and Pb<Superscript>2+</Superscript> cations with 2,6-di(furyl-2yl)-4-(4-methoxy phenyl)pyridine as a new synthesis ligand

The complexation reaction between Tl⁺, Ag⁺ and Pb²⁺ cations with 2,6-di(furyl-2yl)-4-(4-methoxy phenyl)pyridine as a new synthesis ligand in acetonitrile (ACN)–H₂O and methanol (MeOH)–H₂O binary solutions has been studied at different temperatures using conductometric method. The conductometric data show that the stoichiometry of the complexes is 1: 1 [M: L] and the stability constant of complexes changes with the binary solutions identity. Also, the structure of the resulting 1: 1 complexes was optimized using the LanL2dz basis set at the B3LYP level of theory using GAUSSIAN03 software. The results show that the change of logK_f for (DFMP.Pb)²⁺ and (DFMP.Ag)⁺ complexes with the mole ratio of acetonitrile and for (DFMP.Ag)⁺ and (DFMP.Tl)⁺ complexes with the mole ratio of methanol have a linear behavior, while the change of logK_f of (DFMP.Tl)⁺complex in ACN–H₂O binary solutions (with a minimum in X_ACN = 0.5) and (DFMP.Ag)⁺ complex in MeOH–H₂O binary solutions (with a minimum in X_MeOH = 0.75) show a non-linear behavior. The selectivity order of DFMP ligand for these cations in mol % CAN = 25 and 75 obtain Tl⁺ > Pb²⁺ > Ag⁺ but in mol % CAN = 50, the selectivity order observe Pb²⁺ > Tl⁺ > Ag⁺. Also, this selectivity sequence of DFMP in MeOH–H₂O (mol % MeOH = 75 and 100) and (mol % MeOH = 50) is obtained Pb²⁺ > Ag⁺ and Tl⁺ > Ag⁺ > Pb²⁺ respectively. The values of thermodynamic parameters show that these values are influenced by the nature and the composition of binary solution. In all cases, the resulting complexes are enthalpy stabilized and entropy destabilized. The TΔS_C^° versus ΔH_C^° plot of all obtained thermodynamic data shows a fairly good linear correlation which indicates the existence of enthalpy-entropy compensation in the complexation reactions.     

Green synthesis of silver nanoparticles by pepper extracts reduction and its electocatalytic and antibacterial activity

Stable silver nanoparticles were synthesized with the aid of a novel, non-toxic, eco-friendly biological material namely, green pepper extract. The aqueous pepper extract was used for reducing silver nitrate. The synthesized silver nanoparticles were analyzed with transmission electron microscopy (TEM), X-ray diffraction (XRD) and energy dispersive spectrometer (EDS). TEM image shows the formation of silver nanoparticles with average particle size of 20 nm which agrees well with the XRD data. The main advantage of using pepper extract as a stabilizing agent is that it provides long-term stability for nanoparticles by preventing particles agglomeration. To investigate the electrocatalytic efficiency of silver nanoparticles, silver nanoparticles modified carbon-paste electrode (AgNPs–CPE) displayed excellent electrochemical catalytic activities towards hydrogen peroxide (H₂O₂) and hydrogen evolution reaction (HER). The reduction overpotential of H₂O₂ was decreased significantly compared with those obtained at the bare CPE. An abrupt increase of the cathodic current for HER was observed at modified electrode. Also, the antibacterial activity of silver nanoparticle was performed using Escherichia coli and Salmonellae. The approach of plant-mediated synthesis appears to be cost efficient, eco-friendly and easy methods.     

Development and validation of spectrophotometric, TLC and HPLC methods for the determination of lamotrigine in presence of its impurity

Three reliable, rapid and selective methods have been developed and validated for the determination of lamotrigine in the presence of its impurity, 2,3-dichlorobenzoic acid. The first method is spectrophotometric method using p-chloranilic acid forming a colored product with lambda(max) 519+/-2 nm. All variables affecting the reaction have been investigated and the conditions were optimized. Beer's law was obeyed over a concentration range of 10-200 microg ml(-1) with mean accuracy 100.13+/-0.44%. The molar ratio of the formed ion-association complex is found to be 1 : 1 as deduced by Job's method. The conditional stability constant (K(f)), standard free energy (DeltaG), molar absorptivity(epsilon), and sensitivity index were evaluated. The second method is based on TLC separation of the cited drug (Rf=0.75+/-0.01) from its impurity (Rf=0.23+/-0.01) followed by densitometric measurement of the intact drug spots at 275 nm. The separation was carried on silica gel plates using ethyl acetate : methanol : ammonia 35% (17 : 2 : 1 v/v/v) as a mobile phase. The linearity range was 0.5-10 microg/spot with mean accuracy 99.99+/-1.33%. The third method is accurate and sensitive stability-indicating HPLC method based on separation of lamotrigine from its impurity on a reversed phase C(18) column, using a mobile phase of acetonitrile : methanol : 0.01 M potassium orthophosphate (pH 6.7+/-0.1) (30 : 20 : 50 v/v/v) at ambient temperature 25+/-5 degrees C and UV detection at 275 nm in an overall analysis time of about 6 min., based on peak area. The injection repeatability, intraday and interday repeatability were calculated. The procedure provided a linear response over the concentration range 1-12 microg ml(-1) with mean accuracy of 99.50+/-1.30%. The proposed methods were successfully applied for the determination of lamotrigine in bulk powder, in dosage form and in presence of its impurity. The results obtained were analyzed by ANOVA to assess that no significant difference between each of the three methods and the reported one. The validation was performed according to USP guidelines.