Synthesis of fully substituted pyrazolo[3,4-b]pyridine-5-carboxamide derivatives via a one-pot four-component reaction

A one-pot four-component reaction of an aliphatic or aromatic amine, diketene, an aromatic aldehyde and 1,3-diphenyl-1H-pyrazol-5-amine in the presence of p-toluenesulfonic acid as a catalyst has been developed. In this reaction, a new class of fully substituted pyrazolo[3,4-b]pyridine-5-carboxamide derivatives is produced under mild reaction conditions and in good yields at ambient temperature.     

Electrocatalytic oxidation of captopril using a carbon-paste electrode modified with copper-cobalt hexacyanoferrate

A carbon-paste electrode was modified with copper-cobalt hexacyanoferrate by consecutive potential cycling. The kinetic parameters were calculated for the electroactive species. The resulting electrode exhibited electrocatalytic activity towards the oxidation of captopril. The kinetics of the electrocatalytic reaction was studied. A linear relationship was observed between anodic current and the concentration of captopril in the range of 5.0 × 10^?6–3.1 × 10^?5 μM with a detection limit of 4.2 μM (S/N = 3). The modified electrode was used in the analysis of captopril tablets successfully.     

Fluorometric chemosensors. Interaction of toxic heavy metal ions Pb(II), Cd(II), and Hg(II) with novel mixed-donor phenanthroline-containing macrocycles: spectrofluorometric,conductometric, and crystallographic studies

The macrocycles L(1)-L(3) incorporating N(2)S(3)-, N(2)S(2)O-, and N(2)S(2)-donor sets, respectively, and containing the 1,10-phenanthroline unit interact in acetonitrile solution with heavy metal ions such as Pb(II), Cd(II), and Hg(II) to give 1:1 ML, 1:2 ML(2), and 2:1 M(2)L complex species, which specifically modulate the photochemical properties of the ligands. The stoichiometry of the complex species formed during spectrofluorometric titrations and their formation constants in MeCN at 25 degrees C were determined from fluorescence vs M(II)/L molar ratio data. The complexes [Pb(L(1))][ClO(4)](2).(1)/(2)H(2)O (1), [Pb(L(2))][ClO(4)](2).MeNO(2) (1a), [Pb(L(3))(2)][ClO(4)](2).2MeCN (1b), and [Cd(L(3))][NO(3)](2) (2b) were also characterized by X-ray diffraction studies. The conformation adopted by L(1)-L(3) in these species reveals the aliphatic portion of the rings folded over the plane containing the heteroaromatic moiety with the ligands trying to encapsulate the metal center within their cavity. In 1, 1a, and 2b the metal ion completes the coordination sphere by interacting with counteranion units and solvent molecules. On the contrary, the 1:2 complex 1b shows Pb(II) sandwiched between two symmetry-related molecules of L(3) reaching an overall [4N + 4S] eight-coordination.     

Optimization of temperature-controlled ionic liquid homogenous liquid phase microextraction followed by high performance liquid chromatography for analysis of diclofenac and mefenamic acid in urine sample

In this work, a temperature-controlled ionic liquid homogeneous liquid phase microextraction (TCIL-HLPME) technique followed by HPLC–UV was applied for preconcentration and determination of diclofenac (DIC) and mefenamic acid (MEF) in urine samples. 1-butyl-3-methylimidazolium hexafluorophosphate ([C₄mim][PF₆]) was used as the optimum extraction solvent. Experimental design and response surface methodology was used for the optimization process. Firstly, a screening step, using Plackett-Burman design, was carried out to find the significant factors on the extraction efficiency and subsequently, a central composite design (CCD) was employed to find the optimum values of these parameters. The optimal conditions were obtained as extraction solvent volume of 105 µL; sample pH of 2.0, extraction time of 6 min, centrifugation time of 5 min; heating time of 2 min; heating temperature of 50 °C and 20 % of NaCl. Under optimized conditions, the preconcentration factors of 82 and 60 were obtained for DIC and MEF, respectively. The detections limits of 20 and 30 ng mL^?1 were achieved for DIC and MEF by the proposed method, respectively. The calibration curves were linear in the range of 40–1000 and 60–1000 ng mL^?1 for DIC and MEF, respectively. The intra- and inter-assay precisions (RSD %, n = 3) were in the range of 3.5–4.4 % and 7.3–8.0 % at the concentration level of 100 ng mL^?1, respectively. The validated method was successfully applied for the analysis of target analytes in some urine samples.     

Red water treatment by photodegradation process in presence of modified TiO<Subscript>2</Subscript> nanoparticles and validation of treatment efficiency by MLR technique

An active photocatalyst under sunlight irradiation was proposed for treatment of red water of TNT production process. The nanoparticles of TiO₂/S_0.05,Zn_0.05 were prepared by the sol–gel method and were verified by XRD pattern, TEM image, EDXS analysis, BET analysis and DRS spectra. The proposed photocatalyst showed the surface area of 146 m² g^?1, anatase and rutile phases and band-gap energy of 2.92 eV. The prepared nanoparticles were used as photocatalyst in treatment of red water under UV lamp and sun irradiations. The photodegradation process was optimized in conditions of 5 g L^?1 of photocatalyst, irradiation time of 4 h and dilution times of 1000 of real samples. The treatment efficiency of 76 and 69 % and rate constants of 0.368 and 0.319 h^?1 were obtained under UV and sun irradiations, respectively. The multiple linear regression as a statistic technique was used for study of validation and verification of four factors of mole fraction of S dopant, the irradiation intensity of UV lamp, the dose of photocatalyst and dilution times on samples as predictor’s on the treatment efficiency of red water as the response variable. The output of MLR showed the obtained P values <0.05 in confidence level of 95 % for all of the variables. Thus, the null hypothesis is rejected, and a meaningful addition is observed in the model because changes in the predictor’s value are related to changes in the response variable.     

Ammonium chloride catalyzed one-pot synthesis of imidazo[1,2-a]pyridines

Ammonium chloride as a very inexpensive and readily available reagent efficiently catalyzes one-pot, three-component Groebke condensation reactions of aldehydes, isocyanides, and 2-aminopyridines or 2-aminopyrimidines in methanol to afford the corresponding imidazo[1,2-a]pyridines in high yields at room temperature. Correspondence: Ahmad Shaabani, Department of Chemistry, Shahid Beheshti University, PO Box 19396-4716, Tehran, Iran.     

Proton transfer process in synthesis of 3-acetyl-4-(substituted ethylenyl)coumarins and chromeno[3,4-c]pyridines

The triphenylphosphine mediated reactions of electron-deficient carbon-carbon triple bonds with 3-acetylcoumarins in dichloromethane afford functionalized 3-acetyl-4-(substituted ethylenyl)coumarins. Also, triphenylphosphine-catalyzed three-component cascade annulation reactions of 3-acetylcoumarins, activated acetylenic compounds, and hydrazines or amines provide a straightforward access to 3,5-dihydro-2H-chromeno[3,4-c]pyridine-1,2-dicarboxylates. In these strategies, the main step to the target products is proton transfer process. All products were obtained in good to high yields.