Synthesis of 2,3-disubstituted pyrazines and quinoxalines by Heck cross-coupling reactions of 2,3-dichloropyrazine and 2,3-dichloroquinoxaline. Influence of the temperature on the product distribution

Heck cross-coupling reactions of 2,3-dichloropyrazine provide a convenient approach to 2,3-dialkenyl-, 2-alkenyl-3-alkyl-, and 2,3-dialkylpyrazines depending on the reaction conditions.     

Effects of monomer concentration on the structure and properties of polybenzidine micro rods

Polybenzidine was synthesized by interfacial polymerization under various monomer concentrations. Effects of monomer concentration on morphology, structure, and properties of polybenzidine were studied by techniques of Fourier Transform Infrared Spectroscopy, Ultraviolet Visible Absorption Spectroscopy, Scanning Electron Microscopy, Transmission Electron Microscopy, X-ray Diffraction, and Cyclic Voltammetry. The results showed that the synthesized polybenzidine with monomer concentration less than 0.15 mol/L were micro rod-like and the surface of the micro rods was smooth and uniform, However, the micro rod-like polybenzidine cannot be obtained under high monomer concentration because of the explosive polymerization. The results of structural analysis indicated that the monomer concentration should not be very high to obtain the polybenzidine with the optimal degree of conjugation and order arrangement of molecular chain. The polybenzidine synthesized in different monomer concentrations showed different electrochemical activities and the sample with the best electrochemical activity was obtained at monomer concentration of 0.02 mol/L.     

Free Abelian 2-form gauge theory: BRST approach

We discuss various symmetry properties of the Lagrangian density of a four- (3+1)-dimensional (4D) free Abelian 2-form gauge theory within the framework of Becchi–Rouet–Stora–Tyutin (BRST) formalism. The present free Abelian gauge theory is endowed with a Curci–Ferrari type condition, which happens to be a key signature of the 4D non-Abelian 1-form gauge theory. In fact, it is due to the above condition that the nilpotent BRST and anti-BRST symmetries of our present theory are found to be absolutely anticommuting in nature. For the present 2-form theory, we discuss the BRST, anti-BRST, ghost and discrete symmetry properties of the Lagrangian densities and derive the corresponding conserved charges. The algebraic structure, obeyed by the above conserved charges, is deduced and the constraint analysis is performed with the help of physicality criteria, where the conserved and nilpotent (anti-) BRST charges play completely independent roles. These physicality conditions lead to the derivation of the above Curci–Ferrari type restriction, within the framework of the BRST formalism, from the constraint analysis. PACS  11.15.-q; 12.20.-m; 03.70.+k     

Capillary electrophoretic determination of zinc dimethyldithiocarbamate (Ziram) and zinc ethylenebisdithiocarbamate (Zineb)

A simple and sensitive capillary electrophoretic method was developed for the separation and determination of Ziram and Zineb in boric acid buffer by direct UV absorbance detection at lambda=254 nm. The separation is dependent on pH and nature of the buffer. The detection limits (S/N=3) are 1.88x10(-6) mol/l (0.57 mug/ml) and 2.48x10(-6) mol/l (0.68 mug/ml) for Ziram and Zineb, respectively. The method was successfully applied to the analysis of wheat samples spiked with Ziram and Zineb.     

Quantitative treatment of substituent effects in the polarographic investigations of some potential antineoplastic 2-amino-4-aryl-5-phenylazothiazoles

Polarographic reduction of 2-amino-4-aryl-5-phenylazothiazoles takes place in a single 2-electron transfer, giving a diffusion-controlled irreversible wave in the pH range 2.0-10.0. Substituents in the 4-position of the thiazole moiety shift the half-wave potential through conjugation of the system. A correlation of E(sol;1 2 ) with the Brown and Hammett substituent constant has also been established.     

Hyperfine interaction experienced by181Ta nuclei at the Hf site in HfFe2−xSix compounds through a decoupling experiment

The time-differential perturbed angular correlation (TDPAC) experiments involving the 133–482 keV γ-γ cascade in¹⁸¹Ta have been performed in the presence of an external magnetic field along the quantization axis to measure the hyperfine magnetic field experienced by¹⁸¹Ta nuclei at the Hf site in the pseudobinary compounds HfFe_2?xSi_x with x=0.1 and x=0.3. The hyperfine magnetic fields measured at 298 K are H_hf=133.1±12.0 kG in the cubic (C15) Laves phase compound HfFe_1.9Si_0.1 and H_hf=76.8±7.0 kG in the hexagonal (C14) Laves phase compound HfFe_1.7Si_0.3. The measured hyperfine fields are discussed within the framework of the Campbell-Blandin model.