Electronic and thermal properties of B2-type AlRE intermetallic compounds: A first principles study

The ground state electronic structure and thermal properties of B₂-type intermetallic compounds AlRE (RE: Pm, Sm, Eu, Tb, Gd and Dy) have been studied using a self-consistent tight-binding linear muffin-tin orbital (TB-LMTO) method at ambient as well as at high pressure. These compounds show metallic behavior under ambient condition. The band structure, total energy, density of states and ground state properties like lattice parameter, bulk modulus are calculated in the present work. The Debye-Grüneisen model is used to calculate the Debye temperature and the Grüneisen constant. The calculated results are in good agreement with the reported experimental and other theoretical results. The variation in the Debye temperature with pressure has also been reported. We present a detailed analysis of the role of f electrons of RE in the AlRE system.     

Identification and quantification of two antihepatotoxic coumarinolignoids cleomiscosin A and cleomiscosin B in the seeds of Cleome viscosa using liquid chromatography-tandem mass spectrometry

A sensitive liquid chromatography/electrospray ionization tandem mass spectrometric (LC/ESI-MS/MS) method was developed for the identification and quantification of two antihepatotoxic coumarinolignoids cleomiscosin A and cleomiscosin B in different extracts of the seeds of Cleome viscosa. The separation of cleomiscosin A and cleomiscosin B was achieved on an RP(18) column using a solvent system consisting of a mixture of acetonitrile-methanol (1:2, v/v) and acetonitrile-water-formic acid (5:95:0.3, v/v) as a mobile phase in a gradient elution mode. A multiple-reaction monitoring (MRM) method was developed for quantification of cleomiscosin A and cleomiscosin B in the seed extracts of Cleome viscosa. On the basis of signal-to-noise ratio of 3, the limit of detection in MRM mode for cleomiscosin A and cleomiscosin B were 1.0 and 4.0 ng/mL respectively. The method was validated in terms of linearity, accuracy and precision for 6 days. The method developed was found to be useful for identification and quantification of cleomiscosin A and cleomiscosin B in the different extracts of the seeds of Cleome viscosa.     

Uncapped silver nanoparticles synthesized by DC arc thermal plasma technique for conductor paste formulation

Uncapped silver nanoparticles were synthesized by DC arc thermal plasma technique. The synthesized nanoparticles were structurally cubic and showed wide particle size variation (between 20–150 nm). Thick film paste formulated from such uncapped silver nanoparticles was screen-printed on alumina substrates and the resultant ‘green’ films were fired at different firing temperatures. The films fired at 600 °C revealed better microstructure properties and also yielded the lowest value of sheet resistance in comparison to those corresponding to conventional peak firing temperature of 850 °C. Our findings directly support the role of silver nanoparticles in substantially depressing the operative peak firing temperature involved in traditional conductor thick films technology.     

Solvent extraction study of cobalt(II) with 8-mercaptoquinoline

Equilibrium distribution coefficients have been determined for the extraction of cobalt(II) with 8-mercaptoquinoline as a function of pH and reagent concentraton at ambient temperature. The extractable complex is a diadduct, i. e. two molecules of the reagent are coordinated to the cobalt(II) chelate. The adduct formation constant in chloroform and the overall formation constant in the aqueous phase have been determined. Pyridine and its methyl derivatives were found to enhance the extraction of Co(II) into chloroform in the presence of 8-mercaptoquinoline. From the extraction equilibrium data, the adduct formation constants of 12 chelate to nitrogen base adducts were evaluated. The special role of steric factors is discussed.     

Calculation of pressure using the virtual-volume-variation method and the virial method from chain conformations obtained by Monte Carlo simulations on the second nearest neighbor diamond lattice

For a model system of polyethylene of chain lengths 40 and 100 carbon atoms, we calculated the pressure at different densities and compared them with the experimental values. The simulation was conducted on the second nearest neighbor diamond lattice, and the pressure was calculated using the virtual-volume-variation method after the system was reverse mapped to its fully atomistic form in continuous space and energy minimized. In addition, the pressure was also calculated from the virial route by conducting a short molecular dynamics simulation starting from the energy minimized structure. We show that the pressure obtained from our simulations is quite reasonable in the length of simulation time (in Monte Carlo steps) normally employed in our group. These results provide additional evidence for the equilibration of our model systems, and methodology to calculate the pressure in our lattice models.     

Reactions of cobalt resacetophenone oximate with heterocyclic nitrogen bases

Summary Adduct formation constants of the pyridine adducts of the cobalt(II) chelate of resacetophenone oxime in cyclohexanone have been determined spectrophotometrically. Spectral changes in the absorbance were observed in visible range. The stability of the cobalt adducts increases in the following order of the bases: pyridine<4-picoline<3,5-lutidine<1,10-phenanthroline<2,9-neocuproin<2,2-bipyridyl.     

A comparative solvent extraction study of manganese(II) with 8-Mercaptoquinoline, 8-Quinolinol and its analogues

Equilibrium distribution coefficients were determined for the extraction of manganese(II) with 8-mercaptoquinoline, 8-quinolinol and its 2-methyl, 4-methyl, 5-chloro and 5-nitro analogues as a function of pH and reagent concentration at ambient temperature. 8-Mercaptoquinoline forms a mono self-adduct with Mn(II) whereas simple 12 chelate formation was observed in the case of 8-quinolines. The adduct formation constant and the overall formations constants in the aqueous phase have been determined. A linear relationship was observed between the equilibrium constants, formation constants and the pK values of the chelating agents.Synergic enhancement was observed in the extraction of Mn(II) with 8-mercaptoquinoline in presence of pyridine and its methyl derivatives and the adduct formation constants of the 12, chelate to nitrogen base, adducts were evaluated.     

Hetero Diels-Alder reaction: a novel strategy to regioselective synthesis of pyrimido[4,5-d]pyrimidine analogues from Biginelli derivative

A number of potent pyrimido[4,5-d]pyrimidine analogues have been efficiently synthesized by hetero Diels-Alder cycloaddition of 6-methyl-4-phenyl-2-thioxo-1,2,3,4-tetrahydropyrimidine-5-carboxylic acid methyl ester, a Biginelli compound with N-arylidine-N′-methylformamidines and N-arylidine guanidine in dry toluene. Structures of the newly obtained cycloadducts were established on the basis of elemental and spectral (IR, NMR and Mass) data. The molecular mechanism of the observed cycloaddition reaction has been investigated theoretically by means of PM3 semiempirical method. Transition state structure determinations and activation energy calculations have shown the preference for the endo approach over the exo approach of dienophile towards the diene fragments used, which is consistent with the experimental results. The studied cycloadditions proceed via an asynchronous concerted mechanism. It was demonstrated that FMO theory could reasonably predict the relative reactivities between dienes as well as indicating that these reactions belong to normal Diels-Alder type cycloadditions.     

A Validated Chiral LC Method for the Enantiomeric Separation of Repaglinide on Amylose Based Stationary Phase

A simple, isocratic, normal phase chiral HPLC method was developed and validated for the enantiomeric separation of repaglinide, (S)-(+)-2-ethoxy-4-N [1-(2-piperidinophenyl)-3-methyl-1-butyl] aminocarbonylmethyl] benzoic acid, an antidiabetic in bulk drug substance. The enantiomers of repaglinide were resolved on a ChiralPak AD-H (amylose based stationary phase) column using a mobile phase consisting of n-hexane: 2-propanol:trifluoroacetic acid (95:5:0.2 v/v/v) at a flow rate of 1.0 mL min⁻¹. The resolution between the enantiomers was found to be not >3.5 in optimized method. The presence of trifluoroacetic acid in the mobile phase played an important role, in enhancing chromatographic efficiency and resolution between the enantiomers. The developed method was extensively validated and proved to be robust. The calibration curve for (R)-enantiomer showed excellent linearity over the concentration range of 900 ng mL⁻¹ (LOQ) to 6,000 ng mL⁻¹. The limit of detection and limit of quantification for (R)-enantiomer were 300 and 900 ng mL⁻¹, respectively. The percentage recovery of the (R)-enantiomer ranged between 98.3 and 101.05% in bulk drug samples of repaglinide. Repaglinide sample solution and mobile phase were found to be stable up to 48 h. The developed method was found to be enantioselective, accurate, precise and suitable for quantitative determination of (R)-enantiomer in bulk drug substance.