Ricci and Yamabe solitons on second-order symmetric,and plane wave 4-dimensional Lorentzian manifolds

We show that a proper second-order symmetric spacetime, and four-dimensional Lorentzian plane wave manifolds admit different vector fields resulting in expanding, steady and shrinking Ricci and Yamabe solitons. Moreover, it is proved that those Ricci and Yamabe solitons are gradient only in the steady case.     

Experimental detection and theoretical characterization of the H2-NHX van der Waals complex

The H2-NH(X) van der Waals complex has been examined using ab initio theory and detected via fluorescence excitation spectroscopy of the A(3)Pi-X(3)Sigma(-) transition. Electronic structure calculations show that the minimum energy geometry corresponds to collinear H2-NH(X), with a well depth of D(e)=116 cm(-1). The potential-energy surface supports a secondary minimum for a T-shaped geometry, where the H atom of NH points towards the middle of the H2 bond (C(2v) point group). For this geometry the well depth is 73 cm(-1). The laser excitation spectra for the complex show transitions to the H2+NH(A) dissociative continuum. The onset of the continuum establishes a binding energy of D(0)=32+/-2 cm(-1) for H2-NH(X). The fluorescence from bound levels of H2-NH(A) was not detected, most probably due to the rapid reactive decay [H2-NH(A)-->H+NH2]. The complex appears to be a promising candidate for studies of the photoinitiated H2+NH abstraction reaction under conditions were the reactants are prealigned by the van der Waals forces.     

Equilibrium and hydrolysis of α-amino acid esters in mixed-ligand complexes withN-(acetamido)-iminodiacetatecopper(II)

Summary The formation equilibria of the binary and ternary complexes of Cu^II withN-(acetamido)-iminodiacetic acid (ADA) and amino acids or their esters were investigated potentiometrically. The chelation mode was ascertained by conductivity measurements. The kinetics of the base hydrolysis of amino acid esters in the presence of the copper(II)-ADA complex were studied. The rate and catalysis constants were estimated.     

Chemistry of quinuclidines as nitrogen bicyclic bridged‐ring structures

This review summarises the structure, basicity, asymmetric organocatalysis, synthesis and reactions of quinuclidines. Quinuclidines are bicyclic saturated pyridin‐containing compounds with rigid structures and a ring‐juncture nitrogen atom. This review covers the period from 1984–2005.     

Recent progress on coumarin scaffold-based anti-microbial agents (Part III)

The biological, therapeutic, and medicinal properties of coumarins (chromen-2-ones), and its analogs have triggered enormous studies aimed toward growing synthetic routes to these heterocyclic compounds. This review presents a systematic and comprehensive survey of the method of preparation, the chemical reactivity, and the anti-microbial properties associated with this system.     

Symmetrical and Asymmetrical Bisphosphonate Esters. Synthesis, Selective Hydrolysis, and Isomerization

Summary. Two simple and efficient one-pot procedures for the synthesis of a series of α-branched N-heterocycle-substituted methane-1,1-bisphosphonates are outlined. In the first method, the parent halosubstrates were reacted with cyanomethylphosphonate followed by reaction with dialkyl phosphonates to give asymmetrical or symmetrical bisphosphonates (BPs). In the second approach, the same halocompounds were reacted with tetraethyl methyl-1,1-bisphosphonate to give the requisite BPs. Partial and complete hydrolysis of the prepared BPs were also investigated. The products contain functional groups advantageous for further synthetic modification as structural units for coupling with the drug.     

Voltammetric determination of meclizine HCL and its application in pharmaceuticals and biological fluid using CNTS/ZnO nano-carbon modified electrode

In this article, we report a methodology for the voltammetric behavior of meclizine hydrochloride at different nano modified electrodes e.g., Glassy carbon (GCE), pencil graphite (PGE), Carbon Nano tubes-carbon paste (CNTS-CPE) and Carbon Nano tubes-zinc oxide carbon paste (CNTS/ZnO-CPE) using cyclic and square wave voltammetry and the highest performance of them was CPE/CNTs/ZnO electrode and therefore was used as working electrode. The oxidation reaction mechanism of meclizine hydrochloride (MEC-HCL) is proposed to be one electron system. The results obtained with a square wave were linear over the concentration ranges 19.5–102.4 ng mL^?1 with a correlation coefficient 0.998. The square wave technique showed a low of detectable (LOD) of 6.444 ng/mL and a limit of quantification (LOQ) of 19.530 ng/mL at CNTS/ZnO-CPE. Based on these findings, a simple and not time-consuming method was used for the analysis of MEC-HCL in pharmaceutics and biological fluids. The method showed a minimum detectability (LOD) of 0.02, 0.008 and 0.14 lg/mL and a limit of quantitation (LOQ) of 0.06, 0.02 and 0.42 lg/mL at PGE, CPE and GCE, respectively. The method was validated and compared with the reference valid method. It revealed good accuracy and reproducible results. The anticipated voltammetric procedure has the advantage of being simple, precise, inexpensive and highly sensitive.     

Study of the Reactivity of 6,8‐Dimethyl‐4‐oxo‐4H‐1‐benzopyran‐3‐carboxaldehyde Towards Amino‐6‐oxopyridine‐3‐carboxylate Derivatives

The condensation reactions of 6,8‐dimethyl‐4‐oxo‐4H‐1‐benzopyran‐3‐carboxaldehyde ( 1 ) with equimolar amounts of ethyl 2‐amino‐4‐(4‐chlorophenyl)‐5‐cyano‐1‐[(5,6‐diphenyl‐1,2,4‐triazin‐3‐yl)amino]‐6‐oxo‐1,6‐dihydropyridine‐3‐carboxylate ( 2 ) at different reaction conditions gave different chromanone and chromenone products 3 , 4 , 5 . Also, the condensation reactions of compound 1 with ethyl 5‐cyano‐1,2‐diamino‐4‐(3‐nitrophenyl)‐6‐oxo‐1,6‐dihydropyridine‐3‐carboxylate ( 6 ) in absolute ethanol, dry benzene, acetic acid, and/or dry xylene gave a variety of products 7 , 8 , 9 , 10 depending on the solvent used.     

Optimization and validation of an RP-HPLC method for direct determination of metformin hydrochloride in human urine and in a dosage form

A simple, selective, sensitive, accurate, and precise method was developed for determination of metformin hydrochloride (MF) in human urine using RP-HPLC. The method depends upon using an octylsilyl (C8) 5 microm particle size column at ambient temperature with mobile phase consisting of 33 mM sodium dihydrogen phosphate containing 6.38 mM hexanesulfonic acid sodium salt and adjusted to apparent pH 3.0 with phosphoric acid-acetonitrile (93 + 7, v/v) at a flow rate of 1.5 mL/min. Quantitation was achieved with UV detection at 231 nm based on peak area with a linear calibration curve over the concentration range of 0.01-50 microg/mL. The proposed method was applied to the determination of the urinary excretion pattern of MF (the cumulative amounts excreted were calculated without pretreatment of the urine sample) and for determination of the dissolution pattern of MF tablets. The proposed method was completely validated according to the U.S. Food and Drug Administration guidelines.     

HPLC Determination of Imidazoles with Variant Anti-Infective Activity in Their Dosage Forms and Human Plasma

A suitable HPLC method has been selected and validated for rapid simultaneous separation and determination of four imidazole anti-infective drugs, secnidazole, omeprazole, albendazole, and fenbendazole, in their final dosage forms, in addition to human plasma within 5 min. The method suitability was derived from the superiority of using the environmentally benign solvent, methanol over acetonitrile as a mobile phase component in respect of safety issues and migration times. Separation of the four anti-infective drugs was performed on a Thermo Scientific^® BDS Hypersil C₈ column (5 µm, 2.50 × 4.60 mm) using a mobile phase consist of MeOH: 0.025 M KH₂PO₄ (70:30, v/v) adjusted to pH 3.20 with ortho-phosphoric acid at room temperature. The flow rate was 1.00 mL/min and maximum absorption was measured with UV detector set at 300 nm. Limits of detection were reported to be 0.41, 0.13, 0.18, and 0.15 µg/mL for secnidazole, omeprazole, albendazole, and fenbendazole, respectively, showing a high degree of the method sensitivity. The method of analysis was validated according to Food and Drug Administration (FDA)guidelines for the determination of the drugs, either in their dosage forms with highly precise recoveries, or clinically in human plasma, especially regarding pharmacokinetic and bioequivalence studies.