Activation of – N=CH – bond in a Schiff base by divalent nickel monitored by NMR evidence

The Schiff base, 2–salicylidene–4–aminophenyl benzimidazole in ethanol undergoes activation of –N=CH– bond by Ni²⁺ in the presence of ammonia or primary alkyl amine to produce nickel complexes of the formula Ni{o–C₆H₄(O)CH NR}₂ . n H₂O [R = H, Me; n = 0; R = Et, n = 0.5] and 4–aminophenyl benzimidazole. The products have been identified by elemental analysis, magnetic susceptibility measurements and IR, ESR, mass and extensive NMR spectral studies. The possible mechanism for the activation of –N=CH – bond has also been proposed. Copyright © 2012 John Wiley & Sons, Ltd.     

Discotic liquid crystals derived from polycyclic aromatic cores: from the smallest benzene to the utmost graphene cores

ABSTRACT

Past decades we have witnessed many breakthroughs in research on liquid crystals (LCs) as well as significant amplification in the application of LCs. LCs are currently attracting great attention of scientists from all over the world where various researches have been implemented on the varied facets of LCs. In this review we present some recent developments in the field of discotic liquid crystals (DLCs). A large number of DLCs from various aromatic cores have been realised. However, due to paucity of space only DLCs derived from four main aromatic cores, benzene, triphenylene, hexabenzocoronene and graphene, are covered here. An outlook on these emerging two-dimensional organic semiconductor materials with relevant scientific application background has been presented.     

Functional Annotation of <Emphasis Type="Italic">Fibrobacter succinogenes</Emphasis> S85 Carbohydrate Active Enzymes

Fibrobacter succinogenes is a cellulolytic bacterium that degrades plant cell wall biomass in ruminant animals and is among the most rapidly fibrolytic of all mesophilic bacteria. The complete genome sequence of Fisuc was completed by the DOE Joint Genome Institute in late 2009. Using new expression tools developed at Lucigen and C5-6 Technologies and a multi-substrate screen, 5,760 random shotgun expression clones were screened for biomass-degrading enzymes, representing 2× genome expression coverage. From the screen, 169 positive hits were recorded and 33 were unambiguously identified by sequence analysis of the inserts as belonging to CAZy family genes. Eliminating duplicates, 24 unique CAZy genes were found by functional screening. Several previously uncharacterized enzymes were discovered using this approach and a number of potentially mis-annotated enzymes were functionally characterized. To complement this approach, a high-throughput system was developed to clone and express all the annotated glycosyl hydrolases and carbohydrate esterases in the genome. Using this method, six previously described and five novel CAZy enzymes were cloned, expressed, and purified in milligram quantities.     

Ethopropaziniumyl cation perrhenate salt, (C19H25N2S)+[ReO4]−: synthesis and crystal structure

An unusual ethopropaziniumyl cation salt of perrhenate has been prepared and characterized using elemental analysis, molar conductance, and u.v.-vis., i.r., and nmr spectral data. The crystal and molecular structure of the new ionic compound, (EPH)[ReO₄] where EPH⁺ is protonated ethopropazine, has been elucidated by single-crystal X-ray crystallography. Crystals are monoclinic, space groupP2₁/c, in a unit cell with lattice parametersa=10.866(3),b=12.242(2),c=16.01(1)°, =109.00(1)°, volume=2014(2) ³. The structure was solved using heavy-atom methods and refined toR=0.024 with 3181 observed reflections. In the crystal, the ethopropaziniumyl cation, which is protonated at the terminal diethylamino nitrogen, is linked to the ReO ₄ ^– ion through hydrogen bonding.10-(2-diethylaminopropyl)phenothiaziniumyl tetraoxorhenate(VII).     

Extractive spectrophotometric determination of fluoroquinolones and antiallergic drugs in pure and pharmaceutical formulations.

A simple, rapid and sensitive spectrophotometric procedure has been proposed for the assay of fluoroquinolones viz., ciprofloxacin (CPF) and norfloxacin (NRF), and antiallergic drugs viz., methdilazine hydrochloride (MDH) and isothipendyl hydrochloride (IPH) in bulk and pharmaceutical formulations. The method is based on the reaction of selected drugs with Brilliant Blue G (BBG) in NaOAc-AcOH buffer of pH 4.0 for CPF and NRF or in neutral medium for MDH and IPH to give chloroform soluble ion-association complexes. The effects of various parameters have been studied. The ion-association complexes exhibited absorption maxima at 610 nm for CPF, at 614 nm for NRF and MDH, and at 612 nm for IPH. Beer's law plots were obeyed in the concentration ranges of 0.5-6.0, 0.4-8.0, 0.1-6.0 and 0.2-6.1 (mg ml(-1) for CPF, NRF, MDH and IPH, respectively, with correlation coefficients not less than 0.9969. Molar absorptivity values as calculated from the Beer's law data were found to be 2.86 x 10(4), 2.64 x 10(4), 3.13 x 10(4) and 5.51 x 10(4) mol(-1) cm(-1) for CPF, NRF, MDH and IPH, respectively. The influence of commonly employed excipients in the determination of the studied drugs has been studied. The results obtained by the proposed method were statistically validated.     

Oxidation of metronidazole with sodium N‐bromo‐p‐toluenesulfonamide in acid and alkaline media: A kinetic and mechanistic study

A kinetic study of oxidation of metronidazole (Met) with sodium N‐bromo‐p‐toluenesulfonamide or bromamine‐T (BAT) has been carried out in HClO₄ (30°C) and NaOH (40°C) media. The experimental rate laws obtained are –d[BAT]/dt=k[BAT][Met]^x [H⁺]^y in acid medium and –d[BAT]/dt=k[BAT][Met]^x [OH^?]^y/[PTS]^z in alkaline medium, where x, y, and z are less than unity and PTS is p‐toluenesulfonamide. The reaction was subjected to changes in (a) ionic strength, (b) concentration of added reduction product PTS, (c) concentration of added neutral salts, (d) dielectric permittivity, and (e) solvent isotope effect. In both media, the stoichiometry of the reaction was found to be 1:1, and the oxidation product of metronidazole was identified as its aldehyde. The reaction was studied at different temperatures, and the activation parameters have been evaluated. The reaction constants involved in the proposed schemes were deduced. The reaction was found to be faster in acid medium in comparison with alkaline medium, which is attributed to the involvement of different oxidizing species. Mechanisms proposed and the rate laws derived are consistent with the observed kinetics. © 2005 Wiley Periodicals, Inc. Int J Chem Kinet 37: 700–709, 2005     

Extended rigidity percolation and chemical thresholds in Ge-Te-Pb glasses as revealed by MDSC

Thermal analysis of Ge₂₀Te_80−xPb_x (2≤x≤8) glasses has been undertaken using modulated differential scanning calorimetry (MDSC). The compositional dependence of thermal parameters is investigated. The crystallization temperatures (T_c) estimated from the total heat flow show detectable changes at compositions x=4, 6.5 and 7.5. Further, the heat capacity change at the glass transition temperature, measured from the reversible heat flow curve (ΔC_p^R), is found to exhibit a maximum and an inflexion at compositions x=4 and 6.5 and minimum at x=7.5, respectively. Also, the relaxation enthalpy, estimated from the area under the non-reversing heat flow curve (ΔH^NR), exhibits similar features at the said compositions. From the observed MDSC results, it has been proposed that the compositions x=4 and x=6.5 denote to the onset and completion of rigidity percolation and x=7.5 corresponds to the chemical threshold of the system.