Solvent extraction of Cobalt/II/ from thiocyanate solutions by sulphoxides

The extraction of cobalt/II/ from ammonium thiocyanate solutions by di-n-pentyl sulphoxide /DPSO/, di-n-octyl sulphoxide /DOSO/ and their mixtures in carbon tetrachloride has been studied. The species extracted were found to be Co/SCN/₂. 4S /where S=DOSO or DOSO/. Synergic effects have been observed which are ascribed to the formation of mixed ligand metal complexes. The influence of the metal concentration, temperature and the diluent on the extraction of cobalt/II/has been investigated.     

Alkali promoted rare earth metal phosphates for vapour phase O-alkylation of α- and β-naphthols with methanol

The vapor-phase catalytic O-alkylation of - and -naphthols with methanol has been investigated over lanthanum, cerium, samarium, and antimony phosphate catalysts promoted with cesium hydroxide. Among various catalysts investigated, the Cs-SmPO₄ combination catalyst provided better catalytic activity and selectivity. The CsOH promoter suppressed formation of C-alkylated side products and enhanced the O-alkylation selectivity. Characterization of these catalysts by X-ray diffraction and FT-infrared techniques revealed that the cesium promoter has no influence on the bulk structure of the catalysts. Temperature programmed desorption of anhydrous ammonia over promoted and unpromoted catalysts revealed that the cesium promoter decreases total surface acidity of the catalysts.     

Hydrodechlorination of chlorobenzene over supported metal catalysts

The use of supported Pd catalysts, with low and high metal content, for the hydrodechlorination of chlorobenzene is presented in this article. Application of microwave irradiation during preparation of catalysts resulted in the synthesis of large Pd particles at moderate temperatures. The nature of the support played a key role in the formation of cationic Pd species. The extent of interaction of the Pd species with the support, the nature of metal precursor, particularly the residual chlorine on the surface were found to significantly affect the activity of the catalysts. In the case of bimetallic catalysts also microwave heating resulted in creation of bigger particles of Pd compared to those observed in conventionally heated catalysts. Besides, it minimized alloy formation as a result of which the activity of the catalysts in hydrodechlorination was found to be higher compared to that observed on conventionally prepared catalysts. Contrary to the general observation that low dispersed Pd catalysts are preferable for high stability, by means of the deposition-precipitation method adopted for catalyst preparation it was demonstrated that even highly dispersed (low Pd containing) catalysts can exhibit comparable activity and stability. An analysis of the nature of Pd species and its role in the stability of the catalysts is presented.IICT communication No. 051224     

NONPHOTOCHEMICAL HOLE BURNING OF THE B800-B850 ANTENNA COMPLEX OF Rhodopseudomonas acidophila

Detailed burn wavelength-dependent hole-burning studies of the title complex have been performed. The zero-phonon hole (ZPH) widths for B800 at 4.2 K are 6.0 ± 0.3 cm and are discussed in terms of B80O-B850 and B800-B800 energy transfer. The B800* lifetime is 1.8 ± 0.2 ps. The site inhomogeneous broadening (r,) of B800 is 240 cm^?1. The B850 (located at 864 nm at 4.2 K) hole spectra reveal that B850 suffers from significant homogeneous broadening, which is attributed to unit cell exciton level structure and ultrafast interexciton level relaxation. Novel ZPH action spectra lead to the resolution of a minor component at 885 nm, which is the analogue of B870 of Rhodobacter sphaeroides previously assigned as the lowest exciton level of the B850 exciton band. The B870 ZPH width of 2.0 ± 0.2 cm^?1for Rhodopseudomonas acidophila leads to a total dephasing time of 5.3 ps, which is attributed to exciton scattering that stems from the energetic inequivalence of neighboring B850 unit cells.     

Estimation of cephalosporin antibiotics by differential pulse polarography

Differential pulse polarographic (DPP) method of determination of cephalosporins has been developed based on the electrochemistry of the azomethine group in the drugs in universal buffers of pH 2.0-12.0. Quantitative measurements were successful in the concentration range of 1.0 x 10(-5) M-2.5 x 10(-8) M, the lower concentration representing the detection limit by DPP. The described procedure has been applied for the determination of these drugs individually in pharmaceutical formulations and urine samples as well as for simultaneous determination in a single run.     

Gas phase reactions of chloride ion with aryl-substituted nitrocyclohexenes

Chloride ion chemical ionization studies of some aryl-substituted nitrocyclohexenes have demonstrated that benzylic anion formation is favoured in the gas phase. Anchimeric assistance by neighbouring phenyl groups and the effect of olefinic functions have a significant influence on the stability of the carbanions.     

Two new 5-deoxyflavonoids from Calliandra inermis

Two new 5-deoxyflavonoids, 7,2',3',4'-tetramethoxyflavone (1) and 7,2',3',4'-tetramethoxyflavanone (2) together with a known flavone 7,4'-dimethoxy-3'-hydroxyflavone (3) were isolated from the whole plant of Calliandra inermis. The structures of these new compounds were elucidated by high resolution electron impact mass spectrometry (HR-EI-MS) and 1D and 2D-NMR spectral studies including 1H-1H correlation spectroscopy (COSY), heteronuclear single quantum coherence (HSQC), heteronuclear multiple bond connectivity (HMBC) and nuclear Overhauser enhancement spectroscopy (NOESY).     

Protein engineering of nitrile hydratase activity of papain: molecular dynamics study of a mutant and wild-type enzyme

The mechanism of hydrolysis of the nitrile (N-acetyl-phenylalanyl-2-amino-propionitrile, I) catalyzed by Gln19Glu mutant of papain has been studied by nanosecond molecular dynamics (MD) simulations. MD simulations of the complex of mutant enzyme with I and of mutant enzyme covalently attached to both neutral (II) and protonated (III) thioimidate intermediates were performed. An MD simulation with the wild-type enzyme.I complex was undertaken as a reference. The ion pair between protonated His159 and thiolate of Cys25 is coplanar, and the hydrogen bonding interaction S(-)(25).HD1-ND1(159) is observed throughout MD simulation of the mutant enzyme.I complex. Such a sustained hydrogen bond is absent in nitrile-bound wild-type papain due to the flexibility of the imidazole ring of His159. The nature of the residue at position 19 plays a critical role in the hydrolysis of the covalent thioimidate intermediate. When position 19 represents Glu, the imidazolium ion of His159-ND1(+).Cys25-S(-) ion pair is distant, on average, from the nitrile nitrogen of substrate I. Near attack conformers (NACs) have been identified in which His159-ImH(+) is positioned to initiate a general acid-catalyzed addition of Cys-S(-) to nitrile. Though Glu19-CO(2)H is distant from nitrile nitrogen in the mutant.I structure, MD simulations of the mutant.II covalent adduct finds Glu19-CO(2)H hydrogen bonded to the thioimide nitrogen of II. This hydrogen bonded species is much less stable than the hydrogen bonded Glu19-CO(2)(-) with mutant-bound protonated thioimidate (III). This observation supports Glu19-CO(2)H general acid catalysis of the formation of mutant.III. This is the commitment step in the Gln19Glu mutant catalysis of nitrile hydrolysis.     

Thermal neutron activation analysis of essential and trace elements and organic constituents in <Emphasis Type="Italic">Trikatu</Emphasis>: An ayurvedic formulation

Trikatu, an Ayurvedic formulation of three dried powder spices, ginger, black pepper and pipali in equal proportion is widely used to promote digestion, assimilation and bioavailibility of food. It works synergistically, and hence, is more effective than an equal amount of any of its three ingredients taken separately. Five different brands and its three constituents were analyzed for 31 elements by instrumental neutron activation analysis (INAA) using 5-minute and 6-hour thermal neutron irradiation followed by high-resolution γ-ray spectrometry. Heavy toxic metals Cd, Ni and Pb determined by atomic absorption spectrometry (AAS) were found below permissible limits. Most elements in different brands vary in a narrow range. Ginger is particularly enriched in Ca, Fe, Mg and Mn whereas black pepper is enriched in Cr, Se, P and Zn. Cu/Zn shows linear relationship (r = 0.92) with Cu whereas Fe and Mn exhibit inverse correlation (r = −0.89) in different brands. Hydro distillation of pipali yielded an essential oil whereby 10 organic constituents were identified by GC-MS. Also barbituric and tannic acids were isolated from the aqueous methanolic extract of pipali.     

Substoichiometric radiochemical determination of thallium with sodium isopropyl xanthate

A rapid radiochemical method for the determination of thallium(III) has been developed based on the substoichiometric extraction of its 13 complex with sodium isopropyl xanthate into chloroform from pH 9 ammonia buffer. The effect of foreign ions on the extraction was also studied. 10 g amounts of thallium were determined with an average error of 1.9%. The method has been successfully applied for the determination of thallium content present in sphalarite ores collected from Jawar Mines, Rajasthan (India).