[en] Direct titration of uranium with dipicolinic acid, in the presence of Arsenazo I, is a simple, precise, and accurate method for uranium determination. The method is particularly attractive because it can be totally automated. Detecting the end point (color change from blue to pink) depends on the concentration range. For the Micro Method (1 to 20 ppM U in the solution titrated), the gradual color change is monitored spectrophotometrically. For the Macro Method (20 to 300 ppM), the end point is determined either visually or spectrophotometrically. The spectrophotometric end point is computed by fitting the titration curve. The relative standard deviation is +-1 to 3% for the Micro Method and +-0.3% for the Macro Method

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[en] Unpretentious and exclusive methods for the spectrophotometric determination of trace amount of divalent palladium (II) have been developed with rubeanic acid (dithio-oxamide) in presence of secondary ligands like pyridine, piperidine and 3-picoline. Both direct and extraction spectrophotometry showed that coloured rubeanates are only stable in acidic medium. The violent yellow coloured products are formed below ph 5.0 with an absorption maxima at 416.0 and 422.0 (pyridine), 405.0 and 416.5 (piperidine) and 418.0 and 422.0 (3-picoline) both in direct and isoamyl alcohol (IAA) extracted system, respectively. Results indicate that the highest sensitivity and molar absorptivity of Pd-RA pyridine system in direct spectrophotometry were 0.01497 mu g Pd(II) cm/sup -2/ and 7107.89 L mol sup -1/ cm/sup -1/ respectively. IAA extracted Pd-RA-piperidine system was found to give a sensitivity of 0.01087 mu g(Pd(II) cm /sup -2/ and molar absorptivity of 9788.80 L mol /sup -1/ cm/sup -1/ which were the highest of all the system. The effects due to variation of pH, reagent concentrations, order of addition of reagents, time, temperature and solvent media on the absorption spectra have been investigated and the optimum conditions determined. The effects of diverse ions and their tolerance limit have also been studies. (author)

[en] Luminescence spectroscopy and in particular time resolved luminescence spectroscopy has become most suitable technique to characterize the uranyl species, as uranyl complexes are known to emit green light upon photo irradiation. The characteristic luminescence features originate from uranyl ion have been used to identify the specie and help to understand the complexation behavior of uranyl with various ligands. In this work, luminescence of uranyl (UO_2"2"+) - picolinic acid complex has been studied in aqueous and acetonitrile medium. In aqueous medium, the uranyl luminescence gets quenched when complexed with picolinic acid; whereas, uranyl luminescence is found to be enhanced by picolinic acid in acetonitrile medium. The enhancement is due to the sensitization of uranyl luminescence by picolinate ion. UV-Vis spectroscopy studies revealed the formation of 1:2 type complex of uranyl with picolinate in acetonitrile medium. This enhanced luminescence results in very low detection limit for uranium, namely 0.6 ppb. (author)

[en] The ideal gas state thermodynamic properties of 4-methylpyridine have been calculated based on free internal rotation of the methyl group. Selected values are compared with accurate experimental results

[en] Published in suMmary form only

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[en] The synthesis and solvent extraction behavior of dipicolinic acid (pyridine-2,6-dicarboxylic acid, PDCA) and their derivatives have been studied for possible use in selective back extraction of actinides, especially americium. The extraction was performed from an organic phase containing a mixture of trivalent actinides and lanthanides pre-extracted with N,N,N',N'-tetraoctyl diglycolamide (TODGA). The efficiency of the back-extraction was enhanced when the picolinate platform was used in a heterocyclic deca-dentate ligand called h₄tpaen. Beyond selective An/Ln extraction, the aqueous soluble h4tpaen ligand seemed a potential reagent for an intra-group Am(III)/Cm(III) separation with a separation factor SF(Cm/Am) of about 3.5. (authors)

[en] Studies in our laboratory have shown that the thorium(IV) complexes (C₅Me₅)₂ThPh₂ and (C₅Me₅)₂Th(CH₂Ph₂)₂ mediate carbon-nitrogen bond cleavage and dearomatization of the pyridine ring in pyridine N-oxide. Based upon these results, we examined the analogous chemistry with a variety of pyridine compounds to determine if the electron-withdrawing oxygen present in pyridine N-oxide was required for reactivity of this type. Interestingly, reaction of (C₅Me₅)₂An(CH₃)₂ (An = Th, U) with pyridine and substituted analogues produces CH₄ and the corresponding η²-(N,C)-pyridyl complexes by activation of the sp²-hybridized ortho C-H bond. Isotopic labeling studies indicate that the C-H activation reactions are consistent with a σ-bond metathesis mechanism. Additionally, the η²-(N,C)-pyridyl complexes undergo ligand-exchange reactions with both pyridine-d ₅ and α-picoline