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201.
Copper determination in natural water samples by using FAAS after preconcentration onto amberlite XAD-2 loaded with calmagite 总被引:2,自引:0,他引:2
A procedure for separation and preconcentration of trace amounts of copper in natural water samples, has been proposed. It is based on the adsorption of copper(II) ions onto a column of Amberlite XAD-2 resin loaded with calmagite reagent. This way amounts of copper within the range from 0.0125 to 25.0 μg, in a sample volume of 25 to 250 ml, and pH from 3.7 to 10.0 was concentrated as calmagite complex in a column of 0.50 g of Amberlite XAD-2 resin. Copper (II) ion was desorpted by using 5.0 ml of 2 mol l−1 hydrochloric acid. Detection and determination limits of the proposed procedure for 250 ml sample volume were 0.15 and 0.50 μg l−1, respectively. Selectivity test showed that (in the indicated concentration), calcium(II) (500 mg l−1), magnesium(II) (500 mg l−1), strontium(II) (50 mg l−1), iron(III) (10 mg l−1), nickel(II) (10 mg l−1), cobalt(II) (10 mg l−1), cadmium(II) (10 mg l−1) and lead(II) (10 mg l−1) did not interfere in copper determination by this procedure. Precision of the method, evaluated as the relative standard deviation by analyzing a series of seven replicates, was 2.42% for a copper mass of 1.0 μg in a sample volume of 100 ml. The accuracy of the proposed procedure was evaluated by means of copper determination in reference biological samples. The achieved results were in good agreement with certified values. The extractor system had a sorption capacity of 1.59 μmol of copper per gram of resin loaded with calmagite. The proposed procedure was applied for copper determination by FAAS in natural water samples. Samples were collected from different places of Salvador city, Bahia, Brazil. The achieved recovery, measured by the standard addition technique, showed that the proposed procedure had good accuracy. A good enrichment factor (50×) and simplicity are the main advantages in this analytical procedure. 相似文献
202.
Karl Eberhard Bessler Jennifer Alves dos Santos Victor Marcelo Deflon Sebastio de Souza Lemos Elke Niquet 《无机化学与普通化学杂志》2004,630(5):742-745
The preparation and structures of 2, 2′‐dihydroxyazobenzenato‐dibutyl‐tin [Bu2SnL] and 2, 2′‐dihydroxyazobenzenato‐dimethyl‐tin [Me2SnL] are described. The complexes were characterized by IR, NMR (1H, 13C, 119Sn) and UV/VIS spectra. The crystal structures were determined by X‐ray diffraction on single crystals. [Bu2SnL]: monoclinic, space group P21/c, cell constants at 208 K: a = 860.73(5), b = 973, 51(18), c = 2340.0(3) pm, β = 93.615(11)°; R1 = 0.0546. [Me2SnL]: orthorhombic, space group Pbcn, cell constants at 208 K: a = 1914.6(4), b = 1041.3(3), c = 1323.27(14) pm; R1 = 0.0529. 相似文献
203.
Pamela Lemos Cruz Natalja Kulagina Grgory Guirimand Johan-Owen De Craene Sbastien Besseau Arnaud Lanoue Audrey Oudin Nathalie Giglioli-Guivarch Nicolas Papon Marc Clastre Vincent Courdavault 《Molecules (Basel, Switzerland)》2021,26(12)
Plant specialized metabolites are widely used in the pharmaceutical industry, including the monoterpene indole alkaloids (MIAs) vinblastine and vincristine, which both display anticancer activity. Both compounds can be obtained through the chemical condensation of their precursors vindoline and catharanthine extracted from leaves of the Madagascar periwinkle. However, the extensive use of these molecules in chemotherapy increases precursor demand and results in recurrent shortages, explaining why the development of alternative production approaches, such microbial cell factories, is mandatory. In this context, the precursor-directed biosynthesis of vindoline from tabersonine in yeast-expressing heterologous biosynthetic genes is of particular interest but has not reached high production scales to date. To circumvent production bottlenecks, the metabolic flux was channeled towards the MIA of interest by modulating the copy number of the first two genes of the vindoline biosynthetic pathway, namely tabersonine 16-hydroxylase and tabersonine-16-O-methyltransferase. Increasing gene copies resulted in an optimized methoxylation of tabersonine and overcame the competition for tabersonine access with the third enzyme of the pathway, tabersonine 3-oxygenase, which exhibits a high substrate promiscuity. Through this approach, we successfully created a yeast strain that produces the fourth biosynthetic intermediate of vindoline without accumulation of other intermediates or undesired side-products. This optimization will probably pave the way towards the future development of yeast cell factories to produce vindoline at an industrial scale. 相似文献
204.
Lemos TL Monte FJ Santos AK Fonseca AM Santos HS Oliveira MF Costa SM Pessoa OD Braz-Filho R 《Natural product research》2007,21(6):529-550
The present review focus in quinones found in species of Brazilian northeastern Capraria biflora, Lippia sidoides, Lippia microphylla and Tabebuia serratifolia. The review cover ethnopharmacological aspects including photography of species, chemical structure feature, NMR datea and biological properties. Chemical transformations of lapachol to form enamine derivatives and biological activities are discussed. 相似文献
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We consider a model in which dark matter is stable as it is charged under a Z2 symmetry that is residual after an A4 flavour symmetry is broken. We consider the possibility to generate the quark masses by charging the quarks appropriately under A4. We find that it is possible to generate the CKM mixing matrix by an interplay of renormalisable and dimension-six operators. In this set-up, we predict the third neutrino mixing angle to be large and the dark matter relic density to be in the correct range. Low energy observables - in particular meson-antimeson oscillations - are hard to facilitate. We find that only in a situation where there is a strong cancellation between the Standard Model contribution and the contribution of the new Higgs fields, B meson oscillations are under control. 相似文献