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61.
A closed vessel method using a microwave oven was developed for the determination of As, B, Ba, Bi, Cd, Cr, Cu, Fe, Hg, Ni, Pb, Se, Sn and Sb by Inductively Coupled Argon Plasma Optical Emission Spectrometry (ICP OES). The method was applied to samples of polyvinyl acetate-based glue in water emulsions. Parameters such as wavelength, nebulization pressure and RF power were optimized and the residual acidity after the digestion process was determined. The addition of internal standards was evaluated and the accuracy of the proposed method was verified with addition and recovery experiments and also with certified reference materials, achieving good results. Using a nebulization flow rate of 0.73 L min−1and a RF power of 1200 W it was possible to obtain adequate values for limit of detection and limit of quantification as well as recovery values in the range of 80-106%, for all the analytes. The analysis of coloured glue samples (white, black, blue, yellow, red and green), widely used by children, showed no contamination by the elements studied. 相似文献
62.
Maria Aparecida S. SilvaTércio de F. Paulo Solange de O. PinheiroAlzir A. Batista Javier EllenaEduardo H.S. Sousa Luiz G. de F. LopesIzaura C.N. Diógenes 《Polyhedron》2011,30(12):2083-2089
[(SO3)Co(cyclam)(NCS)] and [(SO3)Co(cyclam)-NCS-Ru(NH3)4(NCS)](BF4) complexes were synthesized and characterized by means of X-ray diffraction, electrochemistry, elemental analysis, and spectroscopic techniques. Crystallographic and FTIR data indicated NCS− ligand is coordinated to Co through the nitrogen atom in the monomer species. Electrochemistry and FTIR data of the material isolated after reductive electrolysis of [(SO3)Co(cyclam)(NCS)] hint that NCS− and SO32− are released thus forming [Co(cyclam)(L)2]2+, where L is solvent molecules. The formation of the heterobimetallic mixed-valence complex induced a thermodynamic stabilization of Co and Ru metal atoms in the oxidized and reduced states, respectively. According to the Robin and Day classification, a Class II system with a comproportionation constant of 5.78 × 106 is suggested for the mixed-valence complex based on the electrochemical and UV-Vis-NIR results. 相似文献
63.
64.
Quancard J Labonne A Jacquot Y Chassaing G Lavielle S Karoyan P 《The Journal of organic chemistry》2004,69(23):7940-7948
The amino-zinc-ene-enolate cyclization reaction is a straightforward route to the synthesis of 3-substituted prolines. Herein we report the application of this reaction to the syntheses of proline chimeras of lysine, glutamic acid, glutamine, arginine, and serine. All these compounds were obtained in enantiomerically pure form and suitably protected for peptide synthesis. 相似文献
65.
66.
A system for determination of manganese, after preconcentration with 3% (w/w) 1-(2-pyridylazo)-2-naphthol (PAN), adsorbed on microcrystalline naphthalene is proposed. An amount of 200 mg of this complexing mixture is placed in a glass column and conditioned with a NH4Cl/NH4OH buffer solution (pH 9.5). The aqueous sample, containing manganese, is treated with an ammonium tartrate solution, then with a hydroxylammonium chloride solution and, finally, with a buffer solution. The resulting solution is passed through the column containing microcrystalline naphthalene modified with 1-(2-pyridylazo)-2-naphthol (PAN) where Mn(II) is retained. The column is first washed with deionized water and then with 10.0 ml of dimethylformamide to dissolve the Mn(II)-PAN/naphthalene complex. Manganese is determined by air-acetylene flame atomic absorption spectrometry. About 1 μg of manganese can be concentrated from 200 ml of aqueous sample, allowing a preconcentration factor of 20, a limit of quantification of 5 ng ml−1 and R.S.D. of 3.8%. The accuracy was ascertained using certified reference materials, including samples of urine and glass. Water samples were also analysed and the results are in good agreement with those obtained by graphite furnace atomic absorption spectrometry. 相似文献
67.
Isolda C. Mendes Juliana P. Moreira Antonio S. Mangrich Solange P. Balena Bernardo L. Rodrigues Heloisa Beraldo 《Polyhedron》2007
Five copper(II) complexes with N(4)-ortho, N(4)-meta and N(4)-para-tolyl thiosemicarbazones derived from 2-formyl and 2-acetylpyridine were obtained and thoroughly characterized. The crystal structure of N(4)-meta-tolyl-2-acetylpyridine thiosemicarbazone (H2Ac4mT) was determined, as well as that of its copper(II) complex [Cu(2Ac4mT)Cl], which contains an anionic ligand and a chloride in the coordination sphere of the metal. The in vitro antimicrobial activities of all thiosemicarbazones and their copper(II) complexes were tested against Salmonella typhimurium and Candida albicans. Upon coordination a substantial decrease in the minimum inhibitory concentration, from 225 to 1478 μmol L−1 for the thiosemicarbazones to 5–30 μmol L−1 for the complexes was observe against the growth of Salmonella typhimurium and from 0.7–26 to 0.3–7 μmol L−1 against the growth of C. albicans, suggesting that complexation to copper(II) could be an interesting strategy of dose reduction. 相似文献
68.
Sagan S Quancard J Lequin O Karoyan P Chassaing G Lavielle S 《Chemistry & biology》2005,12(5):555-565
We examined the effect of simultaneously incorporating proline or proline-amino acid chimeras in positions 9, 10, and/or 11 of substance P, on the affinity for the two NK-1 binding sites and on second-messenger activation. Because these 3-substituted prolines constrain not only the (phi,psi) values of the peptide backbone, but also the chi space of the amino acid side chain, we were able to gather data on the structural requirements for high-affinity binding to the NK-1 receptor. We were able to confirm that this C-terminal component is crucial and that it should adopt an extended conformation close to a polyproline II structure when bound to the receptor. The partial additivity of these constraints, more specifically, for the NK-1M site, suggests that the peptide backbone flexibility around the hinge-point residue Gly9 is essential to subtly position crucial side chains. 相似文献
69.
Fernando de C. da Silva James L. Wardell Solange M. S. V. Wardell Vitor F. Ferreira John N. Low Christopher Glidewell 《Acta Crystallographica. Section C, Structural Chemistry》2007,63(10):o568-o571
The title compounds, namely 6‐methoxy‐3,3‐dimethyl‐3H‐benzo[f]chromene, C16H16O2, (III), and racemic 3‐bromo‐2,2,6,6‐tetramethyl‐3,4‐dihydro‐2H,6H‐1,5‐dioxatriphenylene, C20H21BrO2, (IV), were both synthesized in one‐step regioselective Wittig reactions from substituted 1,2‐naphthoquinones. The new ring in both compounds adopts a screw‐boat conformation. A single π–π stacking interaction links the molecules of (III) into centrosymmetric dimeric aggregates, and a single C—H...π(arene) hydrogen bond links the molecules of (IV) into centrosymmetric dimers. 相似文献
70.
R. Alan Howie James L. Wardell Solange M. S. V. Wardell Philip J. Cox 《Acta Crystallographica. Section C, Structural Chemistry》2000,56(5):e179-e180
The structure at 298 K described here, [Sn(C6H5)3(C7H4NO4)], completely confirms the results at 173 K obtained previously [Weng, Das & Robinson (1990), Malays. J. Sci. 12 , 57]. In both structures, weak interaction between Sn and the carbonyl O atom of the benzoate group provides a distorted trigonal‐pyramidal environment at the Sn atom derived from its pseudo‐tetrahedral primary coordination in both molecules of the asymmetric unit. 相似文献