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21.
del Mar Graciani M Rodríguez A Muñoz M Moyá ML 《Langmuir : the ACS journal of surfaces and colloids》2005,21(16):7161-7169
Micellization in water-ethylene glycol (EG) N-dodecyl, N-tetradecyl, and N-hexadecyl-N,N-dimethyl-3-ammonio-1-propanesulfonate (SB3-12, SB3-14, and SB3-16, respectively) micellar solutions, with the weight percent of EG changing within the range 0-40, was studied by means of surface tension measurements. Information about the influence of the added EG on the aggregation number of the sulfobetaine micelles and on the polarity of the interfacial region of micelles was obtained through fluorescence and spectroscopic measurements. Surface tension measurements also provide information about the dependence of the surface excess concentration, the minimum area per surfactant molecule, the surface pressure at the cmc, and the standard Gibbs energy of adsorption on the added weight percent of the organic solvent. The Gordon parameter of the water-EG mixtures was also estimated by means of surface tension measurements. The thermodynamic and structural changes originated by the presence of EG control the micellar kinetic effects observed in the reaction methyl 4-nitrobenzenesulfonate + Br(-) occurring in the water-EG sulfobetaine micellar solutions. Information about the distribution of bromide ions between the bulk and micellar pseudophases was obtained through conductivity measurements. The kinetic micellar effects were quantitatively explained by using the pseudophase kinetic model. 相似文献
22.
Ruiz E Rodríguez-Fortea A Cano J Alvarez S Alemany P 《Journal of computational chemistry》2003,24(8):982-989
The application of theoretical methods based on the density functional theory with hybrid functionals provides good estimates of the exchange coupling constants for polynuclear transition metal complexes. The accuracy is similar to that previously obtained for dinuclear compounds. We present test calculations on simple model systems based on H. He and CH(2). He units to compare with Hartree-Fock and multiconfigurational results. Calculations for complete, nonmodeled polynuclear transition metal complexes yield coupling constants in very good agreement with available experimental data. 相似文献
23.
J. L. Gascón M. Rodríguez J. A. Suárez Del Rey 《Journal of Radioanalytical and Nuclear Chemistry》1996,207(1):63-69
The determination of Am and Cm in typical waste streams from nuclear power plants using anion exchange chromatography has some drawbacks like the contamination by Pu and Po. This improved procedure solves these problems, and it has been applied with success to the analysis of Am and Cm in nuclear waste samples: ion exchange resins, ion exchange resins solidified with cement and evaporator concentrates. 相似文献
24.
Solid-phase extraction of phenols 总被引:9,自引:0,他引:9
Sample preparation for phenol analysis using solid-phase extraction (SPE) is reviewed. The scope of the review has been restricted to the literature dealing with the analysis of phenols as the main objective. The use, advantages and disadvantages of silica sorbents, polymeric, functionalized, carbon-based and mixed available sorbents, when applied to the separation and preconcentration of phenols, as well as the available experimental devices, are discussed. Other aspects such as phenol derivatisation prior to SPE, solid-phase microextraction, matrix effects and the storage of phenols in SPE cartridges, have been also discussed. 相似文献
25.
A. Caubet A. Labarta R. Rodríguez A. Fernandez E. Molins V. Moreno J. Tejada 《Hyperfine Interactions》1986,28(1-4):773-776
By means of57Co Mössbauer emission spectroscopy and magnetic susceptibility measurements, the local symmetries and electronic structure of the Co(II) ions in the Co-5IMO and Co-5GMP complexes in the hydrated and dehydrated forms have been determined. 相似文献
26.
27.
Francisco García-Montelongo María J. Sánchez Miguel A. Rodríguez 《Mikrochimica acta》1989,98(4-6):259-265
A spectrophotometric method for cyanide based on its inhibition of the colour formation reaction between nickel(II) and 3-(4,5-dimethyl-2-thiazolylazo)-2,6-dihydroxybenzoic acid has been developed, and allows the determination of down to 0.1 g of cyanide. Most of the interferences can be avoided by displacement of the hydrogen cyanide using an arsine generator. 相似文献
28.
Methodology based on the cloud-point phenomenon was applied to the comparative study of 3 different polyoxyethylene nonionic surfactants in order to extract and preconcentrate a group of phenolic derivatives in water samples; these phenolic compounds, which were determined by liquid chromatography with UV detection, included 11 pollutants given priority by the U.S. Environmental Protection Agency. The optimum conditions for the extraction and preconcentration of phenolic compounds were established for each surfactant. The surfactant that gave the best extraction and preconcentration of the analytes under study was polyoxyethylene 6 lauryl ether (C12E6) with detection limits of <3.5 microg/L for all the phenolic compounds tested. The method was applied to seawater and depurated wastewater samples. 相似文献
29.
Complexes of osmium tetroxide with nitrogen ligands were developed and used in our laboratory as probes of the DNA structure. Here, we show that the complex of osmium tetroxide with 2,2'-bipyridine (Os,bipy) can be used for modification and electrochemical detection of proteins at neutral pH. Salmon luteinizing hormone (SLH) containing two tryptophan (Trp) residues and human luteinizing hormone (HLH) containing one Trp were modified by Os,bipy and measured by differential pulse adsorptive stripping voltammetry (DPAdSV) at a hanging mercury drop electrode (HMDE). The intensity of the DPAdSV catalytic signals corresponded to the number of Trp residues in the peptide molecule. Decreasing pH of the background electrolyte from 6.6 to 3.8 led to the increase of DPAdSV signals, suggesting that at pH 3.8, the DPAdSV detection limit might be well below 1 ng/ml. Our results suggest that Os,bipy is potentially useful for chemical modification of proteins. 相似文献
30.
Rodríguez AD Ramírez C Rodríguez II Barnes CL 《The Journal of organic chemistry》2000,65(5):1390-1398
Four diterpenes and a nor-diterpenoid, all of which possess unusual carbocyclic skeletons, were isolated from the hexane solubles of the West Indian gorgonian Pseudopterogorgia elisabethae. The structures and relative configurations of novel metabolites elisabethin D (2), elisabethin D acetate (3), 3-epi-elisabanolide (5), elisapterosin A (6), and elisapterosin B (7) were elucidated by interpretation of overall spectral data, which included 2D NMR correlation methods, IR, UV, and accurate mass measurements (HREI-MS and HRFAB-MS), chemical reactions, and X-ray diffraction analyses. The tetracyclic carbon skeleton of the elisapterosins is undescribed and constitutes a new class of C(20) rearranged diterpenes. Elisapterosin B displays strong in vitro anti-tuberculosis activity. 相似文献