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Descroix S Le Potier I Niquet C Minc N Viovy JL Taverna M 《Journal of chromatography. A》2005,1087(1-2):203-209
The potential of the commercially available dye sypro orange for in-capillary derivatization was evaluated for the detection of insulin and one gastrointestinal peptide (Arg-Arg-gastrin) by capillary electrophoresis with laser induced fluorescence (CE-LIF). The fluorescent emission intensity (lambda(ex) = 488 nm, lambda(em) = 610 nm) of this probe is very low in aqueous medium, and increases strongly in less polar solvent, e.g. methanol. The hydrophobic character of the two analyzed peptides is too low to induce sufficient interaction with the fluorescent probe for good sensitivity when the latter is alone in the background electrolyte. Thus, the potential of several neutral, zwitterionic, cationic and anionic surfactants to favor probe/peptide interactions has been evaluated. It was demonstrated that a borate buffer (pH 8.5) containing tetradecyltrimethylammonium bromide (TTAB) in sub-micellar conditions can be considered as the most suitable buffer for insulin CE-LIF analysis. In addition, the method showed a good linearity between insulin concentration and the peak area of the labeled insulin, allowing quantitative measurements. The sensitivity achieved so far is comparable with that achieved with UV absorption detection, but even at this level it is interesting for microchip analysis, in which fluorescence detection is much more commonly available than UV absorption detection. 相似文献
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We use Fermi-liquid relations to address the accuracy of conductances calculated from the single-particle states of exact Kohn-Sham (KS) density functional theory. We demonstrate a systematic failure of this procedure for the calculation of the conductance, and show how it originates from the lack of renormalization in the KS spectral function. In certain limits this failure can lead to a large overestimation of the true conductance. We also show, however, that the KS conductances can be accurate for single-channel molecular junctions and systems where direct Coulomb interactions are strongly dominant. 相似文献
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A. Faivre G. Niquet M. Maglione J. Fornazero J.F. Jal L. David 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,10(2):277-286
The relaxation behaviour of two molecular glass-forming systems, namely sorbitol and maltitol, are investigated in the large
temperature range relevant to the glass-transition. These data are obtained by combining three techniques, i.e. low-frequency mechanical spectroscopy, medium and high frequency dielectric spectroscopy, and viscosity measurements. This
procedure allows to determine the relaxation map of these polyols on a wide time range [10-9-107
s]. Two different relaxation processes can be observed. The principal α-relaxation process exhibits a complex behaviour, comprising
a non-Arrhenius temperature dependence above T
g
(supercooled liquid state), and an Arrhenius behaviour below T
g
(glassy state). A secondary β-relaxation is observed at higher frequencies with an Arrhenius temperature dependence. The
secondary process appears in the same time-temperature range in both polyols. Consequently the molecular root of this relaxation
is most likely the same in these complementary chemical systems. On the other hand, the time scale on which the α and β processes
cross is very different for these two polyols. We relate this feature to the differences in the relative contributions of
intra and inter-molecular interactions due to the different chemical architecture of these polyols. 相似文献
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Synthesis and Structure of Mo2NCl7 The reaction of VN with MoCl5 at 175 °C in a sealed glass ampoule yields the molybdenum(V) nitride chloride Mo2NCl7 in form of air sensitive black crystals with the triclinic space group P1¯ and a = 905.7(8); b = 975.4((6); c = 1283.4(8) pm, α = 103.13(4)°; β = 109.83(5)° und γ = 98.58(5)°. The crystal structure is built up from dinuclear units [Mo2N2Cl7]3— and [Mo2Cl7]3+, which are connected by asymmetric nitrido bridges to form endless chains. Within both dinuclear units the Mo atoms are bridged by three Cl atoms resulting in a Mo‐Mo distance of 349.2(3) pm in the unit [Mo2N2Cl7]3—. In case of [Mo2Cl7]3+, however, a shorter Mo‐Mo distance of 289.4(3) pm is observed, which can be interpreted by a single bond. Correspondingly a reduced magnetic moment of 0.95 B.M. per Mo atom is observed. 相似文献
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Manfredo Hrner Vanessa S. Carratu Jairo Bordinhao Angela Silva Elke Niquet 《Acta Crystallographica. Section C, Structural Chemistry》2004,60(3):m140-m142
In the title compound, [Cd(C12H8F2N3)2(C5H5N)2], the Cd atom lies on a crystallographic twofold axis in space group Iba2. The coordination geometry about the CdII ion corresponds to a rhombically distorted octahedron, with two deprotonated 1,3‐bis(2‐fluorophenyl)triazenide ions, viz. FC6H4NNNC6H4F−, acting as bidentate ligands (four‐electron donors). Two neutral pyridine (py) molecules complete the coordination sphere in positions cis with respect to one another. The triazenide ligand is not planar (r.m.s. deviation = 0.204 Å), the dihedral angle between the phenyl rings of the terminal 2‐fluorophenyl substituents being 24.6 (1)°. The triazenide and pyridine Cd—N distances are 2.3757 (18)/2.3800 (19) and 2.3461 (19) Å, respectively. Intermolecular C—H⋯F interactions generate sheets of molecules in the (010) plane. 相似文献
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Modulation of the voltage applied to a metal-insulator-metal structure induces a modulation of the reflectance, which has been measured with a lock-in amplifier. The spectrum of electroreflectance contains structures which are characteristic of both Ag-Al2O3 and Au-Al2O3 interfaces. 相似文献
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Pedro I. da S. Maia Fernando R. Pavan Clarice Q.F. Leite Sebastião S. Lemos Gerimário F. de Sousa Alzir A. Batista Otaciro R. Nascimento Javier Ellena Eduardo E. Castellano Elke Niquet Victor M. Deflon 《Polyhedron》2009
The development of more efficient anti-tuberculosis drugs is of interest. Three oxovanadium(IV) and three cis-dioxovanadium(V) complexes with thiosemicarbazone derivatives bearing moieties with different lipophilicity have been prepared and had their inhibitory activity against Mycobacteriumtuberculosis H37Rv ATCC 27294 evaluated. The analytical methods used by the complexes’ characterization included IR, EPR, 1H, 13C and 51V NMR spectroscopies, elemental analysis, cyclic voltammetry, magnetic susceptibility measurement and single crystal X-ray diffractometry. [VO(acac)(aptsc)], [VO(acac)(apmtsc)] and [VO(acac)(apptsc)] (acac = acetylacetonate; Haptsc = 2-acetylpyridinethiosemicarbazone; Hapmtsc = 2-acetylpyridine-N(4)-methyl-thiosemicarbazone and Happtsc = 2-acetylpyridine-N(4)-phenyl-thiosemicarbazone) are paramagnetic and their EPR spectra are consistent with the monoanionic N,N,S-tridentate coordination of the thiosemicarbazone ligands, resulting in octahedral structures of rhombic symmetry and with the oxidation state +IV for the vanadium atom. As result of oxidation of the vanadium(IV) complexes above, the diamagnetic cis-dioxovanadium(V) complexes [VO2(aptsc)], [VO2(apmtsc)] and [VO2(apptsc)] are formed. Their 1H, 13C and 51V NMR spectra were acquired and support a distorted square pyramidal geometry for them, in accord with the solid state X-ray structures determined for [VO2(aptsc)] and [VO2(apmtsc)]. In general, the vanadium compounds show comparable or larger anti-M. tuberculosis activities than the free thiosemicarbazone ligands, with MIC values within 62.5–1.56 (μg/mL). 相似文献
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Pedro Ivo da S. Maia Victor M. Deflon Elizeu J. de. Souza Edgardo Garcia Gerimário F. de. Sousa Alzir A. Batista Alberthmeiry T. de. Figueiredo Elke Niquet 《Transition Metal Chemistry》2005,30(4):404-410
Two oxovanadium(IV) and (V) complexes with 2-acetylpyridine-benzoylhydrazone have been prepared and characterized. The analytical methods used included elemental analysis, i.r., FAB+ m.s., 51V-n.m.r. and e.p.r. X-ray diffractometry from single crystals as well as from microcrystalline material were also performed. Molecular modeling was used to calculate the complex structures in a vacuum and their vibrational frequencies. Octahedral coordination is suggested for the complex acetylacetonato(2-acetylpyridine-benzoylhydrazonato)-oxovanadium(IV) (1), for which good agreement was verified between calculated and observed i.r. data. Two crystal structure modifications of (2-acetylpyridine-benzoylhydrazonato)dioxovanadium(V) (2) have been determined by X-ray diffraction methods. In both crystalline modifications the molecular structure of the complex shows a distorted trigonal bipyramidal VN2O3 coordination. The molecular structure, found experimentally for (2), was compared with the theoretically calculated one. The results validate the theoretical method. 相似文献