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31.
Fernandez Romero AJ López Cascales JJ Fernandez Otero T 《The journal of physical chemistry. B》2005,109(2):907-914
Polypyrrole/poly(vinyl sulfonate) (PPy/PVS) films in acetonitrile containing 0.1 M LiClO4 were studied by cyclic voltammetry. Consecutive voltammograms pointed to a continuous increase in the charge involved in the process, suggesting a rise in the number of the electroactive participants involved in the redox process. However, voltammograms obtained for the PPy/ClO4 films in analogous conditions pointed to a steady-state behavior from the very early cycles. Theoretical studies based on the Nernst and Butler-Volmer equations indicated that perchlorate ions are involved during the oxidation/reduction process of the PPy/PVS films when the steady state is reached. This result was confirmed by "ex situ" energy-dispersive X-ray analysis of the films. In this regard, the electrochemical behavior of PPy/PVS polymers was similar to that of PPy/ClO4 films when a high number of cycles were carried out. The exchange of ClO4- during the redox reaction of the PPy/PVS films made it necessary to incorporate Li+ cations inside the polymer during the initial voltammetric cycles to compensate for the negative charges of PVS polyanions. Li+ cations are mainly stabilized inside the polymer by the ion pairs formed with the sulfonated groups of the PVS. An increase and shift of the voltammetric cycles indicated a restructuring of the polymeric chains with consecutive scans. 相似文献
32.
Inmaculada Fernandez Robert Greatrex Norman N. Greenwood 《Journal of solid state chemistry》1980,34(1):121-128
99Ru Mössbauer spectra have been recorded at 4.2 K for the quaternary oxides Ba3Ru2MO9 (M = Mg, Ca, Sr; Co, Ni, Cu, Zn; and Cd), all of which crystallize with the hexagonal barium titanate structure. The Ca, Sr, and Cd compounds give sharp symmetrical singlets with chemical isomer shifts typical of ruthenium in the +5 oxidation state. The absence of magnetic hyperfine splitting is consistent with the published interpretation of magnetic susceptibility data in terms of binuclear intracluster spin pairing which leads to an S = 0 ground state. In contrast, magnetic hyperfine splitting is seen for the Mg, Zn, Co, Ni, and Cu compounds; this can be interpreted only in terms of long-range magnetic order and the absence of such an S = 0 ground state at 4.2 K. This differs from the published interpretation of the magnetic susceptibility data for Ba3Ru2MgO9 in the low-temperature region. The magnetic flux densities at the ruthenium nuclei in the magnetically ordered compounds (32.5–51.6 T) are lower than those normally associated with ruthenium(V), and the spectra cannot be curve fitted satisfactorily with single hyperfine patterns having the natural linewidth. Possible reasons for these observations are discussed. 相似文献
33.
The structure of five conformations of the-lac inhibitor clavulanic acid have been optimized using ab initio gradient methods at the 4-21G level. The conformations of lowest energy possess an intramolecular H bond and also have the lowest pyramidization of N1. Different side-chain conformations lead to (i) differences in anomeric interactions and variations of the hydroxyethylidene geometry and (ii) changes in the geometry of the ring skeleton, which are smaller in the four- than in the five-membered ring.On leave from Universidad de Santiago de Compostela, Departamento de Química Física, Facultad de Química, Galicia (Spain). 相似文献
34.
A routing R of a graph G is a set of n(n ? 1) elementary paths R(u, v) specified for all ordered pairs (u, v) of vertices of G. The vertex-forwarding index ξ(G) of G, is defined by Where ξ(G, R) is the maximum number of paths of the routing R passing through any vertex of G and the minimum is taken over all the routings of G. Let Gp denote the random graph on n vertices with edge probability p and let m = np. It is proved among other things that, under natural growth conditions on the function p = p(n), the ratio Tends to 1 in probability as n tends to infinity. 相似文献
35.
36.
Complexes of Dioxocyanogen (OCN)2 with TiCl4 and ZrCl4 A solution of (OCN)2 was obtained by reaction of AgOCN with Br2 in H2CCl2 at ?70°C. From this the complexes TiCl4(NCO)2 and ZrCl4(NCO)2 were obtained by addition of equimolar amounts of TiCl4 and ZrCl4, respectively. According to the i.r. and Raman spectra, the (NCO)2 ligand is bonded via its N atoms to the metal. 相似文献
37.
Laloup M Ramirez Fernandez Mdel M Wood M De Boeck G Henquet C Maes V Samyn N 《Journal of chromatography. A》2005,1082(1):15-24
A rapid and sensitive method for the analysis of delta9-tetrahydrocannabinol (THC) in preserved oral fluid was developed and fully validated. Oral fluid was collected with the Intercept, a Food and Drug Administration (FDA) approved sampling device that is used on a large scale in the U.S. for workplace drug testing. The method comprised a simple liquid-liquid extraction with hexane, followed by liquid chromatography-tandem mass spectrometry (LC-MS-MS) analysis. Chromatographic separation was achieved using a XTerra MS C18 column, eluted isocratically with 1 mM ammonium formate-methanol (10:90, v/v). Selectivity of the method was achieved by a combination of retention time, and two precursor-product ion transitions. The use of the liquid-liquid extraction was demonstrated to be highly effective and led to significant decreases in the interferences present in the matrix. Validation of the method was performed using both 100 and 500 MicroL of oral fluid. The method was linear over the range investigated (0.5-100 ng/mL and 0. 1-10 ng/mL when 100 and 500 microL, respectively, of oral fluid were used) with an excellent intra-assay and inter-assay precision (relative standard deviations, RSD <6%) for quality control samples spiked at a concentration of 2.5 and 25 ng/mL and 0.5 and 2.5 ng/mL, respectively. Limits of quantification were 0.5 and 0.1 ng/mL when using 100 and 500 microL, respectively. In contrast to existing GC-MS methods, no extensive sample clean-up and time-consuming derivatisation steps were needed. The method was subsequently applied to Intercept samples collected at the roadside and collected during a controlled study with cannabis. 相似文献
38.
V. V. A. Fernandez N. Tepale J. C. Sánchez-Díaz E. Mendizábal J. E. Puig J. F. A. Soltero 《Colloid and polymer science》2006,284(4):387-395
The synthesis of nanostructured poly(N-isopropylacrylamide) (polyNIPA) hydrogels by a two-stage polymerization process is reported here. The process involves the
synthesis of slightly crosslinked polyNIPA nanoparticles by inverse (w/o) microemulsion polymerization; then, these particles
are dried, cleaned and dispersed in an aqueous solution of NIPA and a crosslinking agent (N,N-methylene-bis-acrylamide or NMBA) and polymerized to produce the nanostructured hydrogels. Their swelling and de-swelling
kinetics, volume phase transition temperatures (T
VPT) and mechanical properties at the equilibrium swollen state are investigated as a function of the weight ratio of polyNIPA
particles to monomer (NIPA). The nanostructured gels exhibit larger equilibrium water uptake, faster swelling and de-swelling
rates and similar T
VPT than those of the conventional ones; moreover, the elastic and Young moduli are larger than those of the conventional hydrogels
at similar swelling ratios. The fast swelling and de-swelling kinetics are explained in terms of the controlled inhomogeneities
introduced by the method of synthesis. 相似文献
39.
The operating conditions for the absorptiometric determination of Yb(III) with the reagent 2-(3,5-dichloro-2-pyridylazo)-5-dimethylaminophenol (3,5-diClDMPAP) by a liquid—liquid extraction technique are presented. The complex yields a molar absorptivity of 1.54 × 105l.mole−1.cm−1 (λmax = 588 nm) and an optimum concentration range of 0.025–1.360n mg/l., at pH = 10. The method developed has been applied to the determination of Yb(III) in synthetic and concrete mixtures. 相似文献
40.