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81.
In this paper, the transport of Cu(II) in the presence of lipophilic Cu(II) organic complexes through permeation liquid membranes (PLMs) have been investigated. In natural waters, small organic compounds, which form liposoluble neutral complexes with Cu(II), are potentially toxic and bioavailable. Hence, to understand the role of liposoluble Cu(II) complexes in natural waters, four organic ligands: phthalic acid, bipyridyl, pyrocatechol and hydroxyquinoline, which form uncharged or lipophilic Cu(II) complexes, were tested. The results showed that the transport of lipophilic Cu(II) complexes through PLM depends on the lipophilicity of the complex. Applications of PLMs in natural waters are presented. 相似文献
82.
Jacques Darriet Marc Drillon Gérard Villeneuve Paul Hagenmuller 《Journal of solid state chemistry》1976,19(3):213-220
The cationic ordering in the oxides which crystallize with the 6H structure gives rise to Ru5+Ru5+ pairs in (Ru2O9) clusters. The magnetic properties have been analyzed on the basis of the Heisenberg-Dirac-Van Vleck model: The d electrons are localized on each Ru5+ ion and interact strongly through antiferromagnetic exchange. The susceptibility curves agree with the H.D.V.V. model. The values of the exchange integrals have been determined by fitting the experimental values. 相似文献
83.
Edgar Heilbronner Evi Honegger Jacques Lecoultre Cyril A. Grob Raymond Houriet Eric Rolli 《Helvetica chimica acta》1986,69(8):2114-2126
The n ionization energies I and the gas-phase basicities GB of CH3-, Cl-, or CN-substituted quinuclidines have been measured by PE and ICR spectroscopy. The dependence of the shifts ΔI and ΔGB (relative to the values of the parent molecule) allow conclusions about the charge dispersal accompanying the n ionization or the protonation of quinuclidine in the gas phase. The agreement with the results of a minimal basis set ab initio calculation is excellent. Comparison of the solution pKa values with either I or GB reveals that 2-substituted quinuclidines exhibit sizeable solvent-induced proximity effects, i.e. that the corresponding quinuclidinium ions are more acidic in solution than expected on the basis of the gas-phase basicities. This agrees with earlier results concerning 2-substituted pyridines. 相似文献
84.
Abohachem Laguecir Serge Ulrich Jérôme Labille Nicolas Fatin-Rouge Serge Stoll Jacques Buffle 《European Polymer Journal》2006,42(5):1135-1144
Monte Carlo simulations, experimental titrations and fluorescence correlation spectroscopy experiments were used to investigate the conformational and electrical properties of polyacrylic acids (PAA). On the one hand, titration curves were calculated to get an insight into the role of pH on the degree of ionization and conformation of PAA chains. On the other hand, experimental potentiometric titrations of PAA were also achieved for different PAA molecular weights and compared to the calculated titration curves obtained by Monte Carlo coarse grained simulations. It was found that for a large range at intermediate PAA ionizations, a good correlation is obtained between experimental and simulations data thanks to the prominence of electrostatic interactions in this domain. The effect of ionic concentration and PAA molecular weight on the titration curves was also investigated. In order to get a better understanding of PAA conformational behavior, we also investigated PAA diffusion properties in aqueous solutions as a function of pH and ionic strength by fluorescence correlation spectroscopy (FCS), thanks to its high sensitivity to measure diffusion coefficients of tracer solutes. Good qualitative agreements were observed between experimental diffusivities and polymer properties calculated from MC simulations. It was shown that the high molecular weight PAA chains display more significant changes in diffusivity in agreement with the ionization degrees and conformational changes observed in the simulations. 相似文献
85.
Emmanuel Beyou Pierre Babin Bernard Bennetau Jacques Dunogues Dominique Teyssie Sylvie Boileau 《Journal of polymer science. Part A, Polymer chemistry》1994,32(9):1673-1681
Unsaturated perfluoroalkyl esters derived from undecylenic acid: CH2?CH? (CH2)8? COO? CH2? CH2? RF (with RF?C6F13, 2a and RF?C8F17, 2b ) and C8F17? (CH2)10? COO? CH2? CH?CH2, 2c were prepared with excellent yields. Their hydrosilylation by methylhydrodimethylsiloxane copolymers of various Si? H contents gives new fluorinated polysiloxanes which were examined by 1H- and 13C-NMR, GPC, differential scanning calorimetry, and optical polarizing microscopy. Polymers derived from compounds 2a and 2b exhibit mesomorphic structures. © 1994 John Wiley & Sons, Inc. 相似文献
86.
The catalytic regeneration of depolarizers by certain substrates has been demonstrated by means of cyclic voltammetry. As depolarizers we have employed anion radicals of aromatic hydrocarbons, heteroaromatic compounds, ketones, esters, nitriles, and olefins, and dianions of aromatic hydrocarbons, heteroaromatic compounds, ketones, and esters. As substrates we have investigated simple aromatic and aliphatic halides, 1,2- and 1,3-dihalides, carbon dioxide, and activated olefins. A requirement for the observation of a catalytic wave is that the reduced substrate undergoes a practically irreversible reaction after the reaction with the reduced depolarizer; for simple halides it is a cleavage reaction, for 1,2- and 1,3-dihalides an elimination, for carbon dioxide an addition, and for activated olefins a coupling. Electrochemical investigations of these kinds of reactions may be of interest in connection with the mechanism of several types of reactions in organic chemistry. 相似文献
87.
A simple equation has been derived relating the temperature dependence of activity functions with excess enthalpies and excess heat capacities. Using experimentally determined parameters at 298.15°K, it is possible to predict osmotic coefficients and mean activity coefficients of alkali halides in water up to 1 m from 273°K to about 350°K. In general, the predicted functions agree with the measured values within the uncertainty of the activity data. An equation is also given for the pressure dependence of the excess free energies, but it was not possible to check the limitation of this equation due to lack of activity data at various pressures.To whom correspondence should be addressed. 相似文献
88.
[reaction: see text] Quinodimethanes are highly reactive toward dienophiles since Diels-Alder cycloaddition results in an aromatic product. Density functional-based (13)C, (1)H NMR, NICS, and MO-NICS calculations indicate that the increase of aromatic character of the developing benzenoid ring along the reaction path is especially pronounced after the transition state is reached, even though the number of pi orbitals decreases. The forming aliphatic ring exhibits large ring current effects during the reaction. 相似文献
89.
van Hooft PA El Oualid F Overkleeft HS van der Marel GA van Boom JH Leeuwenburgh MA 《Organic & biomolecular chemistry》2004,2(9):1395-1403
The scope of a stereoselective three-step approach for the synthesis of sugar derived spiroketals is presented. The methodology consists of Grignard addition of vinyl- or allylmagnesium bromide to a carbohydrate lactone, followed by K-10 clay mediated glycosidation with a terminal alkenol and subsequent ring-closing metathesis of the resulting diene. The generality of this procedure is demonstrated by the synthesis of various pyranose- and furanose-derived spiroketals, as well as more advanced tricyclic spiroketal derivatives. It is shown that functionalisation of the double bond in the resulting spiroketals leads to fused polycyclic ethers. 相似文献
90.
Baudouin Jambe Jacqueline Marchand-Brynaert Jacques Devaux 《Journal of polymer science. Part A, Polymer chemistry》1995,33(8):1283-1292
Thermal degradation of poly(methyl-n-hexylsilane) in the solid state in absence of oxygen reveals formation of a cyclic pentamer between 150 and 250°C. Polymer is gradually degraded to an intermediate molecular weight distribution. The weight average of this new distribution is not only temperature-dependent, but is also a function of viscosity of the polymer and nature of chain ends. As no insolubles or Si? H groups are formed, the degradation mechanism is most likely a back-biting mechanism induced by active chain ends such as silyl anions or Si? Cl rather than a homolytic cleavage of the main chain. A concurrent intramolecular rearrangement reaction is also proposed. Moreover, this study proposes an explanation to the trimodal molecular weight distribution obtained by the Wurtz coupling of dichlorosilanes with molten sodium in refluxing toluene. © 1995 John Wiley & Sons, Inc. 相似文献