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71.
The interfering effects of various foreign ions on the determination of arsenic were studied by hydride generation inductively coupled plasma atomic emission spectrometry (HG-ICP-AES). There were serious inhibiting interferences by Cu, Pb, Co, Au, Pd and Ni. However, by using cyanide as a complexing agent these interferences could be completely eliminated over a wide range of interferent concentration. The optimum chemical parameters for continuous arsine generation were studied. A major advantage of this technique is that it only needs low acid concentrations and produces less hazardous waste. Sensivity, selectivity and accuracy of the determination of arsenic by HG-ICP-AES were investigated. The detection limit (in 1 mol/l HCl medium) for arsenic(III) was 0.82 ng/ml. The relative standard deviation for ten determinations of a solution containing 50 ng/ml arsenic was 1.3%. 相似文献
72.
The precipitation of calcium oxalate monohydrate (COM) was monitored at a Langmuir monolayer containing lipid raft domains. The raft-forming monolayer consists of a 2:1:1 mixture of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine/sphingomyelin/dihydrocholesterol, where the raft liquid ordered phase is enriched in sphingomyelin and the sterol. COM crystals, monitored by Brewster angle microscopy, appear at the phase boundary between the raft domains and the expanded phase. 相似文献
73.
MNDO and AMI calculations, including configuration interactions, were performed on cycloheptatriene (2), 1,6-methano[10]annulene (3), and the tautomeric elassovalenes (4), (5), and (6). The goal of this study is to examine these systems and assess indicators of the importance of through space (homoaromatic) interactions. It is established that the two-center energy partitioning terms are capable of detecting favorable (negative two-center term) through space interactions. In cases of cyclic conjugation (homoconjugation), it is also shown that the inclusion of CI is necessary. 相似文献
74.
K. Ardhaoui J. Rogez A. Ben Chérifa M. Jemal P. Satre 《Journal of Thermal Analysis and Calorimetry》2006,86(2):553-559
Lanthanum-bearing silicate-oxyapatites or britholites, Ca10–xLax(PO4)6–x(SiO4)xO with 1≤x≤6, have been synthesized by solid state reaction
at high temperature. They were characterized by X-ray diffraction and IR spectroscopy.
Using two microcalorimeters, the heat of solution of these compounds have
been measured at 298 K in a solution of nitric and hydrofluoric acid. A strained
least squares method was applied to the experimental results to obtain the
solution enthalpies at infinite dilution, and the mixing enthalpy in two steps.
In the first step the mixing enthalpy obtained is referenced to the britholite
monosubstituted and to the oxysilicate. The mixing enthalpy referenced to
the oxyapatite and to the oxysilicate is then extrapolated. In order to determine
the enthalpies of formation of all the terms of the solution, thermochemical
cycles were proposed and complementary experiments were performed. The results
obtained show a decrease of the enthalpy of formation with the amount of Si
and La introduced in the lattice. This was explained by the difference in
the bond energies of (Ca–O, P–O) and (La–O, Si–O). 相似文献
75.
Baurin N Aboul-Ela F Barril X Davis B Drysdale M Dymock B Finch H Fromont C Richardson C Simmonite H Hubbard RE 《Journal of chemical information and computer sciences》2004,44(6):2157-2166
We have designed four generations of a low molecular weight fragment library for use in NMR-based screening against protein targets. The library initially contained 723 fragments which were selected manually from the Available Chemicals Directory. A series of in silico filters and property calculations were developed to automate the selection process, allowing a larger database of 1.79 M available compounds to be searched for a further 357 compounds that were added to the library. A kinase binding pharmacophore was then derived to select 174 kinase-focused fragments. Finally, an additional 61 fragments were selected to increase the number of different pharmacophores represented within the library. All of the fragments added to the library passed quality checks to ensure they were suitable for the screening protocol, with appropriate solubility, purity, chemical stability, and unambiguous NMR spectrum. The successive generations of libraries have been characterized through analysis of structural properties (molecular weight, lipophilicity, polar surface area, number of rotatable bonds, and hydrogen-bonding potential) and by analyzing their pharmacophoric complexity. These calculations have been used to compare the fragment libraries with a drug-like reference set of compounds and a set of molecules that bind to protein active sites. In addition, an analysis of the overall results of screening the library against the ATP binding site of two protein targets (HSP90 and CDK2) reveals different patterns of fragment binding, demonstrating that the approach can find selective compounds that discriminate between related binding sites. 相似文献
76.
Ben Yahia H Gaudin E Darriet J Banks M Kremer RK Villesuzanne A Whangbo MH 《Inorganic chemistry》2005,44(9):3087-3093
A new magnetic oxide, CuMnVO4, was prepared, and its crystal structure was determined by single-crystal X-ray diffraction. The magnetic properties of CuMnVO4 were characterized by magnetic susceptibility and specific heat measurements, and the spin exchange interactions of CuMnVO4 were analyzed on the basis of spin-polarized electronic band structure calculations. CuMnVO4 contains MnO4 chains made up of edge-sharing MnO6 octahedra containing high-spin Mn2+ cations. Our work shows that CuMnVO4 undergoes a three-dimensional antiferromagnetic transition at approximately 20 K. Both the intrachain and interchain spin exchanges are antiferromagnetic, and the interchain spin exchange is not negligible compared to the intrachain spin exchange. 相似文献
77.
Ben C. Freasier 《Chemical physics letters》1975,35(2):280-282
A monte-Carlo calculation has been made for 108 hard core dumbbells of the compressibility factor in the isotropic density range. These compressibility factors are compared to several approximate theories, and comments are made on the utility of these approximate theories. 相似文献
78.
The EPR spectrum of 17O? on partially reduced molybdenum oxide supported on silica-gel has been observed following adsorption of N2O at room temperature. The spectrum is chracterized by g⊥=2.019 and g|=2.002 with a|17O?=96±1 G and a|95MO,97MO=7.5±0.5 G. The O ?ion appears to undergo exchange with oxide ions at the surface. 相似文献
79.
V. Pichon H. Rogniaux N. Fischer-Durand S. Ben Rejeb F. Le Goffic M. -C. Hennion 《Chromatographia》1997,45(1):289-295
Summary The trace-level determination of organic pollutants in complex matrices is difficult and often not reliable because theccurrent
extraction procedures are non-selective. New extraction sorbents involving antigen-antibody interactions, called immunosorbents
(ISs), have been synthesised in order to trap a group of structurally related pollutants. The IS capacity is always high for
the analyte-antigen used to make the antibodies, but can be low for some related compounds. In this work, we show the relationship
that exists between capacity, break-through volume and recovery of analytes because of the competition between the structurally
related compounds for antibody sites. Breakthrough due to the overloading of the column should be avoided because calibration
curves are no longer linear. The capacity of two ISs, one made for trapping the triazine pesticide group and the second for
the phenylurea, group, have been optimised by selecting silica with 50 nm pore size. Calibration curves are linear for all
the compounds in a mixture of ten phenylureas up to a concentration of 5 to 10 μg L−1 for each compound when handling 50 mL water samples through a precolumn packed with 0.22 g of IS. Under these conditions,
reliable quantitative results are obtained because calibration curves are similar when compounds are alone or in a mixture.
Application to the clean-up of soil extracts illustrates the high selectivity and the high potential of these new sorbents
in environmental analysis.
Presented at the 21st ISC held in Stuttgart, Germany, 15th–20th September, 1996 相似文献
80.
Ben Ghoulam M Moatadid N Graciaa A Lachaise J 《Langmuir : the ACS journal of surfaces and colloids》2004,20(7):2584-2589
Phase behaviors of water/nonionic surfactants/isooctane systems are determined experimentally in temperature-global surfactant concentration diagrams. The surfactants are monodistributed polyoxyethylene glycol n-dodecyl ether. They are used as model mixtures of two, three, or five compounds or as constituents of a commercial surfactant. It is found that the phase diagrams of these systems are bent gradually toward the highest temperatures as the global surfactant concentration decreases. Each phase diagram is well-characterized by the curve of the HLB (hydrophile-lipophile balance) temperature versus the global surfactant concentration. For any fixed global surfactant concentration, this temperature is the middle temperature of the three-phase region; it can be calculated from an additive rule of the HLB temperatures of the surfactants weighted by their mole fractions at the water/oil interface. These mole fractions are determined through the pseudophase model using surfactant partitioning. Calculations require the knowledge of the critical micelle concentration, the partition coefficient between water and oil, and the HLB temperature of each surfactant of the mixture. This treatment can be used to correctly predict the variation of the HLB temperatures of the surfactant mixtures studied versus the global surfactant concentration. Furthermore, these calculations show that the observed curvature of the phase diagrams at the lowest global concentrations is due to the most favorable partitioning toward the oil of the lowest ethoxylated surfactant molecules. 相似文献