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791.
Ivana uri
kovi Rmy Claverie Patrice Bourson Mario Marchetti Jean‐Marie Chassot Marc D. Fontana 《Journal of Raman spectroscopy : JRS》2011,42(6):1408-1412
Raman spectroscopy was used to study the liquid–solid water phase transition. Special attention was devoted to the OH stretching band of the Raman spectrum, which shows monotonous changes in the temperature range between 10 and − 15 °C. The interpretation of this spectral change, as well as a careful analysis of its integrated scattered intensity, led to a spectral marker that allows the determination of the water phase (liquid or solid), and the efficient identification of the liquid–solid phase transition itself. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
792.
Hugo Aimar Ivana Gómez Bibiana Iaffei 《Journal of Fourier Analysis and Applications》2010,16(6):1007-1020
We prove space-time parabolic Besov regularity in terms of integrability of Besov norms in the space variable for solutions of the heat equation on cylindrical regions based on Lipschitz domains. 相似文献
793.
Alexandr Jegorov Ladislav Cvak Roman Bednář Jan Čejka Michal Hušák Bohumil Kratochvíl Ivana Císařová 《Structural chemistry》2006,17(1):131-137
Crystal forms of N-[3-(dimethylamino)propyl]-N-(ethylcarbamoyl)-6-allyl-ergoline-8β-carboxamide (cabergoline) originating from various solvents have been examined by X-ray diffraction at 298 or 150 K. Crystal structures of cabergoline anhydrate, (form II, P212121) and solvates (all P212121) with tert-butyl methyl ether (form VIII), cyclohexane (form XV), toluene (form IX), p-xylene (form XVI), and 1,2,4-trimethylbenzene (form XVII) are described. Conformation of cabergoline in these forms was compared with crystal structures of forms I and VII of cabergoline (P21) described in the literature. Despite a high degree of molecular conformational freedom, cabergoline possesses similar conformation in forms I, II, VIII, IX, XV, XVI, and XVII. Molecular conformations, crystal packing and the effect of the solvent on the former two properties are examined. 相似文献
794.
Tsetska Radeva Viktoria Milkova Ivana Petkanchin 《Colloids and surfaces. A, Physicochemical and engineering aspects》2004,240(1-3):27-34
The electro-optical behavior of a multilayer constructed via layer-by-layer deposition of poly(sodium 4-styrenesulfonate) (PSS) and poly(allylamine hydrochloride) (PAH) onto ellipsoidal β-FeOOH particles is examined using electric light scattering method. For fully charged polymers (at pH 4.5), the electro-optical effect is found to increase with polyelectrolyte layer number, showing a tendency to saturation in the linear growth regime. The effect is greater and of lower frequency of relaxation for the films ending with PAH in comparison to those with top PSS layer. Evidence is given that polarization of “condensed” counterions along the chains of the last-adsorbed polymer is mainly responsible for the observed electro-optical behavior of the polyelectrolyte multilayer. Although incorporation of “condensed” small ions into the film bulk seems probable for the PSS/PAH multilayer, their participation in the electro-optical effect is found negligible. The structural changes in the PSS/PAH multilayer due to the PAH deprotonation at pH 7.5 and the corresponding changes in the electro-optical effect confirm the key role of the last-adsorbed polymer for the behavior of the entire PSS/PAH film. 相似文献
795.
Ottinger F Kroslakova I Hametner K Reusser E Nesper R Günther D 《Analytical and bioanalytical chemistry》2005,383(3):489-499
Single crystals of new nitridosilicates and nitridoaluminosilicates with excellent R values in X-ray investigations were analysed quantitatively using 30 to 60 μm single-spot LA-ICP-MS. Significant discrepancies
between expected and measured chemical composition could not be explained by the crystallographic data. High spatial resolution
analysis using electron probe microanalysis (EPMA, 10 μm) leads to the discovery of inhomogeneities in the crystalline material.
The application of standard single-spot LA-ICP-MS with a spatial resolution of 30 to 60 μm is not suitable for the analysis
of these crystals as the existing inhomogeneities dominate and alter the determined concentrations. However, owing to the
better detection capabilities, a scanning LA-ICP-MS procedure enables a more representative analysis of single crystals of
Ca5Si2Al2N8 than single-spot LA-ICP-MS as a result of a larger sampling volume. It is highly likely that these impurities consist of
amorphous, vitreous phases as powder diffraction X-ray data indicates the existence of a significant fraction of an X-ray
amorphous material besides crystalline silicates. These microdomains contain less aluminium, silicon and calcium or are nearly
free of aluminium, which explains the detected discrepancies in the chemical composition. 相似文献
796.
Jaromír Vinklarek Jan Honzíĉek Ivana Císařová Martin Pavliŝta Jana Holubová 《Central European Journal of Chemistry》2005,3(1):157-168
The 1,1’-dimethylvanadocene dichloride ((C5H4CH3)2VCl2) reacts in aqueous solution with various carboxylic acids giving two different types of complexes. The 1,1’-dimethylvanadocene
complexes of monocarboxylic acids (C5H4CH3)2V(OOCR)2 (R=H,CCl3, CF3, C6H5) contain two monodentate carboxylic ligands, whereas oxalic and malonic acids act as chelate compounds of the formula (C5H4CH3)2V(OOC-A-COO) (A=−, CH2). The structure of the (C5H4CH3)2 V(OOCCF3)2 complex was determined by single crystal X-ray diffraction analysis. The isotropic and anisotropic EPR spectra of all the
complexes prepared were recorded. The obtained EPR parameter values were found to be in agreement with proposed structures. 相似文献
797.
Time-resolved gas-phase kinetic and quantum chemical studies of the reaction of silylene with oxygen
Becerra R Bowes SJ Ogden JS Cannady JP Adamovic I Gordon MS Almond MJ Walsh R 《Physical chemistry chemical physics : PCCP》2005,7(15):2900-2908
Time-resolved kinetic studies of the reaction of silylene, SiH2, generated by laser flash photolysis of phenylsilane, have been carried out to obtain rate constants for its bimolecular reaction with O(2). The reaction was studied in the gas phase over the pressure range 1-100 Torr in SF(6) bath gas, at five temperatures in the range 297-600 K. The second order rate constants at 10 Torr were fitted to the Arrhenius equation: [see text] The decrease in rate constant values with increasing temperature, although systematic is very small. The rate constants showed slight increases in value with pressure at each temperature, but this was scarcely beyond experimental uncertainty. From estimates of Lennard-Jones collision rates, this reaction is occurring at ca. 1 in 20 collisions, almost independent of pressure and temperature. Ab initio calculations at the G3 level backed further by multi-configurational (MC) SCF calculations, augmented by second order perturbation theory (MRMP2), support a mechanism in which the initial adduct, H(2)SiOO, formed in the triplet state (T), undergoes intersystem crossing to the more stable singlet state (S) prior to further low energy isomerisation processes leading, via a sequence of steps, ultimately to dissociation products of which the lowest energy pair are H2O+SiO. The decomposition of the intermediate cyclo-siladioxirane, via O-O bond fission, plays an important role in the overall process. The bottleneck for the overall process appears to be the T-->S process in H2SiOO. This process has a small spin-orbit coupling matrix element, consistent with an estimate of its rate constant of 1x10(9) s-1 obtained with the aid of RRKM theory. This interpretation preserves the idea that, as in its reactions in general, SiH2 initially reacts at the encounter rate with O2. The low values for the secondary reaction barriers on the potential energy surface account for the lack of an observed pressure dependence. Some comparisons are drawn with the reactions of CH2+O2 and SiCl2+O2. 相似文献
798.
The hydrazinolysis reaction of 5-perfluoroalkyl-1,2,4-oxadiazoles has been investigated. Nucleophilic addition of the reagent to the C(5)-N(4) double bond of the oxadiazole ring, followed by ring-opening and then ring-closure involving the beta-nitrogen atom of the hydrazino moiety and the C(3) of the oxadiazole ring, explains the formation of 5-perfluoroalkyl-1,2,4-triazoles as final products. Useful applications in synthesis of this uncommon hydrazinolysis can be claimed. 相似文献
799.
Van Hoof F Van Wiele P Acobas F Guinamant JL Bruchet A Schmitz I Bobeldijk I Sacher F Ventura F Boleda R 《Journal of AOAC International》2002,85(2):375-383
As part of a project funded by the European Commission (EC) for the development and evaluation of multiresidue methods for analysis of drinking and related waters, 17 European laboratories evaluated a method using styrene-divinylbenzene copolymer solid-phase extraction followed by liquid chromatography with diode array detection. The main aim of the study was to evaluate whether the method meets the requirements of EC Drinking Water Directive 98/83 in terms of accuracy, precision, and detection limit for 21 pesticides according to the following requirements: limit of detection, < or =0.025 microg/L; accuracy expressed as recovery, between 75 and 125%; and precision expressed as repeatability relative standard deviation of the method, <12.5%, and as reproducibility relative standard deviation of the method, <25%. Analyses for unknown concentrations were performed with commercial bottled and tap waters. All laboratories were able to achieve detection limits of 0.01 microg/L for all pesticides except pirimicarb (0.02 microg/L). The criteria for repeatability were met for all compounds. Terbutryn in bottled water and carbendazim in tap water did not meet the criteria for reproducibility. In terms of accuracy, the method met the requirements for all pesticides in both matrixes, except for metamitron. However, several compounds (linuron, terbutryn, propazine, metobromuron, and isoproturon) showed recoveries slightly below 75%. 相似文献
800.
Photoinduced heterocyclic rearrangements of ON bond-containing azoles have been claimed in the synthesis of target fluorinated heterocyclic compounds. In this context, the photochemical behavior of some fluorinated 1,2,4-oxadiazoles has been investigated. Irradiations of 3-amino-5-perfluoroalkyl-1,2,4-oxadiazoles at λ=313 nm in methanol gave open-chain products arising from a reaction of the nucleophilic solvent with either the first formed ring-photolytic species or with a nitrilimine moiety generated from it. Differently, irradiations in methanol with the presence of triethylamine (TEA) followed competing phototransposition pathways leading to the ring-isomers 2-amino-5-perfluoroalkyl-1,3,4-oxadiazoles (major component) and the ring degenerate isomers 5-amino-3-perfluoroalkyl-1,2,4-oxadiazoles (minor component). On the other hand, 3-amino-5-polyfluorophenyl-1,2,4-oxadiazoles underwent ring-photoisomerization into 1,3,4-oxadiazoles when irradiations were carried out at λ=254 nm. In turn, the irradiation of the 3-phenyl-5-perfluoroheptyl-1,2,4-oxadiazole at λ=254 nm in methanol gave the solvolysis product, but no ring-isomerization was observed. Some mechanistic considerations are reported, and some applications in the synthesis of target fluorinated 1,3,4-oxadiazoles are claimed. 相似文献