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31.
The solid-state structure of the triple-decker salt [Cp*Fe(-5:5-C4Me4P)RuCp*] · CF3SO3 shows orientational disorder for the pseudosymmetric cations. A chemically related compound was used to define a restrained structure model. Comparison of different refinement strategies proves that this restrained model is superior to an unrestrained treatment. 相似文献
32.
Etiënne L. M. Vermeirssen Conrad Dietschweiler Beate I. Escher Jürgen van der Voet Juliane Hollender 《Analytical and bioanalytical chemistry》2013,405(15):5225-5236
The Chemcatcher passive sampler, which uses Empore? disks as sampling phase, is frequently used to monitor polar organic chemicals in river water and effluents. Uptake kinetics need to be quantified to calculate time-weighted average concentrations from Chemcatcher field deployments. Information on release kinetics is needed if performance reference compounds (PRCs) are used to quantify the influence of environmental conditions on the uptake. In a series of uptake and elimination experiments, we used Empore? SDB disks (poly(styrenedivinylbenzene) copolymer modified with sulfonic acid groups) as a sampling phase and 22 compounds with a logK ow (octanol–water partitioning coefficient) range from ?2.6 to 3.8. Uptake experiments were conducted in river water or tap water and lasted up to 25 days. Only 1 of 22 compounds (sulfamethoxazole) approached equilibrium in the uptake trials. Other compounds showed continuing non-linear uptake, even after 25 days. All compounds could be released from SDB disks, and desorption was proportionally higher in disks loaded for shorter periods. Desorption showed two-phase characteristics, and desorption was proportionally higher for passively sorbed compounds compared to actively loaded compounds (active loading was performed by pulling spiked river water over SDB disks using vacuum). We hypothesise that the two-phase kinetics and better retention of actively loaded compounds—and compounds loaded for a longer period—may be caused by slow diffusion of chemicals within the polymer. As sorption and desorption did not show isotropic kinetics, it is not possible to develop robust PRCs for adsorbent material like SDB disks. 相似文献
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35.
Ulf H. Strasser Beate Neumann Hans‐Georg Stammler Norbert W. Mitzel Prof. Dr. 《无机化学与普通化学杂志》2010,636(7):1249-1254
The tetrasilyl ethers calix[4]areneOSiMe2R (R = Me, H, vinyl, allyl) were prepared by salt elimination; the calix[4]arene was deprotonated with sodium hydride and subsequently reacted with chlorosilanes ClSiMe2R. In general, DMF was chosen as solvent in order to steer the reactions in terms of a preference for the cone‐conformation of the products. In the case of calix[4]areneOSiMe3 both, partial‐cone‐ and cone‐conformers, were synthesised. All products were characterised by NMR (1H, 13C, 29Si) spectroscopy, mass spectrometry and single‐crystal X‐ray diffraction. 相似文献
36.
Espinosa CE Guo Q Singh V Behrens SH 《Langmuir : the ACS journal of surfaces and colloids》2010,26(22):16941-16948
The electrostatic stabilization of colloidal dispersions is usually considered the domain of polar media only because of the high energetic cost associated with introducing electric charge in nonpolar environments. Nevertheless, some surfactants referred to as "charge control agents" are known to raise the conductivity of liquids with low electric permittivity and to mediate charge stabilization of nonpolar dispersions. Here we study an example of the particularly counterintuitive charging and electrostatic interaction of colloidal particles in a nonpolar solvent caused by nonionic surfactants. PMMA particles in hexane solutions of nonionic sorbitan oleate (Span) surfactants are found to exhibit a field-dependent electrophoretic mobility. Extrapolation to zero field strength yields evidence for large electrostatic surface potentials that decay with increasing surfactant concentration in a fashion reminiscent of electrostatic screening caused by salt in aqueous solutions. The amount of surface charge and screening ions in the nonpolar bulk is further characterized via measurements of the particles' pair interaction energy. The latter is obtained by liquid structure analysis of quasi-2-dimensional equilibrium particle configurations studied with digital video microscopy. In contrast to the behavior reported for systems with ionic surfactants, we observe particle charging and a screened Coulomb type interaction both above and below the surfactant's critical micelle concentration. 相似文献
37.
Christian Schramm Beate Rinderer Richard Tessadri Heinz Duelli 《Journal of Sol-Gel Science and Technology》2010,53(3):579-586
Based on differential scanning calorimetry data, it was shown that the reaction of (3-triethoxysilylpropyl)succinic anhydride
and (3-amino)propyltriethoxysilane at 110 °C resulted in the formation of polyamic acid, whereas the thermal treatment at
220 °C led to the generation of an aliphatic monoimide-bridged polysilsesquioxane as proved by FT-IR. X-ray powder diffraction
studies showed a prominent reflection at 2θ = 6.66° (d = 1.32 nm) revealing that a crystalline area is formed. 29Si CP-MAS-NMR and 13C CP-TOSS-MAS-NMR measurements proved that no cleavage of the Si–C bond occurred, and a highly condensed material was obtained. 相似文献
38.
In order to apply ab initio wave-function-based correlation methods to metals, it is desirable to split the calculation into a mean-field part and a correlation part. Whereas the mean-field part (here Hartree-Fock) is performed in the extended periodic system, it is necessary to use for the correlation part local wave-function-based correlation methods in finite fragments of the solid. For these finite entities it is necessary to construct an embedding. The authors suggest an embedding scheme which has itself no metallic character but can mimic the metal in the internal region, where the atoms are correlated. With this embedding it is also possible to localize the metallic orbitals in the central part. The long-range nonadditive contributions of metallicity and correlation are treated with the method of increments. In this paper they present different ways to construct such an embedding and discuss the influence of the embedding on the correlation energy of the solid. 相似文献
39.
Nico Schwarze Dr. Simon Steinhauer Beate Neumann Dr. Hans‐Georg Stammler Prof. Dr. Berthold Hoge 《Angewandte Chemie (International ed. in English)》2016,55(52):16161-16164
The tris(pentafluoroethyl)silanide anion is accessible by the deprotonation of Si(C2F5)3H at low temperatures. Subsequent quenching of the resulting salt‐like compounds with suitable electrophiles, such as transition‐metal complexes or Group 14 element halides, leads to a plethora of novel tris(pentafluoroethyl)silane derivatives. This underlines the versatility of Li[Si(C2F5)3] as a powerful nucleophilic transfer reagent. 相似文献
40.
Cho SJ Maysinger D Jain M Röder B Hackbarth S Winnik FM 《Langmuir : the ACS journal of surfaces and colloids》2007,23(4):1974-1980
Several studies suggested that the cytotoxic effects of quantum dots (QDs) may be mediated by cadmium ions (Cd2+) released from the QDs cores. The objective of this work was to assess the intracellular Cd2+ concentration in human breast cancer MCF-7 cells treated with cadmium telluride (CdTe) and core/shell cadmium selenide/zinc sulfide (CdSe/ZnS) nanoparticles capped with mercaptopropionic acid (MPA), cysteamine (Cys), or N-acetylcysteine (NAC) conjugated to cysteamine. The Cd2+ concentration determined by a Cd2+-specific cellular assay was below the assay detection limit (<5 nM) in cells treated with CdSe/ZnS QDs, while in cells incubated with CdTe QDs, it ranged from approximately 30 to 150 nM, depending on the capping molecule. A cell viability assay revealed that CdSe/ZnS QDs were nontoxic, whereas the CdTe QDs were cytotoxic. However, for the various CdTe QD samples, there was no dose-dependent correlation between cell viability and intracellular [Cd2+], implying that their cytotoxicity cannot be attributed solely to the toxic effect of free Cd2+. Confocal laser scanning microscopy of CdTe QDs-treated cells imaged with organelle-specific dyes revealed significant lysosomal damage attributable to the presence of Cd2+ and of reactive oxygen species (ROS), which can be formed via Cd2+-specific cellular pathways and/or via CdTe-triggered photoxidative processes involving singlet oxygen or electron transfer from excited QDs to oxygen. In summary, CdTe QDs induce cell death via mechanisms involving both Cd2+ and ROS accompanied by lysosomal enlargement and intracellular redistribution. 相似文献