排序方式: 共有58条查询结果,搜索用时 15 毫秒
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de la Fuente JM Eaton P Barrientos AG Menéndez M Penadés S 《Journal of the American Chemical Society》2005,127(17):6192-6197
Thermodynamic evidence for the selective Ca(2+)-mediated self-aggregation via carbohydrate-carbohydrate interactions of gold glyconanoparticles functionalized with the disaccharides lactose (lacto-Au) and maltose (malto-Au), or the biologically relevant trisaccharide Lewis X (Le(X)-Au), was obtained by isothermal titration calorimetry. The aggregation process was also directly visualized by atomic force microscopy. It was shown in the case of the trisaccharide Lewis X that the Ca(2+)-mediated aggregation is a slow process that takes place with a decrease in enthalpy of 160 +/- 30 kcal mol(-)(1), while the heat evolved in the case of lactose and maltose glyconanoparticles was very low and thermal equilibrium was quickly achieved. Measurements in the presence of Mg(2+) and Na(+) cations confirm the selectivity for Ca(2+) of Le(X)-Au glyconanoparticles. The relevance of this result to cell-cell adhesion process mediated by carbohydrate-carbohydrate interactions is discussed. 相似文献
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Antonio Monari Jose Pitarch‐Ruiz Gian Luigi Bendazzoli Stefano Evangelisti Jose Sanchez‐Marin 《International journal of quantum chemistry》2010,110(4):874-884
The high‐spin electronic states for lithium, sodium, and potassium four‐atom clusters were studied. In particular, we performed coupled cluster geometry optimization of the quintet state in tetrahedral geometry. The quintet state of these systems is characterized by having all the valence electron unpaired, giving rise to the so‐called no‐pair bonding. Single‐point full configuration interaction computations on the equilibrium geometries for the various clusters are also presented. The analysis of the valence orbitals in a localized representation confirms the importance of the p atomic orbitals to explain this unusual type of bond. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2010 相似文献
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In this work, a multiclass screening method for organic contaminants in natural and wastewater has been developed and validated for qualitative purposes, i.e. to ensure the reliable and sensitive identification of compounds detected in samples at a certain level of concentration. The screening is based on the use of GC-TOF MS, and the sample procedure involves solid phase extraction with C(18) cartridges. Around 150 organic contaminants from different chemical families were investigated, including PAHs, octyl/nonyl phenols, PCBs, PBDEs and a notable number of pesticides, such as insecticides (organochlorines, organophosphorus, carbamates and pyrethroids), herbicides (triazines and chloroacetanilides), fungicides and several relevant metabolites. Surface water, ground water and effluent wastewater were spiked with all target analytes at three concentration levels (0.02, 0.1 and 1 μg/L). Influent wastewater and raw leachate from a municipal solid waste treatment plant were spiked at two levels (0.1 and 1 μg/L). Up to five m/z ions were evaluated for every compound. The identification criterion was the presence of, at least, two m/z ions at the expected retention time, measured at their accurate mass, and the accomplishment of the Q/q(i) intensity ratio within specified tolerances. The vast majority of compounds investigated were correctly identified in the samples spiked at 1 μg/L. When analyte concentration was lowered down to 0.1 μg/L the identification was more problematic, especially in complex-matrix samples like influent wastewater. On the contrary, many contaminants could be properly identified at the lowest level 0.02 μg/L in cleaner matrices. The procedure was applied to the screening of water samples of different origin and matrix composition and allowed the detection of several target contaminants. A highly reliable identification could be carried out thanks to the sensitive full-spectrum acquisition at accurate mass, the high selectivity reached with the use of narrow-mass window extracted ion chromatograms, the low mass errors observed in the positive detections and the Q/q ratio accomplishment. 相似文献
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A metallosupramolecular coordination polyelectrolyte prepared by the reaction of cobalt(II) with a novel bisterpyridine ligand has been assembled as the active component in electrochromic films by sequential deposition using electrostatic layer-by-layer self-assembly. 相似文献
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A rapid and new liquid chromatography-mass spectrometry with ion-trap detection method for the determination of meloxicam (MLX), flunixin meglumine (FLU), carprofen (CPF), and tolfenamic acid (TOLF) in animal tissue is described. MRLs between 10 and 500 microg kg(-1) in muscle and between 65 and 1000 microg kg(-1) in liver, from different animal species have been established in the EU for these compounds. After chemical hydrolysis, an organic extraction from homogenised tissue was performed. Final extract was injected in a liquid chromatograph with an ion-trap mass spectrometer with electrospray interface. Four identification points (one precursor and two product ions) and a minimum of one ion ratio was monitored for each compound. For quantitative purposes flunixin-D3 (FLU-D3) was used as internal standard. The method was validated using fortified blank muscle and liver from different animal species according to the 2002/657/EC European decision criteria. The decision limits (CCalpha) and detection capabilities (CCbeta) were determined and their values were at concentrations near the MRL for each substance. 相似文献
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We have analyzed the frequency-dependent features of diffusive transport of mobile carriers by hopping in a disordered environment composed of varying energy barriers. We developed a simple approach based on the solution of the master equation for a gradient of concentration (chemical potential) under a sinusoidal perturbation. This method extends the well-known result of the steady state case, D = {1 / Γ}−1, to the frequency domain. The results of our calculations are in agreement with the approximate analytical solution of the CTRW formalism. We are able to determine the onset of frequency-dependent diffusivity in terms of probabilities of highest energy barriers. 相似文献
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Isabel Izquierdo-Barba Edesia Sousa Juan Carlos Doadrio Antonio Luis Doadrio Joaquín Pérez Pariente Africa Martínez Florence Babonneau María Vallet-Regí 《Journal of Sol-Gel Science and Technology》2009,50(3):421-429
Ordered mesoporous materials exhibit potential features to be used as controlled drug delivery systems, including their wide
range of chemical compositions and their outstanding textural and structural properties. Therefore, it is possible to control
the drug release kinetics by tailoring such parameters. In this paper, mesoporous materials such as MCM-48 and SBA-15, which
present different pore sizes (3.7 and 8.8 nm) and structural characteristics (3D-bicontinuous cubic and 2D-hexagonal, respectively)
have been synthesized to evaluate their application as drug delivery system and to determine their influence on release kinetic
of ibuprofen. Moreover, a chemical modification of the SBA-15 mesoporous material with octadecyltrimethoxysilane has also
been performed to study its influence on the release rate of ibuprofen. The structural characteristics (3D cubic and 2D hexagonal
pore system) do not affect the release kinetic profiles of ibuprofen. On the contrary, the pore size affects highly to the
release kinetic profiles from first-order kinetic to zero-order kinetic for MCM-48 and SBA-15, respectively. Moreover, the
importance of surface functionalization was demonstrate through the very fast delivery of ibuprofen from SBA-15 mesoporous
materials functionalized with octadecyl chains. 相似文献