排序方式: 共有122条查询结果,搜索用时 46 毫秒
41.
Bultinck P Fias S Van Alsenoy C Ayers PW Carbó-Dorca R 《The Journal of chemical physics》2007,127(3):034102
Different procedures to obtain atom condensed Fukui functions are described. It is shown how the resulting values may differ depending on the exact approach to atom condensed Fukui functions. The condensed Fukui function can be computed using either the fragment of molecular response approach or the response of molecular fragment approach. The two approaches are nonequivalent; only the latter approach corresponds in general with a population difference expression. The Mulliken approach does not depend on the approach taken but has some computational drawbacks. The different resulting expressions are tested for a wide set of molecules. In practice one must make seemingly arbitrary choices about how to compute condensed Fukui functions, which suggests questioning the role of these indicators in conceptual density-functional theory. 相似文献
42.
Elementary growth processes such as kink initiation, adding a molecule to a kink, and adding a molecule between two neighboring kinks and between two grains are theoretically studied in pentacene films by adding one molecule at a time to a predefined aggregate. For each molecule, the potential energy surface is calculated using the MM3 molecular mechanics force field, which allowed one to identify useful parameters like the energy barrier for diffusion and the energy to create kinks, as well as defect configurations. Depending on the properties of the potential energy surface and the resulting growth-condition-dependent probabilities of initiating defect configurations in the film, three types of pentacene defects are identified: a thermally activated defect, an intrinsic defect, and a kinetic defect. Upon film growth, most defects relax into the ideal crystal configuration. Bulk defects that resist relaxation have densities lower than 10(16) defects/cm3 at typical growth conditions. Grain boundary defects, on the other hand, are very stable. Moreover, interstitial molecules at grain boundaries are identified as a source of compressive stress. 相似文献
43.
Joule heating monitoring in a microfluidic channel by observing the Brownian motion of an optically trapped microsphere
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Toon Brans Filip Strubbe Caspar Schreuer Stijn Vandewiele Kristiaan Neyts Filip Beunis 《Electrophoresis》2015,36(17):2102-2109
Electric fields offer a variety of functionalities to Lab‐on‐a‐Chip devices. The use of these fields often results in significant Joule heating, affecting the overall performance of the system. Precise knowledge of the temperature profile inside a microfluidic device is necessary to evaluate the implications of heat dissipation. This article demonstrates how an optically trapped microsphere can be used as a temperature probe to monitor Joule heating in these devices. The Brownian motion of the bead at room temperature is compared with the motion when power is dissipated in the system. This gives an estimate of the temperature increase at a specific location in a microfluidic channel. We demonstrate this method with solutions of different ionic strengths, and establish a precision of 0.9 K and an accuracy of 15%. Furthermore, it is demonstrated that transient heating processes can be monitored with this technique, albeit with a limited time resolution. 相似文献
44.
Colpaert F Mangelinckx S De Brabandere S De Kimpe N 《The Journal of organic chemistry》2011,76(7):2204-2213
New chiral α-chloro-β-amino-N-sulfinyl imidates were synthesized in high yield and excellent diastereomeric excess via highly anti-selective Mannich-type reactions of (R(S))-methyl N-tert-butanesulfinyl-2-chloroethanimidate with aromatic aldimines. The α-chloro-β-amino-N-sulfinylimidates proved to be excellent building blocks for the asymmetric synthesis of β-amino-α-chloro amides and esters, aziridine-2-carboxylic amides and esters, trans-2-aryl-3-chloroazetidines, and methyl 4-phenyloxazolidin-2-one-5-carboxylate. The obtained absolute anti-diastereoselectivity is the opposite of the stereochemical outcome observed for α-methyl-substituted imidates. 相似文献
45.
Mangelinckx S De Sterck B Colpaert F Catak S Jacobs J Rooryck S Waroquier M Van Speybroeck V De Kimpe N 《The Journal of organic chemistry》2012,77(7):3415-3425
Zincated 3-chloro-3-methyl-1-azaallylic anions undergo a stereoselective aldol addition across aromatic aldehydes and subsequent mesylation to produce syn α-chloro-β-mesyloxyketimines, which were isolated in 80-84% yield and high diastereomeric excess (dr > 97/3) after purification via flash chromatography. The syn α-chloro-β-mesyloxyketimines were further stereoselectively reduced to give stereochemically defined 3-aminopropyl mesylates, which were cyclized to 1,2,3,4-tetrasubstituted 3-chloroazetidines containing three contiguous stereogenic centers. DFT calculations on the key aldol addition revealed the presence of a highly ordered bimetallic six-membered twist-boat-like transition state structure with a tetra-coordinated metal cyclic structure. DFT calculations revealed that chelation of both zinc and lithium cations in the transition state structure leads to the experimentally observed high syn diastereoselectivity of aldol reactions. 相似文献
46.
Van de Vyver S Geboers J Helsen S Yu F Thomas J Smet M Dehaen W Sels BF 《Chemical communications (Cambridge, England)》2012,48(29):3497-3499
Acid-catalyzed condensation of levulinic acid and phenol into high yields of diphenolic acid (>50%) is possible with a combination of sulfonated hyperbranched polymers and thiol promotors, either added as a physical mixture or bound to the polymer by ion-pairing. 相似文献
47.
Schaltin S Brooks NR Stappers L Van Hecke K Van Meervelt L Binnemans K Fransaer J 《Physical chemistry chemical physics : PCCP》2012,14(5):1706-1715
Liquid metal salts are electrolytes with the highest possible metal concentration for electrodeposition, because the metal ion is an integral part of the solvent. This paper introduces the new ionic silver complexes [Ag(MeCN)(4)](2)[Ag(Tf(2)N)(3)], [Ag(MeCN)][Tf(2)N] and [Ag(EtIm)(2)][Tf(2)N], where MeCN stands for acetonitrile, EtIm for 1-ethylimidazole and Tf(2)N is bis(trifluoromethylsulfonyl)imide. These complexes have been characterized by differential scanning calorimetry, single crystal X-ray crystallography, thermogravimetrical analysis, Raman spectroscopy and cyclic voltammetry. [Ag(MeCN)(4)](2)[Ag(Tf(2)N)(3)] is a room temperature ionic liquid. Smooth silver layers of good quality could be deposited from it, at current densities of up to 25 A dm(-2) in unstirred solutions. [Ag(EtIm)(2)][Tf(2)N] melts at 65 °C and can be used as an electrolyte for silver deposition above this temperature. [Ag(MeCN)][Tf(2)N] has a melting point that is too high to be useful in electrodeposition. Addition of thiourea or 1H-benzotriazole to the electrolyte decreased the surface roughness of the silver coatings. The morphology of the metal layers was investigated by atomic force microscopy (AFM). Adsorption of 1H-benzotriazole on the silver metal surface has been proven by Raman spectroscopy. This work shows the usefulness of additives in improving the quality of metal films electrodeposited from ionic liquids. 相似文献
48.
Elke Deckers Onur AtakLaurens Coox Roberto D’AmicoHendrik Devriendt Stijn JonckheereKunmo Koo Bert PluymersDirk Vandepitte Wim Desmet 《Wave Motion》2014
The Wave Based Method is a deterministic prediction technique to solve steady-state dynamic problems and is developed to overcome some of the frequency limitations imposed by element-based prediction techniques. The method belongs to the family of indirect Trefftz approaches and uses a weighted sum of so-called wave functions, which are exact solutions of the governing partial differential equations, to approximate the dynamic field variables. By minimising the errors on boundary and interface conditions, a system of equations is obtained which can be solved for the unknown contribution factors of each wave function. As a result, the system of equations is smaller and a higher convergence rate and lower computational loads are obtained as compared to conventional prediction techniques. On the other hand, the method shows its full efficiency for rather moderately complex geometries. As a result, various enhancements have been made to the method through the years, in order to extend the applicability of the Wave Based Method. This paper gives an overview of the current state of the art of the Wave Based Method, elaborating on the modelling procedure, a comparison of the properties of the Wave Based Method and element-based prediction techniques, application areas, extensions to the method such as hybrid and multi-level approaches and the most recent developments. 相似文献
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María Moreno Oliva Juan Casado Dr. Juan T. López Navarrete Prof. Gunther Hennrich Dr. Stijn van Cleuvenbergen Dr. Inge Asselberghs Dr. Koen Clays Dr. M. Carmen Ruiz Delgado Dr. Jean‐Luc Brédas Prof. J. Sérgio Seixas de Melo Prof. Luisa De Cola Prof. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2009,15(33):8223-8234
We have synthesized three new molecules that have three thienylethynyl arms substituting a central benzene core and different electron donor/acceptor groups in the three remaining phenyl positions. The absorption, fluorescence, phosphorescence, and transient triplet–triplet spectra are analyzed in the light of the electronic structure of the ground and excited states obtained from quantum‐chemical calculations. From the above, the relevant photophysical data (including quantum yields, lifetimes, and rate constants) could be derived. It was found that the major deactivation pathway is internal conversion, which competes with the fluorescence and intersystem crossing processes. For the three investigated compounds, we provide convincing theoretical support corroborating these findings and further conclusions based on the theoretical information obtained. These molecules are one of the very few cases in which the depolarization ratios, obtained from the NLO optical measurements, clearly reflect the octopolar configuration. Molecular hyperpolarizabilities have been measured and display a typical dependence on the donor–acceptor substitution pattern. 相似文献