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21.
The protonation of NADH-like dihydropyridines and cyclic enol ethers generates reactive cationic intermediates, which interact with isocyanides to afford α-carbamoylated heterocycles after an aqueous quenching, in Ugi and Passerini-type reactions, thus broadening the scope of these multicomponent processes. 相似文献
22.
Carme Rovira Pere Constans M.-H. Whangbo Juan J. Novoa 《International journal of quantum chemistry》1994,52(1):177-189
Using the Hartree–Fock and MP 2 methods with bases of up to 6-31++G (2d, 2p) quality, the optimum geometry of the 1:2 and 2:1 (H2O)n… (HF)m complexes of water and hydrogen fluoride is searched in a systematic way. Two minimum-energy conformations are found for the 1:2 complex connected through a low-energy transition state. For the 2:1 complex, only one minimum-energy structure is obtained. The analysis of the geometries of the minima and their vibrational frequencies shows that none of them can be used to explain the existence of the H …F? H reverse complex detected experimentally. © 1994 John Wiley & Sons, Inc. 相似文献
23.
The protonation state of the dimethylglyoxime ligands in the B(12) coenzyme biomimetic [Co(CCl=CHCl)(dmgH)(2)(py)].CHCl(3) was investigated by using first-principles molecular dynamics. Our simulations at 173 and 300 K reveal that one of the oxime protons remains bonded to a nitroxyl group, while the proton of the second NO...H-ON unit is essentially shared with similar probability between the two oxygen atoms. This reconciles the results of the experimental determination (Jones, P. G.; Yang, L.; Steinborn, D. Acta Cryst. 1996, C52, 2399), showing all N-O distances as equivalent, with the commonly accepted rule that the protonation state of the dimethylglyoxime ligands can be identified by the different N-O distances. Further aspects of the dynamics of the OH...O units, in relation to the occurrence of weak CH...O intermolecular interactions, are analyzed. 相似文献
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We obtain characterizations of positive Borel measures μ on so that the nonisotropic potential space Kα[Lp(dσ)] is imbedded in the tent space T2q(dμ), where 1<p,q<+∞. We deduce characterizations for pointwise multipliers of the space Hαp. 相似文献
26.
This article reports studies on the feasibility of increasing the decoloring capacity of a granular activated carbon (GAC) by using oxidation with air at 350 degrees C to modify its surface activity and porosity. The GAC, obtained from olive stones, had a maximum decolorization capacity of 92% for doses of 20 g/l, while the maximum decolorization capacity of the modified granular activated carbon (MGAC) was about 96% at a dose of 10 g/l. The increase in decoloring capacity is thought to be due to an increase in mesopore area (from 129 to 340 m2/g) in the MGAC. The maximum decoloring values and the doses needed to attain them are very close to values obtained in previous studies using coconut shell powder-activated carbon (94 and 98% for red and white vinegar for a dose of 10 g/l, respectively). 相似文献
27.
Juan Muñoz-Arnanz Carme Bosch Pilar Fernandez Joan O. Grimalt Begoña Jimenez 《Journal of chromatography. A》2009,1216(33):6141-6145
The enantiomeric fractions present in soil samples may provide information useful in distinguishing recent inputs of DDT from past DDT pollution. In this study, a chromatographic procedure for the determination of the enantiomeric fractions of o,p′-DDT based on heart-cutting multidimensional gas chromatography was developed. The optimization carried out achieved low ratios of DDT degradation (<15%) in the chromatographic system. High selectivity and sensitivity in the detection of the target compounds, with a limit of detection as low as 2.1 pg μL−1, was reached. In addition, high degrees of repeatability (RSD < 2.0%) and reproducibility (RSD < 3.2%) were obtained for the enantiomeric fractions measured in analytical standards and soil samples. 相似文献
28.
M. Carme Calderer Chun Liu Karl Voss 《Mathematical Methods in the Applied Sciences》2001,24(7):473-489
We study planar energy minimizing configurations of smectic A liquid crystal materials and classify the corresponding defect structures. We investigate focal conic configurations in wedge, non‐parallel plates, funnel‐shaped domains, and non‐concentric annuli. The application of the stability condition for focal conics is relevant to the specification of the location of the interfacial defects. Self‐similar structures are discussed for a class of solutions with the same bulk energy. We propose surface energies terms to serve as selection mechanisms of particular self‐similar configurations. We also show how the modelling of chevron texture naturally arises in the present framework. Copyright © 2001 John Wiley & Sons, Ltd. 相似文献
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Andrew J. Thompson Jerome Dabin Javier Iglesias‐Fernndez Albert Ardvol Zoran Dinev Spencer J. Williams Omprakash Bande Aloysius Siriwardena Carl Moreland Ting‐Chou Hu David K. Smith Harry J. Gilbert Carme Rovira Gideon J. Davies 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2012,124(44):11333-11333