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51.
Alkaloids such as cinchonidine, quinine and N-methylephedrine have been N-alkylated using polymeric benzyl halides or co-polymerized and then N-alkylated, thus affording a series of polymer-supported chiral ammonium salts which have been employed as phase-transfer catalysts in the asymmetric benzylation of an N-(diphenylmethylene)glycine ester. These new polymeric catalysts can be easily recovered by simple filtration after the reaction and reused. The best ee's were achieved when Merrifield resin-anchored cinchonidinium ammonium salts were employed. 相似文献
52.
Mineral and short-chain carboxylic acid vapours and NO(x) gases were reacted with cyclohexene oxide (1,2-epoxycyclohexane) to quantitatively produce specific, thermally stable cyclohexyl derivatives. Subsequent analysis of these derivatives by gas chromatography with mass spectroscopy and flame ionisation detection afforded a multi analyte method for the assay of these gaseous acidic atmospheric species. Derivatisation was found to be quantitative for the derivatives tested and the method highly sensitive (to 0.3 mg/m3 for a 30 l sample), accurate, precise and free from apparent interferences. The technique has been applied to "acid stack gases" and a number of other acid rich atmospheres and the results obtained show good agreement with the single analyte wet chemical determinations indicating that the approach has considerable potential as a routine analytical method for measuring such atmospheric pollutants. The high specificity of the reaction mechanism and its potential for the analysis of analyte mixtures is illustrated in the assay of nitric acid and its acid anhydride, dinitrogen pentoxide. 相似文献
53.
The energies of the highest occupied molecular orbital (HOMO) of four simple microsolvated aqua ion clusters (Na+, Ag+, Cl-, CN-) are computed for varying numbers of water molecules. Extrapolating to infinite hydration numbers we find that these energies approach a value of -6 eV. This limiting one-electron energy is within a margin of +/-1 eV independent of the character of the ion and is 4 eV lower compared to the estimate obtained for the HOMO energy of the ions in aqueous solution under periodic boundary conditions. We argue that this discrepancy must the attributed to a shift in the reference of the one-electron potential of the periodic solvent model. 相似文献
54.
Lainez A del Burgo P Junquera E Aicart E 《Langmuir : the ACS journal of surfaces and colloids》2004,20(14):5745-5752
Speed of sound, density, conductivity, and fluorescence spectroscopy experiments were run to analyze the mixed aggregation process of a nonionic-cationic surfactant system in aqueous media at 298.15 K. The mixed system comprises a nonionic surfactant, n-octyl-beta-D-glucopyranoside (OBG), and a cationic surfactant, tetradecyltrimethylammonium bromide (C14TAB), with 8 and 14 carbon atoms on the hydrophobic tails, respectively. From these data, the total and partial critical micellar concentrations, the total and partial aggregation numbers, apparent molar volumes and isentropic compressibilities, hydration numbers, and the corresponding changes in the latest properties due to the mixed aggregation process were determined. Pure and mixed micelles were analyzed from a geometrical point of view by determining the packing parameter of the aggregates. Furthermore, the experimental characterization of both the monomeric and micellar phases was completed with a theoretical study of the mixed micellization phenomena studied herein, by means of some of the most relevant theoretical models. 相似文献
55.
In this paper, we propose a theory of quantum logics which is general enough to enable us to reexamine previous work on quantum logics in the context of this theory. It is then easy to assess the differences between the different systems studied. The quantum logical systems which we incorporate are divided into two groups which we call quantum propositional logics and quantum event logics. We include the work of Kochen and Specker (partial Boolean algebras), Greechie and Gudder (orthomodular partially ordered sets), Domotar (quantum mechanical systems), and Foulis and Randall (operational logics) in quantum propositional logics; and Abbott (semi-Boolean algebras) and Foulis and Randall (manuals) in quantum event logics. In this part of the paper, we develop an axiom system for quantum propositional logics and examine the above structures in the context of this system. 相似文献
56.
On-the-fly CASSCF nonadiabatic dynamics have been used to model the trans-cis isomerization of a model cyanine dye. Our results show that the photochemical generation of the trans versus cis product is dynamically controlled by the presence of an extended cis-trans conical intersection seam that persists along all torsional angles. This in turn suggests that the photochemistry could be completely controlled by controlling the distribution of momentum components in a wave packet excited by laser photolysis in a coherent control experiment. 相似文献
57.
Greco MN Hawkins MJ Powell ET Almond HR Corcoran TW de Garavilla L Kauffman JA Recacha R Chattopadhyay D Andrade-Gordon P Maryanoff BE 《Journal of the American Chemical Society》2002,124(15):3810-3811
The serine protease cathepsin G (EC 3.4.21.20; Cat G), which is stored in the azurophilic granules of neutrophils (polymorphonuclear leukocytes) and released on degranulation, has been implicated in various pathological conditions associated with inflammation. By employing high-throughput screening, we identified beta-ketophosphonic acid 1 as a moderate inhibitor of Cat G (IC(50) = 4.1 microM). We were fortunate to obtain a cocrystal of 1 with Cat G and solve its structure by X-ray crystallography (3.5 A). Structural details from the X-ray analysis of 1.Cat G served as a platform for optimization of this lead compound by structure-based drug design. With the aid of molecular modeling, substituents were attached to the 3-position of the 2-naphthyl ring of 1, which occupies the S1 pocket of Cat G, to provide an extension into the hydrophobic S3 region. Thus, we arrived at analogue 7 with an 80-fold potency improvement over 1 (IC(50) = 53 nM). From these results, it is evident that the beta-ketophosphonic acid unit can form the basis for a novel class of serine protease inhibitors. 相似文献
58.
Merdy P Guillon E Aplincourt M Dumonceau J Vezin H 《Journal of colloid and interface science》2002,245(1):24-31
Spectroscopic and physicochemical data, X-ray photoelectron spectroscopy (XPS), solid-state (13)C cross-polarization magic-angle-spinning NMR, GC/MS, specific surface area, site density, and surface acidity constants have been recorded or determined for a ligno-cellulosic substrate (LS) extracted from straw. Its copper(II)-bound ability has also been studied. The LS solid that exhibits two types of binding sites, carboxylic and phenolic groups, has a great affinity for copper(II), with a maximum of adsorption at around 4 mg g(-1) as early as the pH reaches 6. The structural characterization of the Cu(II) surface complexes has been investigated using EPR spectroscopy. The CuO(4) chromophore of the inner-sphere surface complexes is a slightly distorted square. A surface oxidation occurred simultaneously, which leads to semiquinonic radicals. Furthermore, our empirical approach, which used a correlation between thermodynamics data and EPR parameters, has led to a surface complexation constant log beta equal to 12.6. This indicates that copper(II) surface complexes are relatively stable. 相似文献
59.
Barluenga J Fernández-Rodríguez MA García-García P Aguilar E Merino I 《Chemistry (Weinheim an der Bergstrasse, Germany)》2005,12(1):303-313
The reaction of electron-deficient alkenes with alkoxyalkynyl Fischer carbene complexes (FCCs) represents a straightforward route to a new type of captodative (donor-acceptor) alkynylcyclopropanes, which have been prepared in moderate to high yields and in a diastereoselective manner. Some studies regarding the employment of additives to facilitate the recovery of the metal moiety after the reaction are also described. Finally, the first example of a cyclopropanation reaction through employing Fischer carbene complexes under microwave irradiation is presented; this method proved to be an advantageous alternative to the thermal reaction. 相似文献
60.
Time-resolved laser-induced fluorescence (TRLIF) has been used to study the interaction of uranyl ion with sodium dodecyl sulfate (SDS) micelles in H(3)PO(4) 1 M. The titration curve consists of two curved regions with different slopes, one of them more pronounced at low concentration of SDS and the other, with a less pronounced positive slope at larger [SDS] until a plateau is reached. The fluorescence quenching of uranyl ion by para-substituted phenol compounds was studied by TRLIF and steady-state emission intensity measurements. The results were interpreted in terms of binding of phenolic compounds to the micelle. The binding constant (K(Q)) as well as the entrance and exit rate constants were determined for all the quenchers used. 相似文献