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851.
Moura FC Araujo MH Dalmázio I Alves TM Santos LS Eberlin MN Augusti R Lago RM 《Rapid communications in mass spectrometry : RCM》2006,20(12):1859-1863
Electrospray ionization (ESI) mass spectrometry (MS) and tandem mass spectrometry (MS/MS) were used to monitor the oxidation of phenol by a novel heterogeneous Fenton system based on a Fe(0)/Fe(3)O(4) composite and H(2)O(2). On-line ESI-MS(/MS) shows that this heterogeneous system promotes prompt oxidation of phenol to hydroquinone, which is subsequently oxidized to quinone, other cyclic poly-hydroxylated intermediates and an acyclic carboxylic acid. A peroxide-type intermediate, probably formed via an electrophilic attack of HOO(.) on the phenol ring, was also intercepted and characterized. ESI-MS(/MS) monitoring of the oxidation of two other model aromatic compounds, benzene and chlorobenzene, indicates the participation of analogous intermediates. These results suggest that oxidation by the heterogeneous system is promoted by highly reactive HO(.) and HOO(.) radicals generated from H(2)O(2) on the surface of the Fe(0)/Fe(3)O(4) composite via a classical Fenton-like mechanism. 相似文献
852.
da Silva R Heleno VC de Albuquerque S Bastos JK Andrade e Silva ML Donate PM da Silva GV 《Magnetic resonance in chemistry : MRC》2004,42(11):985-989
We describe the complete 1H and 13C NMR analysis of three aryltetralin lignan lactones (polygamain, morelensin and 4,5-dimethoxymorelensin) using modern NMR techniques such as COSY, HMQC, HMBC, 2D-J-resolved and NOE experiments. The relative stereochemistry of these compounds, which is very important with regard to their biological activity, was completely determined. 相似文献
853.
854.
Marcos Vanella Patrick Rabenold Elias Balaras 《Journal of computational physics》2010,229(18):6427-6449
In the present work we developed a structured adaptive mesh refinement (S-AMR) strategy for fluid–structure interaction problems in laminar and turbulent incompressible flows. The computational grid consists of a number of nested grid blocks at different refinement levels. The coarsest grid blocks always cover the entire computational domain, and local refinement is achieved by the bisection of selected blocks in every coordinate direction. The grid topology and data-structure is managed using the Paramesh toolkit. The filtered Navier–Stokes equations for incompressible flow are advanced in time using an explicit second-order projection scheme, where all spatial derivatives are approximated using second-order central differences on a staggered grid. For transitional and turbulent flow regimes the large-eddy simulation (LES) approach is used, where special attention is paid on the discontinuities introduced by the local refinement. For all the fluid–structure interaction problems reported in this study the complete set of equations governing the dynamics of the flow and the structure are simultaneously advanced in time using a predictor–corrector strategy. An embedded-boundary method is utilized to enforce the boundary conditions on a complex moving body which is not aligned with the grid lines. Several examples of increasing complexity are given to demonstrate the robustness and accuracy of the proposed formulation. 相似文献
855.
We show that if 𝒜 is an abelian category satisfying certain mild conditions, then one can introduce the concept of a moduli space of (semi)stable objects which has the structure of a projective algebraic variety. This idea is applied to several important abelian categories in representation theory, like highest weight categories. 相似文献
856.
Characterization by fourier transform infrared spectroscopy (FT-IR) and 2D IR correlation spectroscopy of PAMAM dendrimer 总被引:1,自引:0,他引:1
Popescu MC Filip D Vasile C Cruz C Rueff JM Marcos M Serrano JL Singurel G 《The journal of physical chemistry. B》2006,110(29):14198-14211
FT-IR and 2D correlation spectroscopy were employed to study the microstructural changes occurring during phase transitions of a liquid crystal poly(amidoamine) codendrimer (PAMAM (L1)16(L2)16) generation 3, functionalized on the terminal groups by one-chain promesogenic calamitic units (4-(4'-decyloxybenzoyloxy)salicylaldehyde (L1)) and two-chain promesogenic calamitic units (4-(3',4'-didecyloxybenzoyloxy)salicylaldehyde (L2)). Spectral modifications associated with molecular conformation rearrangements allowing for molecular shape change on going from a liquid-crystalline organization to another were found. The transition temperatures were calculated, and they are in good agreement with the DSC data. Spectral analysis gives evidence of the LC phase transitions and to an additional transition associated with the existence of conformers. Various types of hydrogen bonding have been established. 相似文献
857.
Aggregation behavior of aqueous solutions of ionic liquids 总被引:8,自引:0,他引:8
Bowers J Butts CP Martin PJ Vergara-Gutierrez MC Heenan RK 《Langmuir : the ACS journal of surfaces and colloids》2004,20(6):2191-2198
The aggregation behavior in aqueous solutions of three ionic liquids based on the 1-alkyl-3-methylimidazolium cation has been investigated by means of surface tension, conductivity, and small-angle neutron scattering (SANS) measurements. From analysis of the SANS data, models for the shapes and sizes of aggregates have been proposed: the short-chain 1-butyl-3-methylimidazolium tetrafluoroborate [C4mim] [BF4] system can be best modeled by treating it as a dispersion of polydisperse spherical aggregates that form above a critical aggregation concentration, whereas the 1-octyl-3-methylimidazolium iodide, [C8mim] [I], solutions can be modeled as a system of regularly sized near-spherical charged micelles that form above a critical micelle concentration. Solutions of 1-octyl-3-methylimidazolium chloride, [C8mim]-[Cl], display weak long-range ordering of possibly disklike particles culminating in the formation of structures with distinct long-range order at higher concentrations. 相似文献
858.
Response surface methodology (RSM) as a tool for optimization in analytical chemistry 总被引:19,自引:0,他引:19
A review about the application of response surface methodology (RSM) in the optimization of analytical methods is presented. The theoretical principles of RSM and steps for its application are described to introduce readers to this multivariate statistical technique. Symmetrical experimental designs (three-level factorial, Box-Behnken, central composite, and Doehlert designs) are compared in terms of characteristics and efficiency. Furthermore, recent references of their uses in analytical chemistry are presented. Multiple response optimization applying desirability functions in RSM and the use of artificial neural networks for modeling are also discussed. 相似文献
859.
860.
Helio G. Bonacorso Mauro N. Muniz Arci D. Wastowski Nilo Zanatta Marcos A. P. Martins 《Heteroatom Chemistry》2003,14(2):132-137
A convenient method for the synthesis of a novel series of 11, specifically substituted, noncondensed 5,5‐bicycles 2‐[3‐phenyl‐5‐hydroxy‐5‐trichloromethyl‐4,5‐dihydro‐1H‐pyrazol‐1‐yl]‐4‐aryl‐5‐alkylthiazoles ( 3a–k ; 65–94% yield) from the reactions of 3‐phenyl‐5‐hydroxy‐5‐trichloromethyl‐4,5‐dihydro‐1H‐1‐pyrazolethiocarboxyamide ( 1 ) with substituted 2‐bromo‐4′‐acetophenones ( 2a–f ) and 2‐bromo‐4′‐propiophenones ( 2g–k ) is reported. Dehydration of compounds 3a–k with a mixture of concentrated sulfuric acid/chloroform furnished the corresponding 2‐[3‐phenyl‐5‐trichloromethyl‐1H‐pyrazol‐1‐yl]‐4‐aryl‐5‐alkylthiazoles ( 4a–k ) in good yields (61–93%). © 2003 Wiley Periodicals, Inc. Heteroatom Chem 14:132–137, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/hc.10113 相似文献