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61.
On-line characterisation of apple polyphenols by liquid chromatography coupled with mass spectrometry and ultraviolet absorbance detection 总被引:5,自引:0,他引:5
Alonso-Salces RM Ndjoko K Queiroz EF Ioset JR Hostettmann K Berrueta LA Gallo B Vicente F 《Journal of chromatography. A》2004,1046(1-2):89-100
Apple polyphenols were characterised by means of hyphenated techniques such as HPLC coupled to UV photodiode array detection (LC-DAD) and to mass spectrometry (LC-MS). LC-MS using atmospheric pressure ionisation (APCI) in the positive ion mode provided the molecular weight, the number of hydroxyl groups, the number of sugars and an idea about the substitution pattern of the polyphenols. LC-DAD with postcolumn addition of UV shift reagents afforded precise structural information about the position of the free hydroxyl groups in the polyphenolic nucleus. Five isorhamnetin glycosides, two hydroxyphloretin glycosides and quercetin were reported in apple peel for the first time. Postcolumn addition of UV shift reagents in LC-DAD analysis confirmed the presence of isorhamnetin glycosides and not the isomeric glycosides of rhamnetin. Moreover, isorhamnetin-3-O-rhamnoglucoside was identified unambiguously by comparison with a standard. These results are relevant not only from a chemotaxonomic point of view, but also in the control of authenticity of fruit derived products in order to detect fraudulent admixtures. 相似文献
62.
This Letter reports on the experimental implementation of the quantum baker's map via a three bit nuclear magnetic resonance quantum information processor. The experiments tested the sensitivity of the quantum chaotic map to perturbations. In the first experiment, the map was iterated forward and then backward to provide benchmarks for intrinsic errors and decoherence. In the second set of experiments, the least significant qubit was perturbed in between the iterations to test the sensitivity of the quantum chaotic map to controlled perturbations. These experiments can be used to investigate existing theoretical predictions for quantum chaotic dynamics. 相似文献
63.
Zhao MM McNamara JM Ho GJ Emerson KM Song ZJ Tschaen DM Brands KM Dolling UH Grabowski EJ Reider PJ Cottrell IF Ashwood MS Bishop BC 《The Journal of organic chemistry》2002,67(19):6743-6747
A streamlined and high-yielding synthesis of aprepitant (1), a potent substance P (SP) receptor antagonist, is described. The enantiopure oxazinone 16 starting material was synthesized via a novel crystallization-induced dynamic resolution process. Conversion of 16 to the penultimate intermediate cis-sec-amine 9 features a highly stereoselective Lewis acid-catalyzed trans acetalization of chiral alcohol 3 with trichloroacetimidate 18 followed by inversion of the adjacent chiral center on the morpholine ring. The six-step process for the synthesis of 9 was accomplished in extremely high overall yield (81%) and with only two isolations. 相似文献
64.
Xiao-Jun Gu David R. Emerson Gui-Hua Tang 《Continuum Mechanics and Thermodynamics》2009,21(5):345-360
A set of linearized 26 moment equations, along with their wall boundary conditions, are derived and used to study low-speed
gas flows dominated by Knudsen layers. Analytical solutions are obtained for Kramers’ defect velocity and the velocity-slip
coefficient. These results are compared to the numerical solution of the BGK kinetic equation. From the analysis, a new effective
viscosity model for the Navier–Stokes equations is proposed. In addition, an analytical expression for the velocity field
in planar pressure-driven Poiseuille flow is derived. The mass flow rate obtained from integrating the velocity profile shows
good agreement with the results from the numerical solution of the linearized Boltzmann equation. These results are good for
Knudsen numbers up to 3 and for a wide range of accommodation coefficients. The Knudsen minimum phenomenon is also well captured
by the present linearized 26-moment equations. 相似文献
65.
Modular Construction of Fluoroarenes from a New Difluorinated Building Block by Cross‐Coupling/Electrocyclisation/Dehydrofluorination Reactions 下载免费PDF全文
Prof. Dr. Jonathan M. Percy Helena Emerson James W. B. Fyfe Dr. Alan R. Kennedy Sergej Maciuk David Orr Lucie Rathouská Dr. Joanna M. Redmond Dr. Peter G. Wilson 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(34):12166-12175
Palladium‐catalysed coupling reactions based on a novel and easy‐to‐synthesise difluorinated organotrifluoroborate were used to assemble precursors to 6π‐electrocyclisations of three different types. Electrocyclisations took place at temperatures between 90 and 240 °C, depending on the central component of the π‐system; nonaromatic trienes were most reactive, but even systems that required the temporary dearomatisation of two arenyl subunits underwent electrocyclisation, albeit at elevated temperatures. Photochemical conditions were effective for these more demanding reactions. The package of methods delivered a structurally diverse set of fluorinated arenes, spanning a 20 kcal mol?1 range of reactivity, by a flexible route. 相似文献
66.
da Silva Bruno Fonseca da Silva Karolayne Esthefany Melo de Farias Emerson Emiliano Gualberto de França Elvis Joacir Martins Mônica Cristina Barroso de Oliveira Santos Mariana Luiza de Lourdes Lacerda Buril Maria da Silva Alves Gustavo Gabriel de Oliveira Silva Andrezza Karla de Lira Júnior Ednaldo Barbalho da Silva Nicácio Herique Pereira Eugênia C. 《Journal of Radioanalytical and Nuclear Chemistry》2022,331(9):3671-3679
Journal of Radioanalytical and Nuclear Chemistry - This study aimed to evaluate the effects of the Rn-222 progeny on the lichen Cladonia verticillaris under controlled conditions. The results... 相似文献
67.
This paper presents an adaptive identification approach based on extreme learning machine (ELM), single hidden layer feedfoward neural networks, high-order neural networks (HONN), and adaptive control theory. Drawing on Lyapunov-like analysis employing Barbalat’s Lemma, the designed identifiers ensure the boundedness of all associated approximation errors and convergence of the residual state error, even in the presence of disturbances and unknown dynamics. Two cases are considered: a standard topology and a modified ELM with high-order regressor. Both with enhanced identification model and learning algorithms. Extensive simulations, to verify the theoretical results, and a comparative study, to show the performance of the proposed schemes, are performed. Simulation results depict that the HONN architecture combined with the ELM technique offers significant advantages over the standard one, insofar as faster training and lower computational burden are considered. 相似文献
68.
Carlos Roque D. Correia Caio C. Oliveira Airton G. Salles Emerson A.F. Santos 《Tetrahedron letters》2012,53(26):3325-3328
Successful enantioselective Heck–Matsuda arylations were accomplished for the first time using chiral bisoxazolines as ligands. Enantioselective Heck arylations were performed with several cyclic nonactivated olefins to provide the Heck products in 63–96% isolated yields and in enantiomeric excesses of 54% up to 84%. 相似文献
69.
Beatriz M. de Campos Paulo S. Calefi Katia J. Ciuffi Emerson H. de Faria Lucas A. Rocha Eduardo J. Nassar Jorge V. L. Silva Marcelo F. Oliveira Izaque A. Maia 《Journal of Thermal Analysis and Calorimetry》2014,115(2):1029-1035
The combination of sol–gel methodology with rapid prototyping (RP) produces functionalized 3D structures with potential applications in various fields. However, this combination has been little explored. In this paper, we used the sol–gel method to deposit vanadium isopropoxide onto polyamide (PA12) constructed by RP and pretreated with acetic acid, to obtain a functionalized substrate with new thermal, physical, and chemical properties. Vanadium isopropoxide (one, five, or ten layers) was deposited onto the PA12 piece by dip-coating. We characterized the coated PA12 by thermal analyses, X-ray diffraction, and infrared spectroscopy, which revealed that V=O and Si–O–Si groups exist on the PA12 surface. PA12 coating with vanadium isopropoxide enhanced the decomposition temperature. Differential scanning calorimetry revealed increased fusion and decomposition enthalpy as a function of the PA12 coating. Therefore, deposition of vanadium isopropoxide onto PA12 pretreated with acetic acid improves the thermal stability of PA12 prepared by RP. 相似文献
70.
In spite of the interference manifested in the double-slit experiment, quantum theory predicts that a measure of interference
defined by Sorkin and involving various outcome probabilities from an experiment with three slits, is identically zero. We adapt Sorkin’s measure into a general operational probabilistic framework for physical theories,
and then study its relationship to the structure of quantum theory. In particular, we characterize the class of probabilistic
theories for which the interference measure is zero as ones in which it is possible to fully determine the state of a system
via specific sets of ‘two-slit’ experiments. 相似文献