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1.
For the determination of traces of boron in iron, low- and high-alloy steels and other materials a direct spectrophotometric method was developed. In this method the absorbance of the boron-Curcumin complex formed in the sample solution is compared with the absorbance of another aliquot of sample solution wherein the boron is rendered inactive with fluoride before the Curcumin is added. 相似文献
2.
Alkoxyallene‐ynes: Selective Preparation of Bicyclo[5.3.0] Ring Systems Including a δ‐Alkoxy Cyclopentadienone 下载免费PDF全文
Dr. Aurélien Tap Camille Lecourt Sabrina Dhambri Mathieu Arnould Dr. Gilles Galvani Dr. Olivier Nguyen Van Buu Dr. Morgan Jouanneau Dr. Jean‐Pierre Férézou Prof. Janick Ardisson Dr. Marie‐Isabelle Lannou Dr. Geoffroy Sorin 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(14):4938-4944
The development of an intramolecular rhodium(I)‐catalyzed Pauson–Khand reaction of alkoxyallene‐ynes with a proximal alkoxy group is reported. This reaction, in the presence of a [Rh(cycloocta‐1,5‐diene)Cl]2/propane‐1,3‐diylbis(diphenylphosphane) system under a CO atmosphere, constitutes a powerful tool for selectively accessing carbo‐ and heterobicyclo[5.3.0] frameworks featuring an enol ether moiety. Through this procedure, a straightforward access to guaiane skeletons with a tertiary hydroxy group at the C10 position was achieved. 相似文献
3.
Maxime Jarret Victor Turpin Aurlien Tap Jean‐Franois Gallard Cyrille Kouklovsky Erwan Poupon Guillaume Vincent Laurent Evanno 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(29):9966-9970
Reported is the enantioselective total syntheses of mavacuran alkaloids, (+)‐taberdivarine H, (+)‐16‐hydroxymethyl‐pleiocarpamine, and (+)‐16‐epi‐pleiocarpamine, and their postulated biosynthetic precursor 16‐formyl‐pleiocarpamine. This family of monoterpene indole alkaloids is a target of choice since some of its members are subunits of intricate bisindole alkaloids such as bipleiophylline. Inspired by the biosynthetic hypothesis, an oxidative coupling approach from the geissoschizine framework to form the N1?C16 bond was explored. Quaternization of the aliphatic nitrogen center was key to achieving the oxidative coupling induced by KHMDS/I2 as it masks the nucleophilicity of the aliphatic nitrogen center and locks in the required cis conformation. 相似文献
4.
Normal mode calculations for two alternating sequence dodecamers in A, B, and Z conformations have been performed in dihedral angle space extended to endocyclic valence angles to account for sugar ring flexibility. Normal modes are analyzed in terms of helicoidal and backbone parameter variations with special attention being paid to global deformations of the double helix such as bending, twisting, or stretching. Results show that the allomorphic form of DNA has the largest influence on the flexibility of the sugar-phosphate backbone. Amplitudes of these vibrations follow the order: B > Z > A. In contrast, the amplitudes of helicoidal parameter variations are much more dependent on the base sequence. Global deformations of the double helix occur with characteristic times in the range of 1 to 10 ps and can be of mixed character, the strongest bending mode being at the same the time strongest stretching mode. © 1997 by John Wiley & Sons, Inc. J Comput Chem 18: 796–811, 1997 相似文献
5.
W.?J.?S.?RamaekersEmail author F.?A.?Tap B.?J.?Boersma 《Flow, Turbulence and Combustion》2018,101(2):457-476
Fuel efficiency improvement and harmful emission reduction are the paramount driving forces for development of gas turbine combustors. Lean-burn combustors can accomplish these goals, but require specific flow topologies to overcome their sensitivity to combustion instabilities. Large Eddy Simulations (LES) can accurately capture these complex and intrinsically unsteady flow fields, but estimating the appropriate numerical resolution and subgrid model(s) still remain challenges. This paper discusses the prediction of non-reacting flow fields in the DLR gas turbine model combustor using LES. Several important features of modern gas turbine combustors are present in this model combustor: multiple air swirlers and recirculation zones for flame stabilisation. Good overall agreement is obtained between LES outcomes and experimental results, both in terms of time-averaged and temporal RMS values. Findings of this study include a strong dependence of the opening angle of the swirling jet inside the combustion chamber on the subgrid viscosity, which acts mainly through the air mass flow split between the two swirlers in the DLR model combustor. This paper illustrates the ability of LES to obtain accurate flow field predictions in complex gas turbine combustors making use of open-source software and computational resources available to industry. 相似文献
6.
Dr. Aurélien Tap Dr. Aurélie Blond Dr. Vijay N. Wakchaure Prof. Dr. Benjamin List 《Angewandte Chemie (International ed. in English)》2016,55(31):8962-8965
Herein we describe the development of a catalytic enantioselective alkynylogous Mukaiyama aldol reaction. The reaction is catalyzed by a newly designed chiral disulfonimide and delivers chiral allenoates in high yields and with excellent regio‐, diastereo‐, and enantioselectivity. Our process tolerates a broad range of aldehydes in combination with diverse alkynyl‐substituted ketene acetals. The reaction products can be readily derivatized to furnish a variety of highly substituted enantiomerically enriched building blocks. 相似文献
7.
Maria Bykhovskaia Boris Gelmont Tatiana Globus Dwight L. Woolard Alan C. Samuels Tap Ha Duong Krystyna Zakrzewska 《Theoretical chemistry accounts》2001,106(1-2):22-27
We present a computational method which couples normal mode analysis in internal coordinates of a molecule with very far
IR spectroscopy. The analytical expression for the dependence of IR absorption on frequency incorporates frequencies and optical
activities of each normal mode. In order to predict far-IR spectra of a molecule we evaluate the optical activity of each
normal mode. This optical activity is determined by the vibration amplitude of the dipole moment produced by a normal mode.
We calculated normal modes of DNA double-helical fragments (dA)12 · (dT)12 and (dA-dT)6 · (dA-dT)6 and evaluated their optical activities. These were found to be very sensitive to the DNA base-pair sequence. The positions
of the resonance peaks in the calculated absorption spectrum of (dA)12 · (dT)12 are in a good agreement with those obtained by Fourier transform IR spectroscopy (Powell JW et al. 1987 Phys Rev A 35: 3929–3939).
Received: 20 June 2000 / Accepted: 5 January 2001/ Published online: 3 May 2001 相似文献
8.
The relation between the dielectric constant and the particle polarizability for a polarizable liquid composed of Lennard-Jones particles carrying a saturable induced dipole is studied by computer simulations. It is shown that the widely accepted Clausius–Mossotti relation is only valid for low polarizabilities and fails for high polarizabilities. The results can be fitted accurately by an Onsager-like relation using an effective particle radius measured in the simulations which is larger than the equivalent hard-sphere radius defined conventionally. Furthermore, the orientational ordering transition found at high polarizabilities is shown to be of anti-ferroelectric type. 相似文献
9.
Bioinspired Oxidative Cyclization of the Geissoschizine Skeleton for the Total Synthesis of (−)‐17‐nor‐Excelsinidine 下载免费PDF全文
Maxime Jarret Dr. Aurélien Tap Prof. Cyrille Kouklovsky Prof. Erwan Poupon Dr. Laurent Evanno Dr. Guillaume Vincent 《Angewandte Chemie (International ed. in English)》2018,57(38):12294-12298
We report the first total synthesis of (?)‐17‐nor‐excelsinidine, a zwitterionic monoterpene indole alkaloid that displays an unusual N4?C16 connection. Inspired by the postulated biosynthesis, we explored an oxidative coupling approach from the geissoschizine framework to forge the key ammonium–acetate connection. Two strategies allowed us to achieve this goal, namely an intramolecular nucleophilic substitution on a 16‐chlorolactam with the N4 nitrogen atom or a direct I2‐mediated N4?C16 oxidative coupling from the enolate of geissoschizine. 相似文献
10.
A generalized flame surface density modelling approach is presented to simulate the transient ignition and flame stabilization of a diesel jet flame, for which experimental data are available. The approach consists of four submodels: a mixing model, a generalized flame surface density model, a generalized progress variable model, and a chemistry model. A database containing the laminar model reaction rates per unit generalized flame surface density is generated by solving the unsteady flamelet equations. The RANS-CFD code solves for the mean flame surface density and mean progress variable. The coupling of the models is done via the progress variable and the scalar dissipation rate. The proposed approach is found to be adapted to simulate such a lifted flame and yields good trend agreement for ignition delay and flame lift-off vs. liquid penetration. These first promising results are encouraging to further explore and to apply this method to a more industrial configuration such as a diesel engine. 相似文献