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排序方式: 共有329条查询结果,搜索用时 15 毫秒
171.
Strained nitroso Diels–Alder bicyclo[2.2.1] or [2.2.2] adducts functionalized with alkene side chains of diverse length undergo a ring‐rearrangement metathesis process with external alkenes and Grubbs II or Hoveyda–Grubbs II ruthenium catalysts, under microwave irradiation or classical heating, to deliver cis‐fused bicycles of various ring sizes, which contain a N? O bond. These scaffolds are of synthetic relevance for the generation of molecular diversity and to the total synthesis of alkaloids. The observation of unexpected reactions, such as epimerization or one‐carbon homologation of the alkene side chain, is also reported. 相似文献
172.
湍流边界层噪声是飞机巡航过程中的主要外部噪声源,对舱内噪声水平的影响尤为重要。因此,对飞机机体表面湍流边界层噪声的研究具有重要意义。本文通过试验获得了某型民机巡航过程中的湍流边界层噪声,试飞工况为3500ft/0.78、3500ft/0.7、2500ft/0.67、1500ft/0.66。对实测数据进行分析,发现湍流边界层噪声与动压、边界层厚度等参数有关。同时,利用计算流体力学的方法得到了飞机机体表面的压力分布,并分析了压力梯度对湍流边界层噪声的影响。最后,基于工程预测方法对湍流边界层噪声进行了预测,对于不存在逆压梯度的区域,预测结果与试验结果吻合较好,仅部分频段存在一定偏差。通过对模型的参数进行优化,改善了预测结果。 相似文献
173.
Cyrille Joutard 《Annals of the Institute of Statistical Mathematics》2013,65(1):49-67
We establish strong large deviation results for an arbitrary sequence of random variables under some assumptions on the normalized cumulant generating function. In other words, we give asymptotic expansions for the tail probabilities of the same kind as those obtained by Bahadur and Rao (Ann. Math. Stat. 31:1015–1027, 1960) for the sample mean. We consider both the case where the random variables are absolutely continuous and the case where they are lattice-valued. Our proofs make use of arguments of Chaganty and Sethuraman (Ann. Probab. 21:1671–1690, 1993) who also obtained strong large deviation results and local limit theorems. We illustrate our results with the kernel density estimator, the sample variance, the Wilcoxon signed-rank statistic and the Kendall tau statistic. 相似文献
174.
Guanghao Huang Prof. Cyrille Kouklovsky Dr. Aurélien de la Torre 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(15):4760-4788
Inverse-electron-demand Diels–Alder (IEDDA) reactions of electron-poor 2-pyrones as electrophilic dienes have been extensively studied in the past fifty years. These reactions provide an efficient access to bridged bicyclic lactones and their derivatives, such as densely functionalized 1,3-cyclohexadienes after CO2 extrusion and polysubstituted aromatic compounds through elimination. This reaction has been used for the synthesis of many biologically active natural products and drug candidates. In this review, the developments of these IEDDA reactions including non-catalytic, Lewis acid-catalyzed and organocatalytic IEDDA reactions, and their applications in total synthesis are discussed in detail. 相似文献
175.
Dr. Margaux Galland Dr. Tangui Le Bahers Dr. Akos Banyasz Dr. Noëlle Lascoux Dr. Alain Duperray Dr. Alexei Grichine Prof. Raphaël Tripier Dr. Yannick Guyot Dr. Marie Maynadier Christophe Nguyen Dr. Magali Gary-Bobo Dr. Chantal Andraud Dr. Cyrille Monnereau Dr. Olivier Maury 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(38):9026-9034
Two trispicolinate 1,4,7-triazacyclonane (TACN)-based ligands bearing three picolinate biphotonic antennae were synthetized and their Yb3+ and Gd3+ complexes isolated. One series differs from the other by the absence ( L1 )/presence ( L2 ) of bromine atoms on the antenna backbone, offering respectively improved optical and singlet-oxygen generation properties. Photophysical properties of the ligands, complexes and micellar Pluronic suspensions were investigated. Complexes exhibit high two-photon absorption cross-section combined either with NIR emission (Yb) or excellent 1O2 generation (Gd). The very large intersystem crossing efficiency induced by the combination of bromine atom and heavy rare-earth element was corroborated with theoretical calculations. The 1O2 generation properties of L2 Gd micellar suspension under two-photon activation leads to tumour cell death, suggesting the potential of such structures for theranostic applications. 相似文献
176.
Alexander H. Soeriyadi Vanessa Trouillet Francesca Bennet Michael Bruns Michael R. Whittaker Cyrille Boyer Philip J. Barker Thomas P. Davis Christopher Barner‐Kowollik 《Journal of polymer science. Part A, Polymer chemistry》2012,50(9):1801-1811
The present study investigates the degradation behavior of various high‐molecular‐weight acrylic polymers (50,000 < Mn/g mol?1 < 100,000), namely poly(methyl methacrylate) (PMMA), poly(n‐butyl methacrylate) (PBMA), poly(n‐butyl acrylate) (PBA), and poly(lauryl methacrylate) (PLMA), under extreme environmental conditions. These polymers were synthesized via various polymerization techniques to create different end‐groups. The polymers chosen are readily applicable in the formulation of surface coatings and were degraded under conditions which replicate the harsh Australian climate, where surface coatings may reach temperatures of up to 95 °C and are exposed to broad‐spectrum UV radiation of up to 1 kW m?2. The degradation behavior of the polymeric materials on their surface was followed via ATR‐IR spectroscopy, high resolution FTIR microscopy, and X‐ray photoelectron spectroscopy. The extent of the observed thermal and photo‐oxidation is directly related to the length of the ester side group, with the degradation susceptibility decreasing in the order of PLMA > PBMA/PBA > PMMA, with PMMA still stable even after 5 months exposure to the harshest condition used (UV light at 95 °C). The general degradation mechanism involves the loss of the ester side groups to form methacrylic acid followed by cross‐linking. The effect of the variable end groups was found to be minimal. The results from this study are in good agreement with previous studies of low‐molecular‐weight model polymers under identical conditions. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012 相似文献
177.
Dr. Alexis Lossouarn Chloé Puteaux Laetitia Bailly Dr. Vincent Tognetti Prof. Laurent Joubert Prof. Pierre-Yves Renard Dr. Cyrille Sabot 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(62):e202202180
Proteins are able to irreversibly assemble biologically active ligands from building blocks bearing complementary reactive functions due their spatial proximity, through a kinetic target-guided synthetic process (also named in situ click chemistry). Although linkages thus formed are mostly passive, some of them have shown to significantly contribute to the protein binding through for instance hydrogen bonding and stacking interactions. Biocompatible reactions and click chemistry are a formidable source of inspiration for developing such new protein-directed ligations. This study reports a proximity-induced thiol-yne synthesis of carbonic anhydrase inhibitors. Not only this example widens the arsenal of kinetic target-guided synthesis (KTGS) eligible reactions, but the obtained product displayed unsuspected photophysical properties. The corresponding vinyl sulfide linkage conjugated to a coumarin core proved to be engaged in a monodirectional Z to E photoisomerization process. Further investigations guided by theoretical calculations showed that fine-tuning of the nature of the substituents on the coumarin moiety allows to obtain a bidirectional photochemical process, thus discovering a new photoswitching moiety, displaying moreover fluorescence properties. Due to the spectral tunability of coumarin derivatives, this work should open new opportunities for the design of vinyl sulfide-based photoswitch systems with modular photophysical properties. 相似文献
178.
Yingchao Dou Prof. Dr. Cyrille Kouklovsky Dr. Guillaume Vincent 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(71):17190-17194
The second-generation synthesis of (−)-cymoside as well as the formation of a new hexacyclic-fused furo[3,2-b]indoline framework is reported. After a Pictet–Spengler condensation between secologanin tetraacetate and tryptamine, the course of the cyclization of the 7-hydroxyindolenine intermediate, generated by oxidation with an oxaziridine, depended on the stereochemistry of the 3-position. The 3-(S)-strictosidine stereochemistry delivered efficiently the scaffold of cymoside via intramolecular coupling with the C16–C17 enol ether, while the 3-(R)-vincoside stereochemistry directed towards the reaction with the C18–C19 terminal alkene and the formation of the unexpected caged compound. 相似文献
179.
Rocio Nohemi Rivas Araiza Cyrille Rochas Laurent David Alain Domard 《Macromolecular Symposia》2008,266(1):1-5
Summary: Chitosan hollow fiber formation with a variable internal diameter was performed from a new wet-spinning method in interrupted coagulation conditions by means of water washings. The main objective of the present study is to provide a better understanding of the physicochemical events involved during the chitosan fiber formation by this new wet-spinning method. 相似文献
180.
We report on high-accuracy angle-resolved optical transmission measurements through anisotropic 2D plasmonic crystals made of gold films with large-area rectangular arrays of nanoscale square holes, deposited on GaAs substrates. The measurements reveal the dispersion relations of air-gold and gold-GaAs surface plasmon polaritons. The crystal anisotropy induces a separation between plasmonic modes propagating in different directions. Their symmetry and dispersion properties are discussed. 相似文献