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101.
Amination of 4-nitrophenol, umbelliferone and 4-methylumbelliferone gave the corresponding oxyamines 1-3. These oxyamines react with aldehydes and ketones to form oximes. In the case of aliphatic aldehydes and electron-poor aromatic aldehydes, the oximes undergo base-catalyzed fragmentation in aqueous buffer in the presence of bovine serum albumin to give the parent phenols, which is the acyclic analog of Kemp's elimination reaction of 5-nitrobenzisoxazole 28. The process can be used as a spectrophotometric assay for formaldehyde under aqueous neutral conditions. 相似文献
102.
Corminboeuf O Renaud P Schiesser CH 《Chemistry (Weinheim an der Bergstrasse, Germany)》2003,9(7):1578-1584
The stereochemical outcome of the radical haloacetal cyclization reaction (Ueno-Stork reaction) has been examined by ab initio and other molecular orbital techniques. It was found that the stereochemistry of 5-exo- and 6-exo trig cyclizations can be accurately predicted from calculations using moderate levels of theory (UHF/6-311G** or B3LYP/6-311G**). A simplified computational procedure, easily run on a standard desktop computer, has been developed that provides excellent predictive ability for the stereochemical outcome for the reactions in question. Interestingly, a novel twist transition state has been identified for the first time in 5-exo-trig radical cyclization reactions. 相似文献
103.
Anthrone has been found to react with N-methyl maleimide in the presence of catalytic amounts of various chiral β-amino alcohols. The optically active cycloadduct 3a has been obtained in excellent yield. Several features of the reaction have been studied. 相似文献
104.
Fontaine P Goldmann M Muller P Fauré MC Konovalov O Krafft MP 《Journal of the American Chemical Society》2005,127(2):512-513
We report the first direct evidence for the formation of circular surface micelles (hemimicelles) on the surface of water. These highly monodisperse 30 nm hemimicelles, made from a semifluorinated alkane deposited as a Langmuir monolayer, form organized hexagonal arrays as determined by small-angle X-ray diffraction conducted directly on the water surface at grazing incidence. 相似文献
105.
The [2.2.2]hericene ( 6 ), a bicyclo[2.2.2]octane bearing three exocyclic s-cis-butadiene units has been prepared in eight steps from coumalic acid and maleic anhydride. The hexaene 6 adds successively three mol-equiv. of strong dienophiles such as ethylenetetracarbonitrile (TCE) and dimethyl acetylenedicarboxylate (DMAD) giving the corresponding monoadducts 17 and 20 (k1), bis-adducts 18 and 21 (k2) and tris-adducts 19 and 22 (k3), respectively. The rate constant ratio k1/k2 is small as in the case of the cycloadditions of 2,3,5,6-tetramethylidene-bicyclo [2.2.2]octane ( 3 ) giving the corresponding monoadducts 23 and 27 (k1) and bis-adducts 25 and 29 (k2) with TCE and DMAD, respectively. Constrastingly, the rate constant ratio k2/k3 is relatively large as the rate constant ratio k1/k2 of the Diels-Alder additions for 5,6,7,8-tetramethylidenebicyclo [2.2.2]oct-2-ene ( 4 ) giving the corresponding monoadducts 24 and 28 (k1) and bis-adducts 26 and 30 (k2). The following second-order rate constants (toluene, 25°) and activation parameters were obtained for the TCE additions: 3 +TCE→ 23 : k1 = 0.591±0.012 mol?1·l·s?1, ΔH≠=10.6±0.4 kcal/mol, and ΔS≠ = ?24.0±1.4 cal/mol·K (e.u.); 23 +TCE→ 25 : k2=0.034±0.0010 mol?1·l·s?1, ΔH≠ = 10.6±0.6 kcal/mol, and ΔS≠ = ?29.7±2.0 e.u.; 4 +TCE→ 26 : k1 = 0.172±0.035 mol?1·l·s?1, ΔH≠ 11.3±0.8 kcal/mol, and ΔS≠ = ?24.0±2.8 e.u.; 24 +TCE→ 26 : k2 = (6.1±0.2)·10?4 mol?1·l·s?1, ΔH≠ = 13.0±0.3 kcal/mol, and ΔS≠ = ?29.5±0.8 e.u.; 6 +TCE→ 17 : k1 = 0.136±0.002 mol?1·l·s?1, ΔH≠ = 11.3±0.2 kcal/mol, and ΔS≠ = ?24.5±0.8 e.u.; 17 +TCE→ 18 : k2 = 0.0156±0.0003 mol?1·l·s?1, ΔH≠ = 10.9±0.5 kcal/mol, and ΔS≠ = ?30.1 ± 1.5 e.u.; 18 +TCE→ 19 : k3=(5±0.2) · 10?5 mol?1 mol?1 ·l·s?1, ΔH≠ = 15±3 kcal/mol, and ΔS≠ = ?28 ± 8 e.u. The following rate constants were evaluated for the DMAD additions (CD2Cl2, 30°): 6 +DMAD→ 20 : k1 = (10±1)·10?4 mol?1 · l·s?1; 20 +DMAD→ 21 : k2 = (6.5±0.1) · 10?4 mol?1 ·l·?1; 21 +DMAD→ 22 : k3 = (1.0±0.1) · 10?4 mol?1 ·l·s?1. The reactions giving the barrelene derivatives 19, 22, 26 and 30 are slower than those leading to adducts that are not barrelenes. The former are estimated less exothermic than the latter. It is proposed that the Diels-Alder reactivity of exocyclic s-cis-butadienes grafted onto bicycle [2.2.1]heptanes and bicyclo [2.2.2]octanes that are modified by remote substitution of the bicyclic skeletons can be affected by changes inthe exothermicity of the cycloadditions, in agreement with the Dimroth and Bell-Evans-Polanyi principle. Force-field calculations (MMPI 1) of 3, 4, 6 and related exocyclic s-cis-butadienes as a moiety of bicyclo [2.2.2]octane suggested single minimum energy hypersurfaces for these systems (eclipsed conformations, planar dienes). Their flexibility decreases with the degree of unsaturation of the bicyclic skeleton. The effect of an endocyclic double bond is larger than that of an exocyclic diene moiety. 相似文献
106.
Jean Bricmont Jean-Raymond Fontaine Joel L. Lebowitz Thomas Spencer 《Communications in Mathematical Physics》1981,78(3):363-371
We consider perturbations of a massless Gaussian lattice field on ? d ,d≧3, which preserves the continuous symmetry of the Hamiltonian, e.g., $$ - H = \sum\limits_{< x,y > } {(\phi _x - \phi _y )^2 + T(\phi _x - \phi _y )^4 ,\phi _x \in \mathbb{R}.} $$ It is known that for allT>0 the correlation functions in this model do not decay exponentially. We derive a power law upper bound for all (truncated) correlation functions. Our method is based on a combination of the log concavity inequalities of Brascamp and Lieb, reflection positivity and the Fortuin, Kasteleyn and Ginibre (F.K.G.) inequalities. 相似文献
107.
D. Drijard H. G. Fischer W. Geist P. G. Innocenti V. Korbel A. Minten A. Norton S. Stein O. Ullaland H. D. Wahl G. Fontaine C. Ghesquière G. Sajot P. Hanke W. Hofmann M. Panter K. Rauschnabel J. Spengler D. Wegener H. Frehse M. Heiden E. E. Kluge A. Putzer M. Della Negra D. Linglin R. Gokieli R. Sosnowski 《Zeitschrift fur Physik C Particles and Fields》1981,9(4):293-303
Inclusive production of ?0,f, andg 0 mesons and ofK s 0 ,K *0 (892), ? andK *0(1430)mesons has been measured at <y>~2.6 and <p T >~1.1 GeV/c in proton-proton interactions at \(\sqrt s = 52.5\) GeV. The negative particle from the two-body decays of these resonances were identified by a threshold Cerenkov counter and used for triggering. Starting from the measured differential cross section, total inclusive cross sections for the vector and tensor mesons were determined using various parametrizations for they andp T dependence of the differential cross section. The experimental results are discussed in the framework of production models based on the parton picture. The strangeness suppresion factor λ=(0.30±0.10) due toSU(3) symmetry breaking of the quark sea is derived. 相似文献
108.
Christelle Peillon Magali Estribeau Pierre Magnan Alice Pelamatti Olivier Saint-Pé Michel Breart de Boisanger 《Optical and Quantum Electronics》2017,49(11):378
The minority carrier continuity equation has been solved with the Green’s function approach in a N/P photodiode under the low-level injection assumption. The analytical solution obtained with this approach depends on the three spatial coordinates and on time. The diffusion and the collection of the excess minority carriers have been studied during the transitional period corresponding to very short integration times. The internal Quantum Efficiency and the diffusion Modulation Transfer Function have been calculated according to time. The simulations showed that they evolve with time until their steady-state values. When the integration time is very short, this evolution has to be taken into account for the estimation of the sensitivity of a photodiode and the contrast on an image of a sensor based on several adjacent N/P-type photodiodes. 相似文献
109.
Maxime Guitet Pinglu Zhang Filipa Marcelo Coralie Tugny Jesús Jimnez‐Barbero Olivier Buriez Christian Amatore Virginie Mouris‐Mansuy Jean‐Philippe Goddard Louis Fensterbank Yongmin Zhang Sylvain Roland Mickaël Mnand Matthieu Sollogoub 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2013,125(28):7354-7359
110.
Mathieu Gaudin Maï Panchal Sophie Ayciriex Erwan Werner Alain Brunelle David Touboul Claire Boursier‐Neyret Nicolas Auzeil Bernard Walther Charles Duyckaerts Olivier Laprévote 《Journal of mass spectrometry : JMS》2014,49(10):1035-1042
The development of ‘omics’ sciences offers new opportunities for the study of neurodegenerative diseases but increases at the same time the sample demand on brain banks that collect and store valuable human post‐mortem tissue. Our study aims to evaluate in lipidomics the potential of formalin‐fixed tissue compared with the cryopreservation method, considered as the gold standard for biochemical research. Two complementary liquid chromatography/mass spectrometry analytical platforms were used on the basis of hybrid quadrupole time‐of‐flight and triple quadrupole mass spectrometers. Untargeted fingerprinting, semitargeted profiling of specific lipid classes and targeted monitoring of lipid species were performed in formalin‐fixed and cryopreserved samples to provide detailed information at the molecular level on the formalin‐induced alterations of the brain tissue. In vitro incubations of lipid standards were also performed to further describe the degradation processes induced by formaldehyde. Phospholipid compounds were found to be extensively hydrolysed, whilst the sphingolipid ones were preserved. N‐methylation and N‐formylation of amine‐containing phospholipids have also been evidenced. These findings show that the potential detrimental effect of formalin on the analytes of interest must be taken into account when analysing formalin‐fixed samples. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献