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排序方式: 共有790条查询结果,搜索用时 11 毫秒
61.
Nada Marquise Philip J. Harford Floris Chevallier Thierry Roisnel Vincent Dorcet Anne-Laure Gagez Sophie Sablé Laurent Picot Valérie Thiéry Andrew E.H. Wheatley Philippe C. Gros Florence Mongin 《Tetrahedron》2013
The efficiency of the deprotocupration–aroylation of 2-chloropyridine using lithiocuprates prepared from CuX (X=Cl, Br) and LiTMP (TMP=2,2,6,6-tetramethylpiperidido, 2 equiv) was investigated. CuCl was identified as a more suitable copper source than CuBr for this purpose. Different diaryl ketones bearing a halogen at the 2 position of one of the aryl groups were synthesized in this way from azines and thiophenes. These were then involved in palladium-catalyzed ring closure: substrates underwent expected CH-activation-type arylation to afford fluorenone-type compounds, and were also subjected to cyclization reactions leading to xanthones, notably in the presence of oxygen-containing substituents or reagents. 相似文献
62.
Summary Two high-performance liquid chromatography (HPLC) techniques were developed for the determination of binding constants in
the interaction of serum albumin with L-tryptophan: internal calibration and external calibration. The results obtained were
compared with those obtained by the classical method of equilibrium dialysis and by gel filtration. While all the methods
are equally reliable, the internal and external calibration techniques seem to be superior in their simplicity, speed and
convenience. 相似文献
63.
Morvan J Saluden M Agasse V Barbot F Cardinael P Bouillon JP Decock G 《Analytical and bioanalytical chemistry》2006,384(6):1409-1415
Bachus et al. [1] recently described a new derivatisation method using 2-furoyl chloride for the characterisation of mixtures of polyethoxylated
alcohols and their corresponding sulfates. This paper deals with the control of the derivatisation steps; hydrolysis and extraction
conditions were optimised. The method is extended to the characterisation of alkyl sulfosuccinates, alkyl sulfoacetates and
alkyl phosphates and to the analysis of residual polyethoxylated alcohols in surfactants. Extraction of non-ionic compounds
using solid-phase extraction cartridges was performed before derivatisation. Residual amounts of alcohol were determined in
five commercial anionic surfactants. Moreover, direct derivatisation without preliminary SPE in the same anionic surfactants
proved to be efficient for dry samples. 相似文献
64.
Kinetic studies of cyanide exchange on [M(CN)(4)](2-) square-planar complexes (M = Pt, Pd, and Ni) were performed as a function of pH by (13)C NMR. The [Pt(CN)(4)](2-) complex has a purely second-order rate law, with CN(-) as acting as the nucleophile, with the following kinetic parameters: (k(2)(Pt,CN))(298) = 11 +/- 1 s(-1) mol(-1) kg, DeltaH(2) (Pt,CN) = 25.1 +/- 1 kJ mol(-1), DeltaS(2) (Pt,CN) = -142 +/- 4 J mol(-1) K(-1), and DeltaV(2) (Pt,CN) = -27 +/- 2 cm(3) mol(-1). The Pd(II) metal center has the same behavior down to pH 6. The kinetic parameters are as follows: (k(2)(Pd,CN))(298) = 82 +/- 2 s(-1) mol(-1) kg, DeltaH(2) (Pd,CN) = 23.5 +/- 1 kJ mol(-1), DeltaS(2) (Pd,CN) = -129 +/- 5 J mol(-1) K(-1), and DeltaV(2) (Pd,CN) = -22 +/- 2 cm(3) mol(-1). At low pH, the tetracyanopalladate is protonated (pK(a)(Pd(4,H)) = 3.0 +/- 0.3) to form [Pd(CN)(3)HCN](-). The rate law of the cyanide exchange on the protonated complex is also purely second order, with (k(2)(PdH,CN))(298) = (4.5 +/- 1.3) x 10(3) s(-1) mol(-1) kg. [Ni(CN)(4)](2-) is involved in various equilibrium reactions, such as the formation of [Ni(CN)(5)](3-), [Ni(CN)(3)HCN](-), and [Ni(CN)(2)(HCN)(2)] complexes. Our (13)C NMR measurements have allowed us to determine that the rate constant leading to the formation of [Ni(CN)(5)](3-) is k(2)(Ni(4),CN) = (2.3 +/- 0.1) x 10(6) s(-1) mol(-1) kg when the following activation parameters are used: DeltaH(2)() (Ni,CN) = 21.6 +/- 1 kJ mol(-1), DeltaS(2) (Ni,CN) = -51 +/- 7 J mol(-1) K(-1), and DeltaV(2) (Ni,CN) = -19 +/- 2 cm(3) mol(-1). The rate constant of the back reaction is k(-2)(Ni(4),CN) = 14 x 10(6) s(-1). The rate law pertaining to [Ni(CN)(2)(HCN)(2)] was found to be second order at pH 3.8, and the value of the rate constant is (k(2)(Ni(4,2H),CN))(298) = (63 +/- 15) x10(6) s(-1) mol(-1) kg when DeltaH(2) (Ni(4,2H),CN) = 47.3 +/- 1 kJ mol(-1), DeltaS(2) (Ni(4,2H),CN) = 63 +/- 3 J mol(-1) K(-1), and DeltaV(2) (Ni(4,2H),CN) = - 6 +/- 1 cm(3) mol(-1). The cyanide-exchange rate constant on [M(CN)(4)](2-) for Pt, Pd, and Ni increases in a 1:7:200 000 ratio. This trend is modified at low pH, and the palladium becomes 400 times more reactive than the platinum because of the formation of [Pd(CN)(3)HCN](-). For all cyanide exchanges on tetracyano complexes (A mechanism) and on their protonated forms (I/I(a) mechanisms), we have always observed a pure second-order rate law: first order for the complex and first order for CN(-). The nucleophilic attack by HCN or solvation by H(2)O is at least nine or six orders of magnitude slower, respectively than is nucleophilic attack by CN(-) for Pt(II), Pd(II), and Ni(II), respectively. 相似文献
65.
Weawkamol Leelapornpisit Minh‐Tan Ton‐That Florence Perrin‐Sarazin Kenneth C. Cole Johanne Denault Benoit Simard 《Journal of Polymer Science.Polymer Physics》2005,43(18):2445-2453
The effect of different concentrations of single‐walled carbon nanotubes (SWNTs) on the nonisothermal crystallization kinetics, morphology, and mechanical properties of polypropylene (PP) matrix composites obtained by melt compounding was investigated by means of X‐ray diffraction, differential scanning calorimetry, optical and scanning electron microscopy, and dynamic mechanical thermal analysis. Microscopy showed well‐dispersed nanotube ropes together with small and large aggregates. The modulus was found to increase by about 75% at a level of 0.5 wt % nanotubes. The SWNTs displayed a clear nucleating effect on the PP crystallization, favoring the α crystalline form rather than the β form. The crystallization kinetics analysis showed a significant increase in activation energy on incorporating nanotubes. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 2445–2453, 2005 相似文献
66.
Kai Huang Dr. Florence Duclairoir Dr. Tiziana Pro Dr. Julien Buckley Dr. Gilles Marchand Dr. Eugénie Martinez Dr. Jean‐Claude Marchon Dr. Barbara De Salvo Dr. Guillaume Delapierre Dr. Françoise Vinet Dr. 《Chemphyschem》2009,10(6):963-971
The missing link : Ferrocene and porphyrin monolayers are tethered on silicon surfaces with short (see picture, left) or long (right) linkers. Electron transfer to the silicon substrate is faster for monolayers with a short linker.
67.
Martin JN Muñoz EM Schwergold C Souard F Asensio JL Jiménez-Barbero J Cañada J Vicent C 《Journal of the American Chemical Society》2005,127(26):9518-9533
Sugar-oligoamides have been designed and synthesized as structurally simple carbohydrate-based ligands to study carbohydrate-DNA interactions. The general design of the ligands 1-3 has been done as to favor the bound conformation of Distamycin-type gamma-linked covalent dimers which is a hairpin conformation. Indeed, NMR analysis of the sugar-oligoamides in the free state has indicated the presence of a percentage of a hairpin conformation in aqueous solution. The DNA binding activity of compounds 1-3 was confirmed by calf thymus DNA (ct-DNA) NMR titration. Interestingly, the binding of the different sugar-oligoamides seems to be modulated by the sugar configuration. Semiquantitative structural information about the DNA ligand complexes has been derived from NMR data. A competition experiment with Netropsin suggested that the sugar-oligoamide 3 bind to DNA in the minor groove. The NMR titrations of 1-3 with poly(dA-dT) and poly(dG-dC) suggested preferential binding to the ATAT sequence. TR-NOE NMR experiments for the sugar-oligoamide 3-ct-DNA complex both in D(2)O and H(2)O have confirmed the complex formation and given information on the conformation of the ligand in the bound state. The data confirmed that the sugar-oligoamide ligand is a hairpin in the bound state. Even more relevant to our goal, structural information on the conformation around the N-glycosidic linkage has been accessed. Thus, the sugar asymmetric centers pointing to the NH-amide and N-methyl rims of the molecule have been characterized. 相似文献
68.
Mathieu Florence 《Inventiones Mathematicae》2008,171(1):175-189
Let p be a prime number, let K be a field of characteristic not p, containing the p-th roots of unity, and let r≥1 be an integer. We compute the essential dimension of ℤ/p
r
ℤ over K (Theorem 4.1). In particular,
i) We have edℚ(ℤ/8ℤ)=4, a result which was conjectured by Buhler and Reichstein in 1995 (unpublished).
ii) We have edℚ(ℤ/p
r
ℤ)≥p
r-1. 相似文献
69.
Caroline Mauve Jean Bleton Camille Bathellier Caroline Lelarge‐Trouverie Florence Guérard Jaleh Ghashghaie Alain Tchapla Guillaume Tcherkez 《Rapid communications in mass spectrometry : RCM》2009,23(16):2499-2506
The natural 13C/12C isotope composition (δ13C) of plants and organic compounds within plant organs is a powerful tool to understand carbon allocation patterns and the regulation of photosynthetic or respiratory metabolism. However, many enzymatic fractionations are currently unknown, thus impeding our understanding of carbon trafficking pathways within plant cells. One of them is the 12C/13C isotope effect associated with invertases (EC 3.2.1.26) that are cornerstone enzymes for Suc metabolism and translocation in plants. Another conundrum of isotopic plant biology is the need to measure accurately the specific δ13C of individual carbohydrates. Here, we examined two complementary methods for measuring the δ13C value of sucrose, glucose and fructose, that is, off‐line high‐performance liquid chromatography (HPLC) purification followed by elemental analysis and isotope ratio mass spectrometry (EA‐IRMS) analysis, and gas chromatography‐combustion (GC‐C)‐IRMS. We also used these methods to determine the in vitro 12C/13C isotope effect associated with the yeast invertase. Our results show that, although providing more variable values than HPLC~EA‐IRMS, and being sensitive to derivatization conditions, the GC‐C‐IRMS method gives reliable results. When applied to the invertase reaction, both methods indicate that the 12C/13C isotope effect is rather small and it is not affected by the use of heavy water (D2O). Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
70.
Soriano Del Amo D Wang W Jiang H Besanceney C Yan AC Levy M Liu Y Marlow FL Wu P 《Journal of the American Chemical Society》2010,132(47):16893-16899
The Cu(I)-catalyzed azide-alkyne cycloaddition (CuAAC) is the standard method for bioorthogonal conjugation. However, current Cu(I) catalyst formulations are toxic, hindering their use in living systems. Here we report that BTTES, a tris(triazolylmethyl)amine-based ligand for Cu(I), promotes the cycloaddition reaction rapidly in living systems without apparent toxicity. This catalyst allows, for the first time, noninvasive imaging of fucosylated glycans during zebrafish early embryogenesis. We microinjected embryos with alkyne-bearing GDP-fucose at the one-cell stage and detected the metabolically incorporated unnatural sugars using the biocompatible click chemistry. Labeled glycans could be imaged in the enveloping layer of zebrafish embryos between blastula and early larval stages. This new method paves the way for rapid, noninvasive imaging of biomolecules in living organisms. 相似文献