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991.
Terrier F Rodriguez-Dafonte P Le Guével E Moutiers G 《Organic & biomolecular chemistry》2006,4(23):4352-4363
Following a potentiometric determination of the relevant pKa values of the (R1R2)C=NOH functionality, the second order rate constants (k(Ox)) for reaction of a large set of oximate bases with two model organophosphorus esters, i.e. bis-(4-nitrophenyl)phenylphosphonate (BNPPP) and bis-(4-nitrophenyl)methylphosphonate (BNPMP), and three toxic compounds, i.e., sarin (GB), soman (GD) and diisopropylphosphorofluoridate (DFP), in aqueous as well as a 30 : 70 (v/v) H2O-Me2SO mixture have been measured. The corresponding Br?nsted-type nucleophilicity plots of log k(Ox)vs. pKa(Ox) reveal a clear tendency of the reactivity of the oximates to suffer a saturation effect with increasing basicity in aqueous solution. In the case of BNPMP and the three toxic esters, this behaviour is reflected in a levelling off at pKa approximately 9 but a more dramatic situation prevails in the BNPPP system where the attainment of maximum reactivity at pKa approximately 9 is followed by a clear decrease in rate at higher pKa's. Interestingly, a number of data reported previously by different authors for the sarin, soman and DFP systems are found to conform rather well to the curvilinear Br?nsted correlations built with our data. Based on this and previous results obtained for reactions at carbon centers, it can be concluded that the observed saturation effect is the reflection of an intrinsic property of the oximate functionality. An explanation of this behavior in terms of an especially strong requirement for desolvation of the oximates prior to nucleophilic attack which becomes more and more difficult with increasing basicity is suggested. This proposal is supported by the observed changes in pKa(Ox) and k(Ox) brought about by a transfer from H2O to a 30 : 70 H2O-Me2SO mixture. The implications of the saturation effect on the efficiency of oximates as nucleophilic catalysts for smooth decontamination are emphasized. Also discussed is the effect of basicity on the exalted (alpha-effect) reactivity of these bases. 相似文献
992.
993.
Mulligan A Lane I Rousseau GB Johnston SM Lennon D Kadodwala M 《The journal of physical chemistry. B》2006,110(2):1083-1090
Naturally occurring metal surfaces possess planes of mirror symmetry on the nanometer-length scale. This mirror symmetry can be lifted and chirality "physically" conveyed onto a surface by adsorbing a chiral molecule. Until now, it has not been known whether the conveying of chirality is limited to just the physical structure or whether it goes deeper and permeates the electronic structure of the underlying surface. By using optically active second harmonic generation (OA-SHG), it is demonstrated that the adsorption of some, but not all, chiral molecules can reversibly, and without significant structural rearrangement, measurably lift the mirror symmetry of the surface electronic structure of a metal. It is proposed that the ability of a chiral molecule to place a significant "chiral perturbation" on the electronic structure of a surface is correlated to its adsorption geometry. The microscopic origins of the observed optical activity are also discussed in terms of classical models of chirality. The results of the study challenge current models of how chiral adsorbates induce enantioselectivity in the chemical/physical behavior of heterogeneous systems, which are based on geometric/stereochemical arguments, by suggesting that chiral electronic perturbations could play a role. 相似文献
994.
995.
996.
Gilles Serre Philippe Lafon Xavier Gloerfelt Christophe Bailly 《Journal of computational physics》2012,231(15):5176-5194
Development of optimal reduced-order models for linearized Euler equations is investigated. Recent methods based on proper orthogonal decomposition (POD), applicable for high-order systems, are presented and compared. Particular attention is paid to the link between the choice of the projection and the efficiency of the reduced model. A stabilizing projection is introduced to induce a stable reduced-order model at finite time even if the energy of the physical model is growing. The proposed method is particularly well adapted for time-dependent hyperbolic systems and intrinsically skew-symmetric models. This paper also provides a common methodology to reliably reduce very large nonsymmetric physical problems. 相似文献
997.
Krystyna Baczko Hélène Fensterbank Bruno Berini Nadège Bordage Gilles Clavier Rachel Méallet‐Renault Chantal Larpent Emmanuel Allard 《Journal of polymer science. Part A, Polymer chemistry》2016,54(1):115-126
This work deals with the covalent coupling of azide‐functionalized polymeric nanoparticles as a reactive core and amino‐terminated PAMAM dendrons as a reactive shell. The nanoassemblies thereby obtained could be modified after the dendronization step by grafting an alkynyl Bodipy dye on the unreacted azide moieties. Only a few steps are required to attain nanoassemblies that could mimic dendrimers of high generation with sizes of nano‐objects beyond those of dendrimers. The structure of the nanoassemblies are composed of a polystyrene core, an inner shell including the Bodipy dyes along with the internal branches of the PAMAM, and the terminal amino groups from the outer shell. The dendritic shell acts as a protective layer that prevents NP from aggregation in a surfactant free aqueous solution. The nano‐objects display absorption and emission maxima above 500 nm with brightness that are the same order of magnitude than Qdots. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 115–126 相似文献
998.
Cellulose functionalization via high-energy irradiation-initiated grafting of glycidyl methacrylate and cyclodextrin immobilization 总被引:2,自引:0,他引:2
Gilles Desmet Erzsébet Takács László Wojnárovits Judit Borsa 《Radiation Physics and Chemistry》2011,80(12):1358-1362
Cotton-cellulose was functionalized using gamma-irradiation-induced grafting of glycidyl methacrylate (GMA) to obtain a hydrophobic cellulose derivative with epoxy groups suitable for further chemical modification. Two grafting techniques were applied. In pre-irradiation grafting (PIG) cellulose was irradiated in air and then immersed in a GMA monomer solution, whereas in simultaneous grafting (SG) cellulose was irradiated in an inert atmosphere in the presence of the monomer. PIG led to a more homogeneous fiber surface, while SG resulted in higher grafting yield but showed clear indications of some GMA-homopolymerization. Effects of the reaction parameters (grafting method, absorbed dose, monomer concentration, solvent composition) were evaluated by SEM, gravimetry (grafting yield) and FTIR spectroscopy. Water uptake of the cellulose decreased while adsorption of a pesticide molecule increased upon grafting. The adsorption was further enhanced by β-cyclodextrin immobilization during SG. This method can be applied to produce adsorbents from cellulose based agricultural wastes. 相似文献
999.
Gilles Olive Gabriela A. Pompeu Torezan Christophe Blecker 《Comptes Rendus Chimie》2012,15(11-12):1037-1047
The enzymatic synthesis of esters is well documented in the literature. A number of parameters have been revised to optimize the operating conditions, in view of a more industrial approach. The experimental conditions presented here are now superior to those of literature and the yields of esters show 78% of fructose laurate. Analytical methods have been perfected and rapid methods (based on different TLC conditions depending on the desired information), accurate methods (based on HPLC) and several purification methods were developed. 相似文献
1000.
Camille Hespel Jean-Bernard Blaisot Matthieu Gazon Gilles Godard 《Experiments in fluids》2012,53(1):245-264
The characterization of diesel jets in the near field of the nozzle exit still presents challenges for experimenters. Detailed velocity measurements are needed to characterize diesel injector performance and also to establish boundary conditions for CFD codes. The present article examines the efficiency of laser correlation velocimetry (LCV) applied to diesel spray characterization. A new optical configuration based on a long-distance microscope was tested, and special care was taken to examine the spatial selectivity of the technique. Results show that the depth of the measurement volume (along the laser beam) of LCV extends beyond the depth of field of the imaging setup. The LCV results were also found to be particularly sensitive to high-speed elements of a spray. Results from high-pressure diesel jets in a back-pressure environment indicate that this technique is particularly suited to the very near field of the nozzle exit, where the flow is the narrowest and where the velocity distribution is not too large. It is also shown that the performance of the LCV technique is controlled by the filtering and windowing parameters used in the processing of the raw signals. 相似文献