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321.
Esseffar M Herrero R Quintanilla E Dávalos JZ Jiménez P Abboud JL Yáñez M Mó O 《Chemistry (Weinheim an der Bergstrasse, Germany)》2007,13(6):1796-1803
Dimethyldisulfide (I) is the simplest model of the biologically relevant family of disubstituted disulfides. The experimental study of its gas-phase protonation has provided, we believe for the first time, a precise value of its gas-phase basicity. This value agrees within 1 kJ mol-1 with the results of G3 calculations. Also obtained for the first time was the reaction rate constant for the bimolecular reaction between I and its protonated form, IH+, to yield methanethiol and a dimethyldithiosulfonium ion. This constant is of the order of magnitude of the collision limit. A computational mechanistic study based on the energetic profile of the reaction, completed with Fukui's and Bader's treatments of the reactants and transition states fully rationalizes the regioselectivity of the reaction as well as the existence of a shallow, flat Gibbs energy surface for the reaction. The mechanistic relevance of the chalcogen-chalcogen interaction and the C--H...S bonds has been demonstrated. 相似文献
322.
We theoretically predict and numerically demonstrate that narrow beams (of the width of few wavelengths) can be efficiently parametrically amplified in nonlinear photonic crystal (with chi((2)) nonlinearity) tuned to sub-diffractive (self-collimating) regimes. We derive relations and give analytic estimations for the efficiency of amplification. 相似文献
323.
Pérez Pavón JL Herrero Martín S García Pinto C Moreno Cordero B 《Analytica chimica acta》2008,629(1-2):6-23
This article reviews the most recent literature addressing the analytical methods applied for trihalomethanes (THMs) determination in water samples. This analysis is usually performed with gas chromatography (GC) combined with a preconcentration step. The detectors most widely used in this type of analyses are mass spectrometers (MS) and electron capture detectors (ECD). Here, we review the analytical characteristics, the time required for analysis, and the simplicity of the optimised methods. The main difference between these methods lies in the sample pretreatment step; therefore, special emphasis is placed on this aspect. The techniques covered are direct aqueous injection (DAI), liquid-liquid extraction (LLE), headspace (HS), and membrane-based techniques. We also review the main chromatographic columns employed and consider novel aspects of chromatographic analysis, such as the use of fast gas chromatography (FGC). Concerning the detection step, besides the common techniques, the use of uncommon detectors such as fluorescence detector, pulsed discharge photoionization detector (PDPID), dry electrolytic conductivity detector (DELCD), atomic emission detector (AED) and inductively coupled plasma-mass spectrometry (ICP-MS) for this type of analysis is described. 相似文献
324.
Mariajesus Lopez‐Herrero 《Mathematical Methods in the Applied Sciences》2017,40(7):2532-2541
Our interest is to quantify the spread of an infective process with latency period and generic incidence rate that takes place in a finite and homogeneous population. Within a stochastic framework, two random variables are defined to describe the variations of the number of secondary cases produced by an index case inside of a closed population. Computational algorithms are presented in order to characterize both random variables. Finally, theoretical and algorithmic results are illustrated by several numerical examples. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
325.
In order to assess the environmental risks of a compound it is imperative to have suitable and reliable techniques for its determination in environmental matrices. In this paper, we focused on a method development for the recently introduced online coupling of a field flow fractionation (FFF) system to an Orbitrap-HRMS, that allows the simultaneous size and concentration determination of different aqueous fullerene aggregates and their concentrations in different size fractions. A 0.05% NH4OH solution in water was identified as the best carrier liquid for the analysis of the three different aqueous fullerene suspensions (C60 [60], [6,6]-phenyl-C61 butyric acid methyl ester ([60]PCBM) and [6,6]-(bis)phenyl-C61 butyric acid methyl ester ([60]bisPCBM)). The multi-angle light scattering (MALS) data received after employing the ammonia solution was consistent with both the theory and calibration using well defined Au and latex particles. The LODs obtained using Orbitrap HRMS detection were 0.1 μg L−1 for an injection volume of 100 μL which are significantly better than the LODs obtained by using UV (20 μg L−1) and MALS detectors (5 μg L−1). However, these LODs can be further improved as in theory there is no limit to the amount of sample that can be injected into the FFF. Environmental samples (river and sewage water) were spiked with fullerenes and the fractograms obtained for these samples revealed that the matrix does affect the size of fullerene aggregates. Information on the size distribution can be useful for the risk assessment of these particles. 相似文献
326.
A numerical linear stability analysis on optimally controlled solutions in a thermoconvective problem is presented. The thermoconvective problem is a stationary Boussinesq Navier-Stokes with a gaussian heating at the bottom with a large horizontal temperature gradient. The numerical method is Chebyshev collocation. The optimal control permits to find a boundary condition such that the vorticity is minimized. For some values of the penalizing parameter the controlled solution is more stable than the corresponding uncontrolled one. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
327.
A. Castieira R. M. Pea C. Herrero S. García‐Martín 《Journal of separation science》2000,23(11):647-652
A simple technique is described for the routine capillary electrophoretic determination of organic acids in wine samples. Several aromatic and non‐aromatic compounds, including phthalic acid, benzoic acid, sorbic acid, boric acid, and phosphate, were evaluated as background electrolytes in order to obtain the highest resolution and detection sensivity. Factors that affect capillary electrophoretic separation such as the concentration and pH of the background electrolyte (BGE), the concentration of the electroosmotic flow modifier (EOF), and methanol addition to the electrolyte were investigated systematically. Tartaric, malic, succinic, acetic, and lactic acids were determined simultaneously in approximately six minutes using an electrolyte containing 3 mM phosphate and 0.5 mM myristyltrimethylammonium bromide (MTAB) as electroosmotic flow modifier at pH 6.5. This method is quantitative, with recoveries in the 90–102% range and linear up to 50 mg L–1. The precision is better than 1% and the procedure shows the appropriate sensibility, with detection limits between 0.015 and 0.054 mg L–1. The proposed method was successfully employed for the determination of organic acids in wine samples by direct sample injection after appropriate dilution and filtration. 相似文献
328.
329.
Dr. Katell Sénéchal-David Dr. Charlotte Buron Dr. Nathalie Ségaud Dr. Jean-Noël Rebilly Amandine Dos Santos Dr. Jonathan Farjon Dr. Régis Guillot Dr. Christian Herrero Tanya Inceoglu Prof. Frédéric Banse 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(53):12405-12411
The reactivity and selectivity of non-heme FeII complexes as oxidation catalysts can be substantially modified by alteration of the ligand backbone or introduction of various substituents. In comparison with the hexadentate ligand N,N,N′,N′-tetrakis(pyridin-2-ylmethyl)ethane-1,2-diamine (TPEN), N,N′-bis[1-(pyridin-2-yl)ethyl]-N,N′-bis(pyridin-2-ylmethyl)ethane-1,2-diamine (2MeL62) has a methyl group on two of the four picolyl positions. FeII complexation by 2MeL62 yields two diastereomeric complexes with very similar structures, which only differ in the axial/equatorial positions occupied by the methylated pyridyl groups. In solution, these two isomers exhibit different magnetic behaviors. Whereas one isomer exhibits temperature-dependent spin-state conversion between the S=0 and S=2 states, the other is more reluctant towards this spin-state equilibrium and is essentially diamagnetic at room temperature. Their catalytic properties for the oxidation of anisole by H2O2 are very different and correlate with their magnetic properties, which reflect their lability/inertness. These different properties most likely depend on the different steric constraints of the methylated pyridyl groups in the two complexes. 相似文献
330.
Amanda Lyn Robinson Dr. Jean-Noël Rebilly Dr. Régis Guillot Christian Herrero Hélène Maisonneuve Prof. Frédéric Banse 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(28):e202200217
We report two new FeIII complexes [L1FeIII(H2O)](OTf)2 and [L2FeIII(OTf)] , obtained by replacing pyridines by phenolates in a known non-heme aminopyridine iron complex. While the original, starting aminopyridine [(L5 2 )FeII(MeCN)](PF6) complex is stable in air, the potentials of the new FeIII/II couples decrease to the point that [L2FeII] spontaneously reduces O2 to superoxide. We used it as an O2 activator in an electrochemical setup, as its presence allows to generate superoxide at a much more accessible potential (>500 mV gain). Our aim was to achieve substrate oxidation via the reductive activation of O2. While L2FeIII(OTf) proved to be a good O2 activator but a poor oxidation system, its association with another complex (TPEN)FeII(PF6)2 generates a complementary tandem couple for electro-assisted oxidation of substrates, working at a very accessible potential: upon reduction, L2FeIII(OTf) activates O2 to superoxide and transfers it to (TPEN)FeII(PF6)2 leading in fine to the oxidation of thioanisole. 相似文献