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101.
Density functional theory has been used to explore the mechanism of cleavage of H2 at a sulfido-bridged molybdenum cluster, CpMo(μ-SH)(μ-S)(μ-S2CH2)MoCp. The addition occurs across a single Mo-S bond, and the disruption of the strong Mo-S π bonding in the ground state leads to a very high-lying transition state (+43 kcal mol−1). Once formed, the adsorbed hydrogen migrates over the cluster via a series of hops from metal to sulphur, formally corresponding to a switch from hydridic to protic character. The low barrier (+15 kcal mol−1) for migration leads to facile hydrogenolysis of coordinated substrates. 相似文献
102.
A method is described for determining sulfite in dried garlic. Garlic is extracted with an HCl solution to inhibit the formation of allicin, which interferes with the determination of sulfite. After cleanup of the extract on a C18 solid-phase extraction column, sulfite is converted to hydroxymethylsulfonate (HMS) by adding formaldehyde and heating to 50 degrees C. HMS is determined by reversed-phase ion-pairing liquid chromatography with post-column detection. The post-column reaction system consists of the addition of KOH to convert HMS to sulfite ion, followed by the addition of 5,5'-dithiobis(2-nitrobenzoic acid) to produce 5-mercapto-2-nitrobenzoic acid which is detected spectrophotometrically at 450 nm. Background levels in unsulfited dried garlic equivalent to < 20 ppm SO2 were found. Recoveries of HMS from spiked garlic averaged 94.8% with a coefficient of variation of 3.8%. Sulfite was found in 13 of 21 samples of dried garlic produced in China, with sulfite ranging from 114 to 445 ppm. Sulfite was found in 60% of commercial dried garlic products purchased locally. The suitability of the Monier-Williams method for determining sulfite in garlic is discussed. 相似文献
103.
Direct, trace level detection of explosives on ambient surfaces by desorption electrospray ionization mass spectrometry 总被引:4,自引:0,他引:4
Takáts Z Cotte-Rodriguez I Talaty N Chen H Cooks RG 《Chemical communications (Cambridge, England)》2005,(15):1950-1952
Desorption electrospray ionization (DESI) mass spectrometry is used to detect trace amounts of explosives present on a variety of ambient surfaces in 5-second analysis times without any sample preparation. 相似文献
104.
Merino S Domènech O Díez-Pérez I Sanz F Montero MT Hernández-Borrell J 《Colloids and surfaces. B, Biointerfaces》2005,44(2-3):93-98
Atomic force microscopy (AFM) was used to study the influence of a membrane protein, lactose permease of Escherichia coli (LacY), on the surface spreading behavior and the features of self-assembled phospholipids bilayers on mica. The miscibility of phospholipids used, 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) and 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC), was investigated by surface pressure area isotherm measurements at the air-water interface. A composition with an equimolar proportion of POPC and DMPC was used to form the liposomes. Surface layers formed with DMPC:POPC (0.5:0.5, mol/mol) or LacY reconstituted in proteoliposomes with the same phospholipid composition were imaged by using AFM. When lactose permease was reconstituted in DMPC:POPC (0.5:0.5, mol/mol), self-assembled structures that remained firmly adsorbed onto the mica surface were observed. These sheets had an irregular shape and their upper layer was more corrugated than that obtained for the phospholipid matrix. 相似文献
105.
O. Y. Morales J. M. Navarrete I. Gracia I. Macías M. Rivera F. Sánchez 《Journal of Radioanalytical and Nuclear Chemistry》2014,299(1):839-841
It is very well known from ancient times that fulvic acids present in nature as a component of dead leaves and vegetables, are the active principle which promotes better crops, acting on mineral ions in soils by picking up them into plants tissues at higher concentrations. Tested in mice, by using radioactive labeled ions such as 32PO4 ?, 45Ca++, 59Fe+++ and 131I?, fulvic acids have demonstrated to stimulate the filtration of these ions from digestive tract to blood and then to urine by a factor larger than two. The following step on this research has been to find the effect caused by the presence in blood of electrolytes at higher concentrations, particularly viral infections resistance as a consequence of antibodies promotion. 相似文献
106.
This paper belongs to a broad line of research leaded by Herrera, which encompasses a good number of numerical methods such as Localized Adjoint Method (LAM), Eulerian-Lagrangian LAM (ELAM) and Trefftz-Herrera Method. The results presented in this paper are required in order to incorporate Herrera's general theory in a Sobolev-space setting. In particular, this article introduces a class of partitions (or domain decompositions) whose internal boundaries belong to a category of manifolds with corners, here also presented. Then a version of Gauss (or divergence) theorem, in a wider sense, is established and an explicit integral formula is associated for any given linear partial differential operator L, its adjoint and concomitant. The structure of the bilinear concomitant induced by L is first determined. Then the required formula is given over that class of domain decompositions. Finally, an integral formula well on the way of the Green-Herrera formula is settled. 相似文献
107.
María de Gracia García-Martín María Violante de Paz Báñez Juan A. Galbis 《Journal of carbohydrate chemistry》2013,32(7):805-815
ABSTRACT 3-Amino-3-deoxy-2,4,5,6-tetra-O-methyl-D-altronic acid hydrochloride was prepared from methyl 3-azido-3-deoxy-4,6-O-benzylidene-α-D-altropyranoside in seven steps. The key intermediate in this synthesis was the 3-acetamido-3-deoxy-2,4,6-tri-O-methyl-D-altrono-1,5-lactone which could be transformed, in one step, into methyl 3-acetamido-3-deoxy-2,4,5,6-tetra-O-methyl-D-altronate. However, attempts to open the 3-azido-3-deoxy-tri-O-methyl (or O-benzyl)-D-altrono-1,5-lactone intermediates gave a mixture of products, mostly, α,β-unsaturated carbonyl compounds. The 3-amino-3-deoxy-2,4,5,6-tetra-O-methyl-D-altronic acid could be transformed into the corresponding β-lactam, (3S,4R)-3-methoxy-4-(D-erythro-trimethoxypropyl) azetidine-2-one, which was further polymerized by anionic ring-opening polymerization giving poly[(2S,3R)-2-methoxy-3-(D-erythro-trimethoxypropyl) propanamide], a chiral nylon 3 analog. 相似文献
108.
The Río de la Plata discharges into the Atlantic Ocean. The particular characteristics of the study area, the variable width and shallowness of the river, the high fluvial discharges and the dynamic processes involving interactions between river discharges, tidal currents and wind, generate complex velocity and salinity fields. We applied the hydrodynamic model RMA-10 to examine the effects of various forcing (tides, flow discharge and winds) on residual currents and salinity fields in the Río de la Plata, focusing on the outer zone of the river. The RMA-10 code, developed by Ian King, is a multiparameter finite element model representing estuarine flow in three dimensions. In this study the model has been applied in a depth-averaged-baroclinic mode and a series of observed data is used for model calibration and verification. The model result shows that it is able to simulate velocity and the salinity fields with a reasonable accuracy. The analysis of residual currents in the river, when forced by freshwater discharge and astronomical tide, shows that the flow discharge takes place mainly over the shallower areas of the river and that the saline water is advected up-river through the deeper channels. The numerical simulations show that the winds from the South-West and North-East quadrants have a great influence over the salinity and velocity fields. 相似文献
109.
Ismael Herrera‐Revilla 《Numerical Methods for Partial Differential Equations》2008,24(3):845-878
This article is devoted to introduce a new approach to iterative substructuring methods that, without recourse to Lagrange multipliers, yields positive definite preconditioned formulations of the Neumann–Neumann and FETI types. To my knowledge, this is the first time that such formulations have been made without resource to Lagrange multipliers. A numerical advantage that is concomitant to such multipliers‐free formulations is the reduction of the degrees of freedom associated with the Lagrange multipliers. Other attractive features are their generality, directness, and simplicity. The general framework of the new approach is rather simple and stems directly from the discretization procedures that are applied; in it, the differential operators act on discontinuous piecewise‐defined functions. Then, the Lagrange multipliers are not required because in such an environment the functions‐discontinuities are not an anomaly that need to be corrected. The resulting algorithms and equations‐systems are also derived with considerable detail. © 2007 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq, 2008 相似文献
110.
Structural Chemistry - The reaction of the anti-Criegee intermediate (anti-CI) of β-pinene with prevalent atmospheric species has been investigated using quantum-chemical calculations. The... 相似文献