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51.
52.
Medana C Calza P Dal Bello F Raso E Minero C Baiocchi C 《Journal of mass spectrometry : JMS》2011,46(1):24-40
This paper deals with the photocatalytic transformation of N,N-diethyl-m-toluamide (DEET), one of the most widespread and efficient mosquito repellents, under simulated solar irradiation using titanium dioxide as the photocatalytic source of oxidizing species. The investigation involved monitoring of the DEET decomposition, the identification of intermediate compounds and the assessment of mineralization. High-resolution mass spectrometry was employed to assess the evolution of the photocatalyzed process over time. Fifty-one main species were identified after DEET transformation. Several isomeric species were formed and were characterized by analyzing MS and MS(n) spectra in full, and by comparison with parent molecule fragmentation pathways. In the DEET molecule, the initial transformation involved mono- and polyhydroxylation followed by oxidation of the alcohol groups, cleavage of the alkyl chains or ring opening. All these intermediates are easily degraded and DEET is completely mineralized after 4 h of irradiation. Microtox bioassay (Vibrio fischeri) was employed to evaluate the ecotoxicity of solutions treated by photocatalysis. 相似文献
53.
J.Y. Bello Cruz L.R. Lucambio Pérez J.G. Melo 《Nonlinear Analysis: Theory, Methods & Applications》2011,74(16):5268-5273
We consider the projected gradient method for solving the problem of finding a Pareto optimum of a quasiconvex multiobjective function. We show convergence of the sequence generated by the algorithm to a stationary point. Furthermore, when the components of the multiobjective function are pseudoconvex, we obtain that the generated sequence converges to a weakly efficient solution. 相似文献
54.
Rami Suleiman Abdelletif Ibdah Bassam El Ali 《Journal of organometallic chemistry》2011,696(11-12):2355-2363
A DFT study on the palladium-bisphosphine catalyzed alkoxycarbonylation and aminocarbonylation of alkyne (propyne) is reported. The theoretical study explores the feasibility and the regioselectivity control of two independent mechanisms: the first is based on the active intermediate [Pd(II)(P2)(H)]+ (where P2 = PH2CH2CH2CH2CH2PH2) for the alkoxycarbonylation reaction, and the second is based on the active species [Pd(II)(P2)(NR2)]+ for the aminocarbonylation reaction. The study explains the role of solvent in increasing the yield and in controlling the selectivity of reaction to produce selectively the trans isomer in the alkoxycarbonylation reaction (hydride cycle) and the gem isomer in the aminocarbonylation reaction (amine cycle). In hydride cycle, the regioselectivity is mainly determined by the stability of the complex [Pd(II)(P2)(COC3H5)(CH3CN)]+; however, for the amine cycle, the regioselectivity is determined by the stability of the complex [Pd(II)(P2)(C3H5CON(CH3)2)]+. The calculations reveal that ligand simplification is not valid in addressing the regioselectivity behavior of alkoxycarbonylation and aminocarbonylation reactions. The kinetic data for the formation of the two key complexes show no difference between the gem and trans isomers which predict the regioselectivity to be a thermodynamically controlled process. 相似文献
55.
56.
Eduardo Vyhmeister Anthony J. Muscat David Suleiman L. Antonio Estvez 《Fluid Phase Equilibria》2008,270(1-2):121-128
Fluid-phase equilibria, including dew points, bubble points, and critical points were measured for four binary systems composed of a chlorosilane and carbon dioxide. The measurements were carried out in a constant-composition, variable-volume cell equipped with a sapphire window, which allowed visual observation of the phases in the cell. A syringe pump was used to inject the CO2 into the cell and to control its pressure. Methyltrichlorosilane, dimethyldichlorosilane, trimethylchlorosilane, and diethyldichlorosilane up to about 0.14 mol fraction were studied in this apparatus and a total of 243 phase-boundary points were obtained. Displacements in the critical point with respect to pure CO2 of up to 11.81 MPa and 348.05 K were observed. Modeling of the fluid-phase equilibria for three of the four binary systems was done using the Peng–Robinson equation of state, standard van der Waals mixing rules with two binary interaction parameters, and a φ–φ formulation of the equilibrium. The binary interaction parameters were obtained by fitting the model to the experimental data. The model produced excellent agreement between computed and experimental data. Graphical representations of the modeling results are presented and compared to experimental results. The results indicate that the largest chlorosilane (diethyldichlorosilane) produced the largest shift in critical pressure and critical temperature with respect to pure CO2. 相似文献
57.
Csar Carlos Gonzlez Jos Manuel Perea Antonio Bello 《Journal of Polymer Science.Polymer Physics》1988,26(7):1397-1408
The dynamic mechanical relaxations of poly(trimethylene glycol terephthalate) (PTMT), poly(ditrimethylene glycol terephthalate) (PDTMT) and two copolymers obtained from them have been studied between ? 150 and 200°C with a dynamic viscoelastometer. The four polymers show three relaxations that are designated α, β, and γ in order of decreasing temperature. The α relaxation is considered to be the glass transition of the polymers. The β relaxation is wider and weaker than the α, as normally occurs in the polyester series. The γ relaxation takes place at temperatures below ? 100°C and is usually overlapped by the β relaxation. The influence of thermal and mechanical histories on the nature, location, and intensity of the three relaxations is studied and discussed. 相似文献
58.
α-Nitro-azides were prepared by two routes involving intermediate radical-anions, and undergo substitution by an SRN1 mechanism with azides, sulphinates, and thiolates to give loss of nitrite, and with nitronates to give loss of azide. 相似文献
59.
60.
A method for the determination of diethylstilbestrol and the related compounds dienestrol and hexestrol residues in meat and organs of treated cattle is described. After extraction and clean-up, these synthetic estrogens are subjected to reaction with pentafluorobenzoyl chloride, which gives very stable perfluoro esters that are suitable for gas chromatographic determination using an electron-capture detector. With the careful clean-up and the very sensitive response of these derivatives, it is possible to reach a limit of detection in the sub-parts per billion (10(9)) range starting with only 5 g of sample. 相似文献