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排序方式: 共有1310条查询结果,搜索用时 890 毫秒
101.
Sergio A. Moya Juana Gajardo Juan C. Araya Jaime J. Cornejo Véronique Guerchais Hubert Le Bozec J. Carles Bayón Alvaro J. Pardey Pedro Aguirre 《应用有机金属化学》2008,22(8):471-478
Novel ruthenium (II) complexes were prepared containing 2‐phenyl‐1,8‐naphthyridine derivatives. The coordination modes of these ligands were modified by addition of coordinating solvents such as water into the ethanolic reaction media. Under these conditions 1,8‐naphthyridine (napy) moieties act as monodentade ligands forming unusual [Ru(CO)2Cl2(η1‐2‐phenyl‐1,8‐naphthyridine‐ kN )(η1‐2‐phenyl‐1,8‐naphthyridine‐kN′)] complexes. The reaction was reproducible when different 2‐phenyl‐1,8‐naphthyridine derivatives were used. On the other hand, when dry ethanol was used as the solvent we obtained complexes with napy moieties acting as a chelating ligand. The structures proposed for these complexes were supported by NMR spectra, and the presence of two ligands in the [Ru(CO)2Cl2(η1‐2‐phenyl‐1,8‐naphthyridine‐ kN )(η1‐2‐phenyl‐1,8‐naphthyridine‐kN′)] type complexes was confirmed using elemental analysis. All complexes were tested as catalysts in the hydroformylation of styrene showing moderate activity in N,N′‐dimethylformamide. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
102.
1-Phenyl-4-vinylpyrazole reacts with methyl propiolate and N-phenylmaleimide giving via the Diels-Alder 1:1 adducts, products (4) and (8), and also the 1:2 adducts (5), (6) and (9) resulting from an “ene” reaction of the initially forced cycloadducts. The obtention of the adducts (5) and (6) in equimolecular amounts is a good example of the non-regioselective character of the “ene” reaction. The reaction with tetracyanoethylene takes place through the olefinic substituent giving the π2 + π2 adduct (10). 相似文献
103.
In this paper,a new approach is devoted to find novel analytical and approximate solutions to the damped quadratic nonlinear Helmholtz equation(HE)in terms of the Weiersrtrass elliptic function.The exact solution for undamped HE(integrable case)and approximate/semi-analytical solution to the damped HE(non-integrable case)are given for any arbitrary initial conditions.As a special case,the necessary and sufficient condition for the integrability of the damped HE using an elementary approach is reported.In general,a new ansatz is suggested to find a semi-analytical solution to the non-integrable case in the form of Weierstrass elliptic function.In addition,the relation between the Weierstrass and Jacobian elliptic functions solutions to the integrable case will be derived in details.Also,we will make a comparison between the semi-analytical solution and the approximate numerical solutions via using Runge-Kutta fourth-order method,finite difference method,and homotopy perturbation method for the first-two approximations.Furthermore,the maximum distance errors between the approximate/semi-analytical solution and the approximate numerical solutions will be estimated.As real applications,the obtained solutions will be devoted to describe the characteristics behavior of the oscillations in RLC series circuits and in various plasma models such as electronegative complex plasma model. 相似文献
104.
Rapid flow injection method for the determination of sulfite in wine using the permanganate-luminol luminescence system 总被引:2,自引:0,他引:2
A simple, rapid and sensitive chemiluminescence method for the determination of sulfite has been developed by combining flow-injection analysis and its sensitizing effect on the known chemiluminescence emission produced by the oxidation of luminol in alkaline medium; in this work permanganate has been proposed as oxidizing reactive. The optimum conditions for the chemiluminescence emission were established. The chemiluminescence was proportional to the sulfite concentration over the range 1.6 × 10−5 and 4.0 × 10−4 mol L−1. The detection limit was 4.7 × 10−6 mol L−1 of sulfite. The method has been satisfactorily used for the determination of free and bound sulfite in wines. 相似文献
105.
Ana B. Ortíz-Magán M. Mercedes Pastor-Blas 《Plasma Chemistry and Plasma Processing》2010,30(2):311-332
The effectiveness of nitrogen, oxygen and air Radio Frequency (RF) plasma treatments on two styrene-butadiene vulcanized rubbers
with a different formulation has been studied. The presence of an antiadherent surface layer containing low-molecular weight
ingredients (sulfur-rich vulcanization agents and wax) from SW (Sulfur-Wax) rubber formulation requires an extended plasma treatment capable of removing this surface layer. When the percentage of
antiadherent moieties is reduced in ZS (Zinc Stearate) rubber formulation, shorter plasma treatment times are enough to modify rubber surface and increase its polarity
by the creation of C–O and C=O polar groups that enhance adhesion towards a polyurethane adhesive. Air and oxygen plasma treatments
are more aggressive than nitrogen plasma and therefore they are more effective in removing the antiadherent layer of the outermost
rubber surface layer prior to oxidation of the rubber surface. 相似文献
106.
Beatriz Jurado-Sánchez Evaristo Ballesteros Mercedes Gallego 《Analytical and bioanalytical chemistry》2010,396(5):1929-1937
Humans are exposed to endogenous or exogenous formation of aromatic amines (AAs) and N-nitrosamines (NAms), which are considered to be potent carcinogens. The objective of this study was to monitor AAs and NAms
in human urine to obtain a way to assess exposure. However, while NAms can be directly detected in urine samples, AAs require
hydrolysis to convert their conjugates into free amines. A semiautomatic flow-base method is proposed for the simultaneous
determination of aliphatic and aromatic NAms, anilines and chloroanilines in human urine in one analytical run. Conjugated
AAs are released from urine by on-line microwave-assisted acid hydrolysis without degradation of NAms; all amines were then
preconcentrated using solid-phase extraction. Separation/determinations are carried out by gas chromatography and mass spectrometry
operating in selected ion monitoring mode. The method is fast (∼15 min for 25 mL of sample) and provides low limits of detection
(from 2 to 26 ng/L) with good precision (relative standard deviation within and between days less than 7%). Finally, the proposed
method was successfully applied to check AAs and NAms in the human urine of exposed and unexposed researchers. The kinetics
of amine excretion in the urine of the researchers exposed is calculated after termination of the exposure and shows half-life
times between 1.3 and 2.1 h, and that the dosage absorbed was eliminated within 6 h after exposure. 相似文献
107.
Van Zyla RL Seatlholof ST Van Vuuren SF Viljoen A 《Natural product communications》2010,5(9):1381-1386
Complex interactions between numerous components of essential oils often contribute to the pharmacological effect and therapeutic outcome. To further elucidate these interactions, several essential oil constituents (EOCs) were combined in different ratios and their inhibitory effects on the growth of bacteria and yeast determined using the minimum inhibitory concentration (MIC) microplate assay. When combined and tested against Candida albicans, (+)-beta-pinene interacted antagonistically with (-)-menthone (sigmaFIC(T) = 9.80), but synergistically with 1,8-cineole (sigmaFIC(T) = 0.35). Against Escherichia coli, the combination of E- and Z-(+/-)-nerolidol and geranyl acetate displayed an additive interaction (sigmaFIC(T) = 1.04); while a variable interaction was observed between E- and Z-(+/-)-nerolidol and eugenol with antagonism and synergy being observed at different ratios of each EOC. The combination of either carvacrol or eugenol with an antimicrobial agent (ciprofloxacin or amphotericin B) resulted in synergistic interactions against all microorganisms tested. These favourable results further support the use of essential oil constituents as adjuvants in the development of a new generation of phytopharmaceuticals that can be used in combination with synthetic drugs against drug-resistant microorganisms. 相似文献
108.
San Martin A Rovirosa J Carrasco A Orejarena S Soto-Delgado J Contreras R Chamy MC 《Natural product communications》2010,5(12):1859-1864
The sesquiterpene pacifenol is one of the main constituents of the red alga Laurencia claviformis. Earlier work on the semisynthetic derivatives of pacifenol afforded a series of halogenated sesquiterpenes. The aim of the present work was to obtain new hydroxylated derivatives of halogenated sesquiterpenes by means of microbial transformation using Aspergillus niger, Gibberella fujikuroi and Mucor plumbeus. The best results were obtained with M. plumbeus. The microbiological transformation by M. plumbeus of pacifenol, and two semisynthetic derivatives, is described. The structures of the new compounds obtained were determined by spectroscopic means. 相似文献
109.
Mercedes Gallego-Gallegos María Liva Garrido Riansares Muñoz Olivas Patricia Baravalle Claudio Baggiani Carmen Cámara 《Journal of chromatography. A》2010,1217(20):3400-3407
Molecular imprinting technology has been employed for the first time to prepare a specifically affinity chromatographic stationary phase for speciation purposes. Tributyltin has been chosen as the template molecule and the non-covalent approach has been applied. Three different polymerization methods have been evaluated: (i) a composite material, (ii) a polymer prepared via-Iniferter grafting; (iii) an emulsion polymer. Columns packed with different polymers have been evaluated by liquid chromatography (LC) coupled to inductively coupled plasma mass spectrometry (ICP-MS). The chromatographic conditions as well as the analytical characteristics of the developed method are discussed in this paper. Our findings have shown formation of specific cavities in the grafted Iniferter as well as in the emulsion polymers with the latter achieving resolution of four organotin compounds. Detection limits are similar to those obtained with commercial, but not specific, stationary phases (6 pg for monobutyltin, MBT; 10 pg for both tributyltin, TBT, and triphenyltin, TPhT; and 20 pg for dibutyltin, DBT). The main advantage of this proposed stationary phase is that good recovery is obtained for all species, including MBT. Baseline resolution for TBT and TPhT has also been obtained. The high selectivity of this column prevents matrix interferences. The method has been validated by analyzing two biota reference materials (ERM-CE477 mussel tissue and T-38 oyster tissue). 相似文献
110.
Paul T. Allen Lars Andersson Alvaro Restuccia 《Communications in Mathematical Physics》2011,301(2):383-410
In this paper we consider the classical initial value problem for the bosonic membrane in light cone gauge. A Hamiltonian
reduction gives a system with one constraint, the area preserving constraint. The Hamiltonian evolution equations corresponding
to this system, however, fail to be hyperbolic. Making use of the area preserving constraint, an equivalent system of evolution
equations is found, which is hyperbolic and has a well-posed initial value problem. We are thus able to solve the initial
value problem for the Hamiltonian evolution equations by means of this equivalent system. We furthermore obtain a blowup criterion
for the membrane evolution equations, and show, making use of the constraint, that one may achieve improved regularity estimates. 相似文献