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排序方式: 共有626条查询结果,搜索用时 31 毫秒
51.
A one pot method for the synthesis of ethyl 2-acetoxy-6-aroylcyclohex-1-ene-1-carboxylates and ethyl 2-acetoxy-6-heterocarbonylcyclohex-1-ene-1-carboxylates through Michael addition of the anions of ethyl carbonates of cyanohydrins to cyclohex-2-en-1-one and subsequent reaction with acetic anhydride is described. These compounds are potential intermediates for the synthesis of 9,10-anthraquinone and heterofused 1,4-naphthoquinone derivatives. 相似文献
52.
Efficient Evaluation of the Elastic Forces and the Jacobian in the Absolute Nodal Coordinate Formulation 总被引:1,自引:0,他引:1
This paper develops a new procedure for evaluating the elastic forces, the elastic energy and the jacobian of the elastic
forces in the absolute nodal coordinate formulation. For this procedure, it is fundamental to use some invariant sparse matrices
that are integrated in advance and have the property of transforming the evaluation of the elastic forces in a matrix multiplication
process. The use of the invariant matrices avoids the integration over the volume of the element for every evaluation of the
elastic forces. Great advantages can be achieved from these invariant matrices when evaluating the elastic energy and calculating
the jacobian of the elastic forces as well. The exact expression of the jacobian of the differential system of equations of
motion is obtained, and some advantages of using the absolute nodal coordinate formulation are pointed out. Numerical results
show that there is important time saving as a result of the use of the invariant matrices. 相似文献
53.
Elena Gómez Noelia Calvar Ángeles Domínguez Eugénia A. Macedo 《The Journal of chemical thermodynamics》2010,42(11):1324-1329
In this paper, the ionic liquids 1,2-diethylpyridinium ethylsulfate, EEpyESO4; 1-methylpyridinium methylsulfate, MpyMSO4; 1,3-dimethylpyridinium methylsulfate, MMpyMSO4; and 2-ethyl-1-methylpyridinium methylsulfate, EMpyMSO4; were synthesized in our laboratory, and their experimental densities, speeds of sound, dynamic viscosities, and refractive indices were studied as a function of temperature at atmospheric pressure. Thermal expansion coefficient, molar volume, and molar refraction of these ionic liquids were calculated from the experimental density and refractive index values. 相似文献
54.
Selenium is a trace element of environmental relevance. Studies on its solution chemistry are scarce and were mostly carried
out under experimental conditions of little relevance to environmental research. Thus, we have performed new studies of selenium
speciation in solutions of low ionic strength, in contrast to those prevailing in the literature data. In this work, potentiometric
titrations (at 20.0 °C, and I=0.15 mol⋅L−1 NaClO4) were carried out for systems containing Se(VI) or Se(IV) oxyanions and divalent metal ions (Mg, Ca, Sr, Ba, Mn, Fe, Co,
Ni, Cu, Zn, Cd, Hg, and Pb). Ion pairs such as [M(SeO4)] and [M(HSeO4)2], or [M(HSeO3)]+ and [M(SeO3)], exist in solutions. The data reported here provide the basis for determining selenium speciation in natural aquatic systems,
on which the bioavailability and toxicity of this element depends. 相似文献
55.
Karina B. Hueso Domínguez Ildikó V. Tóth M. Renata S. Souto Filipa Mendes Cándido García De María Isabel Vasconcelos António O. S. S. Rangel 《Applied biochemistry and biotechnology》2010,160(6):1664-1673
A sequential injection system to monitor glycerol in a Saccharomyces cerevisiae fermentation process was developed. The method relies on the rate of formation of nicotinamide adenine dinucleotide in its
reduced form (NADH, measured spectrophotometrically at 340 nm) from the reaction of glycerol with NAD+ cofactor, catalysed by the enzyme glycerol dehydrogenase present in solution. This procedure enables the determination of
glycerol between 0.046 and 0.46 g/l, (corresponding to yeast fermentation samples with concentrations up to 50 g/l) with good
repeatability (relative standard deviation for n = 10 lower than 2.2% for three different samples) at a sampling frequency of 25/h. The detection and quantification limits
using a miniaturised spectrophotometer were 0.13 and 0.44 mM, respectively. Reagent consumption was of 0.45 μmol NAD+ and 1.8 μg enzyme per assay, and the waste production was 2.8 ml per determination. Results obtained for samples were in
agreement with those obtained with a high-performance liquid chromatography method. 相似文献
56.
Carlos Rodríguez-Abreu Margarita Sanchez-Domínguez Bojan Šarac Marija Bešter Rogač Rekha Goswami Shrestha Lok Kumar Shrestha Dharmesh Varade Goutam Ghosh Vinod K. Aswal 《Colloid and polymer science》2010,288(8):923-935
Mixtures of a hydrophobic triblock copolymer (L121, PEO5PPO68PEO5) and a hydrophobic anionic surfactant (AOT, Sodium bis(2-ethylhexyl)sulfosuccinate), each alone forming turbid vesicular
solutions in water, aggregate to produce a thermodynamically stable, transparent and isotropic solution. Mixed AOT/L121 aggregates
could be confirmed by fluorescence, surface tension, differential scanning calorimetry (DSC) and isothermal titration calorimetry
(ITC). In an isotropic region, where mixed aggregates are formed, there is a synergistic interaction between monomers of AOT
and L121 in the mixture. In addition, Small Angle Neutron Scattering (SANS) experiments provided evidence that mixed aggregates
have the shape of either spheres (with a certain polydispersity) or very short ellipsoids (axial ratio below 2), confirming
a transition from giant multilamellar vesicles to small aggregates upon mixing the two hydrophobic amphiphiles. Upon dilution,
the morphology changes to disk-like. From an examination of the results of all the methods the peculiar behavior of the mixed
AOT/L121 system is explained. 相似文献
57.
Josep Esteve-Romero Adria Martinavarro-Domínguez José V. Marcos-Tomás Enrique Ochoa-Aranda Maria Rambla-Alegre 《Chromatographia》2010,71(3-4):273-277
Micellar liquid chromatography was employed for the monitoring of procainamide and its metabolite N-acetylprocainamide using a C18 column. Sodium dodecyl sulphate (SDS) and modifier concentrations were optimised in order to obtain minimum analysis time, maximum sensitivity and good resolution. The optimum chromatographic conditions were as follows: flow rate 1 mL min?1, injection volume 20 μL, temperature at 25 °C, respectively. The mobile phase consisted of 0.05 M SDS-1% (v/v) butanol–phosphate buffer (10 mM, pH 7, 0.9%, w/v) NaCl using a detection wavelength at 280 nm. Validation studies were carried out according to the ICH guideline and included the determination of calibration curves (r 2 > 0.999), intra- and inter-day precisions (CV < 3.9%), robustness and interference studies, respectively. The recoveries in spiked serum samples were adjusted. Finally, the optimized method was applied to serum samples of patients treated with antiarrhythmics, and the results were compared with those given by a reference method where a good correlation was obtained. 相似文献
58.
Elena Gómez Irene Domínguez Noelia Calvar Ángeles Domínguez 《The Journal of chemical thermodynamics》2010,42(10):1234-1239
The (liquid + liquid) equilibrium (LLE) data for ternary mixtures {alkane + benzene + 1-ethylpyridinium ethylsulfate ([EPy][EtSO4])} at T = (283.15 and 298.15) K and atmospheric pressure are presented. The alkanes used were hexane and heptane. The cloud point method was used to determinate the binodal curve, and the tie-line compositions were obtained by density measurements. The LLE data obtained were used to calculate distribution coefficients and selectivity values. The consistency of tie-line data was ascertained by applying the Othmer-Tobias and Hand equations. Correlation of the experimental tie-lines was conducted through the use of NRTL equation, which provides good correlation of the experimental data.The results show that [EPy][EtSO4] can be used as an alternative solvent in liquid extraction processes for the removal of benzene from its mixtures with alkanes. 相似文献
59.
Gil Garrote Herminia Domínguez Juan C. Parajó 《Applied biochemistry and biotechnology》2001,95(3):195-207
Milled corncob samples were mixed with water and heated to obtain a liquid phase containing oligosaccharides, sugars, and
acetic acid as main reaction products (autohydrolysis reaction). To hydrolyze the sugar oligomers to the correspondent monomers,
sulfuric acid was added to the autohydrolysis liquors to reach 0.5–2 wt% of solution, and the reaction media were heated at
101.5–135°C. With this operational procedure, sugar solutions suitable as fermentation media (containing xylose as the major
component) were obtained. The kinetics of the posthydrolysis step was characterized on the basis of experimental data concerning
the time courses of the concentrations of xylooligosaccharides, xylose, furfural, and acetic acid. The concentrations of other
reaction byproducts (glucose or arabinose) were also measured. 相似文献
60.
Marta Barbadillo Elena Casero Maria Dolores Petit-Domínguez Félix Pariente Encarnación Lorenzo Luis Vázquez 《Journal of Sol-Gel Science and Technology》2011,58(2):452-462
We have studied, by scanning electron and atomic force (AFM) microscopies, how each step involved in the building process
of massive carbon-based sol–gel enzymatic biosensors changes and determines the resulting surface morphology and nano-mechanical
properties. The biosensor, selected as a model, is developed by the entrapment of glucose oxidase (GOx), a redox mediator
and a material conferring conductivity (graphite powder, C) into a polymeric tridimensional network generated by sol–gel technology
using tetraethoxysilane (TEOS) as precursor. The smooth TEOS morphology is formed by an irregular nanoporous network, which
is very adequate for enzyme encapsulation. Upon addition of carbon powder to the system (TEOS/C), the surface morphology changes
but it is still rather irregular since carbon powder micro-grains are found scattered on it. This morphology results in a
rather rough surface at the micro- scale whereas at the nano- scale both atomically flat graphitic and nanoporous TEOS domains
are found. In contrast, the final biosensing device surface is quite homogeneous and composed by flat platelets separated
by deep crevices. On top of most of these platelets there is a soft, as assessed by AFM force indentation experiments, layer
of globular structures whose dimensions are compatible with GOx molecules. The final device surface architecture results to
be open and accessible both at the micro and nano scales, which turns it as adequate to enhance both the accessibility of
the analytes to entrapped proteins and the mass-transfer rates. Finally, in order to show the applicability of the studied
biosensor, its response was evaluated towards varying glucose concentrations, displaying a clear electrocatalytic activity. 相似文献