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71.
Angel Alberola Luis Calvo Teresa Rodríguez Rodríguez Carmen Saudo 《Journal of heterocyclic chemistry》1992,29(2):445-450
The reactivity of 3-methyl-5-phenylisoxazole against electrophilic compounds in the presence of different bases is studied. With n-BuLi, alkylated products at C-4 position and C-3 methyl group, and, in a few cases, dialkylated isoxazoles are obtained. When the reactions are carried out with LICA, the nature of the alkylated products depends on the alkyl halide used. By using LICA-TMEDA, as deprotonating system, regio-selective reaction at the C-3 methyl group is found. 相似文献
72.
A capillary electrophoresis (CE) method has been applied for the quantitative determination of alpha(s1)- and alpha(s2)-CN in goat's milk. Several analytical parameters were evaluated showing the reliability of this CE method. Coefficients of determination (R2) greater than 99% were obtained and determination limits of 1.23 and 0.98 mg/ml were achieved for alpha(s1)- and alpha(s2)-CN, respectively. The analytical parameters studied in terms of accuracy, precision and recovery were within acceptable limits. Among 18 samples of 4 different genotypes (BB, EE, BF and FF) for alpha(s1)-CN were analysed, different amounts were obtained from the genotypes. 相似文献
73.
René Guardiola Romero Angel Dago Morales Julio Duque Rodríguez José Fernández Bertrán 《Transition Metal Chemistry》1992,17(6):573-574
The structure of K3(Me4N)3[Co(CN)6]2·3H2O has been determined from three-dimensional X-ray diffraction data. The unit cell is formed by parallel layers of cobalt
octahedra [CoC6] and potassium octahedra, [K(1)N5O(1)], separated byc/2. In each layer both types of octahedra are located alternatively. The [MeN4]+ tetrahedra are located in the cavities between the two layers of octahedra. The crystal structure of this compound is the
first example of its type.
TMC 2483 相似文献
74.
Chakraborty R Das AK Cervera ML De La Guardia M 《Analytical and bioanalytical chemistry》1996,355(1):43-47
The determination of cadmium in different sample types has been carried out by electrothermal atomization atomic absorption spectrometry with D(2)-background correction using a unpyrocoated graphite tube, after pressurized microwave-assisted digestion. Five chemical modifiers [(NH(4))(2)HPO(4), Pd(NO)(3))(2), Ni(NO(3))(2), thiourea and Triton X-100] have been assayed and nickel nitrate has been found to be most effective for an accurate determination of cadmium in mussel tissue, pig kidney and sewage sludge. The characteristic mass of the method is of the order of 1 pg and the limit of detection is lower than 0.1 ng/ml. 相似文献
75.
Juan M. Quintana-Melgoza Antonio Gómez-cortés Miguel Avalos-Borja 《Reaction Kinetics and Catalysis Letters》2002,76(1):131-140
We present a comparative study of NiWO4, NiO, and WO3 catalysts for simultaneous conversion of NO and CO. Samples were synthesized by reacting ammonium metatungstate and/or nickel nitrate at high temperature (773 K to 903 K) under an oxygen stream. Catalysts were characterized by X-ray diffraction, surface area measurements, energy dispersive spectroscopy and scanning electron microscopy. The catalytic reduction of NO by CO took place in the temperature range (523 to 973) K under highly reductive conditions (NO:CO= 1:5) over NiWO4NiO, and WO3, respectively. The 100 % NO conversion at GHSV of 11460 h-1 was achieved at 773 K over NiWO4 and at 848 K over NiO. The WO3 was deactivated at 898 K. However, in the range (523 to 723) K NiO was more active than NiWO4 and WO3 catalysts. 相似文献
76.
Alexandra E. BotchkarevaFabiana Fini Sergei EreminJosep V. Mercader Angel MontoyaStefano Girotti 《Analytica chimica acta》2002,453(1):43-52
A heterogeneous chemiluminescent (CL) flow immunoassay for DDT was optimized comparing different types of immunoaffinity supports: beads, nylon coils and membranes (membranes HyBondN+). In order to characterize solid immunoaffinity supports two basic immunoassay formats were performed, using (1) enzyme-labeled secondary and (2) enzyme-labeled specific monoclonal antibodies (MAbs). In both formats, hapten DDT5 conjugated to ovalbumin immobilized on solid supports according to the appropriate immobilization procedure, enzyme label (horseradish peroxidase, HRP) and luminescent detection (luminol/H2O2/p-iodophenol) were used. The lowest limit of detection (LOD), 1 nM p,p-DDT, was obtained with a membrane-based flow immunoassay with HRP-labeled specific antibody. Beads and packed tubing were discarded as appropriate supports because of the difficulties encountered for reproducible packing and the occurrence of light scatterring (beads), which seriously compromised the performance and reproducibility of the flow immunoassay. 相似文献
77.
Conejo-García A Campos JM Entrena A Sánchez-Martín RM Gallo MA Espinosa A 《The Journal of organic chemistry》2003,68(22):8697-8699
A complete study of the conformational behavior of 4,8-diaza-3(1,4),9(4,1)-dipyridina-1,6(1,4)-dibenzenacyclodecaphan-3(1),9(1)-bis(ilium) bishexafluorophosphate is described. This study allows us to conclude that the process observed by which the different chemical shifts of the pyridinium protons show coalescence at a high-temperature 1H NMR is the rotation around the C-N bond, whereas the conformational equilibrium between the four conformers is produced at low temperature. 相似文献
78.
A pressure-assisted capillary chromatography-mass spectrometry method based on the use of a monolithic octadecylsilica (ODS) capillary is proposed for the determination of aliphatic amines. A 25 mM citric acid buffer containing 10% methanol is used as running electrolyte. Separation is achieved by simultaneously applying a capillary electrophoresis (CE) voltage of 13 kV and an overimposed pressure of 8 bar. The use of pressure is required to ensure stable electrospray conditions. Analysis times are reduced by using a capillary column consisting of a 30 cm long monolithic silica capillary column bound with ODS and a fused-silica capillary column also 30 cm long. The proposed method was successfully applied to the determination of low-molecular-weight aliphatic amines in tap and river water. The analysis of real samples requires cleanup and preconcentration, which can be performed automatically by inserting a minicolumn in the replenishment system of the commercial instrument. 相似文献
79.
On the basis of a detailed study of the pilocarpine-induced nickel(II) pre-wave using various polarographic techniques, an electrode process mechanism is proposed in which the formation of a catalytic complex between aquo-nickel(II) and veronalate-nickel(II) on the one hand and unprotonated pilocarpine adsorbed on the electrode surface on the other is followed by the reduction of nickel(II) in the complex and the release of the catalytic ligand. The pre-peak recorded by differential-pulse polarography in the system 1 × 10?3 M Ni(II)-1 × 10?2 M sodium veronal, nitric acid (pH 8.5) (with ionic strength maintained at 0.2 with sodium nitrate) can be used for quantitative determination of pilocarpine at concentrations in the range 2.5 × 10?7-8 × 10?6 M. 相似文献
80.
Optimization of culture medium and conditions for penicillin acylase production by Streptomyces lavendulae ATCC 13664 总被引:1,自引:0,他引:1
Torres-Bacete J Arroyo M Torres-Guzmán R De La Mata I Acebal C Castillón MP 《Applied biochemistry and biotechnology》2005,126(2):119-132
The culture medium for Streptomyces lavendulae ATCC 13664 was optimized on a shake-flask scale by using a statistical factorial design for enhanced production of penicillin acylase. This extracellular enzyme recently has been reported to be a penicillin K acylase, presenting also high hydrolytic activity against penicillin V and other natural aliphatic penicillins such as penicillin K, penicillin F, and penicillin dihydroF. The factorial design indicated that the main factors that positively affect penicillin acylase production by S. lavendulae were the concentration of yeast extract and the presence of oligoelements in the fermentation medium, whereas the presence of olive oil in the medium had no effect on enzyme production. An initial concentration of 2.5% (w/v) yeast extract and 3 microg/mL of CuSO4 x 5H2O was found to be best for acylase production. In such optimized culture medium, fermentation of the microorganism yielded 289 IU/L of enzyme in 72 h when employing a volume medium/volume flask ratio of 0.4 and a 300-rpm shaking speed. The presence of copper, alone and in combination with other metals, stimulated biomass as well as penicillin acylase production. The time course of penicillin acylase production was also studied in the optimized medium and conditions. Enzyme production showed catabolite repression by different carbon sources such as glucose, lactose, citrate, glycerol, and glycine. 相似文献