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991.
Characterization of CuO supported on tetragonal ZrO2 catalysts for N2O decomposition to N2 总被引:1,自引:0,他引:1
A series of tetragonal zirconia-supported CuO oxide catalysts with various CuO loadings were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), electron spin resonance (ESR), ultraviolet and visible diffuse reflectance spectroscopy (UV/vis-DRS), and temperature-programmed reduction (TPR) measurements. The results indicate that the dispersion capacity of copper oxide on this support is approximately 8.6 Cu(2+) ions/nm(2) ZrO(2). The state of the resulting supported copper species depends on the CuO loading. At CuO loadings below the dispersion capacity, only highly dispersed copper ion species are present on the surface of t-ZrO(2). In particular, isolated Cu ions are the predominant species at low loadings. In contrast, pair Cu ions become the most abundant species at loadings near the dispersion capacity. It has been proposed that these dispersed CuO (isolated and paired Cu ions) have a symmetric 5-fold-oxygen-coordination symmetry (C(3)(v) symmetry) and can be described as distorted octahedra with a missing corner or a trigonal bipyramids. Finally, at CuO loadings above the dispersion capacity the formation of crystalline CuO is observed. TPR results reveal that the dispersed Cu ion species have a different reducibility from CuO crystallites, presumably due to strong interactions between these species and the t-ZrO(2) support. The catalytic activity of these CuO/t-ZrO(2) catalysts for the decomposition of N(2)O can also be directly correlated to CuO dispersion, with paired Cu ions being the most active species for this reaction. 相似文献
992.
从TGEV 3CL蛋白酶二聚体结构出发,研究了TGEV 3CL蛋白酶二聚体单体之间的静电和疏水相互作用.蛋白质的静电相互作用通过有限差分方法求解Poisson-Boltzmann方程得到,疏水相互作用通过分析溶剂可及性表面模型得到.考察了不同pH值对TGEV 3CL蛋白酶二聚体静电和疏水相互作用的影响,在pH值为5.5~8.5时,二聚体静电相互作用能、静电去溶剂化能和疏水自由能都较小,表明在该条件下静电和疏水相互作用有利于二聚体的稳定存在,这符合实验结晶所需条件.pH值对静电去溶剂化能的影响大于疏水自由能,表明静电作用是造成强酸或强碱条件下二聚体不能稳定存在的主要原因. 相似文献
993.
A new method for inductively coupled plasma atomic emission spectrometry (ICP-AES) determination of trace Sc and Y, based on gaseous compound introduction into the plasma as their thenoyltrifluoroacetone (TTA) complexes by electrothermal vaporization was developed. Using the reagent TTA as chemical modifier can not only enhance the analytical signals, but also reduce the vaporization temperature. At a temperature of 1,000 °C the trace Sc and Y can be vaporized completely into ICP. The factors affecting the formation of the chelate and its vaporization behavior, such as drying time, vaporization temperature/time, reaction medium and the amount of TTA, were investigated in detail. Under the optimized conditions (drying temperature/time 100 °C/10 s, vaporization temperature/time 1,000 °C/4 s), the limits of detection for Sc and Y were 19 pg and 34 pg (3), respectively, and the relative standard deviations for Sc and Y were 4.2% (c
Sc=0.2 g mL–1; n=7) and 2.6% (c
Y=0.5 g mL–1; n=7). The linear ranges of the calibration graphs cover three orders of magnitude. The method was applied to the analysis of the biological reference materials (GBW 07602, bush branches and leaves; GBW 07604, poplar leaves), and the results obtained were in good agreement with the certified values. 相似文献
994.
Microcalorimetry and measurement of culture turbidity using a Bioscreen C Analyzer System were applied to study the toxic effect of phenanthrene on Cunninghamella elegans IM 1785/21Gp spore germination. The results of C. elegans spore incubation in Bioscreen C microbiology reader showed the inhibition of spore germination by 70% (with 25 mg l−1 of phenanthrene) and total inhibition of the fungus growth with a higher content of the xenobiotic (50-100 mg l−1). The microcalorimetric technique showed to be useful for the estimation of metabolic activity of C. elegans spores in growth medium up to xenobiotic concentrations of 90 mg l−1. These data corresponded with the microscopic observations. The obtained results showed that the microcalorimetry method could be a valuable supplement in the study on the mechanism of PAHs detoxification by fungi. 相似文献
995.
Gas hydrates are non-stoichiometric crystalline compounds of water with gas at a certain temperature and pressure. Compared to the thermodynamics of hydrate formation, our knowledge on the kinetics aspect is rather immature. It is well known that the kinetics of hydrate formation/dissociation plays an important role in many industrial cases, such as the exploitation of methane hydrate underground, the storage and transportation of natural gas in solid hydrate state, the inhibition of hydrate i… 相似文献
996.
A highly accurate gas chromatographic analytical method has been developed for the determination of the composition of gas
mixtures. It was tested using a reference gas as an example consisting of 3.5% of CO, 14% of CO2, 0.2% of propane and residual N2 intended for the use in vehicle emission measurements. The method is based on comparison measurements with samples of a calibration
gas, whose composition is iteratively adapted to that of the sample investigated using a gravimetric gas mixing method. For
the gas chromatographic measurement, a molecular sieve column and a polymer column are used in parallel and in isothermal
operation. All gas components can be determined by a single gas chromatographic measurement, and the relative uncertainty
of measurement achievable is ?0.4%.
Received: 6 March 1996/Revised: 30 May 1996/Accepted: 6 June 1996 相似文献
997.
Vidal E Palomeque ME Lista AG Fernández Band BS 《Analytical and bioanalytical chemistry》2003,376(1):38-41
A novel flow injection analysis (FIA) method with Rayleigh light scattering (RLS) detection was developed for the determination of total protein concentrations. This method is based on the weak intensity of RLS of bromothymol blue (BB) (3',3"-dibromothymolsulfonephthalein) which can be enhanced by the addition of protein in weakly acidic solution. A common spectrofluorimeter was used as a detector. It was proved that the application of this method to quantify the total proteins in real samples by using bovine serum albumin was possible. The RLS signal was detected at lambda(ex)= lambda(em)=572 nm. The linear range was 7.0-70.0 microg mL(-1), the detection limit was 3.75 microg mL(-1), the reproducibility was 5.5% (n=7), and the sample throughput was 26 h(-1). 相似文献
998.
The electric conduction in the fibrous medium constructed by a homogeneous array of parallel, identical, charged, circular cylinders having an arbitrary zeta potential filled with the solution of a symmetrically charged electrolyte is analytically examined. The thickness of the electric double layers surrounding the dielectric cylinders is assumed to be small relative to the radius of each cylinder and to the gap width between two neighboring cylinders, but the polarization of the mobile ions in the diffuse layers is allowed. The effect of interactions among individual cylinders is taken into explicit account by employing a unit cell model. The appropriate equations of conservation of electrochemical potential energies of ionic species are solved for each cell, in which a cylinder is envisaged to be surrounded by a coaxial cylindrical shell of the fluid solution. Analytical expressions for the effective electric conductivity are obtained in closed forms as functions of the porosity of the fiber matrix and other characteristics of the porous system. Comparisons of the results of the cell model with different conditions at the outer boundary of the cell are made. Under an otherwise identical condition, the electric conductivity in a porous medium composed of an array of parallel cylinders in the transverse direction is smaller than that of a suspension of spheres. The effect of interactions among the cylinders or spheres on the effective conductivity can be quite significant under appropriate conditions. 相似文献
999.
LiMn2O4的湿法合成及锰的光度法测定研究 总被引:2,自引:0,他引:2
The LiMn2O4 spinel was prepared by wet method using Li2CO3, Mn(CH3COO)2·4H2O and CO2 as raw ma-terials. The products were measured by TG/DTA, XRD, IR. The results Showed that the sample calcined at 800℃ for 10h was well crystallized monophase product. The contents of Mn(Ⅲ) and Mn(Ⅳ) of LiMn2O4 spinel were determined simultaneously by spectrophotometric analysis with pyrophosphoric acid. 相似文献
1000.
Biosensors based on enzyme field-effect transistors for determination of some substrates and inhibitors 总被引:3,自引:0,他引:3
Dzyadevych SV Soldatkin AP Korpan YI Arkhypova VN El'skaya AV Chovelon JM Martelet C Jaffrezic-Renault N 《Analytical and bioanalytical chemistry》2003,377(3):496-506
This paper is a review of the authors' publications concerning the development of biosensors based on enzyme field-effect transistors (ENFETs) for direct substrates or inhibitors analysis. Such biosensors were designed by using immobilised enzymes and ion-selective field-effect transistors (ISFETs). Highly specific, sensitive, simple, fast and cheap determination of different substances renders them as promising tools in medicine, biotechnology, environmental control, agriculture and the food industry.The biosensors based on ENFETs and direct enzyme analysis for determination of concentrations of different substrates (glucose, urea, penicillin, formaldehyde, creatinine, etc.) have been developed and their laboratory prototypes were fabricated. Improvement of the analytical characteristics of such biosensors may be achieved by using a differential mode of measurement, working solutions with different buffer concentrations and specific agents, negatively or positively charged additional membranes, or genetically modified enzymes. These approaches allow one to decrease the effect of the buffer capacity influence on the sensor response in an aim to increase the sensitivity of the biosensors and to extend their dynamic ranges.Biosensors for the determination of concentrations of different toxic substances (organophosphorous pesticides, heavy metal ions, hypochlorite, glycoalkaloids, etc.) were designed on the basis of reversible and/or irreversible enzyme inhibition effect(s). The conception of an enzymatic multibiosensor for the determination of different toxic substances based on the enzyme inhibition effect is also described.We will discuss the respective advantages and disadvantages of biosensors based on the ENFETs developed and also demonstrate their practical application. 相似文献