共查询到20条相似文献,搜索用时 15 毫秒
1.
B. I. Podlovchenko Yu. M. Maksimov T. D. Gladysheva E. A. Kolyadko 《Russian Journal of Electrochemistry》2000,36(7):731-735
Steady-state current densities of electrooxidation of CH3OH, HCOOH, and CO at the Pt-PAN-GC electrodes (where PAN and GC stand for polyaniline and glassy carbon, respectively) and
those of electrooxidation of HCOOH at the Pd-PAN-GC electrodes are measured (per cm2 of the true metal-catalyst surface area). The found higher activity of Pt and Pd particles incorporated in PAN, as compared
with Pt/Pt and Pd/Pt, is attributed to interaction between metal-catalyst particles and the polymeric matrix. The activation
effect is the most pronounced for the HCOOH electrooxidation at Pd-PAN-GC. The data concerning hydrogen evolution testify
in favor of a decrease in exchange currents of this reaction upon going from Pt to Pt-PAN-GC electrodes 相似文献
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V. Boldescu I. Bratu Gh. Borodi I. Kacso A. Bende Gh. Duca F. Macaev S. Pogrebnoi Z. Ribkovskaia 《Journal of inclusion phenomena and macrocyclic chemistry》2012,74(1-4):129-135
The present research paper is dedicated to the obtaining and physicochemical characterization of a highly potential anti-mycobacterial drug candidate with β-cyclodextrin (βCD). The active substance is a 1,3,4-oxadiazole derivative, 2-phenyl-5-{[(2-phenyl-1,3-dioxolan-2-yl)methyl]sulfanyl}-1,3,4-oxadiazole, further named DIOX. DIOX–βCD binary systems were obtained as a physical mixture and a lyophilized product with molar ratio between the main components equal to 1:1 and 1:2. The obtained systems were submitted to physicochemical characterization applying the following instrumental methods: infrared spectrometry, differential scanning calorimetry, and X-ray crystallographic analysis. Besides, a molecular modeling analysis has been performed. The research data suggested certain intermolecular interaction between DIOX and βCD, suggesting formation of a three-molecular inclusion complex DIOX:βCD, including one DIOX molecule and two molecules of βCD. The main parts of the DIOX molecule included in the hydrophobic cavity of the cyclodextrin molecules most probably are dioxolane cycle and two benzene rings. 相似文献
4.
Kirillova N. V. Kuznetsova N. I. Kuznetsova L. I. Likholobov V. A. 《Russian Chemical Bulletin》2002,51(6):975-981
The oxidation of cyclohexane, saturated and aromatic hydrocarbons with an O2—H2 gaseous mixture was applied to study the catalytic properties of bicomponent systems based on platinum and heteropoly compounds (HPC). The consumption of gases and the yield of the products depend on the surface area, accessibility of the platinum species to the reactant, and composition of the HPC. The solid Pt samples suspended in an HPC solution, the Pt(5%)—PMo12/Al2O3 bicomponent supported system, and the solid bicomponent sample prepared from the [Pt(NH3)4][H2PMo12O40]2·7H2O complex salt were used as catalysts. Among the catalysts with the same molar compositions of the active components, the bicomponent materials are much more active in the oxidation than a combination of the Pt catalyst with an HPC solution. The bulk catalyst is a crystalline solid substance with the HPC structure with incorporated Pt species. Molybdenum is predominantly oxidized, and platinum is present in both the reduced and ionic states. The oxidation of saturated hydrocarbons affords alcohols and ketones. The yield of the positional isomers of the oxygenated products increases in the series primary << secondary < tertiary C-atoms. Benzene and toluene are converted into the corresponding phenols in equal yields. The scheme proposed for oxidation assumes the participation of the active hydroxyl radical. 相似文献
5.
Márcia C. Breitkreitz Isabel C.S.F. Jardim Roy E. Bruns 《Journal of chromatography. A》2009,1216(9):1439-1449
A statistical approach for the simultaneous optimization of the mobile and stationary phases used in reversed-phase liquid chromatography is presented. Mixture designs using aqueous mixtures of acetonitrile (ACN), methanol (MeOH) and tetrahydrofuran (THF) organic modifiers were performed simultaneously with column type optimization, according to a split-plot design, to achieve the best separation of compounds in two sample sets: one containing 10 neutral compounds with similar retention factors and another containing 11 pesticides. Combined models were obtained by multiplying a linear model for column type, C8 or C18, by quadratic or special cubic mixture models. Instead of using an objective response function, combined models were built for elementary chromatographic criteria (retention factors, resolution and relative retention) of each solute or pair of solutes and, after their validation, the global separation was accomplished by means of Derringer's desirability functions. For neutral compounds a 37:12:8:43 (v/v/v/v) percentage mixture of ACN:MeOH:THF:H2O with the C18 column and for pesticides a 15:15:70 (v/v/v) ACN:THF:H2O mixture with the C8 column provide excellent resolution of all peaks. 相似文献
6.
A complete potential harmonic scheme is presented,including the linked coupled hyperradial ordi nary differential equations and the secular equation of eigencnergy It has been used to directly solve the Scchrodinger equations of helium-like three-body systems (nuclear charge Z=1-9),and very accurate ground state eigonenergies as well as low-lying singlet excited state ones have been obtained 相似文献
7.
A method for the determination of vapor–liquid phase diagram structure of five-component systems based on the analysis of types and Poincare indexes of singular points of the geometric scan and full structure of the concentration simplex is proposed. Validity of the proposed method was demonstrated by vapor–liquid equilibrium modeling in five-component mixtures: ethanol + water + toluene + butanol + chlorbenzene and acetone + chloroform + ethanol + cyclohexane + water. 相似文献
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《Solid State Sciences》2012,14(7):885-889
Oxides with the spinel structure are some of the most studied compounds in solid-state science due to their wide range of applications. In this, the system Zn1−xNixFeCrO4 was prepared by sol–gel auto-combustion method. The formation of spinel phase was identified using X-ray diffraction technique. All the compounds exhibited cubic spinel symmetry and lattice constant shows the decreasing trend with substitution of nickel. The morphology and size of the particles were studied by scanning electron microscope while an elemental composition of the metals in system is found to be equal to the relative compositions of the metals used for synthesis by stoichiometric calculations. Electrical properties of the system investigated for the compounds in the form of pellets indicate the semi-conducting nature of all the spinels which show the n to p-type conduction with nickel content. 相似文献
10.
Low-temperature condensates of water and water-methane mixture are studied in the temperature range of 65–200 K. Amorphous
samples are obtained by molecular beam deposition under vacuum conditions on the substrate cooled with liquid nitrogen. The
vitrification and crystallization temperatures are determined from the changes in the dielectric properties of the condensates
upon heating. The kinetics of crystallization of amorphous water layers is studied by differential thermal analysis. The temperature
conditions for the growth of thick methane crystalline hydrate layers during the low-temperature condensation of molecular
water-gas mixture beams are found. 相似文献
11.
Boron Nitride (BN) particles were functionalized with vinyl-trimethoxysilane (VTMS) and incorporated into a hybrid polymer (ORMOCER®) resin. The thermal conductivity and mechanical properties of the resulting composite were compared to materials prepared using unmodified particles. Results indicate that the chemical bonding between grain surface and ORMOCER® matrix has a pronounced effect on the final performance of the respective compounds. 相似文献
12.
The harmonic and anharmonic potential (force) constants of heteronuclear diatomic molecules, which are usually available from normal coordinate analyses, are applied to problems of determining the molecular chemical potential changes on formation of such molecules. The approach developed here is mainly based on density—functional theory, that is, the respective atomic energies in a molecule are expanded with the numbers of electrons and the nuclear potentials. These expansions are allowable because the ground-state energy for a system of N electrons and given nuclear potential ν(r) is a functional of N and ν(r). To test the reliability of the approach, we have calculated the molecular chemical potentials of alkali halides and other heteronuclear diatomic molecules, and their results have been compared favorably with the data obtained from Sanderson's Principle and the ab initio SCF calculation. We have also estimated apparent chemical hardnesses as well as integral terms including Fukui functions that provide good measures for electron transfers between atoms on molecule formation. Brief discussions on the molecular chemical potential changes are given. 相似文献
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The effect of particle size on peak intensities of FT—IR photoacoustic spectra was investigated by use of naturally occurring quartz in our Laboratory. It is observed that the PAS peak intensities increases with a decrease in particle diameter and that the peak intensity ratios are not constant for particles of different diameters. The relations among particle size, peak intensity and thermal diffusion length are discussed. 相似文献
15.
《Fluid Phase Equilibria》1988,44(1):53-75
The effect of sodium chloride, calcium chloride and zinc chloride at concentrations 5–20% by weight on the liquid—liquid equilibrium (LLE) data of the ternary system ethyl acetate(S)—methanol(C)—water(A) has been investigated experimentally at 30 °C. The region of heterogeneity is significantly increased with the addition of sodium and calcium chloride salts. A change in the direction of tie-line was observed for 10% sodium chloride, 20% calcium chloride and saturated zinc chloride exhibiting thereby a tendency to form solutropism for this system, which is non-solutropic under a no-salt condition. The selectivity values are also altered in comparison with that of a no-salt condition. The tie-line data have been correlated by the Eisen—Joffe equation. The solubility envelopes for the salt systems have been predicted using the NRTL model, from a knowledge of the binary vapor—liquid equilibria (VLE) determined experimentally in our laboratory employing the iso-activity criterion. 相似文献
16.
Anne-Lena Fabricius Lars Duester Björn Meermann Thomas A. Ternes 《Analytical and bioanalytical chemistry》2014,406(2):467-479
Validated and easily applicable analytical tools are required to develop and implement regulatory frameworks and an appropriate risk assessment for engineered nanoparticles (ENPs). Concerning metal-based ENPs, two main aspects are the quantification of the absolute mass concentration and of the “dissolved” fraction in, e.g., (eco)toxicity and environmental studies. To provide information on preparative aspects and on potential uncertainties, preferably simple off-line methods were compared to determine (1) the total concentration of suspensions of five metal-based ENP materials (Ag, TiO2, CeO2, ZnO, and Au; two sizes), and (2) six methods to quantify the “dissolved” fraction of an Ag ENP suspension. Focusing on inductively coupled plasma–mass spectrometry, the total concentration of the ENP suspensions was determined by direct measurement, after acidification and after microwave-assisted digestion. Except for Au 10 nm, the total concentrations determined by direct measurements were clearly lower than those measured after digestion (between 61.1 % for Au 200 nm and 93.7 % for ZnO). In general, acidified suspensions delivered better recoveries from 89.3 % (ZnO) to 99.3 % (Ag). For the quantification of dissolved fractions two filtration methods (ultrafiltration and tangential flow filtration), centrifugation and ion selective electrode were mainly appropriate with certain limitations, while dialysis and cloud point extraction cannot be recommended. With respect to precision, time consumption, applicability, as well as to economic demands, ultrafiltration in combination with microwave digestion was identified as best practice. Figure
A Multi-method approach to identify best practice for ICP-MS based off-line characterization of ENP suspensions. 相似文献
17.
The data on adsorption of cyclopentane, benzene, and their mixture on active carbon were analyzed by the statistical thermodynamic
model. A method to describe the state of a binary mixture in single micropores was offered. A substantial negative deviation
from Raoult's law predicted by the concept of an ideal adsorption solution is a consequence of a decrease in the excessive
Helmholtz energy brought about by progressive filling when values of the excessive energy are positive over a wide range of
adsorption. The excessive values found for the entropy and internal energy of a mixture of molecules in a single micropore
are negative due to the heterogeneity of the adsorption field. The approach suggested adequately describes the experimental
data and can be used for the determination of differential heats of adsorption.
Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1070–1076, June, 1999. 相似文献
18.
Summary A new method has been developed for the quantitative determination of gas mixture composition where air penetration during
gas sample collection would lead to erroneous results. It requires the use of a stationary phase that separates gas sample
components and the air and involves 4–5 analyses of samples of equal volumes containing different amounts of air. By graphical
extrapolation of the air peak area (S
air
) as a function of the peak areas of the individual components (S
comp
) the areas for these components in the absence of air can be obtained forS
air
=0.
Using calibration curves for the pure gas components the true quantitative composition of the gas mixture is estimated. 相似文献
19.
《Journal of membrane science》1999,156(1):81-96
A study of single proteins, β-lactoglobulin and lysozyme of different sizes and electrical characteristic as a function of pH, ionic strength and nature of salt (NaCl or CaCl2) allows to evaluate the filtration performances. Streaming potential measurements confirm that proteins contribute to the net charge of the system and that the protein tranfer through mineral membranes is governed by ionic and steric exclusion phenomena.This work shows the correlation between protein transmission and streaming potential values which takes into account steric and ionic exclusion. The ionic repulsion decreases the transmission. This one depends on membrane net charge characterised by streaming potential, which depends on the solution composition. This model, which does not take into account interactions between protein and membrane fouling leads to an overestimation of calculated transmission values when proteins are in a mixture. However, it allows a correct estimation of transmission variations versus the studied variables: pH and ionic strength. 相似文献
20.
A convenient method has been developed for the synthesis of 9-allyloxymethylguanine. The direct alkylation of the trimethylsilyl derivative of guanine allyloxymethyl chloride gives a 64% yield of 9- and 7-allyloxymethylguanine (31). A mixture of 9- and 7-allyloxymethyl-N-acetylguanine (74) can be obtained in 56% yield by the condensation of diacetylguanine with allyloxymethyl acetate in dimethyl sulfoxide in the presences of p-toluenesulfonic acid.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 8, pp. 1109–1113, August, 1993. 相似文献