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61.
The acid—base constants of ten nitrophenol, sulfonphthalein and phthalein indicators in 80% dimethyl sulfoxide—20% water are reported. The indicators were selected so that their transitional intervals cover a large part of the pH-scale. The relationship between the constants in the mixed solvent and in water is linear: (pKHI)SH = 1.48 (pKHI)H2O— 1.68. 相似文献
62.
Some drawbacks of the phosphate modifier such as reagent blank contribution and background absorption in electrothermal atomic absorption spectrometric determination of cadmium and lead are substantially alleviated by application of small amounts of phosphate, approximately 0.2 mumol (25 mug of NH(4)H(2)PO(4) or (NH(4))(2)HPO(4)), on the integrated platform of transversely heated graphite atomizer pre-treated with 2.7 mumol of Zr (250 mug) or W (500 mug) and 0.1 mumol of Ir (20 mug). Pyrolysis temperatures for Cd and Pb are up to 900 and 1100 degrees C for aqueous solutions and within 400-600 degrees C (Cd) and 750-850 degrees C (Pb) for biological fluids (urine, blood) and tissues (hair, liver, muscle) solubilized with tetraethylammonium hydroxide. The thermally stabilized phosphate on Zr-Ir or W-Ir treated platforms serves as a permanent modifier in analyses of environmental waters by multiple hot injections of large sample aliquots. Applications to water and biological certified reference materials are tabulated and show good agreement with certified values. Characteristic masses are 0.7-1.0 pg for Cd and 26-31 pg for Pb. 相似文献
63.
The kinetics of thermal decomposition of 13 selenites has been studied under isothermal heating conditions with a derivatographer. Values of the activation energy and frequency factor in the Arrenius equation are found. It is found that between these parameters and the radius of selenite cations a close relationship exists: the greater the cation radius, the higher the thermal stability of selenites. The obtained results of the change in these parameters are interpreted by the theory of polarization interactions between ions and by the general Klopman and Hudson’s perturbation theory for ionic orbitals. 相似文献
64.
Georgieva R Moya S Donath E Bäumler H 《Langmuir : the ACS journal of surfaces and colloids》2004,20(5):1895-1900
The permeability of ions and small polar molecules through polyelectrolyte multilayer capsules templated on red blood cells was studied by means of confocal microscopy and electrorotation. Capsules were obtained by removing the cell after polyelectrolyte multilayer formation by means of NaOCl treatment. This procedure results in cross-linking of poly(allylamine hydrochloride) (PAH) molecules and destroying poly(styrene sulfonate) (PSS) within the multilayer. Capsules are obtained being remarkably different from layer-by-layer (LbL) capsules. These capsules are rather permeable for low as well as for high molecular weight species. However, upon adsorption of extra polyelectrolyte layers the permeability decreased remarkably. The assembly of six supplementary layers of PAH and PSS rendered the capsule almost impermeable for fluorescein. Resealing by supplementary layers is a potential means for filling and release control. By means of electrorotation measurements, it was shown that the capsule walls obtained isolating properties in electrolyte solutions. Conclusions are drawn concerning the mechanism of permeability through cell templated polyelectrolyte multilayer capsules. 相似文献
65.
L. T. Vlaev V. G. Georgieva S. D. Genieva 《Journal of Thermal Analysis and Calorimetry》2007,88(3):805-812
The kinetics of dehydration and decomposition of VOSO4·2H2O, VOSO4 and VOSeO3·H2O was studied under non-isothermal heating on a derivatograph. The stages and products of the thermal decomposition were determined.
It was proved that VOSO4·2H2O decomposes to V2O5 while VOSeO3·H2O − to V2O4. A number of kinetic models and calculation procedures were used to determine the values of the kinetic parameters characterizing
the process. The parameters calculated were compared and analyzed. IR-spectra of the initial substances and the solid residue
after decomposition are presented. 相似文献
66.
Adsorptive accumulation of the Pd(II) complex with dimethylglyoxime was evaluated for stripping voltammetry with respect
to different parameters. The sensitivity of the method and the linearity between the peak current and the concentration of
Pd(II) depends on the ionic strength, the electrode area, the preconcentration time, the transport rate to the electrode,
and the potential scan rate. The most appropriate medium was 0.1 mol/L acetate buffer between pH 3.5 and 4. Using 2 min of
preconcentration at a 2.6 mm2 electrode and the differential pulse mode, a detection limit of 0.05 μg/L Pd was achieved for liquid samples and 50 ng/g
for solid samples. Different aqueous and solid samples were analysed and the recovery from biological and inorganic materials
investigated.
Received: 29 February 1996/Revised: 29 July 1996/Accepted: 1 August 1996 相似文献
67.
Summary The influence of the type and the positions of the ring substituents on the conformational energies and thermodynamic stabilities of a series of Pt(II) complexes of the general formula [1,2-bis(hydroxyphenyl)ethylenediamine]PtL
2(L
2=2Cl–, 2I–, SO
4
2–
) has been studied by molecular mechanics. The calculations were carried out for the ligand conformations (R,S/S,R)-, (R,S/S,R)-, (R,R)-, and (S,S)-. The obtained energies and thermodynamic stabilities are in agreement with experimental data on the reactivity and antitumor activity of the compounds.
Molecular Modelling von Pt(II)-Komplexen mit Antitumoraktivität. Einfluß von Art und Position von Substituenten auf Konformationsenergien und thermodynamische Stabilitäten
Zusammenfassung Die konformationellen Energien und thermodynamischen Stabilitäten einer Reihe von Pt(II)-Komplexen mit der allgemeinen Formel [1,2-bis(Hydroxyphenyl) ethylendiamin]PtL 2(L 2=2Cl–, 2I–, SO 4 2– ) wurden mittels molekularmechanischer Methoden in Abhängigkeit von Art und Stellung der Substituenten an den Phenylringen untersucht. Die Berechnungen wurden für die Ligandenkonformationen (R,S/S,R)-, (R,S/S,R)-, (R,R)- und (S,S)- durchgeführt. Die erhaltenen Energien und Stabilitäten stimmen mit experimentellen Daten über Reaktivität und Antitumoraktivität der Verbindungen überein.相似文献
68.
The temperature and concentration dependences of the electrical conductance of aqueous solutions of sulfuric acid, selenic acid, and potassium tellurate were studied. The coefficients of the corresponding empirical equations were determined, and the values of equivalent conductances of the anions were evaluated at infinite dilution at the experimental temperatures. The values of the coefficients in the Fuoss and Onsager equation were evaluated for the three electrolytes at 298 K. The values of the molecular and ionic coefficients of self-diffusion at infinite dilution were calculated in the temperature range 288–318 K. The change of the translational energy Δ E∘tr. of water molecules in the ionic hydration sphere was determined. The number of water molecules participating in the ionic hydration sphere at 298 K and the changes of Gibbs free energy, enthalpy, and entropy of activation of ionic conductance were calculated. The results obtained were interpreted according to the Samoylov’s theory of positive and negative hydration of ions. The differences observed in the temperature dependences of the mentioned parameters were explained in terms of the different radii and hydration numbers of the ions. 相似文献
69.
Thermophilic ethanol fermentation of wet-exploded wheat straw hydrolysate was investigated in a continuous immobilized reactor
system. The experiments were carried out in a lab-scale fluidized bed reactor (FBR) at 70°C. Undetoxified wheat straw hydrolysate
was used (3–12% dry matter), corresponding to sugar mixtures of glucose and xylose ranging from 12 to 41 g/l. The organism,
thermophilic anaerobic bacterium Thermoanaerobacter BG1L1, exhibited significant resistance to high levels of acetic acid (up to 10 g/l) and other metabolic inhibitors present
in the hydrolysate. Although the hydrolysate was not detoxified, ethanol yield in a range of 0.39–0.42 g/g was obtained. Overall,
sugar efficiency to ethanol was 68–76%. The reactor was operated continuously for approximately 143 days, and no contamination
was seen without the use of any agent for preventing bacterial infections. The tested microorganism has considerable potential
to be a novel candidate for lignocellulose bioconversion into ethanol. The work reported here also demonstrates that the use
of FBR configuration might be a viable approach for thermophilic anaerobic ethanol fermentation. 相似文献
70.