排序方式: 共有54条查询结果,搜索用时 31 毫秒
41.
The electrical permittivity of 1,4-dioxane and benzene solutions of some poly(oxyethylene) glycols up to the average molecular weight of 1590 were measured at 298.15 K. From the experimental data the limiting apparent specific polarization and partial molar polarization were calculated. The electrical dipole moment of the investigated solutes was estimated according to the Debye, Onsager, and Kirkwood theoretical approaches. The calculated dipole moments increase linearly with the square root of the number of monomeric units. The group dipole moment of the polar monomeric unit was calculated from the corresponding limiting partial molar volume, the refraction and polarization of the solute. The factor g, which takes into account the degree of flexibility of the chain, was estimated and found to be greater than 0.92, which means that the lower members of the poly(oxyethylene) glycols possess almost free rotation within the chain backbone of polymer. 相似文献
42.
Darja?Rudan-Tasic Cveto?KlofutarEmail author 《Monatshefte für Chemie / Chemical Monthly》2003,134(9):1185-1193
Summary. The density and refractive index of aqueous, 1,4-dioxane, and benzene solutions of poly (oxyethylene) glycols of the type HO–(CH2CH2O)
n
–H (n varying from 1 to 4) were measured at 298.15K. From these experimental data the apparent molar volume and the apparent molar refraction at infinite dilution were calculated. The limiting apparent molar volume of the investigated compounds in a definite solvent depends linearly on the number of oxyethylene groups. From these data, the volume of the monomeric unit was evaluated and found to be greater in non-aqueous solvents than in water. The limiting apparent molar refraction of the solute for the investigated systems, within the experimental uncertainties, is equal to the molar refraction of the pure solute. The electronic polarizability of the solute molecule depends linearly on the number of monomeric units and the ratio of the electronic polarizability to the molecular van der Waals volume is constant and independent of the number of oxyethylene groups.Received February 24, 2003; accepted (revised) April 10, 2003
Published online August 18, 2003 相似文献
43.
Darja?Rudan-Tasic Tanja??upec Cveto?Klofutar Marija?Be?ter-Roga?Email author 《Journal of solution chemistry》2005,34(6):631-644
The electric conductivities of aqueous solutions of the lithium, sodium, potassium and ammonium salts of cyclohexylsulfamic acid were measured from 5 to 35 ∘C (in steps of 5 ∘C) in the concentration range 3 × 10−4 < c/mol-dm−3 < 0.01. Data analysis based on a chemical model of electrolyte solutions yielded the limiting molar conductance Λ∞ and the association constant KA. Using the known values of the limiting conductances of lithium, sodium and potassium ions, the limiting conductances of the cyclohexylsulfamic ion were evaluated. Total dissociation of the investigated salts in water and negligible hydration of the cyclohexylsulfamate anion are evident. 相似文献
44.
Darja?LisjakEmail author Mitja?Bukovec Klementina?Zupan 《Journal of nanoparticle research》2016,18(2):44
The effect of the substitution of Sc3+ for Fe3+ in barium ferrite on the size of the resulting nanoparticles was studied. These nanoparticles, with the nominal compositions BaFe12O19 and BaFe11.5Sc0.5O19, were synthesized hydrothermally at 90–240 °C or by coprecipitation under reflux at 140 °C. The precursors were obtained using (co)precipitation at room temperature. The sizes and morphologies of the precursors and nanoparticles were inspected with transmission electron microscopy, while their structures were confirmed with a combination of X-ray powder and electron diffraction. The samples’ compositions were analyzed with energy-dispersive X-ray spectroscopy. The evolution of the particle size and its distribution with the synthesis temperature and time were studied in pure and Sc-substituted barium ferrite and correlated with the evolution of the magnetic properties. The Sc substitution in the barium ferrite results in the formation of magnetic nanoparticles with applicable magnetic properties and in a significant reduction of the exaggerated particle growth. This was explained on the basis of the reaction kinetics. 相似文献
45.
Vončina Maja Volšak Darja Petrič Mitja Medved Jožef 《Journal of Thermal Analysis and Calorimetry》2018,134(3):1749-1755
Journal of Thermal Analysis and Calorimetry - The effect of various neodymium additions on the characteristic solidification temperatures and on the microstructure development of the... 相似文献
46.
Ultra high-performance liquid chromatography–mass spectrometry (UHPLC–MS) profiling of a polar solvent extract of juvenile stem tissue of Salix acutifolia Willd. identified a range of phenolic metabolites. Salicortin, 1, a well-known salicinoid, was the major compound present and the study identified young stem tissue of this species as a potential source of this compound for future studies. Three further known metabolites (salicin 2, catechin 3 and tremuloidin 4) were also present. The UHPLC–MS analysis also revealed the presence of a further, less polar, unknown compound, which was isolated via HPLC peak collection. The structure was elucidated by high-resolution mass spectroscopic analysis, 1- and 2-D NMR analysis and chemical derivatisation and was shown to be a novel benzoic acid glycoside 5, which we have named as acutifoliside. 相似文献
47.
Determination of glutathione content in grape juice and wine by high-performance liquid chromatography with fluorescence detection 总被引:2,自引:0,他引:2
A modified preparation of sample was developed for the determination of glutathione content in grape juice and wine by high-performance liquid chromatography with fluorescence detection, using on-line pre-column derivatization. Ice-cold deoxygenated methanol was used to deactivate the oxidation enzymes in juices or wines and keep the glutathione stable. The optimum recovery of glutathione content in grape juice and wine was obtained when either the sample of grape juice or wine was mixed in ice-cold deoxygenated methanol in the ratio 10:90 (v:v) and further diluted in sodium acetate buffer in the ratio 1:1 (v:v). The optimized method was validated for linearity, limit of detection, limit of quantification, precision and uncertainty. According to the validation data the method is appropriate for the determination of glutathione content in grape juice and wine. Glutathione contents in grape juices made from White Muscat grapes and Sauvignon Blanc wines were analysed. The average glutathione content in 28 young Sauvignon Blanc wines was 12.5 mg L−1. 相似文献
48.
The purpose of this work was the development of a method for the determination of Se compounds in leaves of plants. Water-soluble Se compounds were extracted from samples by water. Enzymatic hydrolysis with the non-specific enzyme protease XIV was used for the release of Se compounds bound to proteins. Separation of Se species was made by ion exchange chromatography, using an anion exchange column for SeIV, SeVI and selenomethionine (SeMet), and a cation exchange column for selenomethylselenocysteine (SeMeSeCys) and selenocystine (SeCys2). Columns were connected “on line” to a hydride generation atomic fluorescence spectrometer (HG-AFS) using a UV lamp between the separation and detection system. The repeatability of the results obtained by the developed method was under 15% (R.S.D.) for all Se species; the detection limit was 2-10 ng Se/g of supernatant. The accuracy was checked by comparison with some literature data for reference materials since there were no suitable certified reference materials available. The method was used for the determination of Se compounds in chicory (Cichorium intybus L.) leaves from plants which were cultivated aeroponically with elevated concentrations of Na2SeO4 for different periods. Se accumulated efficiently in chicory leaves; up to 480 μg/g after 41 days of exposure, mostly (64%) as SeVI, i.e. in the form of Se added. Beside inorganic Se, in the extracts from enzyme hydrolysis we also found SeMet (4.2-8.4%) and SeMeSeCys (<DL−0.7%). Some unidentified peaks were also observed in the chromatograms of plant extracts. 相似文献
49.
The density and refractive index of aqueous, 1,4-dioxane, and benzene solutions of poly (oxyethylene) glycols of the type HO–(CH2CH2O) n –H (n varying from 1 to 4) were measured at 298.15K. From these experimental data the apparent molar volume and the apparent molar refraction at infinite dilution were calculated. The limiting apparent molar volume of the investigated compounds in a definite solvent depends linearly on the number of oxyethylene groups. From these data, the volume of the monomeric unit was evaluated and found to be greater in non-aqueous solvents than in water. The limiting apparent molar refraction of the solute for the investigated systems, within the experimental uncertainties, is equal to the molar refraction of the pure solute. The electronic polarizability of the solute molecule depends linearly on the number of monomeric units and the ratio of the electronic polarizability to the molecular van der Waals volume is constant and independent of the number of oxyethylene groups. 相似文献
50.
Cveto?Klofutar Darja?Rudan-TasicEmail author 《Monatshefte für Chemie / Chemical Monthly》2005,136(10):1727-1736
Summary. The apparent molar volume of lithium, sodium, potassium, and tetramethylammonium cyclohexylsulfamate was determined from the
density data of their aqueous solutions at 293.15, 298.15, 303.15, 313.15, and 323.15 K. The apparent molar expansibility
was calculated from the apparent molar volume at various temperatures. The limiting apparent molar volume and apparent molar
expansibility were evaluated and divided into their ionic components. The partial molar ionic expansibilities were discussed
in terms of the hydration of the ion in solution, as well as in terms of the hydration effects on the solute as a whole. From
the partial molar expansibility of the solute at infinite dilution the partial molar expansibility of the hydration shell
was deduced. The coefficients of thermal expansion of the investigated solutions at 298.15 K were calculated and are presented
graphically. The density of the investigated solutions can be adequately represented by an equation derived by Root. 相似文献