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101.
Nuclear magnetic resonance spectroscopic study on ionic liquids of 1-alkyl-3-methylimidazolium salts
Chemical shifts of 1H and 13C NMR of series of methylimidazolium salts (MIM+, X=Br−, BF4− and PF6−) function on the length of alkyl groups on the ring, type of solvents and the concentration. The bromides series demonstrate more chemical shift variation on H2 upon the change of solvents and concentration. Unexpected H-D exchange reactions were also observed in the MIM+Br− by using CD3OD and D2O. The exchange rates strongly depend on the length of the alkyl group, which could cause more steric factor to reduce the interaction between deuterium atom from solvent and C2 of the ring. 相似文献
102.
Cadmium selenide quantum dots with cubic crystal structure are chemically deposited in thin film form using selenosulfate as a precursor for selenide ions and ammonia buffer with double role: as a ligand and as a pH value controller. The optical band gap energies of as-deposited and thermally treated cadmium selenide thin films, calculated within the framework of parabolic approximation for the dispersion relation, on the basis of equations which arise from the Fermi's golden rule for electronic transitions from valence to conduction band, are 2.08 and 1.77 eV, correspondingly. The blue shift of band gap energy of 0.34 eV for as-deposited thin films with respect to the bulk value is due to the quantum size effects (i.e., nanocrystals behave as quantum dots) and this finding is in agreement with the theoretical predictions. During the thermal treatment the nanocrystals are sintered, the increase of crystal size being in correlation with the decrease of band gap energy. The annealed thin films are practically non-quantized. From the resistance-temperature measurements, on the basis of the dependence of ln(R/Ω) vs 1/T in the region of intrinsic conduction, the thermal band gap energy (at 0 K) of 1.85 eV was calculated. 相似文献
103.
Stavroula Theodorolea 《Analytica chimica acta》2005,547(1):132-137
A method was developed for the determination of selenium in human milk using electrothermal atomic absorption spectrometry. The use of chemical modifiers as well as their implications during the pyrolysis step was examined. The chemical modifiers that were studied were Zr, Ir as well as the mixed modifier Zr-Ir. The Ir modifier stabilized selenium at 1000 °C, Zr at 800 °C, while the mixed modifier at 1200 °C. The effect of modifier mass was studied and was found that better results are achieved with addition of 2 μg Zr and 2 μg Ir. The characteristic masses of selenium in the presence of Zr, Ir and the mixed modifier were found to be 73.3, 18.0 and 14.7 pg, respectively, while the corresponding limits of detection were found 2.0, 0.50 and 0.41 μg l−1. Consequently better results were obtained with the mixed modifier. The developed method was applied for the determination of selenium in human milk, which was digested with a HNO3 + H2O2 mixture in a microwave oven. The limit of detection of the method was 1.37 μg l−1, the characteristic mass, m0, was 48.8 pg and the repeatability was less than 5% as R.S.D.(%). Matrix matched calibration was used. Recoveries were estimated to be 93-105%. The method was applied to breast milk of Greek women (n = 9) and the Se content was found to be in the range 16.7-42.6 μg l−1 with mean value 27.4 ± 5.5 μg l−1. 相似文献
104.
We previously reported the use of imidazole as starting compound for preparing a bicyclic imidazolium ionic liquid, [b-3C-im][NTf2], with an overall 29% isolated yield in four synthetic steps. This new room temperature ionic liquid was shown to be far more chemically stable than commonly used [bmim][PF6], [bdmim][PF6], and [bdmim][NTf2]. Because of this intriguing chemical stability, it prompted us to develop a more generalized and high yielding synthesis so that molecular diversity of bicyclic ionic liquids may be explored. In this work, we amended the previous synthetic route by employing 4-chlorobutyronitrile or 5-chlorovaleronitrile as starting materials and successfully developed a five-step synthesis of a series of novel bicyclic imidazolium-based ionic liquids in 40-53% overall isolated yields. We investigated intrinsic reactivity of all bicyclic ionic liquids prepared and found that, under strongly basic conditions, among all tested ionic liquids the 5,5-membered [R-3C-im][NTf2] ionic liquids were most stable to solvent deuterium isotope exchange while the previously reported [bdmim][NTf2] ionic liquid was 50% deuterium exchanged at its C-2 methyl in 30 min at ambient temperature. Under identical condition, the commonly used [bmim][NTf2] ionic liquid was deuterium exchanged instantaneously at its C-2 hydrogen. In the absence of bases, only [bmim][PF6] was deuterium exchanged (50% within 1 h) and all other ionic liquids gave no detectable exchanges even after 25 days at ambient temperature. Moreover, both [bmim][NTf2] and [bdmim][NTf2] ionic liquids were readily methylated at C-2 position with methyl iodide under basic condition at room temperature. Under the same condition, [R-3C-im][NTf2] and [R-4C-im][NTf2] ionic liquids were completely stable and chemically inert. We envisioned that [R-3C-im][NTf2] should be well suited as solvents for organic synthesis. 相似文献
105.
Recent trends in research and development of electrolyte-insulator-semiconductor (EIS) field-effect chemical sensors (ion-selective field-effect transistors, light-addressable potentiometric sensors, capacitive EIS-sensors) with inorganic gate insulators (oxide, nitride and chalcogenide films) are reviewed. Physical properties of EIS systems and basic mechanisms of their chemical sensitivity are examined. Analytical characteristics and sensing mechanisms of EIS pH sensors with oxide and nitride films, as well as metal ions sensors with chalcogenide films, are critically discussed. Prospects of future research on EIS field-effect biosensors are briefly outlined. 相似文献
106.
Two 60-residue snake toxins with four disulfide bridges, cardiotoxin II and IV, of Taiwan cobra (Naja naja atra) have been rapidly prepared in overall yields of 3.9% (cardiotoxin II) and 3.7% (cardiotoxin IV) within three weeks using the chemical method. Physicochemical characterization of these synthetic cardiotoxins was carried out by amino acid analysis, mass spectroscopy, capillary electrophoresis, peptide mapping, circular dichroism spectroscopy, and lethal toxicity. As compared with natural cardiotoxins, the results indicated that the synthetic cardiotoxins possessed the same physicochemical properties as those of natural ones. Therefore, in addition to preparation of various important toxins with satisfactory quantities for biochemical and pharmacological studies within a short lime, this rapid method also provides an important route to obtain many interesting toxins and designed toxin analogues for structure/function relationship studies in the near further. 相似文献
107.
《Arabian Journal of Chemistry》2022,15(12):104329
To reduce the amount of hazardous chemical bottle waste in the environment, we report the optimization research of silica extraction in chemical bottle waste into silica gel. Alkali fusion and sol–gel process were utilised to prepare silica gel effectively. The alkali fusion process was carried out by adding sodium hydroxide to produce sodium silicate. Afterwards, silica gel was prepared by the sol–gel method using hydrochloric acid. Box-Behnken Design (BBD) was applied to Optimisation factors the poptimiseactors affecting the silica recovery. The factors that optimised mass ratio, particle size, and temperature. The optimum recovery of silica gel was obtained by SiO2: NaOH mass ratio of 1:3, the particle size of 63–74 µm, and a temperature of 800 °C. The purity of silica gel optimum is 63.74% characterised using X-ray fluorescence. The structure of silica gel is the appearance of amorphous peaks at 2θ 20-30° characterised using an x-ray diffractogram. The silica gel surface was characterises using scanning electron microscopy-energy dispersive x-ray. It showed an irregular surface and characteristic showed that silica gel had a radius of 15.74 nm and a specific surface area of 297.08 m2. 相似文献
108.
Ftima R. Moreira Cristina B. Maia Akie K. vila 《Spectrochimica Acta Part B: Atomic Spectroscopy》2002,57(12):2141-2149
The determination of cobalt in marine sediments by electrothermal atomic absorption spectrometry was studied using no modifier and magnesium and titanium as modifiers. Titanium is one of the major sediment constituents, which widely affects the cobalt determination and it was studied as a chemical modifier since it was the only concomitant that increased the cobalt signal in the concentration range usually found in sediments. The performance of Mg and Ti as chemical modifiers was compared relative to maximum pyrolysis and atomization temperatures, linear calibration range, sensitivity and matrix effects. The pyrolysis curves showed that the analyte could be stabilized up to 1400 °C when either Ti or Mg(NO3)2 was present, while only 1000 °C could be used in the absence of a modifier. The optimum atomization temperature was 2500 °C in all cases. Analytical curves were compared using no modifier, 5 μg Ti and 100 μg Mg(NO3)2 as modifiers, and the linear range found was up to approximately 4 ng Co whether a modifier was used or not. With Ti as a chemical modifier, analytical curves for cobalt in aqueous solution and in a synthetic matrix resulted in the same sensitivity (m0=55 pg), whereas the use of Mg led to characteristic mass values of 59 and 72 pg in aqueous solution and in a synthetic matrix, respectively, showing some matrix effect. The detection limits (3σ, n=10) were 0.4 μg g−1 using no modifier and 0.3 μg g−1 with Ti as a modifier in the original matrix. A reference estuarine sediment NIST 1646 with a non-certified content of 10.5 μg g−1 Co was analyzed and the found value of 10.9±2.4 μg g−1, (n=3), using Ti as chemical modifier and calibration against aqueous standards, was in good agreement with the recommended value. 相似文献
109.
Nanocrystalline Mo2C powders were successfully synthesized at 500 °C by reacting molybdenum chloride (MoCl5) with C (graphite or carbon nanotube) in metallic sodium medium. X-ray powder diffractometer (XRD), transmission electron microscope (TEM), X-ray photoelectron spectroscope (XPS) and surface area analyzer (BET method) were used to characterize the samples. Experiments reveal that the carbon source used for the carbide synthesis has a great effect on the particle size and the surface area of the samples. When micro-sized graphite was used as C source the obtained nanocrystalline Mo2C powder consists of particles of 30∼100 nm, with a surface area of 2.311 m2/g. When carbon nanotubes were used as C source, the as-synthesized Mo2C sample is composed of particles of 20∼50 nm, with a surface area of 23.458 m2/g, which is an order of magnitude larger than that of the carbide prepared from the graphite. 相似文献
110.
Fu-Sheng S 《Talanta》1983,30(6):446-448
The conditions for the reaction between phenylarsenazo (PAA) (2-[(2-arsonophenyl)azoj-7-(phenylazo)-1, 8-dihydroxynaphthalene-3,6-disulphonic acid) and chromium(III) have been studied. A blue 1:1 complex is formed at pH 2.2 on heating the reactants at 100 degrees for 15 min. It has maximum absorption at 635 nm and is stable for at least 24 hr. The molar absorptivity is 3.3 x 10(4) 1.mole(-1).cm(-1). Beer's law is obeyed in the chromium concentration range 0-1.4 mug ml . The reaction has been successfully applied to determination of chromium in alloy steel. 相似文献