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991.
With P(CH3)3 as the probe molecule adsorbed on titanium silicalite (TS-1) zeolite, the special and important role of T12 site in MFI-type zeolite was clearly elucidated. There are altogether three active sites present in TS-1 zeolite with Ti at the T12 site. Owing to the preferential adsorption of probe molecules on the first Brönsted acidic site, the Ti12 center will probably fail to show Lewis acidity. The ionic [HP(CH3)3]+ species can be stabilized by the first or second Brönsted acidic site, with the former energetically favored. The latter was formed through the transfer of the ionic [HP(CH3)3]+ species from the first to the second Brönsted acidic site. 相似文献
992.
Young Hyun Cho Wanno Lee Kun Ho Chung Geun Sik Choi Chang Woo Lee 《Journal of Radioanalytical and Nuclear Chemistry》2007,274(3):531-538
The seasonal variation of the 7Be activities in air and the size distribution of the 7Be aerosols were studied by using a continuous air sampler and a five stage cascade impactor. The mean monthly activity level
of 7Be at the Korea Atomic Energy Research Institute (KAERI) site varied from 0.5 to 4.8 Bq·m−3 and revealed a seasonal variation, in which the 7Be activity levels were high in winter and low in summer. The mass size distribution showed a bi-modal distribution with a
higher peak around 0.49 μm and a smaller peak between 3 μm and 7.2 μm. The activity median aerodynamic diameter (AMAD) decreased
with increasing ambient 7Be concentrations. The mean residence times by using a mean growth rate of 0.004 μm·h−1 were estimated to be 2.5–6.4 days. The AMAD has an increasing tendency with higher relative humidity. It seemed that the
high humidity condition facilitated the growth of the aerosol, resulting in increased deposition rates of the aerosols and
the low 7Be content in the surface air. The AMAD of the 7Be aerosols increased with an increasing temperature, but the temperature dependency of AMAD should be explained with geological
and meteorological conditions. 相似文献
993.
994.
A. L. Chistyakov I. V. Stankevich N. P. Gambaryan I. A. Tikhonova V. B. Shur 《Russian Chemical Bulletin》1995,44(6):997-1004
Geometries and electronic structures of the complexes of halide anions with cyclic trimerico-phenylenemercury, (o-C6H4Hg)3, perfluoro-o-phenylenemercury, (o-C6F4Hg)3, vinylenemercury, (C2H2Hg)3, and perfluorovinylenemercury, (C2F2Hg)3, were modelled by the MNDO method. Calculations were performed for [L-X]– semisandwich complexes, [X-L-X]2– bipyramidal complexes, and [L-X-L]– sandwich complexes (where X=Hal,L is a mercury-containing macrocycle). Based on the results of calculations, we concluded that it was advantageous to describe the chemical bonding between halide anions and mercury-containing macrocycles in terms of generalized chemical bonds, which were successfully used for -complexes of transition metals. In the [L-X]– semisandwich complexes, the halide anion and the metallacycle are involved in the formation of three generalized chemical bonds: one headlight-shaped -bond and two two-lobe -bonds. In the [X-L-X]2– bipyramidal complexes, each halide anion forms three generalized chemical bonds with the macrocycle. It is possible because the macrocycleL has unoccupied molecular orbitals suitable for the formation of such bonds; these MOs consist mainly of the orbitals of mercury atoms directed toward both the upper and lower halogen atoms. In the [L-X-L]– sandwich complexes, the halide anion cannot be bonded to each ringvia three bonds, and, hence, an unsymmetrical structure is formed, in which the rings are located at different distances from the central atom: the [L-X]– semisandwich complex solvated by macrocycleL.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1035–1042, June, 1995.The authors are grateful to V. I. Faustov for valuable remarks.This work was supported by the Russian Foundation for Basic Research (Project No. 93-03-18342). 相似文献
995.
Ya-Guang Chen Fan-Xia Meng Hai-Jun Pang Dong-Mei Shi Yu Sun 《Journal of Cluster Science》2007,18(2):396-405
A novel uranyl complex with dimeric lacunary polyoxoanion like open-mouthed clam, Na5[(A-α-SiW9O33H3)2K{UO2(H2O)}2], was prepared and characterized by elemental analysis, infrared and ultraviolet–visible spectroscopy and single crystal
X-ray diffraction. In the anion, two A-α-SiW9O3410− groups share two terminal oxygen atoms Od′ derived from removal of three corner-shared W atoms from saturated α-Keggin anion, forming a dimeric anion with an open
mouth in which potassium ion and uranyl ions are coordinated. Uranium atom adopts a pentagonal bipyramidal geometry. The coordinating
anions are linked by sodium ions via coordination of terminal or bridging oxygen atoms, forming two-dimensional layer arrangement.
Between the layers are the hydrogen bonds from which a supramolecular architecture is created. UV–VIS spectrum gives W–O and
U–O charge transfer transitions at 230–265 and 432 nm, showing the change of geometry of the polyanion and weakening of the
U–O bonds of the uranyl cation.
Electronic supplementary material The online version of this article () contains supplementary material, which is available to authorized users. 相似文献
996.
Yan Xiao Jian Wang Wang Xia Guang Feng Huai You Wang 《Journal of Analytical Chemistry》2007,62(5):438-443
The maximum emission wavelength of dopamine is 317 nm with excitation at 290 nm. The relative fluorescence intensity of dopamine
decreased in the presence of enoxacin, which showed that fluorescence quenching occurred. The Stern-Volmer (S-V) plot showed
a nonlinear relationship between the relative fluorescence intensity of dopamine and the concentration of enoxain. The quenching
mechanism was studied and the results suggested that both dynamic and static quenching processes were responsible for the
observed positive deviation in the S-V plot. When the S-V plot was modified by logarithm, the linear relationship was obtained
between logF
0/F and C in the range of 0.10 to 13.0 μg/mL (where F
0 is the relative fluorescence intensity of dopamine, F is the relative fluorescence intensity of dopamine in the presence of enoxacin, and C is the concentration of enoxacin). The fluorescence quenching method for the determination of enoxacin was developed. The
linear regression equation of the calibration graph of enoxacin was C = 13.70 (logF
0/F) − 0.5836, with the correlation coefficient 0.9984. The detection limit was 2.0 ng/mL and the relative standard deviation
was 2.52%. The effects of pH, the stability of dopamine in the presence of enoxacin, and foreign ions on the determination
of enoxacin have been examined. The recovery of enoxacin was from 94.9 to 103.0% in a human serum sample and from 94.9 to
108.0% in a urine sample. The method is simple, rapid, and can be used for the determination of enoxacin in human serum and
urine samples with satisfactory results.
The text was submitted by the authors in English. 相似文献
997.
Rosa Maria Rojas K. Petrov G. Avdeev J. M. Amarilla L. Pascual J. M. Rojo 《Journal of Thermal Analysis and Calorimetry》2007,90(1):67-72
Chromium doped spinels LiCrYMn2−YO4 (0.2≤Y≤0.8) has been synthesized by the sucrose-aided combustion procedure. The thermal behaviour, phase homogeneity and structural
characteristics of the samples were studied by thermal analysis, coupled mass spectrometry, and room-and high-temperature
X-ray diffraction methods. It was found that the ‘as prepared’ samples contained residual organic impurities undetectable
for X-ray diffraction, that burn out completely at 400°C. Samples treated between 400 and 750°C are single phase spinels,
whose crystallites size increase from 10 to 50 nm on increasing the temperature. Cr-doping enhances the thermal stability
of the spinels, which augments on increasing the Cr content Y. The enhanced thermal stability of the spinels has been accounted
for based on the high excess stabilization energy of Cr3+ in octahedral ligand field. 相似文献
998.
The factors influencing the electrochemical behaviour of a supercapacitor have been partly examined in this work. The effects
of so-called intrinsic parameters, i.e. exchange current density, unit cell length and double layer (DL) capacitance; as well
as the so-called application parameters, i.e. cell current, on the cell potential discharge time have been considered. The
contributions of each type of capacitors, DL capacitor and faradaic supercapacitor under various states of operation and material
have been analyzed, and the competing (compensating) effects of the two types of capacitors as regards to the discharge and
power characteristics manifested by current–potential and energy–power (Ragone plots) are elucidated. 相似文献
999.
Capillary electrophoresis with wavelength-resolved laser-induced fluorescence detection 总被引:5,自引:0,他引:5
Capillary electrophoresis (CE) enables rapid separations with high separation efficiency and compatibility with small sample volumes. Laser-induced fluorescence detection can result in extremely low limits of detection in CE. Single-channel fluorescence detection, however, furnishes little qualitative information about a species being detected, except for its CE migration time. Use of multidimensional information often enables unambiguous identification of analytes. Combination of CE with information-rich wavelength-resolved fluorescence detection is analogous with ultraviolet-visible diode-array detection and furnishes both qualitative and quantitative chemical information about target species. This review discusses recent advances in wavelength-resolved laser-induced fluorescence detection coupled with CE, with an emphasis on instrument design. 相似文献
1000.
A type of high visible-light active titanium oxinitride(TiO2-xNx) powder was prepared by a simple proc-ess:the calcination of the hydrated titanium dioxide at the atmosphere of ammonia-argon using a tu-bular electric furnace at high temperatures. The hydrated titanium dioxide was synthesized as the precursor of TiO2-xNx using titanic acid as raw material,which came from sulfate technique of produc-ing titanium white. The effects of temperature and reaction time on the nitrogen content,grain size and crystal structure were studied. The visible-light activity and photocatalysis capability of the powder were also investigated. 相似文献