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991.
Duan SW Li Y Liu YY Zou YQ Shi DQ Xiao WJ 《Chemical communications (Cambridge, England)》2012,48(42):5160-5162
An efficient organocatalytic Michael-aldol cascade reaction for the asymmetric synthesis of spirocyclic oxindole derivatives fused with tetrahydrothiophenes has been developed through a formal [3+2] annulation strategy. 相似文献
992.
Liu JY Guan YL Zou LB Gong YX Hua HM Xu YN Zhang H Yu ZG Fan WH 《Molecules (Basel, Switzerland)》2012,17(5):5520-5531
Four new oleanene-type triterpenoid saponins together with six known saponins were isolated from the roots of Pulsatilla cernua and their structures were elucidated on the basis of spectroscopic data, including 2D NMR spectra and chemical evidence. Among these one of the aglycones (gypsogenin) is reported for the first time from this genus. Some of these compounds showed significant neuroprotective effects against the cytotoxicity induced by β-amyloid(25-35) (Aβ(25-35)) on human neuroblastoma SH-SY5Y cells. 相似文献
993.
Huang Wenzhi Wang Chunjie Yang Jili Zou Binglin Meng Xiangsheng Wang Ying Cao Xueqiang Wang Zhen 《Journal of Sol-Gel Science and Technology》2012,61(1):213-223
In this investigation, Zr1−x
Ce
x
O2 coatings were fabricated on quartz fiber reinforced polyimide matrix composites via sol–gel process at 400 °C. The phase
evolution, structural and morphological characteristic of specimens were investigated by differential scanning calorimetric,
Fourier transform infrared spectroscopy, powder X-ray diffraction and scanning electron microscopy. The significant phase
evolution of final powders with the decreasing Zr/Ce molar ratio could be observed as follows: tetragonal (t′) → cubic + tetragonal (t′) → tetragonal (t″). BET specific surface areas of powders exhibited a decreased tendency with the increasing calcination temperature as well
as the decreasing Zr/Ce molar ratio. The average crystallite size and the mean particle size increased with the elevated calcination
temperature, while the particle size also increased with the increase in Ce content. The progressive addition of Ce could
promote the sintering process and the densification of coating. Morphologies of coatings changed with the variation of the
Zr/Ce molar ratio. The results indicate that Zr0.75Ce0.25O2 coating with the Zr/Ce molar ratio of 3 is a stable uniform coating with excellent adhesion. 相似文献
994.
Huanqiang Liu Minghua Zhang Xuedong Wang Yujie Zou Wenwei Wang Meiping Ma Yanyan Li Huili Wang 《Mikrochimica acta》2012,176(3-4):303-309
We have developed a method, termed solidification of floating organic drop microextraction (SFOME), for the extraction of polybrominated diphenyl ethers (PBDEs) in water and urine samples, this followed by quantification via HPLC. This method requires very small quantities of organic solvent consumption. It is based on exposing a floating solidified drop of an organic solvent on the surface of aqueous solution in a sealed vial. The organic drop is easily collected with a spatula, molten (at ambient temperature), and then submitted to HPLC. Experimental parameters including extraction solvent and its volume, disperser solvent and its volume, extraction time, ionic strength, stirring speed and extraction temperature were optimized. The enrichment factors of analytes are in the range from 921 to 1,462, and acceptable extraction recoveries (92%–118%) are obtained. The dynamic linear range for five PBDE congeners is in the range of 0.5–75?μg.L?1 and from 5 to 500?μg.L?1 for BDE 209. The correlation coefficients range from 0.9960 to 0.9999. The limits of detection (at S/N?=?3) for PBDE congeners vary between 0.01 and 0.04?μg.L?1. This method has been successfully applied to detecting PBDEs in two environmental waters and in human urine. Figure
Under optimized conditions, the enrichment factors of PBDEs by solidification of floating organic drop microextraction were from 921 to 1,462, and extraction recoveries (92%–118%) were obtained. The correlation coefficients ranged from 0.9960 to 0.9999. The limits of detection (at S/N?=?3) for PBDE congeners varied between 0.01 and 0.04?μg.L?1. 相似文献
995.
More than green alternatives to traditional volatile molecular organic solvents, protic ionic liquids as dual solvent-catalysts have been successfully used to promote reactions of organoamines with oxadiazoles to afford sterically hindered 1,2,4-triazoles. Among the tested protic ionic liquids, pyridinium trifluoroacetate and acetate showed the highest efficiency for the reactions of arylamines and alkylamines, respectively, indicating that tunable catalysis could be readily effected with protic ionic liquid solvent-catalysts by simply tuning their cation and anion counterparts. A general and efficient approach has been developed for synthesis of multiply substituted 1,2,4-triazoles based on the tunable protic ionic liquid solvent-catalyst systems. 相似文献
996.
Beiqiong Lu Jianmin Zhang Jia Li Jianhua Yao Minjian Wang Yuanhai Zou Shizheng Zhu 《Tetrahedron》2012,68(43):8924-8930
A series of pyrazolino[60]fullerene–1,8-naphthalimide (Pz[60]–NI) fluorescent derivatives were synthesized in one pot by a [3+2] dipolar cycloaddition between C60 and functionalized hydrazones in good yield. In contrast with 4-aziridino[60]fullerene–1,8-naphtalimide dyads, Pz[60]–NI derivatives present stronger fluorescence intensity. Electrochemical study revealed that Pz[60]–NI presents better electron accepting character than the parent C60. The natural bond orbital of the dyads were calculated using density functional theory method and found that the sp3 nitrogen atom in the pyrazoline ring plays a key role in the charge transfer process. 相似文献
997.
In this note, we improve and generalize some existing inequalities for unitarily invariant norms and singular values, and present some other inequalities for unitarily invariant norms. 相似文献
998.
Yu-Chih Tseng Yow-Jon Lin Hsing-Cheng Chang Ya-Hui Chen Chia-Jyi Liu Yi-Yan Zou 《Journal of luminescence》2012,132(2):491-494
This study investigates the effect of Ti content on the optical and structural properties of the Ti-doped ZnO (TixZn1?xO) nanoparticles by x-ray diffraction, scanning electron microscopy, photoluminescence and Raman scattering measurements. A dependence of luminescent properties and crystal structure upon Ti content has been found. The band-edge-luminescence (BEL) intensity of Ti0.10Zn0.90O at room temperature was nearly 1.7 times higher than that of ZnO. The enhanced BEL intensity is attributed to a decrease in the oxygen-vacancy density. However, the lower BEL intensity of Ti0.15Zn0.85O than Ti0.10Zn0.90O is attributed to an increase in the probability of nonradiative recombination. In addition, the intensity of the x-ray diffraction peaks remarkably decreases with increasing Ti content, suggesting weakened crystallinity. 相似文献
999.
Luminescent CuInS2 nanocrystals have been synthesized in dodecanethiol using air-stable precursors. The nanocrystals were characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD) and Raman spectroscopy. The optical properties of the CuInS2 nanocrystals can be controlled by changing the reaction conditions, such as reaction time, temperature, and addition of ligands. It was found that the steady-state photoluminescence spectrum of the close-packed CuInS2 nanocrystals on glass substrate peaked at longer wavelength than that of the colloidal ones and the close-packed nanocrystals possessed a shorter luminescence decay time. This behavior was explained on the basis of Förster resonant energy transfer due to the shorter distance between nanocrystals on substrate. 相似文献
1000.
A novel oxonitridosilicate phosphor host Sr(3)Si(2)O(4)N(2) was synthesized in N(2)/H(2) (6%) atmosphere by solid state reaction at high temperature using SrCO(3), SiO(2), and Si(3)N(4) as starting materials. The crystal structure was determined by a Rietveld analysis on powder X-ray and neutron diffraction data. Sr(3)Si(2)O(4)N(2) crystallizes in cubic symmetry with space group Pa ?3, Z = 24, and cell parameter a = 15.6593(1) ?. The structure of Sr(3)Si(2)O(4)N(2) is constructed by isolated and highly corrugated 12 rings which are composed of 12 vertex-sharing [SiO(2)N(2)] tetrahedra with bridging N and terminal O to form three-dimensional tunnels to accommodate the Sr(2+) ions. The calculated band structure shows that Sr(3)Si(2)O(4)N(2) is an indirect semiconductor with a band gap ≈ 2.84 eV, which is close to the experimental value ≈ 2.71 eV from linear extrapolation of the diffuse reflection spectrum. Sr(3-x)Si(2)O(4)N(2):xEu(2+) shows a typical emission band peaking at ~600 nm under 460 nm excitation, which perfectly matches the emission of blue InGaN light-emitting diodes. For Ce(3+)/Li(+)-codoped Sr(3)Si(2)O(4)N(2), one excitation band is in the UV range (280-350 nm) and the other in the UV blue range (380-420 nm), which matches emission of near-UV light-emitting diodes. Emission of Sr(3-2x)Si(2)O(4)N(2):xCe(3+),xLi(+) shows a asymmetric broad band peaking at ~520 nm. The long-wavelength excitation and emission of Eu(2+) and Ce(3+)/Li(+)-doped Sr(3)Si(2)O(4)N(2) make them attractive for applications in phosphor-converted white light-emitting diodes. 相似文献