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971.
设计开发了一种无需溶剂,通过热处理固相转化制备沸石咪唑酯骨架材料(ZIFs)的简易方法.该方法无需溶剂及其它预处理,只需将金属源与有机配体固相混合后于低温(200℃)热处理即可实现多孔晶体材料的制备.所合成材料H-ZIF-67为具有方纳石拓扑结构的纳米晶体,与传统方式合成的ZIFs材料一致.粉末X射线衍射(PXRD)分析结果表明产物的晶体结构与标准ZIFs谱图一致.通过扫描电子显微镜(SEM)、透射电子显微镜(TEM)、N2吸附-脱附分析、热重分析(TGA)和傅里叶变换红外光谱(FTIR)等手段对合成的材料进行了表征,发现H-ZIF-67材料具有与ZIFs材料类似的特性.该方法经济、高效,摒弃了传统方法合成ZIFs材料周期长、处理过程复杂的弊端,为ZIFs材料的量产提供了新思路. 相似文献
972.
K. Andjelković R. Tellgren S.R. Niketić D. Sladić D. Poleti 《Journal of chemical crystallography》1999,29(5):575-580
The title compound was obtained by a template synthesis from 2,6-diacetylpyridine, ethylhydrazinoacetate and CuCl2·2H2O (molar ratio 1:2:1, in methanol), and its structure has been determined by single-crystal X-ray diffraction: monoclinic space group P21/c, a = 13.906(5), b = 18.199(6), c = 16.641(6) Å, = 107.18(3)°, and z = 4. The ligand was found to be tridentate in a trigonal-bipyramidal coordination geometry with two chloride ligands. There are two independent complex molecules, one of which is hydrogen bonded to the water of crystallization. 相似文献
973.
Conrad T. Pfeiffer Justin D. Northrup Jae Eun Cheong Melody A. Pham Matthew F.L. Parker Christian E. Schafmeister 《Tetrahedron letters》2018,59(30):2884-2888
Spiroligomers are a class of peptidomimetics that connect interchangeable, stereochemically pure, cyclic monomers through pairs of amide bonds to form diketopiperazines between the monomers. This enables them to adopt predictable and programmable structure due to the rigidity of the final molecule. We present a new method for the solid phase synthesis of highly functionalized spiroligomers that incorporates the use of the p-nitrobenzyloxycarbonyl (pNZ) as a temporary amine protecting group and the pentafluorophenyl ester for monomer activation. This new method allows for the synthesis of spiroligomers with higher purity and increased yields when compared to previous methods. This improved method of synthesis of functionalized spiroligomers will facilitate the development of applications as catalysts, therapeutics and membrane channels. 相似文献
974.
《无机化学与普通化学杂志》2018,644(16):893-900
Sr8MgCe(PO4)7:Eu2+,Mn2+ phosphor with whitlockite‐type structure was prepared by a combustion‐assisted solid‐state reaction. The crystal structure and luminescence properties were investigated. Under UV radiation, Sr8MgCe(PO4)7 host exhibits a violet‐blue emission band from Ce3+ ions. When Eu2+/Mn2+ are doped into the host, the samples excited with 270 nm UV radiation present multicolor emissions due to the energy transfer (ET) from Ce3+ to Eu2+/Mn2+. The emitting color of Sr8MgCe(PO4)7:Eu2+ can be tuned from violet‐blue to yellow‐green, whereas Sr8MgCe(PO4)7:Mn2+ can emit red light. Under excitation with long wavelength at 360 nm, Sr8MgCe(PO4)7:Eu2+ phosphor shows a broadband emission from 390 to 700 nm, which is attributed to the 4f65d1→4f7 transition of Eu2+ without the contribution from Ce3+ emission. Tunable full‐color emitting light can be achieved in the Eu2+ and Mn2+‐codoped Sr8MgCe(PO4)7 phosphor by ETEu–Mn through control of the levels of doped Eu2+ and Mn2+ ions. These results suggest that Sr8MgCe(PO4)7:Eu2+,Mn2+ phosphor has potential applications in NUV chip pumped white LEDs. 相似文献
975.
Microextraction-based sample preparation techniques have exhibited remarkable importance in analytical chemistry since they were first developed in the 1980s. The application of these techniques involves efficient and, at the same time, environmentally-friendly analytical methodologies. They are also generally faster when compared with classical sample preparation techniques, requiring low solvent and sample volumes, and also allowing for automated or semi-automated procedures. This paper provides an overview of the basic principles of sample preparation techniques and the important applications and developments that have taken place in this area over the past five years. These procedures include solid-phase microextraction (SPME), stir bar sorptive extraction (SBSE), bar adsorptive microextraction (BAμE), rotating disk sorptive extraction (RDSE), micro solid-phase extraction (μ-SPE) and liquid-phase microextraction (LPME). The main variations are discussed with a focus on recent applications in the analysis of environmental water samples. Lastly, some of the trends and perspectives associated with these outstanding microextraction sample preparation approaches are highlighted. 相似文献
976.
In this work, a new polymer resin with a functional groups capable of holding trace metals has been synthesized. The structure of polymer resin has been examined by BET-N2 method analyzer, IR spectrometer, scanning electron microscope (SEM) and elemental microanalyser. The synthesized polymer resin was used for the simultaneous separation and preconcentration of the trace metals from various tea and herbal plants samples. After extraction process, flame atomic absorption spectrometry (FAAS) was used to determine the trace metals. The analytical parameters and solid phase extraction (SPE) performance such as pH, sample volume, flow rates of sample, flow rates of eluent, concentration, volume and type of eluent and effect of interference ions, were investigated. The limits of detection (DL) of the SPE procedure for trace metals, were calculated to be (3s) in the range of 0.9?4.0 μg L?1 (n = 21) and the factors of preconcentration (PF) were obtained at 200 for Cd, Co, Cu, Fe, Ni and Zn, and at 50 for Cr, Mn and Pb ions and the relative standard deviation (RSD) at ≤ 2% (n = 11). 相似文献
977.
Photolysis of α-bromopropiophenones in acetonitrile results in formation of β-bromopropiophenones with good product selectivity, which can be coined as 1,2-Br shift reaction. The product selectivity increases when the reaction is done in neat or solid state, where only the 1,2-Br shift product is formed in some cases. The reaction is suggested to proceed by CBr bond homolysis to give a radical pair, followed by disproportionation and conjugate addition of HBr to the α,β-unsaturated ketone intermediate. When the unsaturated intermediate is stabilized by an extra conjugation, the reaction stops at the stage, in which the unsaturated ketone becomes a major product. The synthetic method described in this research fits in a category of eco-friendly organic synthesis nicely since the reaction does not use volatile organic solvents and any other additives such as acid, base or metal catalysts, etc. Besides, the method fits into perfect atom economy, which does not give any side products. The synthetic method should find much advantage over other alternative methods to obtain β-bromo carbonyl compounds. 相似文献
978.
Yingting Wang Jiangfeng Huang Xiaomeng Xia Xinhua Peng 《Journal of Saudi Chemical Society》2018,22(2):129-135
A highly efficient catalyst Fe–Co/sulfonated polystyrene (Fe–Co/SPS) was introduced and synthesized, which catalyzed BV oxidation of ketones with aqueous hydrogen peroxide to give the corresponding lactones in high yield and selectivity. Solid acid catalyst of Fe–Co/SPS has been prepared by using the 98-wt% sulfuric acid as the sulfonating agent and CoCl2 combined FeCl3 as sources of metal ions. Various physical–chemical characterizations including FT-IR, XRD, SEM and TGA, revealed that bimetallic ions Fe3+–Co2+ species in the sulfonated polystyrene framework were responsible for the catalytic activities. The BV reaction catalyzed by Fe–Co/SPS highlighted the special effects between metal ions and protonic acids as well as solvent-free heterogeneous catalytic oxidation with excellent conversion. 相似文献
979.
Convexity and the Average Curvature of Plane Curves 总被引:1,自引:0,他引:1
The average curvature of a rectifiable closed curve in R2 is its total absolute curvature divided by its length. If a rectifiable closed curve in R2 is contained in the interior of a convex set D then its average curvature is at least as large as the average curvature of the simple closed curve D which bounds the convex set. 相似文献
980.
Hyperbolic Geometry with Clifford Algebra 总被引:3,自引:0,他引:3
Hongbo Li 《Acta Appl Math》1997,48(3):317-358
The Clifford algebra in D. Hestenes formulation is used to study hyperbolic geometry and some interesting theorems are obtained. The computational power of this formulation is fully revealed by the ease of extending old results and discovering new ones. An important new result is the formulas on the area and perimeter of a convex polygon, based on extending Gauss equalities. 相似文献