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排序方式: 共有463条查询结果,搜索用时 31 毫秒
31.
Anshu Dandia Shyam L. Gupta Aayushi Indora Pratibha Saini Vijay Parewa Kuldeep S. Rathore 《Tetrahedron letters》2017,58(12):1170-1175
We have synthesized and characterized Ag NPs decked GO composite and studied its role as reusable catalyst for the ‘ON WATER’ chemoselective synthesis of pyranodipyrazolones via the reaction of different carbonyl compounds with 3-methyl-1-phenyl-1H-pyrazol-5(4H)-one. This method illustrates significant selectivity for pyranodipyrazolones over arylmethylene bispyrazolols and arylmethylenepyrazolones. Synergistic effect of heterogenic nature of water with reactants and Ag NPs/GO had profuse outcome on reaction as indicated by high TOF (18.03 × 10?5 mol g?1 min?1). Furthermore, catalyst was recycled for 7-times without significant loss of activity. 相似文献
32.
Sangeeta Ray Banerjee Jon Zubieta 《Acta Crystallographica. Section C, Structural Chemistry》2004,60(5):m208-m209
The title compound, methylene bis[bis(N,N‐diethylamino)carbeniumdithiocarboxylate] pentachlorooxorhenium, (C21H42N4S4)[ReCl5O], is the result of an unusual dimerization of the ligand bis(N,N‐diethylamino)carbeniumdithiocarboxylate [(Et2N)2C2S2] upon reaction with [ReOCl3(PPh3)2] in chloroform under reflux conditions. The compound was obtained as a dicationic moiety, with the molecular [ReOCl5]2− anion providing the charge compensation. The planes of the carbenium and thiocarboxylate moieties are nearly perpendicular to one another and the backbone C—C bond length in the N2CCS2 group is the same as a normal C—C single‐bond length. 相似文献
33.
Hsu KF Chung DY Lal S Mrotzek A Kyratsi T Hogan T Kanatzidis MG 《Journal of the American Chemical Society》2002,124(11):2410-2411
The new materials CsPbBi(3)Te(6) and CsPb(2)Bi(3)Te(7) were discovered through reactions of CsBi(4)Te(6) with PbTe, whereas the isostructural materials CsSnBi(3)Te(6) and CsSn(2)Bi(3)Te(7) were discovered through corresponding reactions with SnTe. The compounds can also be prepared from stoichiometric mixtures of Cs(2)Te, Pb (Sn), Bi, and Te. The crystal structures show a layered architecture of NaCl-type slabs alternating with layers of Cs atoms. This group of compounds offers a new quaternary system, Cs-M-Bi-Te (M = Pb and Sn), available for thermoelectric investigations, including fine-tuning of compositions and doping. 相似文献
34.
Food authentication has been evolving continually to situations that were basically governed by a global market trend. Analytical techniques have been developed or modified to give plausible solutions to the devious adulterations at each moment. Classical tests have largely been replaced with newer technical procedures, most of which are based on gas chromatography, with some being based on high-performance liquid chromatography. Determination of trans-fatty acid and sterolic composition, together with sterol-dehydration products, have been used most frequently used to detect contamination and adulteration. Sophisticated new adulterations, e.g., olive oil with hazelnut oil, represent a new challenge for the next millennium, although suggestive proposals for detecting these kinds of adulterations are emerging with the contribution of databases and mathematical algorithms. 相似文献
35.
Embryogenic tissues of Dioscorea bulbifera were cryopreserved using the encapsulation-dehydration technique. Genetic stability of plants regenerated from cryopreserved embryogenic tissues was assessed using molecular, biochemical and morphological analysis. The random amplified polymorphic DNA (RAPD) analysis of 60 cryopreserved-derived and 20 in vitro grown (control) plantlets showed that 10 primers produced 62 clear reproducible DNA fragment profiles. The amplification products were monomorphic for all the plantlets except one. A total of 4960 DNA fragments were obtained from this study showing no variation in RAPD profiles. The diosgenin content of cryopreserved-derived plants, analyzed using HPLC, was similar to that of control plants. Morphology and the ability to form microtuber were also found to be unaltered in cryopreserved embryo-derived plantlets. Thus, the D. bulbifera plants regenerated from cryopreserved embryogenic tissues were genetically stable at the molecular, biochemical and morphological levels. 相似文献
36.
Observations of high-redshift supernovae indicate that the Universe is accelerating. Here we present a model-independent method for estimating the form of the potential V(phi) of the scalar field driving this acceleration, and the associated equation of state w(phi). Our method is based on a versatile analytical form for the luminosity distance D(L), optimized to fit observed distances to distant supernovae and differentiated to yield V(straight phi) and w(straight phi). Our results favor w(phi) approximately -1 at the present epoch, steadily increasing with redshift. A cosmological constant is consistent with our results. 相似文献
37.
N.L. Saini A. Lanzara A. Bianconi H. Oyanagi 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,18(2):257-261
Instantaneous in-plane Cu-O bond distribution in the Bi2Sr2CaCu2O8+β (Bi2212) superconductor has been investigated by high k-resolution Cu K-edge extended X-ray absorption fine structure (EXAFS) measured with polarized vector parallel to the two
orthogonal Cu-O-Cu bonds of the CuO2 square plane. The results show an anisotropic Cu-O distribution in the two directions and provide further information on
the local atomic displacements in the lattice-charge stripes.
Received 5 June 2000 相似文献
38.
39.
Krishna C. Joshi Anshu Dandia Sangeeta Sanan 《Journal of heterocyclic chemistry》1989,26(5):1397-1400
The reaction of 3-(2-oxocycloalkylidene)indol-2-one 1 with thiourea and urea derivatives has been investigated. Reaction of 1 with thiourea and urea in ethanolic potassium hydroxide media leads to the formation of spiro-2-indolinones 2a-f in 40–50% yield and a novel tetracyclic ring system 4,5-cycloalkyl-1,3-diazepino-[4,5-b]indole-2-thione/one 3a-f in 30–35% yield. 3-(2-Oxocyclopentylidene)indol-2-one afforded 5′,6′-cyclopenta-2′-thioxo/ oxospiro[3H-indole-3,4′(3′H)pyrimidin]-2(1H)-ones 2a,b and 3-(2-oxocyclohexylidene)indol-2-one gave 2′,4′a,5′,6′,7′,8′- hexahydro-2′-thioxo/oxospiro[3H-indole-3,4′ (3′H)-quinazolin]-2(1H)-ones 2c-f . Under exactly similar conditions, reaction of 1 with fluorinated phenylthiourea/cyclohexylthiourea/phenylurea gave exclusively spiro products 2g-1 in 60–75% yield. The products have been characterized by elemental analyses, ir pmr. 19F nmr and mass spectral studies. 相似文献
40.
Hui H. Chin Leonid V. Azroff Agya R. Saini Robert W. Lenz 《Journal of Polymer Science.Polymer Physics》1989,27(10):2001-2009
Semiflexible thermotropic aromatic polyesters with lateral groups were aligned magnetically and mechanically in monodomains after separation into high-molecular-weight (polymer) and low-molecular-weight (oligomer) fractions. Based on the x-ray intensity distributions recorded for a series of seven different substituents in the arylsulfonyl substituted group, a novel smectic structure was determined for H, F, Cl, OCH3, and CH3 in the para position while a normal nematic alignment prevailed when it contained Br or NO2. 相似文献