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991.
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995.
<正>A novel caged-prenylxanthone xanthone,neobractatin(1),was isolated from the twig of Garcinia bracteata.Its structure was elucidated by spectroscopic methods,especially 2D NMR techniques. 相似文献
996.
Bin Du Adam Langlois Daniel Fortin Christine Stern Pierre D. Harvey 《Journal of Cluster Science》2012,23(3):737-751
The title cluster is luminescent at 77?K and exhibits an unsaturated site for binding anions when the counter ion is PF6 ?. A series of five non-luminescent metalloporphyrins exhibiting carboxylate anchoring groups were synthesized and characterized. These are the sodium salts of the 5-carboxyphenyl-tri-10,15,20-tolyl-, trans-di-5,10-carboxyphenyl-di-15,20-tolyl-, and tetra-5,10,15,20-carboxyphenyl(metallo)porphyrin (metallo?=?chloroiron(III), nickel(II)) anions. Evidence for supramolecular assemblies between the carboxylates and the cluster is provided by 31P NMR and UV?Cvis spectroscopy. The binding constant, K1n, extracted from the UV?Cvis data via Benesi-Hildebrand, Scott and Scatchard plots are approximately 21,000?±?5,000?M?1 for the nickel(II) species, in agreement with the previously reported zinc(II) ones (K11?=?20,000?±?2,000?M?1), but those for the chloroiron(III) are measured to be lower (12,500?±?3,500?M?1). This association is accompanied by a complete quenching of the luminescence of the cluster which can only be due to an efficient energy transfer to the d?Cd states of the chloroiron(III) and nickel(II) species but an electron transfer from the nickel(II)-containing chromophore to the cluster is also possible. This work demonstrates the profound effect that supramolecular interactions may have on the photophysical properties despite the long donor?Cacceptor separation. 相似文献
997.
Guowei Wang Bin Hu Xiaoshan Fan Yannan Zhang Junlian Huang 《Journal of polymer science. Part A, Polymer chemistry》2012,50(11):2227-2235
The tadpole‐shaped copolymers polystyrene (PS)‐b‐[cyclic poly(ethylene oxide) (PEO)] [PS‐b‐(c‐PEO)] contained linear tail chains of PS and cyclic head chains of PEO were synthesized by combination of Glaser coupling with living anionic polymerization (LAP) and ring‐opening polymerization (ROP). First, the functionalized polystyrene‐glycerol (PS‐Gly) with two active hydroxyl groups at ω end was synthesized by LAP of St and the subsequent capping with 1‐ethoxyethyl glycidyl ether and then deprotection of protected hydroxyl group in acid condition. Then, using PS‐Gly as macroinitiator, the ROP of EO was performed using diphenylmethylpotassium as cocatalyst for AB2 star‐shaped copolymers PS‐b‐(PEO‐OH)2, and the alkyne group was introduced onto PEO arm end for PS‐b‐(PEO‐Alkyne)2. Finally, the intramolecular cyclization was performed by Glaser coupling reaction in pyridine/Cu(I)Br/N,N,N′,N″,N″‐pentamethyldiethylenetriamine system under room temperature, and tadpole‐shaped PS‐b‐(c‐PEO) was formed. The target copolymers and their intermediates were well characterized by size‐exclusion chromatography, proton nuclear magnetic resonance spectroscopy, and fourier transform infrared spectroscopy in details. The thermal properties was also determined and compared to investigate the influence of architecture on properties. The results showed that tadpole‐shaped copolymers had lower Tm, Tc, and Xc than that of their precursors of AB2 star‐shaped copolymers. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012 相似文献
998.
999.
Let M
n
denote the partial maximum of a strictly stationary sequence (X
n
). Suppose that some of the random variables of (X
n
) can be observed and let [(M)\tilde]n\tilde M_n
stand for the maximum of observed random variables from the set {X
1, ..., X
n
}. In this paper, the almost sure limit theorems related to random vector ([(M)\tilde]n\tilde M_n
, M
n
) are considered in terms of i.i.d. case. The related results are also extended to weakly dependent stationary Gaussian sequence as its covariance function satisfies
some regular conditions. 相似文献
1000.
A Pd-catalyzed coupling reaction of ArBr/ArCl/ArOTf with sodium thiosulfate takes place in presence of Cs2CO3 at 80 °C. The reaction mixture is directly treated with Zn/HCl to afford aryl thiols in good to excellent yields. 相似文献