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971.
F. Diaz Camacho R. Le Lagadec Alexander D. Ryabov L. Alexandrova 《Journal of polymer science. Part A, Polymer chemistry》2008,46(12):4193-4204
The cyclometalated complex [RuII(o‐C6H4‐py)(MeCN)4]PF6 ( 1 ) with a σ‐Ru? C bond and four substitutionally labile acetonitrile ligands mediates radical polymerization of different vinyl monomers, viz. n‐butyl acrylate, methyl methacrylate, and styrene, initiated by three alkyl bromides: ethyl 2‐bromoisobutyrate, methyl 2‐bromopropionate, and 1‐phenylethyl bromide. The polymerization requires the presence of Al(OiPr)3 and occurs uncontrollably as a conventional radical process. The variation of the molar ratio of the components of the reaction mixture, such as initiator, Al(OiPr)3 and catalyst, affected the polymerization rates and the molecular weights but did not improve the control. A certain level of control has been achieved by adding 0.5 eq of SnCl2 as a reducing agent. Tin(II) chloride decreased the rate of polymerization and simultaneously the molecular weights became conversion‐dependent and the polydispersities were also narrowed. Remarkably, the level of control was radically improved in the presence of excess of the poorly soluble catalyst ( 1 ), when the added amount of ( 1 ) was not soluble any more, i.e., under heterogeneous conditions, the system became adjustable and the living polymerization of all three monomers was finally achieved. Possible mechanisms of the ( 1 )‐catalyzed polymerization are discussed. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 4193–4204, 2008 相似文献
972.
Laurent Divay Pierre Le Barny Brigitte Loiseaux Jacques A. Delaire 《Research on Chemical Intermediates》2008,34(2-3):127-136
Bimacrocyclic and monomacrocyclic erbium phtalocyanines have been synthesized and their luminescence spectra and lifetimes have been studied. The bi-planar structure of ErPc2 complexes, although interesting at first sight, is non-luminescent because of a strong absorption band near 1.5 μm. However, the luminescence of the erbium ion can be recovered after oxidation or reduction of the macrocycle. Monomacrocyclic erbium phtalocyanines exhibit a strong luminescence of erbium as a result of the energy transfer between the excited phtalocyanine macrocycle and the erbium ion. With a perchlorinated phtalocyanine and a perdeuterated axial ligand in a deuterated solvent, the luminescence lifetime reaches 5 μs, which is the maximum lifetime found for conventional perdeutarated ligands. The large absorption cross-section of phtalocyanine in the red may counterbalance the fast luminescence lifetime, allowing the hope for a new all-organic integrated optical amplifier device. 相似文献
973.
Blandine Destrez Gaud Pinel Emmanuelle Bichon Fabrice Monteau Ren Lafont Bruno Le Bizec 《Rapid communications in mass spectrometry : RCM》2008,22(24):4073-4080
Ecdysteroids, which are steroid hormones in invertebrates, but which are also present in plants, could potentially be used as anabolic agents in food‐producing animals. The control of ecdysteroid misuse in cattle relies on the development of an efficient method for their detection in biological matrices at trace levels (µg L−1). In order to propose an analytical procedure dedicated to the identification of excreted 20‐hydroxyecdysone (20E) in urine and faecal samples of breeding animals, a comparative study of the spectrometric behaviour of these compounds was carried out both by LC/(ESI‐)/HRMSn (hybrid linear ion trap – orbital trap) and by LC/(ESI+)/MS/MS (triple quadrupole). This study revealed the formation of a large number of product ions both in positive and negative ion mode, corresponding to losses of water molecules and specific cleavages on the side chain. The sample preparation consisted of sequential purification on two solid‐phase extraction cartridges (SPE octadecylsilyl and SPE silica). The detection limits were around 0.5 µg L−1 in the selected reaction monitoring (SRM) mode and recoveries above 60% were obtained. The method was successfully applied to the analysis of real samples collected from calves treated with 60 mg 20E over 4 days. Analysis of the samples allowed the investigation of the kinetics of elimination of 20E in calf urine and determination of the time‐frame for the control of potential abuse. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
974.
Zinc derivatives of propargylic ethers silylated on the acetylenic carbon atom react smoothly with 17-keto steroids, affording almost stereospecifically 22-silylated 17β-hydroxy 20-alcoxy ω-homo pregn 21-ynes. The reaction mechanism appears different from that followed with aldehydes.The silyl group can be easily removed in alkali. When the ether substituent is tetrahydropyranyloxy, acidic cleavage under moderate conditions leads to the corresponding 17,20-diol. 相似文献
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979.
Lieven Le Bruyn 《Israel Journal of Mathematics》1985,52(4):355-360
In this note we give a rational expression for the Poincaré series of Πm,2, the trace ring ofm generic 2×2 matrices. This result extends the computations of E. Formanek form⩽4. As a consequence, we prove that the Poincaré series satisfies the functional equation(IIm,2;1/t)=-t4m.P(IIm,2,t) (m>2) supporting the conjecture that Πm,2 is a Gorenstein ring.
Work supported by an NFWO/FNRS grant. 相似文献
980.