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11.
Rutger J. I. Knoop Gijs J. M. Habraken Nicolas Gogibus Simone Steig Henning Menzel Cor E. Koning Andreas Heise 《Journal of polymer science. Part A, Polymer chemistry》2008,46(9):3068-3077
We have developed a metal free synthetic pathway to homopolypeptide rod‐coil block copolymers. The concept was proven for the synthesis of poly(benzyl‐L ‐glutamate‐b‐styrene). A dual initiator containing a primary amine and a nitroxide group was used in a macroinitiation approach with high initiation efficiency. Good control over the molecular weight in the ring opening polymerization of benzyl‐L ‐glutamate N‐carboxyanhydride was obtained in DMF at 0 °C yielding poly(benzyl‐L ‐glutamates) with low polydispersities around 1.1. The almost quantitative incorporation of the dual initiator was confirmed by MALDI‐ToF analysis. Macroinitiation of styrene by nitroxide‐mediated controlled radical polymerization yielded the block copolymer with high structural control. The diblock structure was confirmed by molecular weight increase upon macroinitiation by size exclusion chromatography and retention time comparison with homopolymers using gradient polymer elution chromatography. Both polymerizations were also successfully conducted in one pot without intermediate isolation owing to the high compatibility of both polymerization techniques. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 3068–3077, 2008 相似文献
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Kilian Muñiz Prof. Dr. Claas H. Hövelmann Esther Campos‐Gómez José Barluenga Prof. Dr. José M. González Prof. Dr. Jan Streuff Martin Nieger Dr. 《化学:亚洲杂志》2008,3(4):776-788
The oxidative intramolecular diamination of alkenes with tethered ureas and related groups as the nitrogen source has been investigated both with the iodonium reagent IPy2BF4 (Py=pyridine) and under palladium catalysis in the presence of copper(II) bromide as a reoxidant. For terminal alkenes, the two procedures enable selective and high‐yielding transformations. Studies with deuterated material led to the conclusion that the reactions proceed through different stereochemical pathways. An advanced protocol for palladium‐catalyzed diamination through six‐membered‐ring annulation was also developed, and the first examples of the intramolecular diamination of internal alkenes are described. In this case, the same stereochemical outcome was observed for the iodonium‐promoted and palladium‐catalyzed transformations. On this basis, it was possible to determine the importance of aminohalogenated intermediates in both diamination reactions. Overall, the disclosed procedures broaden significantly the synthetic applicability of the oxidative intramolecular diamination of alkenes. 相似文献
14.
Hövelmann CH Streuff J Brelot L Muñiz K 《Chemical communications (Cambridge, England)》2008,(20):2334-2336
Palladium catalysed intramolecular guanidine transfer to alkenes can be accomplished with copper chloride as the oxidant to give bicyclic guanidines with complete selectivity and in high yields. 相似文献
15.
Claas P Droppelmann G Schulz CP Mudrich M Stienkemeier F 《The journal of physical chemistry. A》2007,111(31):7537-7541
The dynamics of vibrational wave packets excited in Na2 dimers in the triplet ground and excited states is investigated by means of helium nanodroplet isolation (HENDI) combined with femtosecond pump-probe spectroscopy. Different pathways in the employed resonant multiphoton ionization scheme are identified. Within the precision of the method, the wave packet dynamics appears to be unperturbed by the helium droplet environment. 相似文献
16.
New ONS Ligands and their Zinc Complexes with Relation to the Zinc Enzyme Alcoholdehydrogenase By ring opening of dimethyl thiirane with ethanolamine or by Schiff base condensation between salicylic aldehydes and 2‐mercaptoisobutylamine the tridentate ONS ligands H2MIEA, H2MIIMP, and H2MIIMTP were obtained. The former yielded the zinc complex (MIEA)Zn(ethanolamine) ( 1 ) with a trigonal bipyramidal ZnO2N2S coordination. The latter two and Zn[N(SiMe3)2]2 yielded the presumably dimeric complexes Zn(MIIMP) and Zn(MIIMTP) ( 2 a , b ). Benzoyl pyridine and phenylhydroxymethylpyridine as bidentate coligands L could be combined with H2MIIMP in the complexes L · Zn(MIIMP) ( 3 , 4 ) whose ZnO2N2S coordination corresponds to that of 1 . Partial hydrolytic degradation led to the unusual trinuclear complex 5 which contains, inter alia, the condensation product of the salicylic aldimine and benzoyl pyridine as a ligand. The complexes obtained and the coordination patterns observed represent new structural analogies with the environment of zinc in the enzyme horse liver alcoholdehydrogenase. 相似文献
17.
射频囚禁离子被广泛应用于量子信息和冷分子制备. 对于从单个离子到10^6个离子不等的样品,这些原子的内能和外能可以被控制到非常高的精度. 重点讨论了利用射频囚禁的Ca+来作为频率计量的标准方法. 相似文献
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19.
Claas Becker 《Journal of Geometry and Physics》1993,11(1-4):529-543
Wilson loops exp (i A (x) dx) are investigated in two-dimensional Euclidean space-time. The electromagnetic vector potential A is regarded as a generalized random field given by the stochastic partial differential equation A = F where is a first-order differential operator and F is white noise. We give a rigorous definition of Wilson loops and examine the properties of the N-loop Schwinger functions. 相似文献
20.
Tobias Schulte Christoph Alexander Knoop Armido Studer 《Journal of polymer science. Part A, Polymer chemistry》2004,42(13):3342-3351
The effect of the variation of the alkoxyamine concentration on the conversion and polydispersity of the nitroxide‐mediated living free‐radical polymerization of styrene is discussed. Four different alkoxyamines ( 1 – 4 ) have been used for these studies. For an alkoxyamine with a small equilibrium rate constant (K), such as styryl–TEMPO 2 , the conversion is governed by the autopolymerization of styrene. For efficient alkoxyamines 1 , 3 , and 4 , the conversion at high alkoxyamine concentrations is higher than the conversion obtained by autopolymerization. At high alkoxyamine concentrations, the conversions vary to a small extent for all the alkoxyamines studied. As long as the conversion remains high, the polydispersity index is small. In addition, simulations of polymerizations with a program for modeling nonlinear dynamics are discussed. Polymerizations with efficient alkoxyamines at high alkoxyamine concentrations are well described by the kinetic scheme applied. K for alkoxyamines 1 and 4 has been estimated with the simulations. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 3342–3351, 2004 相似文献