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排序方式: 共有319条查询结果,搜索用时 15 毫秒
281.
Salo Gronowitz Anna-Britta Hrnfeldt Ecaterina Temciuc 《Journal of heterocyclic chemistry》1993,30(2):533-535
The 3-position of dithieno[3,4-b:3′,2′-d]pyridine was found to be most reactive with regard to lithiation, bromination and halogen-metal exchange. The lithium compounds were trapped as the formyl derivatives by reaction with N,N-dimethylformamide. 相似文献
282.
Dan Peters Anna-Britta Hrnfeldt Salo Gronowitz Nils Gunnar Johansson 《Journal of heterocyclic chemistry》1991,28(2):529-531
The Pd(0)-catalyzed coupling reaction of β-5-iodo-2′-deoxy-3′,5′-di-O-acetyluridine with various heteroaryltrimethylstannyl compounds gave the corresponding β-5-heteroaryl-2′-deoxy-3′,5′-di-O-acetyluridines in moderate yields. This direct coupling approach for nucleosides represented an interesting alternative to the 5-heteroaryl functionalization of pyrimidines followed by the Hilbert-Johnson glycosylation reaction which often yields mixtures of the α and β anomers. 相似文献
283.
Ulf Wellmar Anna-Britta Hörnfeldt Salo Gronowitz Nils Gunnar Johansson 《Chemistry of Heterocyclic Compounds》1996,32(11-12):1312-1318
A series pf 5-aryl-2′-deoxyuridines has been prepared and evaluated as antiviral agents. The following substituents have been used in position 3 of the phenyl ring: chloro, iodo, amino, azido, methylthio, and vinyl. None of the new compounds showed any significant activity when tested against human immunodeficiency virus 1 (HI V-I), herpes simplex virus 1 (HSV-I), or human cytomegalovirus (HCMV). 相似文献
284.
Bromination of dithieno[3,4-b:3′,4′-d]pyridine ( 1 ) and dithieno[2,3-b:3′,2′-d]pyridine ( 2 ) has been studied. Disubstitution occurred at both positions of the C ring. The substitution pattern is found to be similar to that of the nitration reaction. The structures of bromo derivatives were established by 1H and 13C nmr spectroscopy. 相似文献
285.
Mikko Karesoja Harri Jokinen Erno Karjalainen Petri Pulkkinen Mika Torkkeli Antti Soininen Janne Ruokolainen Heikki Tenhu 《Journal of polymer science. Part A, Polymer chemistry》2009,47(12):3086-3097
11‐(2‐Bromo‐2‐methyl)propionyl‐oxy‐undecyl trichlorosilane atom transfer radical polymerization (ATRP) initiator was covalently attached on montmorillonite clay platelets via silylation reactions. The initiator clay was used to polymerize butyl acrylate (BuA) and methyl methacrylate (MMA) on the clay surface. Polymerization was performed in bulk monomer solution or in DMSO. Polymer modified clay was mixed with a poly(BuA‐co‐MMA) matrix. Small angle X‐ray scattering (SAXS) and transmission electron microscopy (TEM) showed that clay modified in DMSO gave exfoliated composites when mixed with the matrix copolymer. Mechanical properties of the composites were studied by dynamic mechanical thermal analysis (DMTA). The results showed that the mechanical properties were improved as a function of clay content, as well with an increasing homogeneity of the nanocomposite. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 3086–3097, 2009 相似文献
286.
Cellulose nanofibrils—adsorption with poly(amideamine) epichlorohydrin studied by QCM-D and application as a paper strength additive 总被引:1,自引:0,他引:1
In this paper cellulose nanofibrils were used together with a cationic polylelectrolyte, poly(amideamine) epichlorohydrin
(PAE), to enhance the wet and the dry strength of paper. The adsorption of nanofibrils and PAE on cellulose model surfaces
was studied using quartz crystal microbalance with dissipation (QCM-D) and atomic force microscopy (AFM). The differences
in fibril and polyelectrolyte adding strategies onto cellulose fibres were studied by comparing layer-structures and nano-aggregates
formed by the nanofibrils and PAE. The results showed that when PAE was first adsorbed on the model fibre surface a uniform
and viscous layer of nanofibrils could be adsorbed. When PAE and nanofibrils were adsorbed as cationic aggregates a non-uniform
and more rigid layer was adsorbed. Paper sheets were prepared using both the bi-layer and nano-aggregate adding strategy of
the nanofibrils and PAE. When PAE and nanofibrils were adsorbed on pulp fibres as a bi-layer system significant increase in
both wet and dry tensile strength of paper could be achieved even at low added amounts of PAE. When the substances were added
as nano-aggregates the improvements in paper strength properties were not as significant. Bulk and surface nitrogen content
analyses of the paper samples showed that the adding strategy does not affect the total adsorbed amount of PAE but it has
a strong effect on distribution of substances in the paper matrix which has a crucial effect on paper wet and dry strength
development. 相似文献
287.
Virve A. Karttunen Tapani A. Pakkanen John R. Severn Janne Maaranen Anneli Pakkanen 《Journal of organometallic chemistry》2008,693(26):3915-3922
Ligand effects on chain termination reactions in hafnocene-catalyzed ethene polymerization process have been systematically studied by quantum chemical methods. β-hydrogen transfer to metal, β-hydrogen transfer to monomer and hydrogenolysis were studied for 27 hafnocenes, initiating the chain termination reactions after insertion of the second ethene monomer. The results of the calculations were studied as a function of the ligand structure, focusing on the effects of various ancillary ligands, ligand substituents and bridging units. The ligand effects on chain termination reactions are strongly affected by combined effects of various structural units, in particular, in the cases of β-hydrogen transfer to monomer and hydrogenolysis. The results are expected to aid in design and development of new hafnocene polymerization catalysts. 相似文献
288.
Patricia Alves Jean-Pierre Kaiser Janne Haack Natalie Salk Arie Bruinink Hermínio C. de Sousa Maria Helena Gil 《Colloid and polymer science》2009,287(12):1469-1474
Recently, the definition of coating procedures which leads to strong cell repellent surfaces has been an extremely important issue. In the present study, the cell repellency of thermoplastic polyurethane material (Elastollan®1180A50) surfaces was achieved by chemical treatment. Samples of Elastollan®1180A50 processed by injection molding, were oxidized with hydrogen peroxide (H2O2) and then impregnated with poly(ethylene glycol). The oxidation time was evaluated as were the effects of the PEG impregnation. Of all the evaluated modifications, a surface oxidation for 2 h, followed by impregnation with poly(ethylene glycol) resulted in the best cell repellent surface. 相似文献
289.
Mitsuhiro Hashimoto Kenji Miura Hiroaki Muraoka Hajime Aoi Roger Wood Michael Salo Yoshihiro Ikeda 《Journal of magnetism and magnetic materials》2008
The read/write characteristics of non-patterned media (NPM), discrete track media (DTM), and bit patterned media (BPM) are examined by modeling the magnetization distribution of NPM and patterning fluctuation of DTM. By comparing spin-stand measurement with calculation, the magnetization distribution of NPM was well characterized with a new Voronoi cell magnetic cluster model, in which the cluster size at the track edge, 〈Dedge〉, was larger than that at the track center, 〈Dcenter〉 by a factor of two. Based on an analysis of patterning fluctuations seen in SEM images of DTM, line-edge roughness (LER) was modeled as a long-wavelength center-line roughness (CLR) plus a short-wavelength line-width roughness (LWR). It was confirmed that the standard deviation of the patterning fluctuation was much smaller than that of the magnetic fluctuation for NPM. This allowed DTM to achieve higher off-track performance than NPM. By examining the 747 curves, it was revealed that DTM could have an advantage in track-density of up to approximately 25% assuming patterning fluctuations can be well controlled at high track density. In BPM, fabricating accurate dots is essential. The relationship between dot defect rate and patterning fluctuation was examined, and the maximum allowable standard deviation of LER was derived as 2 nm for achieving 1 Tbspi. 相似文献
290.
Rondón M Morales A Amaro-Luis JM Bahsas A Rojas J Buitrago D 《Natural product research》2005,19(6):597-602
A new lathyrane-type diterpene 8alpha,15beta-diacetoxy-7beta-benzoyloxy-3beta-(2-methylpropanoyloxy)-4alphaH,9alphaH, 11alphaH-lathyra-5E,12E-dien-14-one (latazienone) has been isolated from the latex of Euphorbia latazi Kunth. The structure of the new diterpene was determined by a combination of ID- and 2D-NMR techniques. 相似文献