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991.
Li C Lee D Graf TN Phifer SS Nakanishi Y Burgess JP Riswan S Setyowati FM Saribi AM Soejarto DD Farnsworth NR Falkinham JO Kroll DJ Kinghorn AD Wani MC Oberlies NH 《Organic letters》2005,7(25):5709-5712
[chemical reaction: see text]. Three new ent-trachylobane diterpenoids (1-3) were isolated and structures elucidated from Mitrephora glabra Scheff. (Annonaceae). Mitrephorone A (1) possesses a hexacyclic ring system with adjacent ketone moieties and an oxetane ring, both of which are unprecedented among trachylobanes. All compounds were evaluated for cytotoxicity against a panel of cancer cells, where 1 displayed the most potent and broadest activity, and against a battery of antimicrobial assays, where all compounds were approximately equipotent. 相似文献
992.
Xiong JY Narayanan J Liu XY Chong TK Chen SB Chung TS 《The journal of physical chemistry. B》2005,109(12):5638-5643
Kinetics as well as the evolution of the agarose gel topology is discussed, and the agarose gelation mechanism is identified. Aqueous high melting (HM) agarose solution (0.5% w/v) is used as the model system. It is found that the gelation process can be clearly divided into three stages: induction stage, gelation stage, and pseudoequilibrium stage. The induction stage of the gelation mechanism is identified using an advanced rheological expansion system (ARES, Rheometric Scientific). When a quench rate as large as 30 deg C/min is applied, gelation seems to occur through a nucleation and growth mechanism with a well-defined induction time (time required for the formation of the critical nuclei which enable further growth). The relationship between the induction time and the driving force which is determined by the final setting temperature follows the 3D nucleation model. A schematic representation of the three stages of the gelation mechanism is given based on turbidity and rheological measurements. Aggregation of agarose chains is promoted in the polymer-rich phase and this effect is evident from the increasing mass/length ratio of the fiber bundles upon gelation. Continuously increasing pore size during gelation may be attributed to the coagulation of the local polymer-rich phase in order to achieve the global minimum of the free energy of the gelling system. The gel pore size determined using turbidity measurements has been verified by electrophoretic mobility measurements. 相似文献
993.
Suyun Jie Tianzhu Zhang Jiutong Chen Dongbing Liu Wei Chen 《Journal of organometallic chemistry》2005,690(7):1739-1749
A series of bridged bis(pyridinylimino) ligands were efficiently synthesized through the condensation reaction of 4,4′-methylene-bis(2,6-disubstituted aniline) with 2-pyridinecarboxaldehyde or 2-benzoylpyridine. They reacted with (DME)NiBr2 to form dinuclear Ni(II) complexes. All resultant compounds were characterized by elemental analysis, IR spectra as well as the single-crystal X-ray diffraction to confirm the structures of ligands and complexes. Activated with methylaluminoxane (MAO), these nickel complexes showed considerably good activities for ethylene oligomerization and polymerization. Their catalytic activities and the properties of PEs obtained were depended on the arched environment of ligand and reaction conditions. 相似文献
994.
ADSORPTION OF 2,4-DICHLOROBENZOXYACETIC ACID ONTO HYPERCROSSLINKED RESIN MODIFIED BY PHENOLIC HYDROXYL GROUP (AM-1) 总被引:2,自引:0,他引:2
INTRODUCTIONAdsorption has been considered to be the best available technology for removing organics from water in the USSafe Drinking Water Act[1]. Due to many drawbacks of activated carbon[2-7], the most widely used adsorbent,hypercrosslinked polymeric adsorbents developed by Tsyurupa and Davankov[8] have been increasingly viewedas an alternative to activated carbon for selective removal of specific organic substances from contaminatedwater[9-12], and series of researches have been do… 相似文献
995.
0IntroductionConstructionoflow鄄dimensionalorganic鄄inorgan鄄icsupramoleculararrayswithnovelpropertiesrepre鄄sentsnewdirectionsinsolid鄄statechemistry[1,2].Gener鄄allythephysicalpropertiesofsuchlowdimensionalcompoundsdifferfromthoseoftheparentcompound.Our 相似文献
996.
The room temperature ionic liquid n‐butylpyridinium tetrafluoroborate (BPyBF4) is used as a ‘green’ recyclable alternative to classical molecular solvents for the cyclocondensation of α‐tosyloxyketones with 1‐aminoisoquinoline to prepare imidazo[2,1‐a]isoquinolines in good yields. 相似文献
997.
用等离子体增强化学气相沉积(PECVD)的方法,以固定的氢气(H2)流量和不同的硅烷(SiH4)和甲烷(CH4)流量比沉积了一系列的氢化非晶SiC(a-Si,C1-x-H)膜。用这种宽带隙的a-SixC1-x-H材料作为掺铒的基体材料,通过离子注入的方法得到掺铒的a-SixC1-x-H(a-SixC1-x-H:Er)膜。注入以后的样品经过不同温度的退火。用X射线光电子能谱(XPS)、红外吸收光谱(IR)、拉曼散射谱(Raman)等技术研究不同的SiH4/CH4流量比和退火温度对a-SixC1-x-H:Er发光强度的影响。结果表明,高温退火引起了膜中C的分凝,对饵的发光是不利的。通过低温和室温下铒发光强度的比较,表明这种材料具有较弱的温度猝灭效应。 相似文献
998.
Junfeng Zhou Xiaochen Dong Tao Chen Qiang Yang Qiaohua Tan Jianjun Wang 《European Polymer Journal》2007,43(5):2088-2095
A series of well-defined two-armed polymers containing a crown ether core, poly(stearyl methacrylate)-crown ether-poly(stearyl methacrylate) (PSMA-crown-PSMA), with different molecular weight were synthesized via atom transfer radical polymerization (ATRP). The resultant polymers were characterized by 1H NMR and GPC. The self-assembly behaviors of this kind of polymer in selective solvents were studied by TEM, and it was found that polymers with different molecular weight can directly self-assemble into hollow spheres, solid spheres and a monolayer film with regular pores by varying molecular weight and water content. The possible molecular packing motels for their self-assembly behaviors were proposed. 相似文献
999.
High density (98% of theoretical) was achieved at 900°C for an all-alkoxide derived bulk celsian gel prior to crystallisation. TEM indicated that crystallisation was dominated by volume nucleation and growth of hexagonal disc shaped hexacelsian. Kinetic studies using SEM indicate a maximum nucleation rate at 980°C and an activation energy for crystal growth of 566 KJ/mol. The high rates of densification and of nucleation are attributed to the high OH content in the gel-derived glass. 相似文献
1000.
PVDF/PAN共混超滤膜 总被引:11,自引:0,他引:11
PVDF/PAN共混超滤膜尹秀丽*宋艳秋(天津纺织工学院材料科学系天津300160)关键词聚偏氟乙烯,聚丙烯腈,共混,超滤膜1996-11-20收稿,1997-05-07修回共混是改变高分子材料性能的重要手段,已发现用聚合物共混的方法能制得性能优异的... 相似文献