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981.
A kind of aziridine crosslinkers was synthesized and used to crosslink acrylate copolymers. The crosslinkingproperties and curing kinetics of the resin were studied. It was found that with the increase of the content of crosslinker in theemulsion, the mechanical properties and solvent resistance of the resin will be apparently improved, but its glass transitiontemperature (T_g) is very low. The lowest amount of crosslinker used in the acrylic resin emulsion is 0.25%. Curing kineticsstudied by DSC show that this curing reaction occurs readily because the apparent activation energy of the reaction is low(65.1 kJ/mol). These results demonstrate that the aziridine crosslinker is indeed a low temperature crosslinking agent and canbe used at room temperature. 相似文献
982.
The Pd-catalyzed annulation of arynes by 2-halobiaryls and related vinylic halides provides a very efficient, high yielding synthesis of polycyclic aromatic and heteroaromatic hydrocarbons. This process appears to involve the catalytic, stepwise coupling of two very reactive substrates, an aryne and an organopalladium species, to generate excellent yields of cross-coupled products. 相似文献
983.
As a natural diterpenoid, crotophorbolone possesses a challenging trans,trans-5/7/6 framework decorated with six contiguous stereogenic centers and is structurally and biogenetically related to tigliane-type diterpenoids with intriguing bioactivities such as phorbol and prostratin. Based on the convergent strategy, we completed an eighteen-step total synthesis of crotophorbolone starting from (−)-carvone and (+)-dimethyl-2,3-O-isopropylidene-l-tartrate. The key elements of the synthesis involve expedient installation of the six-membered ring and the five-membered ring with multiple functional groups at an early stage, cyclization of the seven-membered ring through alkenylation of the ketone between the five-membered ring and the six-membered ring, functional group-sensitive ring-closing metathesis and final selective introduction of hydroxyls at C20 and C4.Convergent total synthesis of crotophorbolone was accomplished in 18 longest linear steps. Observation of unexpected thermodynamic stability of a cis,trans-5/7/6 tricycle would benefit synthetic design of tigliane- and daphnane-related diterpenoids. 相似文献
984.
Liu Y Vinje J Pacifico C Natile G Sletten E 《Journal of the American Chemical Society》2002,124(43):12854-12862
The reactions of the anticancer complex trans-[PtCl2{(E)-HN=C(OMe)Me}2] (trans-EE) with a series of ribo and deoxyribodinucleotides have been studied by HPLC and 2D [1H, 15N] HMQC NMR spectroscopy and compared with those of the inactive trans isomer of cisplatin, trans-[PtCl2(NH3)2] (trans-DDP). Reactions of trans-EE with r(ApG) and d(ApG) take place through solvolysis of the starting substrate and subsequent formation of trans G-N7/monochloro and G-N7/monoaqua adducts. Slowly, the monofunctional adducts evolve to a bifunctional adduct forming an unprecedented and unexpected A-N3/G-N7 platinum cross-link spanning two trans positions. For stereochemical reasons, trans platinum complexes cannot form N7/N7 cross-links between adjacent purines in di- or polynucleotides. For the reverse sequence r(GpA), no chelate structure was formed even after a two-week reaction. The reaction of trans-DDP with r(ApG) produces many more products than the analogous reaction with trans-EE. One of these products was identified as the A-N3/G-N7 trans-chelate. 相似文献
985.
Z H Liu W S Tu D R Li Y D Li C H Xie Y Z Yang B B Qin 《Biomedical chromatography : BMC》1990,4(2):83-86
A high performance liquid chromatographic (HPLC) method for the analysis of aflatoxin M1 (AFM1) in urine is described. Urine samples were treated with saturated lead acetate and AFM1 was extracted with chloroform. After washing with water to remove impurities the compound was derivatized with trifluoroacetic acid and the AFM1 derivative was analyzed quantitatively by HPLC. The sample pretreatment is simple and more selective. A good line correlation between AFM1 peak height and its concentration was obtained when AFM1 content was in the range of 50-400 pg. The ratio of recovery was 87.42%. Sensitivity is 0.01 ppb. The method is applicable to trace analysis. Results in urine of residents who live in the high/low liver cancer incidence area in Fushui county were the same as that of previous epidemiological investigation. 相似文献
986.
南药巴戟天中十二种无机元素与药效关系的进一步研究 总被引:4,自引:0,他引:4
在初步研究的基础上,进一步研究了不同产地巴戟天的无机元素含量差异,通过对比各元素含量、相关系数及TE图谱,说明地道药材与非地道药材的巴戟天,其特征元素的含量存在非常明显的差异,要使大面积扩种的药材提高药效,建议根据当地土壤含Mn、Fe、Cr、Co、Ni的含量,以旋微量元素肥料的方法来补充这些元素在土壤中的不足。但在微量元素肥料配方中,应注意巴戟天吸收土壤中的元素时的协同作用和拮抗作用。 相似文献
987.
原子簇化合物的合成方法,由于条件限制,只有B、C、St等非金属元素与过渡金属袈基化合物等较为成熟.贵金属原子簇的合成则较困难.然而,应用激光等离子体反应,可使周期表内几乎所有元素都生成原子簇,为原子簇的生成与研究提供了一条新途径.该方法生成的原子簇在飞行时间质谱仪上可记录到一系列信号,某些信号呈现区域极大(或被称为‘匈数’吵].郑兰芬等用纯化的红磷粉分别与金粉、银粉混合,在激光等离子作源飞行时间质谱仪上得到一系列谱图【2]:ig与P作用只得到单核xg与P形成的lgy:iE离子簇.谱图较简单,*沪X最大可达叱叱… 相似文献
988.
Study on flame-retardant mechanism of polycarbonate containing sulfonate-silsesquioxane-fluoro retardants by TGA and FTIR 总被引:1,自引:0,他引:1
Shumei Liu Yongsheng Zhou Zhijie Jiang Xianbo Huang 《Polymer Degradation and Stability》2006,91(8):1808-1814
The flame retardancy of bisphenol A polycarbonate (PC) containing potassium diphenylsulfone sulfonate (KSS), poly(aminopropyl/phenylsilsesquioxane) (PAPSQ) and poly(vinylidenefluoride) (PVDF) was measured by limited oxygen index (LOI) and examined according to UL94. A high LOI and UL94 V-0 rating for 1.6 mm thickness samples were obtained by a combined use of equivalent KSS, PAPSQ and PVDF at 0.1-0.3 wt% loading, respectively. The improvement in flame retardancy of PC compositions arose from the synergistic interaction of three additives. Thermogravimetric analysis (TGA) indicated that the combination decreased the activation energy (E) of PC degradation and elevated the thermal degradation rate of PC to ensure the formation of an insulating carbon layer. FTIR analysis showed that the LOI char of PC containing the three additives took on a highly cross-linking aromatic ester and ether structure. 相似文献
989.
The solvent composition induced reentrant behavior of poly(N-isopropylacrylamide) (PNIPAM) chains grafted on a SiO2 surface in water-methanol mixtures was investigated using a quartz crystal microbalance with dissipation monitoring (QCM-D) at 20 degrees C. The frequency and energy dissipation responses showed that the grafted PNIPAM chains sharply collapse when the methanol content (x(m)) reaches approximately 17 mol %. In the range 17-50 mol %, the grafted chains remain in a collapsed state. Further increase of the methanol content leads to an abrupt reswelling of the collapsed chains at x(m) > approximately 50 mol %. The sharp reentrant swelling-to-collapse-to-swelling transition was attributed to the water-methanol complexation instead of the preferential adsorption effect. Our results also suggest that the water-methanol complexation is not induced by hydrophobic interaction but by hydrogen bonding. 相似文献
990.
A capillary electrophoresis (CE) method was developed for the separation of heparin oligosaccharides compatible to study the interactions between the oligosaccharides and granulocyte-colony stimulating factor (G-CSF). Unfractionated heparin was eliminitively degraded to heparin oligosaccharides by an endolytic heparinase. The degraded smaller oligosaccharides (M(r) < 1000) were baseline-separated by CE under a 50 mM phosphate buffer (pH 9.0) in 10 min. Standard heparin disaccharides and larger oligosaccharides (1000 < M(r) < 8000) were all separated under optimized separation conditions. Compared with standard heparin disaccharides, smaller oligosaccharides contained one nonsulfated, two monosulfated, and two disulfated disaccharides, but trisulfated disaccharides were not found. The smaller oligosaccharides were also identified and molecular mass was deduced by electrospray ionization-mass spectrometry (ESI-MS). Furthermore, interactions between G-CSF and the oligosaccharides were studied by using capillary zone electrophoresis (CZE) under the above separation conditions. It was found that larger oligosaccharides could interact with G-CSF while smaller oligosaccharides were not observed to bind to G-CSF under the experimental conditions. In conclusion, the purified heparinase could selectively degrade heparin into oligosaccharides and the interaction between G-CSF and heparin was correlated with the chain length of heparin. 相似文献