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Suzuki K Matsuo T Hashizume D Fueno H Tanaka K Tamao K 《Science (New York, N.Y.)》2011,331(6022):1306-1309
The cyclobutadiene (CBD) molecule C(4)H(4) deviates from a high-symmetry square geometry to compensate for its antiaromatic electronic structure. Here, we report a CBD silicon analog, Si(4)(EMind)(4) (1), stabilized by the bulky 1,1,7,7-tetraethyl-3,3,5,5-tetramethyl-s-hydrindacen-4-yl (EMind) groups, obtained as air- and moisture-sensitive orange crystals by the reduction of (EMind)SiBr(3) with three equivalents of lithium naphthalenide. X-ray crystallography reveals a planar and rhombic structure of the Si(4) four-membered ring, with alternating pyramidal and planar configurations at the silicon atoms. The large (29)Si chemical shift differences (Δδ > 350 parts per million) in the solid-state nuclear magnetic resonance spectra suggest a contribution of an alternately charge-separated structure. The rhombic-shaped charge-separated singlet state of compound 1 thus stabilizes its cyclic 4π-electron antiaromaticity in a manner that contrasts sharply with the bond-length alternation, characterizing the rectangular distortion of carbon-based CBD. 相似文献
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为探讨基于油水混溶剂的复方精油对空气中沉降菌的抑制作用,本研究测定了一种复方精油的抑菌效果、精油型抑菌制剂的抑菌效果和油水混溶剂对精油抑菌效果的影响。通过平板沉降法测定该复方精油的抑菌效果,并选取PEG-40氢化蓖麻油(PEG-40)、吐温80、二甲基亚砜(DMSO)、司盘85、双脱乙醇5种油水混溶剂,在复方精油和油水混溶剂比例分别介于1:1~1:6之间时配制精油抑菌制剂,并验证该均匀水溶液的抑菌效果,同时采用棋盘稀释法测定油水混溶剂对该复方精油抑菌效果的影响。结果表明:该复方精油的抑菌率达到80 %以上,精油抑菌制剂在平板暴露6 h的抑菌率最佳,为48.92 %。油水混溶剂中PEG-40的增溶效果最佳,复方精油浓度为1 %时,精油、PEG-40、双脱乙醇的最佳比例为1:2:2;浓度为3 %时,精油、PEG-40、双脱乙醇的最佳比例为1:3:3。PEG-40对空气中沉降菌无抑制效果,双脱乙醇和复方精油对空气中沉降菌的抑菌效果表现为相加作用。研究对植物精油应用于产业化生产时,油水混溶剂的种类和比例对精油类产品实际效果的影响有一定的参考价值。 相似文献
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Marder SR Gorman CB Meyers F Perry JW Bourhill G Brédas JL Pierce BM 《Science (New York, N.Y.)》1994,265(5172):632-635
An internal or external electric field F can drive the chemical structure, bond order alternation, and electronic structure of linear polymethine dyes from a neutral, bond-alternated, polyene-like structure, through a cyanine-like structure, and ultimately to a zwitterionic (charge-separated) bond-alternated structure. As the structure evolves under the influence of F, the linear polarizability alpha, the first hyperpolarizability beta, and the second hyperpolarizability gamma are seen to be derivatives, with respect to F, of their next lower order polarization (for alpha) or polarizability (for beta and gamma). These derivative relations provide a unified picture of the dependence of the polarizability and hyperpolarizabilities on the structure in linear polymethine dyes. In addition, they allow for predictions of structure-property relations of higher order hyperpolarizabilities. 相似文献
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【目的】蜂王浆是具有医疗保健功效的天然产品,含有丰富的小分子活性成分,目前蜂王浆代谢物的提取尚缺乏系统研究。通过蜂王浆代谢轮廓分析,比较不同溶剂对蜂王浆小分子化合物的提取效果,优化蜂王浆代谢物提取方法,鉴定蜂王浆中的代谢物。【方法】分别使用6种溶剂(50%和80%的甲醇、乙醇和乙腈)提取蜂王浆代谢物,运用反相液相色谱(reverse phase liquid chromatography,RPLC)和亲水相互作用色谱(hydrophilic interaction liquid chromatography,HILIC)分别联合四级杆-静电场轨道阱高分辨质谱技术(Q-exactive orbitrap HRMS)进行检测。比较不同溶剂组的代谢特征离子数量和相对标准偏差(relative standard deviation,RSD),并进行主成分分析(principal component analysis,PCA)。利用质谱数据库定性代谢物,并经标准品验证,比较其RSD差异,进行聚类热图(clustering heatmap)分析。通过正交偏最小二乘判别分析(orthogonal partial least squares-discriminant analysis,OPLS-DA)、单变量统计分析(student’s t-test)和倍数变化(fold change,FC)筛选溶剂组间具有显著差异的代谢物。【结果】强极性化合物,包括葡萄糖与果糖等同分异构体,在HILIC条件下分离良好,而脂类等中低极性化合物在RPLC条件下得到较好的分离。两种色谱分离方法的应用实现了对不同极性代谢物的检测,在蜂王浆中共鉴定到70种高丰度化合物,涵盖了糖、氨基酸、脂类、维生素等,其丰度差异高达8 340倍,其中有17种化合物为本研究首次报道。乙腈溶剂得到的代谢特征离子数量最少,80%乙腈比50%乙腈的提取效果更差;对甲醇和乙醇而言,高浓度时的代谢特征离子数量更多。所有溶剂组得到的RSD值集中分布在20%范围内,但80%乙腈组在10%内的占比最低,已鉴定的70种代谢物的RSD值进一步证明80%乙腈的重复性较差。PCA结果表明,来自同一提取溶剂的蜂王浆代谢谱高度相似,不同溶剂提取的样品间存在差异,其中,80%乙腈组与其他5组差异最大。聚类热图等分析结果表明,中低极性物质在50%溶剂组丰度较低,强极性物质特别是果糖、葡萄糖、蔗糖、赖氨酸、腺苷、胆碱、磷酸胆碱和葡萄糖酸在80%乙腈组丰度最低。【结论】RPLC和HILIC分别联合高分辨质谱技术能够较全面准确地检测蜂王浆中的小分子化合物,80%甲醇或80%乙醇是提取蜂王浆代谢物的最佳溶剂。 相似文献
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We have identified cobalt-base superalloys showing a high-temperature strength greater than those of conventional nickel-base superalloys. The cobalt-base alloys are strengthened by a ternary compound with the L1(2) structure, gamma' Co3(Al,W), which precipitates in the disordered gamma face-centered cubic cobalt matrix with high coherency and with high melting points. We also identified a ternary compound, gamma' Ir3(Al,W), with the L1(2) structure, which suggests that the Co-Ir-Al-W-base systems with gamma+gamma' (Co,Ir)3(Al,W) structures offer great promise as candidates for next-generation high-temperature materials. 相似文献
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大豆粕溶剂残留测定方法研究 总被引:1,自引:0,他引:1
[目的]建立大豆粕中溶剂残留的测定方法。[方法]讨论了新旧国标以及AOCS 2种方法对豆粕中六号溶剂残留测定结果的影响,分析了溶剂提取过程机理,寻找较合适的提取溶剂。[结果]N,N-二甲基甲酰胺(DMF)作为提取溶剂能够有效地提取豆粕中的六号溶剂,提取效率达到90%以上,同时气液平衡常数k3也较大,方法灵敏度高,重现性好。[结论]该研究在方法质控水平上获得了满意的结果,可为大豆粕中溶剂残留的测定提供参考。 相似文献
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麦胚黄酮类化合物提取方法的研究 总被引:7,自引:0,他引:7
采用水提法、加碱浸提法、醇提法分别从麦胚中提取黄酮类化合物,进行工艺方法比较,选出提取率高,工艺条件可行的最佳方法。实验结果表明,碱提法、水提法提取的黄酮类化合物得率低于醇提法,醇提法后续过滤、回收溶剂、浓缩等操作比水提法简单且不费时。因此,醇提法的提取效果最好。 相似文献
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From nitrogen-15 spin-lattice relaxation times and nuclear Overhauser enhancements, the rotational correlation time (c) for (15)NH(4)(+) was determined in a series of solvents. Values of (c) range from 0.46 to 20 picoseconds. The solvent dependence of (c) cannot be explained in terms of solvent polarity, molecular dipole moment, solvent basicity, solvent dielectric relaxation, or solvent viscosity. The rapid rotation and the variation with solvent can be accounted for by a model that involves hydrogen bonding of an NH proton to more than one solvent molecule in a disordered solvation environment. 相似文献
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《农业科学学报》2016,(3)
Deoxynivalenol(DON) is a type B trichothecenes mycotoxin produced by several Fusarium species, often found in foodstuffs for humans and animals. DON is in great demand for the toxicological researches both in vivo and in vitro. In this work, wheat culture was inoculated with a Fusarium graminearum PH-1 strain for DON production. The solvent system for crude extraction was acetonitrile-water(84:16, v/v). A simple two-step silica gel column chromatography was employed to separate the DON mycotoxin from wheat culture, combined with preparative high performance liquid chromatography(preparative HPLC) to purify the compound. The solvent system for the second silica gel column chromatography was methylene chloride-methanol(17:1, v/v), which provided a good elution effect selected on thin layer chromatography(TLC). The target compound was identified by HPLC, and the chemical structure was confirmed by mass spectrometry(MS) and ~1H and ~(13)C nuclear magnetic resonance(NMR) spectroscopy. A total of 433 mg of purified DON was obtained from 1 kg of wheat culture, with a purity of 99.01%. The study had provided an easy-operating and cost-effective method to isolate an expensive compound in a simple way. 相似文献
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我国水体蓝藻水华主要产生两种微囊藻毒素microcystin-LR(MCLR)和microcystin-RR(MCRR),针对蓝藻藻细胞内微囊藻毒素的提取和检测问题,提出微波和沸水浴取代传统溶剂萃取前处理的改善方法,采用标准品和实际样品分析了方法的可行性和提取效率.结果表明,沸水浴和微波(800W)处理10 min不会引起标准品的变异;以实验室培养的产毒铜绿微囊藻(Microcystis.aeruginosa)PCC7820为样品的提取实验表明,两种快速提取方法与传统的5%乙酸、70%甲醇萃取法提取效率的相对误差分别为4.6%(MCLR)和1.7%(MCRR).两种方法操作方便,并且可以有效地避免有机溶剂耗费和甲醇等有机溶剂残留对后续检测的干扰.应用该方法分析了天然水样,表明方法具有实用性. 相似文献
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在罂粟果实膨大期,对正茬、迎茬、连作2 a、连作4 a处理的叶片光合生理生态参数进行了测定,旨在研究连作对罂粟光合作用的影响。结果表明:罂粟正茬、迎茬、连作2 a处理的光合速率日变化呈双峰曲线,具有明显的"午休"现象;连作4 a处理的光合速率变化呈单峰曲线.正茬、迎茬和连作4 a处理的光合速率下降(午休)是由气孔因素引起的,而连作2 a处理的光合速率下降(午休)主要原因是由非气孔因素引起的.正茬处理的光合速率显著高于迎茬、连作2 a和连作4 a处理的光合速率,分别高出2.71、2.28、2.31μmol/(m2.s). 相似文献
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比较了微生物源的鬼臼毒素在氘代氯仿(CDCl3)和二甲亚砜(DMSO)2种溶剂中的核磁共振数据,结果表明:在溶剂DMSO中,核磁共振能提供更多可靠的信号;据解析,确定了在2种溶剂中所有13C NMR、1HNMR谱的信号归属。 相似文献
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玉米中黄曲霉毒素提取方法的评价 总被引:2,自引:0,他引:2
用多种溶剂与玉米的不同比例对玉米中黄曲霉毒素 B1 的提取效率进行评价。结果发现,用60 % 甲醇水溶液为提取剂,与样品比例为6 :1( ml/g) ;80 % 丙酮水溶液,与样品比例为5 :1 ,6 :1( ml/g) 及90 % 乙腈水溶液,与样品比例为4 :1( ml/g) 的提取效果较好。 相似文献
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[目的]研究伏毛铁棒锤(Aconitumflavum)对菜青虫(Pieris rapae)的毒杀和拒食活性。[方法]采用浸虫法测定伏毛铁棒锤乙醇粗提物和石油醚、乙醚、乙酸乙酯、正丁醇和水5种不同极性溶剂萃取物对菜青虫的触杀活性;采用叶蝶法测定石油醚、乙醚、正丁醇、乙酸乙酯、水的5种溶剂萃取物对菜青虫的拒食活性。[结果]伏毛铁棒锤粗提物对菜青虫具有较高的触杀活性,浓度为100.00 mg/ml时,48h的校正死亡率达97.24%,5种萃取物对菜青虫的触杀活性次序为水>正丁醇>乙酸乙酯>乙醚>石油醚,水萃取物48 h的校正死亡率达95.87%;5种溶剂萃取物拒食活性顺序为水>正丁醇>乙酸乙酯>乙醚>石油醚。[结论]伏毛铁棒锤提取物对菜青虫具有较强的触杀和拒食活性,且杀虫和拒食活性物质是一类极性较大的化合物。 相似文献