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921.
922.
Aminohalogenation reaction of β-nitrostyrenes with N-halosuccinimides(N-chloro and N-bromosuccinimides) has been successfully conducted by using nickel acetate as a catalyst in the presence of potassium carbonate and succinimide as co-additives.The reaction was easily performed at room temperature under nitrogen gas protection to give dihalorinaed haloamino products in good to excellent yields(60%-98%).The structure has been confirmed by X-ray crystal structure analysis. 相似文献
923.
Dan Yang Prof. Guo‐Jun Liu Yu Hao Dr. Wei Li Dr. Ze‐Min Dong Dr. Dan‐Wei Zhang Prof. Nian‐Yong Zhu Dr. 《化学:亚洲杂志》2010,5(6):1356-1363
Peptides of homochiral α‐aminoxy acids of nonpolar side chains can form a 1.88‐helix. In this paper, we report the conformational studies of α‐aminoxy peptides 1 , 2 , 3 , which have functionalized side chains, in both nonpolar and polar solvents. 1H NMR, XRD, and FTIR absorption studies confirm the presence of the eight‐membered‐ring intramolecular hydrogen bonds (the N‐O turns) in nonpolar solvents as well as in methanol. CD studies of peptides 1 , 2 , 3 in different solvents indicate that a substantial degree of helical content is retained in methanol and acidic aqueous buffers. The introduction of functionalized side chains in α‐aminoxy peptides provides opportunities for designing biologically active peptides. 相似文献
924.
由于粒子堆积膜的孔隙率有限,用聚合物乳液直接组装的纳米孔隙膜在膜厚和折射率的调节能力方面都受到限制,需要可以单独调控粒子膜孔隙率的手段.将聚甲基丙烯酸甲酯(PMMA)和聚苯乙烯(PS)的二元混合乳液在PMMA基板上旋涂,再用环己烷选择性溶去PS粒子得到了超低反射的纳米孔隙膜.改变混合乳液的组成可以调节多孔膜的空隙率,使多层纳米孔隙膜的有效折射率从1.36降低到1.07;调节旋涂速度和成膜乳液的浓度可以控制孔隙膜的厚度.在优化的条件下,在PMMA基板上制备的孔隙膜在波长585nm处的最低反射率仅0.03%、在450~800nm的可见光谱范围内的平均反射率低于0.4%.以本方法制备的纳米孔隙膜有较好的稳定性,在水中用超声波清洗30min后,膜的低反射性能几乎不变. 相似文献
925.
926.
离子液体双水相萃取-蒸气发生原子荧光法测定痕量镉 总被引:2,自引:0,他引:2
研究了离子液体1-异戊基-3-甲基咪唑溴代盐-K2HPO4-水双水相体系对镉-双硫腙络合物的萃取性能,建立了测定痕量镉的蒸气发生-原子荧光光谱法.经离子液体双水相萃取后,在离子液体相中的镉-双硫腙络合物经酸化后可直接与还原剂(NaBH4)混合进行蒸气发生反应,并经气液分离后将蒸气引入原子化器中进行原子荧光检测,离子液体的存在不影响蒸气发生过程.考察了双水相系统的组成以及相关实验条件对镉-双硫腙络合物萃取的影响.在最佳实验条件下,样品体积为1 mL时,测定痕量镉的线性范围为0.25~5.0 μg/L,检出限为0.07 μg/L; 相对标准偏差为3.4%(n=9, 2.0 μg/L Cd2+).用国家标准物质GBW08608(水中镉、铬、铜、镍、铅、锌成分分析标准物质)验证了方法的准确性,并对实际水样中的痕量镉进行了测定. 相似文献
927.
Shu‐Wei Tang Jing‐Dong Feng Yong‐Qing Qiu Hao Sun Feng‐Di Wang Ying‐Fei Chang Rong‐Shun Wang 《Journal of computational chemistry》2010,31(14):2650-2657
Electronic structures and nonlinear optical properties of two highly deformed halofullerenes C3v C60F18 and D3d C60Cl30 have been systematically studied by means of density functional theory. The large energy gaps (3.62 and 2.61 eV) between the highest occupied and lowest unoccupied molecular orbitals (HOMOs and LUMOs) and the strong aromatic character (with nucleus‐independent chemical shifts varying from ?15.08 to ?23.71 ppm) of C60F18 and C60Cl30 indicate their high stabilities. Further investigations of electronic property show that C60F18 and C60Cl30 could be excellent electron acceptors for potential photonic/photovoltaic applications in consequence of their large vertical electron affinities. The density of states and frontier molecular orbitals are also calculated, which present that HOMOs and LUMOs are mainly distributed in the tortoise shell subunit of C60F18 and the aromatic [18] trannulene ring of C60Cl30, and the influence from halogen atoms is secondary. In addition, the static linear polarizability and second‐order hyperpolarizability of C60F18 and C60Cl30 are calculated using finite‐field approach. The values of and for C60F18 and C60Cl30 molecules are significantly larger than those of C60 because of their lower symmetric structures and high delocalization of π electrons. © 2010 Wiley Periodicals, Inc. J Comput Chem 2010 相似文献
928.
A simple and fast method of low-density extraction solvent-based solvent terminated dispersive liquid–liquid microextraction (ST-DLLME) was developed for the highly sensitive determination of carbamate pesticides in the water samples by gas chromatography-tandem mass spectrometry (GC-MSMS). After dispersing, the obtained emulsion cleared into two phases quickly when an aliquot of acetonitrile was introduced as a chemical demulsifier into the aqueous bulk. Therefore, the developed procedure does not need centrifugation to achieve phase separation. It was convenient for the usage of low-density extraction solvents in DLLME. Under the optimized conditions, the limits of detection for all target carbamate pesticides were in range of 0.001–0.50 ng mL−1 and the precisions were in the range of 2.3–6.8% (RSDs, 2 ng mL−1, n = 5). The proposed method has been successfully applied to the analysis of real water samples and good spiked recoveries over the range of 94.5–104% were obtained. 相似文献
929.
930.
By controlling the reflux time and the quantity of the shell materials, different sizes of thioglycollic acid (TGA) modified
CdTe/CdSe core/shell quantum dots were synthesized in aqueous solution. This type of QDs was used for sensitive and selective
determination of ascorbic acid in commercial tablets. Under optimal conditions, a good linearity was observed between the
relative fluorescence (FL) intensity and the concentration of ascorbic acid in the range of 4.0 to 64.0 μg/mL with a correlation
coefficient of 0.9968. The limit of detection was 2.4 μg/mL. This method was applied to the determination of the ascorbic
acid in Vitamin C tablets and Vitamin C Yinqiao pills, and satisfactory results were obtained. 相似文献