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911.
Bao-Min Wang Zhang Yuan Zhi-Qiang Guo Hai-Nan Ma Chuan Fook Lai 《Russian Journal of Physical Chemistry A, Focus on Chemistry》2013,87(13):2253-2259
As a new nano-scale functional material, it is necessary to achieve a uniform distribution in the composites for gaining the CNFs’ excellent reinforcing effect. In this paper, CNFs were purified by the method of high temperature annealing treatment. Six surfactants, methylcellulose (MC), hydroxypropyl methylcellulose (HPMC), sodium dodecyl sulfate (SDS), dodecylamine (DDA), N, N-dimethyl formamide (DMF) and cetyltrimethyl ammonium bromide (CTAB) were used individually and combinatorially in a certain concentration to disperse the CNFs in aqueous solution. To achieve a good dispersion of the CNFs, a method utilizing ultrasonic processing was employed. The CNFs treated by the method of high temperature annealing treatment were characterized by differential thermal analysis (DTA) and thermogravimetry analysis (TGA), and the ultrasonication-driven dispersion of CNFs in aqueous solutions were monitored by UVvis spectroscopy and transmission electron microscopy (TEM). The experiments reveal that the method of high temperature annealing treatment purified the CNFs and the maximum achievable dispersion of CNFs corresponds to the maximum UV absorbance of the solution. All results show that the surfactants mixture of MC and SDS in a certain concentration of 0.4 and 2.0 g/L has the maximum dispersion effect on CNFs in aqueous solution, the optimum concentration ratio of MC, SDS, and CNFs was 2: 10: 1. 相似文献
912.
We present here a practical stereoselective synthetic method to produce enantiopure isomers of a new muscarinic receptor antagonist, HL‐031120 (3‐quinuclidinyl‐2′‐cyclopentyl‐2′‐hydroxy‐2′‐phenylacetate, I). Four optical isomers were effectively by stereoselective synthesized using pivaldehyde as steric hindrance agent from the chiral starting material, (S) or (R)‐mandelic acid. The isomers were obtained with 70–76% yields in 98–99% e.e. 相似文献
913.
1,3‐Dimethylbenzimidazolidine reacts with ketones, which can provide activating α hydrogens and primary or secondary amines under acidic conditions, to yield aminomethylation derivatives by a covert Mannich reaction. 相似文献
914.
A practical copper-catalyzed amination of benzoxazole with secondary amine in water has been developed. This reaction has proved to be effective to some cyclic amines, and the substituted group of nitrogen has a great impact on the amination reaction. A copper-catalyzed/ amine-induced ring opening of the benzoxazole and recyclization/oxidation mechanism was also proposed. 相似文献
915.
Jun‐Ju Xu Da‐Ke Zhao Hong‐Lian Ai Li‐Mei Zhang Shi‐Qing Xie Shu‐Hui Zi Sheng‐Chao Yang Yong Shen 《Helvetica chimica acta》2013,96(11):2155-2159
A further study of the alkaloid constituents of Aconitum forrestii led to the isolation of three new C19‐diterpenoid alkaloids, named 14‐acetoxy‐8‐O‐methylsachaconitine ( 1 ), 14‐acetoxyscaconine ( 2 ), and 8‐O‐ethylcammaconine ( 3 ). Their structures were determined by UV, IR, and MS, 1D‐ and 2D‐NMR analyses. 相似文献
916.
Run‐Ning Zhao Yanhong Yuan Fuyi Liu Ju‐Guang Han LiuSi Sheng 《International journal of quantum chemistry》2013,113(19):2220-2227
The geometries, stabilities, and antioxidant activities of L‐Ascorbic acid (1a), D‐erythroascorbate (2a), and D‐erythroascorbate glucoside (3a) as well as their sulfur and selenium derivatives are systematically investigated by using density functional theory. Emphasis is placed on studies of the two main mechanisms, that is, hydrogen atom donation and single‐electron transfer, and the O—H bond dissociation enthalpy and the ionization potential are computed in the gas phase and water solution. The calculated results indicate that the 2‐OH group in the five‐membered ring acts as an important H atom donor to free radicals. The 2‐OH radical spin density distribution shows that the unpaired electron is mostly located at the C3 atom of the five‐membered ring and partially at the vicinal O atoms, proving that a certain delocalization of the odd electron is effective in the five‐membered ring. In water aqueous solution, the antioxidant capacity and the electron donating ability are increased as the O atom in the five‐membered ring of 1a, 2a, and 3a is replaced by S and Se, respectively, in good agreement with experimental measurements; Furthermore, their antioxidant capacities are enhanced as compared with the standard antioxidant (resveratrol). © 2013 Wiley Periodicals, Inc. 相似文献
917.
A facile one‐pot synthesis of 2,5‐disubstituted oxazoles was developed via cyclization of aldoximes and phenylacetylene then dehydrogenation oxidation. 2,3‐dichloro‐5,6‐dicyano‐1,4‐benzoquinone was studied for the selective oxidation of oxazolines using Cu2+/Li+ as catalyst and O2 as indirect oxidant. The reaction results showed that this catalyst system can effectively catalyze the oxidation of oxazolines to the corresponding oxazoles. Thus, a variety of polysubstituted oxazoles was easily synthesized in high yields by catalytic oxidation of 2,3‐dichloro‐5,6‐dicyano‐1,4‐benzoquinone/CuCl2/LiCl/O2. 相似文献
918.
Li Zhang Sheng-mei Yuan Li-ming Yang Zhen Fang Guang-chao Zhao 《Mikrochimica acta》2013,180(7-8):627-633
A glassy carbon electrode was modified with β-manganese dioxide (β-MnO2), and glucose oxidase (GOx) was immobilized on its surface. The β-MnO2 nanowires were prepared by a hydrothermal method and characterized by scanning electron microscopy and powder X-ray diffraction. They were then dispersed in Nafion solution and cast on the glassy carbon electrode (GCE) to form an electrode modified with β-MnO2 nanowires that exhibits improved sensitivity toward hydrogen peroxide. If GOx is immobilized in the surface, the β-MnO2 acts as a mediator, and Nafion as a polymer backbone. The fabrication process was characterized by electrochemical impedance spectroscopy, and the sensor and its materials were characterized by cyclic voltammetry and amperometry. The biosensor enables amperometric detection of glucose with a sensitivity of 38.2 μA?·?mM?1?·?cm?2, and a response time of?<?5 s. This study also demonstrates the feasibility of realizing inexpensive, reliable, and high-performance biosensors using MnO2 nanowires. Figure
The sensitive determination of glucose was realized at a β-MnO2 NWs modified glassy carbon electrode by amperometry. The relatively fast, reproducible and low-cost manufacturing procedure suggests that it can offer an excellent platform for glucose oxidase-biosensing applications. 相似文献
919.
We are reviewing the state of electrochemical sensing of H2O2 based on the use of metal nanoparticles. The article is divided into subsections on sensors based on nanoparticles made from Ag, Pt, Pd, Cu, bimetallic nanoparticles and other metals. Some sensors display high sensitivity, fast response, and good stability. The review is subdivided into sections on sensors based on heme proteins and on nonenzymatic sensors. We also discussed the challenges of nanoscaled sensors and their future aspects. Figure
Sensing mechanism of (A) mediator-based enzyme biosensor, (B) mediator-less enzyme biosensor and (C) nonenzymatic sensors with metal nanoparticles for the electrocatalytic reduction toward H2O2 相似文献
920.
DNAzyme based electrochemical sensors for trace uranium 总被引:1,自引:0,他引:1
Qiong Tang Yali Yuan Xilin Xiao Ping Guo Jianbang Hu Dandan Ma Yangyang Gao 《Mikrochimica acta》2013,180(11-12):1059-1064
We have developed a uranyl-specific DNAzyme that was immobilized on the surface of a gold electrode to give a highly sensitive and selective biosensor for uranyl ion. The typical DNAzyme system consisted of the RNA (rA) as the substrate (ADNA), and the other strand is the enzyme (TDNA) with a ferrocene (Fc). The presence of uranyl ion induces the cleavage of the DNA substrate strand at the rA position to form two fragments. The Fc unit thereby is released from the surface of the electrode, and this results in a decreased peak current. This electrochemical biosensor has a dynamic range from 2 nM to 14 nM of uranyl ion, with a detection limit at 1 nM. It exhibits high sensitivity and excellent selectivity over other metal ions, and thus represents a promising technique for simple, fast, on-site, and real-time electrochemical sensing of UO2(II) ion. It also serves as a guide in choosing different methods for designing electrochemical sensors for other metal ions. Figure
We have developed a uranyl-specific DNAzyme that was immobilized on the surface of a gold electrode to give a highly sensitive and selective biosensor for uranyl ion. The typical DNAzyme system consisted of the RNA as the substrate and the other strand is the enzyme with a ferrocene (Fc). This electrochemical biosensor exhibits high sensitivity and excellent selectivity, and represents a promising technique for simple, fast, on-site, and real-time electrochemical sensing of UO2(II) ion. 相似文献