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991.
Wenwen Tu Jianping Lei Dr. Huangxian Ju Prof. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2009,15(3):779-784
A functional composite of single‐walled carbon nanotubes (SWNTs) with hematin, a water‐insoluble porphyrin, was first prepared in 1‐butyl‐3‐methylimidazolium hexafluorophosphate ([BMIM][PF6]) ionic liquid. The novel composite in ionic liquid was characterized by scanning electron microscopy, ultraviolet absorption spectroscopy, and electrochemical impedance spectroscopy, and showed a pair of direct redox peaks of the FeIII/FeII couple. The composite–[BMIM][PF6]‐modified glassy carbon electrode showed excellent electrocatalytic activity toward the reduction of trichloroacetic acid (TCA) in neutral media due to the synergic effect among SWNTs, [BMIM][PF6], and porphyrin, which led to a highly sensitive and stable amperometric biosensor for TCA with a linear range from 9.0×10?7 to 1.4×10?4 M . The detection limit was 3.8×10?7 M at a signal‐to‐noise ratio of 3. The TCA biosensor had good analytical performance, such as rapid response, good reproducibility, and acceptable accuracy, and could be successfully used for the detection of residual TCA in polluted water. The functional composite in ionic liquid provides a facile way to not only obtain the direct electrochemistry of water‐insoluble porphyrin, but also construct novel biosensors for monitoring analytes in real environmental samples. 相似文献
992.
Bogdan Kralj Andrej Šmidovnik Jože Kobe 《Rapid communications in mass spectrometry : RCM》2009,23(1):171-180
The mass spectrometric characterization of aqueous solutions of α‐ and β‐cyclodextrins (CDs) and o‐, m‐ and p‐coumaric acids (CAs) by negative ion electrospray ionization (ESI) indicates that the [CD+CA]? ions were sourced from the inclusion complex present in solution and from the anion attached to CD molecules formed in the spray processes. The anion adducts formed in the spray process contribute significantly to the signal intensity of an ionized inclusion complex thus overestimating the calculated stability constant (K) of solution‐phase complexes by one to two orders of magnitude. The relative intensities of anion adducts in mass spectra depend on the concentration ratio of the anion and the CD in spray droplets, while the relative intensity of the ionized inclusion complex depends on CD and CA concentrations in solutions and the value of K. Ion Mobility Spectrometry Mass Spectrometry [IMS‐MS] measurements show that the collision cross‐section (Ω) values of the [CD+CA]? or [(CD)2+CA]2? and [CD+CA] complex ions are 5–6% larger than or equal to CD? or [CD], respectively. Therefore, in the gas phase the anion adducts [CD+CA?] on cyclodextrin molecules possess the same conformations as the ionized inclusion complexes [CD+CA]?. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
993.
994.
Guoqiang Cai Zhengjian Chen Kehua Tu Liqun Wang Kangjie Zhu 《European Polymer Journal》2009,45(6):1674-3144
A facile strategy was proposed for synthesizing chitosan-O-poly(ε-caprolactone) (CS-O-PCL). Stoichiometric sodium dodecyl sulfate-chitosan complex (SCC) which was soluble in common organic solvents was adopted as an intermediate. Regioselective conjugation of PCL onto SCC could be achieved through condensation reaction between isocyanate-terminated PCL and hydroxyl groups of chitosan. The grafting level of PCL could be modulated by varying PCL/SCC weight ratio. SDS was removed from SCC-O-PCL using trihydroxymethylamine (Tris) as a decomplexation agent. The self-assemble behavior of the amphiphilic copolymers was studied by fluorometry, TEM and laser light scattering. The morphology of the CS-O-PCL nanoparticles was found to be dependent on PCL grafting level. Both spherical micelles and vesicle could be formed by dialysis method. 相似文献
995.
Herba Cistanche (Rou Cong Rong in Chinese), dried succulent stems of Cistanche deserticola or C. tubulosa, is a famous Chinese herbal medicine and has been recorded in the Chinese Pharmacopoeia. In recent years, another two non-official species, C. salsa and C. sinensis have also been used as Herba Cistanche in some regions of China. To investigate the possibility of using these two non-official species as alternatives to the official species, a high-performance liquid chromatography-diode array detection-mass spectrometry (HPLC-DAD-MS) fingerprint method was developed to comparatively analyze the crude herbs of these four species. The fingerprint of C. deserticola, a historically certified species of Herba Cistanche, serves as 'standard pattern' for comparing the similarities with the other species by means of similarity and Principle Component Analysis. Additionally, 18 characteristic peaks in the fingerprints were identified by comparing their retention times, UV spectra and ESI-MS data with those of the reference substances and/or the data in the literatures. The comparative results demonstrate that the fingerprints of C. tubulosa and C. salsa possess high similarity to the standard pattern, suggesting that these two species may be used as alternative species; while that of C. sinensis has low similarity (0.053 correlation coefficient) to the standard pattern, indicating that it cannot be used as the substitute of the official herb. However, the varying fingerprint patterns among the samples of C. deserticola collected from various habitats illustrate that the quality consistency of crude herbs is still a problem worthy of serious concern. 相似文献
996.
Yuxin Wang Guangji Wang Pengfei Tu Yan Liang Hao Yang Chaonan Zheng Nan Cui 《Talanta》2009,80(2):572-1747
Metabolite identification for the compounds that undergo multiple and sequential metabolism is still a great challenge. Echinacoside (ECH), a typical phenylethanoid glycoside, contains multiple unstable chemical bonds and high reactive functional groups which are susceptible to multiple pathways of degradation and metabolism, leading great difficulties for its metabolite identification. This study proposed a novel approach for rapidly identifying the complicated and unpredictable metabolites of ECH, based on the powerful liquid chromatography hybrid ion trap and time of flight mass spectrometry (LC/MS-IT-TOF) analysis. Four degradation products were rapidly identified via the “fragmentation-degradation” comparisons. Five phase I and phase II metabolites of the degradation products were rapidly characterized via the crossover mass differences comparisons of their quasi-molecular ions with the potential precursors. Four direct phase I and phase II metabolites of the parent compound were identified by the mass differences analysis of the molecular ions between metabolites and the parent compound. Multiple stages of fragmentation patterns were used to confirm the metabolites characterizations. This study provides a novel approach to characterizing the complicated metabolites, and would be widely applicable for the metabolite identification of natural products. 相似文献
997.
A versatile strategy is described for the synthesis of new 2-amino-1,4-dihydroquinolines. It involved a Knoevenagel condensation of N-protected-2-amino-5-bromobenzaldehyde with ethylcyanoacetate, followed by a cyclization and protection of the NH group to afford the key intermediates 7 or 19. Then various 1,4 addition reactions have been performed to introduce substituents on the upper part of the 2-amino-1,4-dihydroquinolines. 相似文献
998.
Francisco Alcaide Garbiñe Álvarez Oscar Miguel María Jesús Lázaro Rafael Moliner Ana López-Cudero José Solla-Gullón Enrique Herrero Antonio Aldaz 《Electrochemistry communications》2009,11(5):1081-1084
Carbon nanofibers synthesized via the thermo catalytic decomposition of methane were investigated for the first time as an electrocatalyst support in PEMFC cathodes. Their textural and physical properties make them a highly efficient catalyst support for cathodic oxygen reduction in low temperature PEMFC. Tests performed in MEAs showed that Pt supported on carbon nanofibers exhibited an enhancement of ca. 94% in power density at 0.600 V, in comparison with a commercial catalyst supported on conventional carbon black, Pt/Vulcan XC-72R. 相似文献
999.
Fátima Duarte Freire C. Flávio Soares Aragão T. Flávio Accioly de Lima e Moura Fernanda Nervo Raffin 《Journal of Thermal Analysis and Calorimetry》2009,97(1):355-357
Chlorpropamide ((4-chloro-N-(propylamino)-carbonyl)-benzenesulfonamide) belongs to compounds having sulfonylurea group and is widely used as an oral
antidiabetic agent. In this work differential scanning calorimetry (DSC) was used during pre-formulation of chlorpropamide
tablets to determine the drug-excipients compatibility. The DSC curves of chlorpropamide and binary mixtures with excipients
(sodium croscarmellose, sodium lauryl sulfate, microcrystalline cellulose, magnesium stearate and calcium carbonate) showed
that chlorpropamide exhibited interaction with magnesium stearate and sodium lauryl sulfate. The binary mixtures of chlorpropamide–magnesium
stearate presented a single endothermic process at 96–108 °C and chlorpropamide–sodium lauryl sulfate showed a wide endotherm
at 99–120 °C. 相似文献
1000.
Guo-Bin Jung Cheng-Hsin Tu Pei-Hung Chi Ay Su Fang-Bor Weng Yur-Tsai Lin Yu-Chun Chiang Chi-Yuan Lee Wei-Mon Yan 《Journal of Solid State Electrochemistry》2009,13(9):1455-1465
An experimental and simulation research had been performed to investigate the performance as well as the flow distribution
in the cathode flow field in the case of direct methanol fuel cells (DMFCs). The gas was well distributed in serpentine flow
field, whereas stagnation of the gas was observed in parallel flow field. These would contribute to the cell performance greatly
due to mass transfer effect when the cells start operating. In addition, the durability test of DMFC was drastically affected
in parallel flow field due to poor ability to drain flooded water produced electrochemically at cathode and crossover from
anode. In addition, pressure drops of different flow fields were also investigated to evaluate their contribution and feasibility
as an economic application for DMFC. DMFC with serpentine flow field featuring higher pressure difference resulted in a larger
parasitic energy demand. However, the optimal flow field designs are needed to balance the performance and pressure loss to
achieve a uniform fluid distribution and simultaneously minimize energy demand for mass transport. Consequently, flow field
with grid pattern appears to be the optimal design for the DMFC cathode. 相似文献