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911.
Yuan-zong Li Hong-fei Liu Zhu-qing Dong Wen-bao Chang Yun-xiang Ci 《Microchemical Journal》1996,53(4):428-436
N,N′-Dicyanomethyl-o-phenylenediamine was synthesized with a 90% yield by a reaction ofo-phenylenediamine with chloroacetonitrile in triethylamine. Our experimental results showed that it was the effective fluorogenic substrate for horseradish peroxidase (HRP) and hemin. TheKmfor the HRP system was 48 μM,and that for hemin was 1.3 μM.Properties of the substrate were evaluated from the detection limits of enzymes and H2O2. The linear ranges for the determination of HRP and hemin were 21–150 pMand 2–20 nM,respectively. The linear range for the determination of H2O2using HRP or hemin was 18–140 and 60–1000 nM,respectively. The structural elucidation of the fluorescent product using NMR and mass spectral techniques was proposed to be 1,2-dihydro-2-imido-imidazo[1,2-a] quinoxaline. Based on the product structure and earlier reports, the possible reaction mechanism of HRP and the substrate was also proposed, i.e., two steps for ring closures, one step of isomerization, and a final step of oxidative dehydrogenation. 相似文献
912.
913.
生物,环境样品和食品中铅的痕量分析 总被引:2,自引:0,他引:2
主要根据近七年来发表的有关论文,综述了我国生物、环境样品和食品中铅和痕量分析技术进展,内容包括分子光谱、原子光谱、电化学和其他分析方法,以及联用技术和前处理等方面,收集文献393篇。 相似文献
914.
915.
An electrodynamics-based model was formulated for simulation of ion diffusion in microbial polysaccharides. The fixed charges and electrostatic double layers that may associate with microbial polysaccharides and their effects on ion diffusion were explicitly built into the model. The model extends a common multicomponent ion diffusion formulation that is based on irreversible thermodynamics under a zero ionic charge flux condition, which is only applicable to the regions without fixed charges and electrostatic double layers. An efficient numerical procedure was presented to solve the differential equations in the model. The model well described key features of experimental observations of ion diffusion in negatively charged microbial polysaccharides including accelerated diffusive transport of cations, exclusion of anions, and increased rate of cation transport with increasing negative charge density. The simulated diffusive fluxes of cations and anions were consistent with a cation exchange diffusion concept in negatively charged polysaccharides at the interface of plant roots and soils; and the developed model allows to mathematically study such diffusion phenomena. An illustrative example was also provided to simulate dynamic behavior of ionic current during ion diffusion within a charged bacterial cell wall polysaccharide and the effects of the ionic current on the compression or expansion of the bacterial electrostatic double layer at the interface of the cell wall and bulk solution. 相似文献
916.
Zhihong Liu 《Analytica chimica acta》2004,519(2):147-153
Two kinds of polymeric pH indicators PPF (phenolphthalein-formaldehyde product) and CPF (o-cresolphthalein-formaldehyde product) immobilized cross-linked poly(vinyl alcohol) membranes (PPF-PVA and CPF-PVA) for optical intermittent determination of high basicity ([OH−] = 1-8 M) based on a kinetic process were developed. In our previous work, we had demonstrated that PPF-PVA and CPF-PVA could perform the determination of high pH values from pH 10.0 to 14.0. Here the discoloring kinetic behaviors of PPF-PVA and CPF-PVA were compared with those of free phenolphthalein, o-cresolphthalein and thymolphthalein. Experimental results and theoretical analysis indicated that the response behaviors of the optodes’ membranes in concentrated NaOH solutions were diffusion-independent and still complied with the pseudo-first-order kinetics. In addition, two data analysis methods for determination were presented. One was directly based on the reduced absorbance; the other was based on the discoloring kinetic constant. It was found that the latter could perform a rapid (60 s) and reliable (relative standard deviation: 2.6%) determination for high basicity. These kinds of optodes can be used repeatedly when they are immersed in low-pH solutions to regain the protonated form after each determination. 相似文献
917.
The structure of a complex, disordered type A-B carbonate apatite (CAp) of approximate composition Ca10(PO4)6−y(CO3)x+(3/2)y(OH)2−2x, x-0.7, y-0.6, synthesized at 3 GPa, 1400°C has been determined using single-crystal X-ray diffraction and FTIR spectroscopy at room temperature and pressure. Crystal data are: hexagonal, space group P63/m, Z=1; a=9.5143(3), c=6.8821(2) Å, V=539.5 Å3, and R=0.025. There are three structural locations for the carbonate ion. The channel carbonate is mainly in the closed vertical configuration of the structure, with two of its oxygen atoms close to the c-axis (A1 carbonate; IR bands at 1541 and 1449 cm−1), but subordinate amounts are also located in an open vertical configuration (A2 carbonate; IR bands at 1563 and 1506 cm−1). The type B carbonate ion is located close to the sloping faces of the PO4 tetrahedron (IR bands at 1474 and 1406 cm−1), confirming earlier inferences from polarized IR spectra. 相似文献
918.
A fully automated nanoelectrospray tandem mass spectrometric method for analysis of Caco-2 samples 总被引:1,自引:0,他引:1
Van Pelt CK Zhang S Fung E Chu I Liu T Li C Korfmacher WA Henion J 《Rapid communications in mass spectrometry : RCM》2003,17(14):1573-1578
Caco-2 cells offer a means to rapidly screen permeability of drug candidates, allowing pharmaceutical companies to eliminate candidates unable to cross the intestinal barrier early in the discovery process. This screening process is typically performed by conventional liquid chromatography/tandem mass spectrometry (LC/MS/MS), which can require time-consuming method development. An alternative to LC/MS/MS, automated nanoelectrospray tandem mass spectrometry (nanoESI-MS/MS), is introduced. This novel approach requires an off-line ZipTip desalting step followed by automated nanoESI-MS/MS, using the NanoMate 100 and ESI Chip. In addition to reduced method development time, automated nanoESI-MS/MS also offers no carry-over between samples, low sample consumption, and ease-of-use as compared with conventional pulled-capillary nanoelectrospray. Furthermore, the infusion system described has the potential to be high-throughput. A comparison of Caco-2 samples analyzed both by LC/MS/MS and by automated nanoESI-MS/MS is presented. The permeability and recovery data of the two compounds analyzed in this study obtained from conventional LC/MS/MS and by automated nanoESI-MS/MS were in excellent agreement. 相似文献
919.
Theoretical study of the unimolecular decomposition mechanisms of energetic TNAD and TNAZ explosives
Min‐Hsien Liu Cheng Chen Yaw‐Shun Hong 《International journal of quantum chemistry》2005,102(4):398-408
Calculation methods based on hybrid Density Functional Theory (DFT) with the basis sets of the B3LYP/6‐31+G(d)//B3LYP/4‐31G(d) method and the differential overlap (INDO) program were used to derive reasonable decomposition mechanisms of 1,4,5,8‐tetranitro‐1,4,5,8‐tetraazadecalin (TNAD) and 1,3,3‐trinitroazetidine (TNAZ) explosives. All possible decomposition species and transition states, including intermediates and products, were identified and their corresponding enthalpy of formation and Gibbs free energy of formation were obtained using polyparametric modification equations. INDO bond energy calculation results reveal the weakest bonding site for reference and determine where cleavage can occur easily. This work is concerned mainly with eliminating HONO (cis or trans form). The activation energy for trans‐form HONO elimination is lower than that of cis‐form HONO elimination in the initial steps of both TNAD and TNAZ decomposition, being 18.5 kJ/mol and 33.3 kJ/mol, respectively. © 2004 Wiley Periodicals, Inc. Int J Quantum Chem, 2005 相似文献
920.
Ya-Ping Tu Guan-Yu Yang Yu-Hua Liu Shao-Nong Chen Yao-Zu Chen 《Journal of mass spectrometry : JMS》1991,26(7):645-648
The reaction mass spectrometry of cyclic glycols and monosaccharides with methylene chloride as reagent was studied. In the presence of ammonia, it was found that methylene chloride reacted stereoselectively with the quasi-molecular ions of cyclic glycols and monosaccharides to form characteristic ions, by comparison of the relative abundances of which the stereoisomers of cyclopentane-l,2-diols and cyclohexane-l,2-diols and some monosaccharides could be definitely distinguished. 相似文献