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971.
The hydrogen peroxide-oxidation of o-phenylenediamine (OPD) catalyzed by horseradish peroxidase (HRP) at 37 °C in 50 mM phosphate buffer (pH 7.0) was studied by calorimetry. The apparent molar reaction enthalpy with respect to OPD and hydrogen peroxide were −447 ± 8 kJ mol−1 and −298 ± 9 kJ mol−1, respectively. Oxidation of OPD by H2O2 catalyzed by HRP (1.25 nM) at pH 7.0 and 37 °C follows a ping-pong mechanism. The maximum rate Vmax (0.91 ± 0.05 μM s−1), Michaelis constant for OPD Km,S (51 ± 3 μM), Michaelis constant for hydrogen peroxide Km,H2O2 (136 ± 8 μM), the catalytic constant kcat (364 ± 18 s−1) and the second-order rate constants k+1 = (2.7 ± 0.3) × 106 M−1 s−1 and k+5 = (7.1 ± 0.8) × 106 M−1 s−1 were obtained by the initial rate method. 相似文献
972.
Cerium-doped mesoporous TiO2 nanoparticles with high surface area and thermal stable anatase wall were synthesized via hydrothermal process in a cetyltrimethylammonium bromide (CTAB)/Ti(SO4)2/Ce(NO3)4/H2O system. The obtained materials were characterized by XRD, FESEM, HRTEM, FTIR spectroscopy, nitrogen adsorption and DRS spectra. Experimental results indicated that the doping of cerium not only increased the surface area of mesoporous TiO2 nanoparticles, but also inhibited the mesopores collapse and the anatase-to-rutile phase transformation. Moreover, the undoped, doped anatase mesoporous nanoparticles exhibit higher photocatalytic activity than commercial photocatalyst (Degussa, P25), but the maximum photodegradation rate corresponds to the undoped mesoporous TiO2 nanoparticles. The lower photocatalytic activities of cerium-doped samples compared with undoped one may be ascribed to that the doped cerium partially blocks titania's surface sites available for the photodegradation and absorption of Rhodamine B (RB). 相似文献
973.
An online UV photolysis and UV/TiO2 photocatalysis reduction device (UV–UV/TiO2 PCRD) and an electrochemical vapor generation (ECVG) cell have been used for the first time as an interface between high-performance liquid chromatography (HPLC) and atomic fluorescence spectrometry (AFS) for selenium speciation. The newly designed ECVG cell of approximately 115 L dead volume consists of a carbon fiber cathode and a platinum loop anode; the atomic hydrogen generated on the cathode was used to reduce selenium to vapor species for AFS determination. The noise was greatly reduced compared with that obtained by use of the UV–UV/TiO2 PCRD–KBH4–acid interface. The detection limits obtained for seleno-DL-cystine (SeCys), selenite (SeIV), seleno-DL-methionine (SeMet), and selenate (SeVI) were 2.1, 2.9, 4.3, and 3.5 ng mL–1, respectively. The proposed method was successfully applied to the speciation of selenium in water-soluble extracts of garlic shoots cultured with different selenium species. The results obtained suggested that UV–UV/TiO2 PCRD–ECVG should be an effective interface between HPLC and AFS for the speciation of elements amenable to vapor generation, and is superior to methods involving KBH4. 相似文献
974.
Chinchilla D Zavaleta J Martinez K Gomez FA 《Analytical and bioanalytical chemistry》2005,383(4):625-631
Multiple-injection affinity capillary electrophoresis (MIACE) is used to determine binding constants (K
b) between receptors and ligands using as model systems vancomycin and teicoplanin from Streptomyces orientalis and Actinoplanes teichomyceticus, respectively, and their binding to D-Ala-D-Ala peptides and carbonic anhydrase B (CAB. EC 4.2.1.1) and the binding of the latter to arylsulfonamides. A sample plug
containing a non-interacting standard is first injected followed by multiple plugs of sample containing the receptor and then
a final injection of sample containing a second standard. Between each injection of sample, a small plug of buffer is injected
which contains an increasing concentration of ligand to effect separation between the multiple injections of sample. Electrophoresis
is then carried out in an increasing concentration of ligand in the running buffer. Continued electrophoresis results in a
shift in the migration time of the receptor in the sample plugs upon binding to their respective ligand. Analysis of the change
in the relative migration time ratio (RMTR) or electrophoretic mobility (μ) of the resultant receptor–ligand complex relative to the non-interacting standards, as a function of the concentration of
ligand yields a value for K
b. The MIACE technique is a modification in the ACE method that allows for the estimation of binding affinities between biological
interactions on a timescale faster than that found for standard ACE. In addition sample volume requirements for the technique
are reduced compared to traditional ACE assays. These findings demonstrate the advantage of using MIACE to estimate binding
parameters between receptors and ligands. 相似文献
975.
976.
The ISO/IEC 17025:1999 standard requires chemical testing laboratories to have an estimate of the uncertainty of their measurements. This is a new requirement for many laboratories and there is confusion as to how to estimate uncertainty. Concerns have been raised about the time and effort required to obtain uncertainty estimates.Uncertainty budgets were prepared for the measurement of benzene, toluene, ethyl benzene and xylenes (BTEX) in water using purge and trap coupled with GC/MS. A time limit of one working afternoon (2 pm–5.30 pm) was imposed for preparing the uncertainty estimate. Details of the uncertainty estimate for toluene are described.The method in question had been in routine use for several years and the laboratory held third party (NATA) accreditation for the test. Consequently a considerable amount of performance data was readily available. Relevant information was extracted from the documented test method, validation data, instrument calibration and from routine quality control. This data was combined according to the principles of the ISO Guide to the Expression of Uncertainty, as promulgated in the Eurachem document "Quantifying Uncertainty in Analytical Measurement."The uncertainty estimates were compared to estimates obtained from generalised empirical models (the Horwitz and Lowthian equations), and from interlaboratory studies of this analysis.A traceability chain from routine measurements to the SI units of metre, kilogram and mole is described.Realistic and useful uncertainty estimates were obtained with a few hours work using data extant in the laboratory. 相似文献
977.
978.
Silicalite-filled poly(siloxane imide) membranes for removal of VOCs from water by pervaporation 总被引:3,自引:0,他引:3
Silicalite-filled poly(siloxane imide) (PSI) membranes were prepared for the separation of volatile organic compounds (VOCs) from water via pervaporation. PSI copolymer was synthesized by polycondensation of 3,3′,4,4′-benzophenonetetracarboxylic dianhydride (BTDA) with a siloxane-containing diamine, e.g., poly(dimethylsiloxane), bis(3-aminopropyl) terminated (PSX), added with 3,3-diaminodiphenyl sulfone (DDS). 2,4,6-Triamine pyrimidine (TAP) was added into the casting solution in order to enhance the compatibility between the polymeric matrix and the filler, silicalite. The PSI membranes were characterized by SEM. The surface morphology for the membrane with the addition of TAP differs from that without TAP. The latter seems to be consisting of particles in the membrane surface. The sorption selectivity of the PSI membranes for chloroform/water solutions was investigated, and there was a highest value for it around 50 wt.% of PSX content. The pervaporation performance of the membranes was studied with the separation of chloroform/water mixture. The silicalite-filled membrane with 120 μm thickness exhibit a high total permeation flux of 280 g m−2 h−1 with separation factor of 52.2 for 1.2 wt.% of the chloroform/water mixture. 相似文献
979.
Wei Sheng Feng Hong Wei Li Xiao Ke Zheng Sui Qing Chen 《中国化学快报》2007,18(12):1518-1520
Two new megastigmane O-glucopyranosides,named (2R,3R,5R,6S,9R)-3-hydroxy-5,6-epoxy-β-ionol-2-O-β-D-glucopyrano- side(1) and (2R,3R,5R,6S,9R)-3-hydroxyl-5,6-epoxy-acety-β-ionol-2-O-β-D-glucopyranoside(2) together with six known mega- stigmanes,were isolated from the leaves of Broussonetia papyrifera (Linn.) Vent.Their structures were established by chemical methods and spectroscopic techniques including 2D NMR. 相似文献
980.
Storage-Reduction of NOx over Combined Catalysts of Pt/Ba/Al2O3-Mn/Ba/Al2O3: Carbon Monoxide as Reductant
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Sha Deng Xuehui Li Jianhua Xiao Furong Wang Lefu Wang 《天然气化学杂志》2007,16(2):213-216
Storage-reduction of NOx by carbon monoxide was investigated over combined catalysts of Mn/Ba/Al2O3-Pt/Ba/Al2O3. Combination of Mn/Ba/Al2O3 and Pt/Ba/Al2O3 catalysts in different ways showed excellent NOx storage-reduction performance and the content of Pt could be reduced by 50%. Not only the addition of 5Mn/15Ba/Al2O3 to lPt/15Ba/Al2O3 could improve its storage ability, but also enhance the NOx conversion consequently. NOx conversion over the combined catalysts (the combined catalysts I and II) was increased under dynamic lean-rich burn conditions, the maximum NOx conversion increased from 69.4% to respectively 78.8% and 75.7% over two combined catalysts. 相似文献