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41.
Goldsmith JI Hudson WR Lowry MS Anderson TH Bernhard S 《Journal of the American Chemical Society》2005,127(20):7502-7510
The catalytic process of photoinduced hydrogen generation via the reduction of water has been investigated. The use of parallel synthetic techniques has facilitated the synthesis of a 32 member library of heteroleptic iridium complexes that was screened, using high-throughput photophysical techniques, to identify six potential photosensitizers for use in catalytic photoinduced hydrogen production. A Pd/Ni thin film hydrogen selective sensor allowed for rapid quantification of hydrogen produced via illumination of aqueous systems of the photosensitizer, tris(2,2'-dipyridyl)dichlorocobalt ([Co(bpy)(3)]Cl(2)), and triethanolamine (a sacrificial reductant) with ultra-bright light emitting diodes (LEDs). The use of an 8-well parallel photoreactor expedited the investigation of the hydrogen evolution process and facilitated mechanistic studies. All six compounds investigated produced considerably more hydrogen than commonly utilized photosensitizers and had relative quantum efficiencies of hydrogen production up to 37 times greater than that of Ru(bpy)(3)(2+). 相似文献
42.
Summary A fully integrated chromatographic system was developed for the determination of leukotrienes in biological samples using
photodiode-array detection (PDAD), which eliminates time consuming manual sample handling steps. A special solid phase extraction,
(SPE) methodology for leucotriene metabolite stability was developed which increased the recoveries and eliminates the contamination
risk of biological samples. The inherent instability (autooxidation) of many of the leukotriene mediators, and the adsorption
effects onto exposed surfaces in vials and in the chromatographic system were found to be very important parameters to control
in order to circumvent high loss of sample analytes. By binding the cell supernatants to the functionalities of the SPE support
stabilised these mediators. Cell culture samples were eluted through a disposable C18 SPE column. The SPE columns were allowed to thaw and deposited in an automated sample handling unit (ASPEC XL). Desorption
of the analytes was followed by a second on-line SPE step, to eliminate remaining interfering matrix compounds. Typical recoveries
when stored at −70°C were in-between 55–97% except for (LTE4) which was found to be around 40% after 72 days of storage. Seven reversed-phase packings were studied. Selectivity factors,
as well as the separation efficiencies, were found to differ for the various C18 bonded silica stationary phases. This integrated on-line column liquid chromatographic system was applied to the determination
of leukotriene B4, leukotriene C4, leukotriene D4, leukotriene and E4 in human cell extracts using prostaglandin B2 as the internal standard. More than 1500 biological samples were analysed. Some validation data are presented for unattended
operations. 相似文献
43.
Thermal decomposition of RDX from reactive molecular dynamics 总被引:1,自引:0,他引:1
Strachan A Kober EM van Duin AC Oxgaard J Goddard WA 《The Journal of chemical physics》2005,122(5):54502
We use the recently developed reactive force field ReaxFF with molecular dynamics to study thermal induced chemistry in RDX [cyclic-[CH(2)N(NO(2))](3)] at various temperatures and densities. We find that the time evolution of the potential energy can be described reasonably well with a single exponential function from which we obtain an overall characteristic time of decomposition that increases with decreasing density and shows an Arrhenius temperature dependence. These characteristic timescales are in reasonable quantitative agreement with experimental measurements in a similar energetic material, HMX [cyclic-[CH(2)N(NO(2))](4)]. Our simulations show that the equilibrium population of CO and CO(2) (as well as their time evolution) depend strongly of density: at low density almost all carbon atoms form CO molecules; as the density increases larger aggregates of carbon appear leading to a C deficient gas phase and the appearance of CO(2) molecules. The equilibrium populations of N(2) and H(2)O are more insensitive with respect to density and form in the early stages of the decomposition process with similar timescales. 相似文献
44.
Compton scattering normalization method is described for the analysis of uranium bearing ore respect to the usage of K X-rays of uranium. Minimum backscatter energy is obtained at a scatter angle of 180° with fixed point source geometry and collimation in appropriate conclusions. By normalizing the intensities of uranium K-lines to the Compton profile in the measured spectra, the results do not depend on several measuring parameters such as primary radiation intensity, matrix, composition, mass of the sample and measuring time. The method presented in this study indicates the convenience of uranium K-lines analysis for thick targets with an adequate measuring geometry. 相似文献
45.
Süleyman Özçeli Hakan Sezgin 《Journal of inclusion phenomena and macrocyclic chemistry》2003,45(3-4):185-190
New Hofmann-diaminohexane(dahxn)-type clathrates of the form M(1,6-dahxn)Ni(CN)4.G (M = Co, Ni or Cd; G = chlorobenzene, 1,2-, 1,3 or 1,4-dichlorobenzene) were prepared inpowder form and their infrared spectra are reported. The spectral data suggest that these compounds are similar in structure to those of the Hofmann-diam-type clathrates. Their structure consists of planar polymeric layers, {M–Ni(CN)4}, formedfrom Ni(CN)4 anions coordinated to the bridging 1,6-diaminohexane molecules bound directly to the metal (M). The M atoms are bound to four N atoms of the CN ions and, the Ni atoms are surrounded by four C atoms of the CN groups in a square-planar layer. 相似文献
46.
47.
Labeling conditions of synkavit (2-methyl-1,4-naphthoquinol disodium phosphate) with iodine-125 have been studied. In this study, labeling temperature, reaction time, successive using of iodogen coated tubes, iodogen amount and synkavit concentrations have been determined to get optimum conditions for maximum labeling. Final results showed that when the labeling temperature, reaction time, synkavit concentration, and iodogen amount were, at room temperature, 15 min (in the case of successive using of three iodogen coated tubes), 2 mg ml–1 and 5 mg, respectively; labeling yield was 90% and specific activities of the order of 555 GBq mmol–1 (15 Ci mmol–1) have been obtained. 相似文献
48.
Fluoride ions and, in about 0.005M concentration, tungstate ions form gelatinous precipitates, poorly soluble in water, with calcium ions. The radiometric determinations
of the above ions are based on these reactions. Accurate radiometric determination can be carried out only if the gelatinous
precipitate formed during titration can be properly separated from the solution. It has been found that in the case of fluoride
ions the application of crystalline, easily filtrable Ca(COO)2·H2O or CaCO3, and in the case of tungstate ions the application of CaWO4 precipitate improves the filtration properties of45CaF2 and45CaWO4, respectively, formed during titration, whereby the radiometric determinations of the above ions become possible. Titrations
were carried out with 0.05M and 0.005M CaCl2 solutions, labelled with45Ca. 相似文献
49.
The influence of hydrolyzable metal ions (Mn(II) and Ca(II)) adsorption on the surface chemistry, particle interactions, flocculation, and dewatering behavior of kaolinite dispersions has been investigated at pH 7.5 and 10.5. Metal ion adsorption was strongly cation type- and pH-dependent and significantly influenced the zeta potential, anionic polyacrylamide-acrylate flocculant (PAM) adsorption, shear yield stress, settling rate, and consolidation of kaolinite slurries. The presence of Mn(II) and Ca(II) ions alone led to a systematic reduction in zeta potential due to specific adsorption of positively charged metal ion-based hydrolysis products at the kaolinite-water interface. Metal ion-mediated zeta potential changes were reflected by lower dispersion shear yield stresses and improved clarification (higher settling rates) but had no detectable effect on dispersion consolidation. The adsorption of PAM was significantly improved by prior addition of the metal ions. In the presence of Mn(II) or Ca(II) ions, the flocculant adsorption density was enhanced at pH 7.5 for Mn(II) and pH 10.5 for Ca(II). Optimum flocculation conditions, involving partial rather than complete particle surface coverage by both metal ions and flocculant, were identified. As a consequence, the metal ions and flocculant acted synergistically to enhance dewatering, producing particle interactions that were more conducive to high settling rates and greater consolidation of kaolinite dispersions at pH 7.5 than 10.5. 相似文献
50.
Air samples collected at the second Bosporus bridge of Istanbul which carries a heavy traffic load between Asia and Europe,
were analyzed for 22 elements by the INAA method. Pb, Cd and Fe concentrations in the samples were determined by AAS. Iron
concentrations were used as a cross check between the two methods. In order to define the enrichment factors for the elements
in the bridge area, a sample collected from our university campus which can be considered as a rural site, was also analyzed.
Differences were observed especially for Br, Al, Mg, Ti, Cu and Na between the two sites. Based on the results of the samples
from the bridge, we got a value of 0.58(16) for the Br/Pb-ratio. 相似文献