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471.
A highly sensitive, non-selective trace metal detector based on chemiluminescence has been developed. The metals, separated by simple ion-exchange chromatography, bring about the displacement of cobalt from a Co-EDTA post-column reagent. The liberated cobalt is then detected by the luminol-peroxide chemiluminescence reaction using a modified spectrofluorimeter as the detector. The metals determined are Mg, Ca, Sr, Ba, Fe(II), Fe(III), Co, Ni, Cu, Zn, the lanthanides, Th, Al, Ga, In, Pb and Bi. The detection limits (three times the baseline noise) range between 2 and 100 μg l?1, depending on the analyte, for a 200-μl injection. To demonstrate the quantitative performance of the detector, the zinc and aluminium contents of a fresh water certified reference material was determined and gave good agreement with the certificate values. 相似文献
472.
Kalin Dragnevski Athene Donald Phil Taylor Martin Murray Simon Davies Elizabeth Bone 《Macromolecular Symposia》2009,281(1):119-125
Summary: Environmental scanning electron microscopy (ESEM) was used to study the film formation mechanisms and extent of coalescence of three acrylic latex compositions with different glass transition temperatures (Tg), here defined as standard-low Tg, standard-high Tg (both carboxymethyl cellulose- stabilised) and novel (stabilised with a novel polysaccharide derived from agricultural waste). The ESEM analysis revealed that the microstructure of the standard – low-Tg system consisted of individual particles in dispersion and upon evaporation a continuous film formed, whereas in the case of the standard - high Tg latex particle deformation was not observed, but particle aggregation resulted in the formation of crystal-like structures that have formed via the formation of stacking faults. However, in the case of the novel system the microstructure consisted of individual particles and clusters and during evaporation a discontinuous film formed with voids present within its structure and some of the clusters accumulating on the surface of the specimens. 相似文献
473.
Arenz M Mayrhofer KJ Stamenkovic V Blizanac BB Tomoyuki T Ross PN Markovic NM 《Journal of the American Chemical Society》2005,127(18):6819-6829
Using high-resolution transmission electron microscopy (TEM), infrared reflection-absorption spectroscopy (IRAS), and electrochemical (EC) measurements, platinum nanoparticles ranging in size from 1 to 30 nm are characterized and their catalytic activity for CO electrooxidation is evaluated. TEM analysis reveals that Pt crystallites are not perfect cubooctahedrons, and that large particles have "rougher" surfaces than small particles, which have some fairly smooth (111) facets. The importance of "defect" sites for the catalytic properties of nanoparticles is probed in IRAS experiments by monitoring how the vibrational frequencies of atop CO (nu(CO)) as well as the concomitant development of dissolved CO(2) are affected by the number of defects on the Pt nanoparticles. It is found that defects play a significant role in CO "clustering"on nanoparticles, causing CO to decrease/increase in local coverage, which yields to anomalous redshift/blueshift nu(CO) frequency deviations from the normal Stark-tuning behavior. The observed deviations are accompanied by CO(2) production, which increases by increasing the number of defects on the nanoparticles, that is, 1 < or = 2 < 5 < 30 nm. We suggest that the catalytic activity for CO adlayer oxidation is predominantly influenced by the ability of the surface to dissociate water and to form OH(ad) on defect sites rather than by CO energetics. These results are complemented by chronoamperometric and rotating disk electrode (RDE) data. In contrast to CO stripping experiments, we found that in the backsweep of CO bulk oxidation, the activity increases with decreasing particle size, that is, with increasing oxophilicity of the particles. 相似文献
474.
475.
Khairul WM Fox MA Schauer PA Yufit DS Albesa-Jové D Howard JA Low PJ 《Dalton transactions (Cambridge, England : 2003)》2010,39(48):11605-11615
The complexes [{Cp'(L(2))Ru}C≡CC(6)H(4)C≡CC(6)H(2)(OMe)(2)C≡CC(6)H(4)C≡C{Ru(L(2))Cp'}](L(2) = (PPh(3))(2), Cp' = Cp; L(2) = dppe, Cp' = Cp*) in which the metal centres are bridged by an oligomeric phenylene ethynylene (OPE) ligand have been prepared and the electronic structure of these representative ruthenium-capped OPEs investigated using a combination of electrochemical, UV-vis-NIR and IR spectroelectrochemical methods, and DFT-based calculations. The diruthenium complexes are oxidised to the thermodynamically stable dications [Cp'Ru(L(2))C≡CC(6)H(4)C≡CC(6)H(2)(OMe)(2)C≡CC(6)H(4)C≡CRu(L(2))Cp'](2+), which on the basis of the spectroelectrochemical and computational results can be described in terms of two non-interacting Ru(C≡CAr)(L(2))Cp' moieties. X-ray structures of the oligophenyleneethynylene HC≡CC(6)H(4)C≡CC(6)H(2)(OMe)(2)C≡CC(6)H(4)C≡CH, the bis(gold) complex Ph(3)PAuC≡CC(6)H(4)C≡CC(6)H(2)(OMe)(2)C≡CC(6)H(4)C≡CAuPPh(3) and the precursor 1-ethynyl-4-(trimethylsilylethynyl)benzene are also reported. 相似文献
476.
Shi J Manolikakes G Yeh CH Guerrero CA Shenvi RA Shigehisa H Baran PS 《Journal of the American Chemical Society》2011,133(20):8014-8027
Full details are provided for an improved synthesis of cortistatin A and related structures as well as the underlying logic and evolution of strategy. The highly functionalized cortistatin A-ring embedded with a key heteroadamantane was synthesized by a simple and scalable five-step sequence. A chemoselective, tandem geminal dihalogenation of an unactivated methyl group, a reductive fragmentation/trapping/elimination of a bromocyclopropane, and a facile chemoselective etherification reaction afforded the cortistatin A core, dubbed "cortistatinone". A selective Δ(16)-alkene reduction with Raney Ni provided cortistatin A. With this scalable and practical route, copious quantities of cortistatinone, Δ(16)-cortistatin A (the equipotent direct precursor to cortistatin A), and its related analogues were prepared for further biological studies. 相似文献
477.
Phil Howlett Amie Albrecht Charles Pearce 《Journal of Mathematical Analysis and Applications》2010,366(1):112-110
In this paper we find necessary and sufficient conditions for the existence of a Laurent series expansion with a finite order pole at the origin for the inverse of a linearly perturbed bounded linear operator mapping one Banach space to another. In particular we show that the inversion defines linear projections that separate the Banach spaces into corresponding complementary subspaces. We present two pertinent applications. 相似文献
478.
479.
480.
The photoreactivity of four 8-styryl-substituted coralyne derivatives was examined by UV/VIS- and 1H-NMR-spectroscopy. Except for the dimethylamino-substituted derivative, these cationic azoniaheterocyclic dyes undergo photocyclization that most likely proceeds through an initial E-Z-isomerization of the double bond. Subsequent oxidation of the intermediates under aerobic conditions gave the pyrrolo-annelated quinolizinium derivatives as final products, thus providing a useful synthetic route to polycyclic azoniahetarene derivatives. The 6-(4-chlorophenyl)-substituted pyrroloquinolizinium derivative was isolated on a preparative scale, and the investigation of its photophysical properties revealed significantly red-shifted absorption (λabs = 465–480 nm) and emission bands (λfl = 550–562 nm) in comparison to the parent coralyne and the styryl-substituted derivatives. 相似文献