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961.
Rojo I Teixidor F Kivekäs R Sillanpää R Viñas C 《Journal of the American Chemical Society》2003,125(48):14720-14721
The unprecedented metal-mediated transformation of an alkyne into a B,B' bridging alkene is reported. Also, the unprecedented synthesis of a conjugated dialkene derivative of [3,3'-Co(1,2-C2B9H11)2]- generated only from an alkyne, contrary to the usual case where an alkyne and an alkene are needed, is described. This has been possible through the singular capacity of a B-H to produce hydroboration. 相似文献
962.
Isotypic pseudooctahedral complexes of Co, Ni, and Cu with two chelating oxalurate ligands and two water molecules, trans-[M(oxalurate)(2)(H(2)O)(2)], have been synthesized and isolated by a novel progressive crystallization technique. Diffraction analyses reveal that the three complexes form isotypic solid-state structures in which the molecular connectivity and complex network of noncovalent interactions are qualitatively identical throughout the series. The oxalurate groups form unbounded chains through two different self-recognition patterns-a typical DA-AD motif and an unusual DDA'-A'DD form (D = hydrogen bond donor, A' = double acceptor). The unsymmetrical oxalurate group possesses the topological properties necessary to form aggregates of higher symmetry, and the "M(oxalurate)(2)" fragments form a rhombic 2-D motif with hydrogen-bonded corners and with hydrogen-bond acceptors directed to the inside of the cyclic aggregate. The 2-D net is stacked to form a channeled 3-D structure, in which the coordinated aqua ligands form the principal interlayer interactions. The slanted channels are occupied by the axial waters and by waters of crystallization, which are hydrogen bonded to the channel walls to form an ordered bushing. The extensive 3-D hydrogen-bonded superstructure is flexible enough to accommodate the distortion produced by the Jahn-Teller effect in the copper compound without requiring a qualitative structural change. The bonds affected by Jahn-Teller distortion in the Cu complex [Cu-O = 2.3788(15) A] are significantly longer than their analogues in the Co and Ni complexes [Co-O = 2.175(2), Ni-O = 2.094(9) A]. 相似文献
963.
Batistoni DA Garavaglia RN Rodríguez RE 《Fresenius' Journal of Analytical Chemistry》2000,366(3):221-227
The simultaneous injection of volatile hydride species and hydrogen gas, originating in reagent decomposition, was monitored during the operation of a continuous hydride generation manifold employed for the determination of trace arsenic by HG-ICP-AES. Line and background intensities as well as the FWHM of the hydrogen Hgamma and Hdelta lines were measured, and electron number densities (ne) estimated from Stark broadening of the line profiles. Results were compared with those obtained by conventional pneumatic injection of aqueous solutions. Overlapping with atomic nitrogen lines at 410 nm and 411 nm tends to distort the Hdelta line profile for the hydrogen-seeded plasma, rendering unreliable results. The N I lines seem to be quenched by the presence of water aerosol. More consistent results were obtained with the Hgamma line. When no solutions are pumped through the hydride generation manifold ("dry" plasma), the measured ne value was (1.57 +/- 0.22) x 10(15)cm(-3). Conversely, when the reducing reagent flow was replaced by pure water (corresponding to the injection of water vapor in equilibrium that is swept by the argon carrier gas passing through the phase separator), the electron concentration is 25% higher. In that case the ne value agrees between the experimental error with that obtained for a plasma in which a water aerosol is introduced at a flow rate of 1 mL/min. An enhancement of 52% relative is observed in ne when the system is operated under optimized conditions for arsine generation, employing sodium tetrahydroborate in acidic medium as reducing agent (i.e. hydrogen seeded plasma). It was also observed that the continuum emission near 410 nm for the hydrogen containing plasma correlates with the measured electron number density, suggesting that the background enhancement under hydride generation conditions may respond to the ion-electron recombination mechanism. 相似文献
964.
S. M. Bardavid G. C. Pedrosa M. Katz M. A. Postigo P. García 《Journal of solution chemistry》1996,25(11):1125-1135
Exces molar volumes, and excess viscosities of then-hexane+dichloromethane+tetrahydrofuran system have been determined at 25°C by measuring densities and viscosities. Different expressions exist in the literature to predict these excess properties from binary data. The empirical correlation of Cibulka is shown to be the best in this system. 相似文献
965.
Romero R Bagur MG Sánchez-Viñas M Gázquez D 《Analytical and bioanalytical chemistry》2003,376(2):162-167
Biogenic amines, as dabsyl derivatives, were determined in beer samples, intermediate products, and raw materials (malt and maize) by HPLC. A procedure for the extraction of the amines from malt and maize with diluted hydrochloric acid was optimised by combining a Response Surface Methodology with a Simultaneous Decision Making Approach. The results of the analysis indicate that, in brewing, technology and hygiene are the decisive factors that determine the amine concentrations in the final product. 相似文献
966.
Summary A numerically stable and well-parallelizable curve variational algorithm is described for determining tangent curves of vector fields between two given stationary points. In particular, the method is suitable for finding reaction paths and saddle points on potential energy hypersurfaces (PHS). The stability of the procedure is illustrated by an artificial mathematical function, showing phases of following the reaction on the PHS.Dedicated to Professor Zoltán G. Szabó, the great teacher and scientist in reaction kinetics and in many other fields of physical chemistry, on his 84th birthday. 相似文献
967.
P. Vaňura V. Jedináková-Křížová M. Vobecký 《Journal of Radioanalytical and Nuclear Chemistry》2006,267(2):501-503
Summary An extraction technique for the separation of 90Sr from a high excess of90Y has been developed. This procedure can be used for the determination of trace amounts of90Sr in90Y prepared by a radiochemical90Y/90Sr generator by liquid scintillation. 相似文献
968.
Izaskun Bustero García Ainara Obieta Isabel Muñoz Roberto Rincón Inés Arteche Amaya 《Mikrochimica acta》2006,152(3-4):239-247
Interest in carbon nanotubes (CNT) has grown at a very rapid rate in the last decade. Their interesting physical and chemical
properties open attractive possibilities in many application areas. These properties depend on the process conditions during
synthesis and on subsequent purification steps. Recent studies have demonstrated that CNT can promote the electron transfer
of biomolecules. These exceptional properties make them attractive for use in electrochemical biosensors.
Multi walled nanotubes have been synthesized by the Chemical Vapor Deposition (CVD) method using methane as a carbon source
and Ni–Al2O3–SiO2 as the catalyst. The influence of the variation of certain reaction parameters such as feed gas composition, catalyst mass,
temperature and reaction time in the yield of the CVD process has been established. In addition, the structural and chemical
characteristics of the CNTs have been studied and a purification process to eliminate the catalyst and amorphous carbon has
been developed that involves a gaseous oxidative process and acid treatment. The efficiency of the purification step has been
determined by analytical techniques.
Atomic force microscopy, Raman scattering, thermogravimetric analysis, inductively coupled plasma atomic spectroscopy are
the characterization techniques employed in this work. 相似文献
969.
Cheikhousman R Zude M Bouveresse DJ Léger CL Rutledge DN Birlouez-Aragon I 《Analytical and bioanalytical chemistry》2005,382(6):1438-1443
The potential of fluorescence spectroscopy for characterizing the deterioration of extra virgin olive oil (EVOO) during heating was investigated. Two commercial EVOO were analysed by HPLC to determine changes in EVOO vitamin E and polyphenols as a result of heating at 170°C for 3 h. This thermal oxidation of EVOO caused an exponential decrease in hydroxytyrosol and vitamin E (R2=0.90 and 0.93, respectively) whereas the tyrosol content was relatively stable. At the same time, amounts of preformed hydroperoxides (ROOH), analysed by an indirect colorimetric method, decreased exponentially during the heating process (R2=0.94), as a result of their degradation into secondary peroxidation products. Fluorescence excitation spectra with emission at 330 and 450 nm were recorded to monitor polyphenols and vitamin E evolution and ROOH degradation, respectively. Partial least-squares calibration models were built to predict these indicators of EVOO quality from oil fluorescence spectra. A global approach was then proposed to monitor the heat charge from the overall fluorescence fingerprint. Different data pretreatment methods were tested. This study indicates that fluorescence spectroscopy is a promising, rapid, and cost-effective approach for evaluating the quality of heat-treated EVOO, and is an alternative to time-consuming conventional analyses. In future work, calibration models will be developed using a wide range of EVOO samples. 相似文献
970.
Yingyongnarongkul BE How SE Díaz-Mochón JJ Muzerelle M Bradley M 《Combinatorial chemistry & high throughput screening》2003,6(7):577-587
Advances in high throughput screening (HTS), together with the rapid progress in combinatorial chemistry, genomic and proteomic sciences have dramatically stimulated the development of a variety tools to enable the drug discovery process to become more efficient. Major future challenges in HTS include obtaining high density and good quality data based on assays that are rapid, reliable, inexpensive, sensitive, simple and miniaturised. This paper reviews the development and role of bead-based assays for HTS including DNA and single nucleotide polymorphism (SNP) assays, particularly from a multiplex perspective and evaluating the recent advances in bead-based arrays. The encoding strategies that are commonly used in bead-based assays are highlighted, while the importance of magnetic beads in genomic and proteomic purifications is discussed. In conclusion, bead-based assays offer a powerful promising approach for many aspects of drug discovery. 相似文献