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861.
A. A. Trifonov L. N. Zakharov M. N. Bochkarev Yu. T. Struchkov 《Russian Chemical Bulletin》1994,43(1):145-148
Ytterbium complexes, Cp2Yb(-2:2-DAB)Li(DME) (1) and CpYb(DAB)K(THF)2 (2), containing a bridging diazadiene ligand were prepared by the reaction of CpYbCl2(THF)3 with (DAB)Li2 (11) and (DAB)–K+ (12) (DAB = But-N=CH-CH=N-But). The structure of complex1 was established by X-ray diffraction analysis. The complex is binuclear: the Yb atom of the Cp2Yb fragment and the Li atom, which is bonded as well with the chelating DME molecule, are linked by the DAB ligand.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 148–151, January, 1994. 相似文献
862.
V. Pichon H. Rogniaux N. Fischer-Durand S. Ben Rejeb F. Le Goffic M. -C. Hennion 《Chromatographia》1997,45(1):289-295
Summary The trace-level determination of organic pollutants in complex matrices is difficult and often not reliable because theccurrent
extraction procedures are non-selective. New extraction sorbents involving antigen-antibody interactions, called immunosorbents
(ISs), have been synthesised in order to trap a group of structurally related pollutants. The IS capacity is always high for
the analyte-antigen used to make the antibodies, but can be low for some related compounds. In this work, we show the relationship
that exists between capacity, break-through volume and recovery of analytes because of the competition between the structurally
related compounds for antibody sites. Breakthrough due to the overloading of the column should be avoided because calibration
curves are no longer linear. The capacity of two ISs, one made for trapping the triazine pesticide group and the second for
the phenylurea, group, have been optimised by selecting silica with 50 nm pore size. Calibration curves are linear for all
the compounds in a mixture of ten phenylureas up to a concentration of 5 to 10 μg L−1 for each compound when handling 50 mL water samples through a precolumn packed with 0.22 g of IS. Under these conditions,
reliable quantitative results are obtained because calibration curves are similar when compounds are alone or in a mixture.
Application to the clean-up of soil extracts illustrates the high selectivity and the high potential of these new sorbents
in environmental analysis.
Presented at the 21st ISC held in Stuttgart, Germany, 15th–20th September, 1996 相似文献
863.
Hong Shen James E. Mark Carl J. Seliskar Harry B. Mark Jr. William R. Heineman 《Journal of Solid State Electrochemistry》1997,1(3):241-247
One problem associated with using bare solid metal electrodes, such as gold and platinum, in stripping analysis to determine
heavy metal ions such as lead and copper ions in dilute solutions is that underpotential deposition (UPD) gives multiple stripping
peaks in the analysis of mixtures. These peaks are often overlapped and cannot be conveniently used for analytical purposes.
Bifunctional alkylthiols, such as 3-mercaptopropionic acid, with an ionizable group on the other terminal end of the thiol
can form self-assembled monolayers (SAMs) on the surface of the gold electrode. It is shown that such an SAM-modified gold
electrode minimizes the UPD effects for the stripping analysis of lead and copper. The anodic peak potential shifts and the
peak shape changes, indicating that the SAM changes the deposition and stripping steps of these heavy metal ions. Thus, the
sensitivity levels for both single species and mixtures can be significantly improved for the conventional solid electrodes.
The mechanism of the deposition reaction at the SAM-modified gold electrodes is discussed.
Received: 29 May 1997 / Accepted: 24 June 1997 相似文献
864.
Summary A method has been developed for the determination of trace levels of 32 pesticides, 19 explosives and 16 polycyclic aromatic
hydrocarbons (PAH) in water in three individual steps. Solid-phase enrichment (SPE) is coupled to high-performance liquid
chromatography (HPLC) with a fully automated system. The organic pollutants are enriched on reusable cartridges packed with
adsorbent materials: pesticides and explosives on a mixed bed of divinylbenzene-ethylvinylbenzene copolymers (LiChrolut EN?) and perfluorinated polyethylene (PolyF?), and polycyclic aromatic hydrocarbons on C18-modified silica (Zorbax? ODS1). Thermally assisted desorption (TAD) has been shown to increase the recovery of analytes significantly. As all enriched
analytes are transferred to the detector, only fifty millilitres of sample is needed for each single on-line analysis, compared
with at least a litre for conventional methods. The separation of the enriched organic analytes is performed on specialized
HPLC columns based on reversed-phase materials. The limits of detection of the system employed were found to be below 100
ng L−1. Use of fluorescence detection for the polycyclic aromatic hydrocarbons resulted in limits of detection in the upper pg L−1 range. Thek values, number of theoretical plates, the recovery rates and the limits of detection of this method for fast screening of
organic pollutants from three fifty-millilitre aqueous samples are described.
Presented at the 21st ISC held in Stuttgart, Germany, 15th–20th September, 1996 相似文献
865.
V. Manríquez C. Díaz G. González I. Brito 《Journal of Thermal Analysis and Calorimetry》1996,46(6):1875-1880
Benzenesulfenamides with the formula R-S-N-(R)2 (R=C6H5 andR=NC4H8O, C7H7 and C6H11) and their chromium carbonyl complexes were studied by means of TG and mass spectrometric methods. The thermal behaviour of the compounds the stabilities of free sulfenamides are lower than those observed for the corresponding chromium carbonyl complexes. Combined thermogravimetry — mass spectrometry results suggest that the fragmentation mechanism of the carbonyl complexes involves cleavage of the Cr-S and Cr-CO bonds while that of sulfenamide depends mainly on the dissociation rates of the NR2 groups.This work was partially supported by the Departamento técnico de Investigation of the Universidad de Chile, Grant Q3280/9324. 相似文献
866.
Li6[TeMo6O24] · 18 H2O is triclinic (space group P1 , a = 1 041.7(1), b = 1 058.6(1), c = 1 070.8(1) pm, α = 61.08(1), β = 60.44(1), γ = 73.95(1)°). Single crystal X-ray structure analysis (Z = 1, 295 K, 317 parameters, 3 973 reflections, Rg = 0.0250) revealed an infinite branched chain of edge-sharing Li coordination polyhedra to be the prominent structural feature. One of the four crystallographically independent Li+ is coordinated octahedrally. The coordination polyhedra of the remaining Li+ are distorted trigonal bipyramids. Only three unique oxygen atoms (O(9), O(10), O(12)) of the centrosymmetric [TeMo6O24]6? anion are bound to Li+. The further positions in the coordination spheres of the Li+ are occupied by water molecules. Intermolecular hydrogen bonds involve mainly oxygen atoms of the [TeMo6O24]6? anion as nearly equivalent proton acceptors without regard to their different bonding modes to Te and Mo, respectively. Li6[TeMo6O24] · Te(OH)6 · 18 H2O crystallizes monoclinically in space group P21/n with Z = 4, a = 994.1(3), b = 2 344.8(10), c = 1 764.9(4) pm, and β = 91.36(4)°. Single crystal structure analysis with least squares refinement of 627 parameters (5 900 reflections, 295 K) converged to Rg = 0.0324. There are six unique Li+ cations. The coordination polyhedra of Li(1), Li(2), Li(3), and Li(4) are linked by common edges to yield an eight membered centrosymmetric strand. The coordination polyhedra of the remaining two Li+ sites (Li(5), Li(6)) are connected to a dimeric unit via a common corner. All oxygen atoms of the Te(OH)6 molecule are involved in the coordination of Li+. However, only three oxygen atoms (O(13), O(18), O(23)) of the [TeMo6O24]6? anion which lacks crystallographic symmetry are involved in the coordination of Li+. The oxygen atoms of the anion act as proton acceptors in hydrogen bonds of predominantly medium strength. Te(OH)6 molecules and [TeMo6O24]6? anions connected by strong hydrogen bonds form an infinite chain. 相似文献
867.
Hai Pham Tuan Hans-Gerd Janssen Ellen M. Kuiper-van Loo Harm Vlap 《Journal of separation science》1995,18(9):525-534
Determination of trace concentrations of sulfur components in natural gas is a true analytical challenge. Only analytical procedures based on gas chromatography can meet the sensitivity and accuracy requirements dictated by environmental regulation institutions and modern chemical industry. In the present contribution the sample pretreatment and chromatographic separation steps have been evaluated and optimized based on the use of a flamebased sulfur chemiluminescence detector (SCD) for target compound detection. The proposed instrument consists of a programmed temperature vaporizing (PTV) injector employing a liner packed with Chromosorb 104, a 4 μm thick film apolar column and a flame-based SCD. Using a 13 mL sample loop the detection limit achievable with the new method is 3 μg S/m3. The precision of replicate measure. ments is generally in the range of 5–15% relative standard deviation. Lower detection limits can be achieved by preconcentrating larger sample volumes, e.g. 100 mL. 相似文献
868.
The methodology of J-based analysis applied to 1,3-methylcarboamido systems allowed us to deduce the relative configurations of the two leucine-like fragments of a new tetrachloro amino acid derivative dysithiazolamide, which was isolated from an unidentified sponge of the genus Dysidea. Furthermore, the absolute configuration was also proposed by comparison with analogous systems. 相似文献
869.
A. V. Virovets S. N. Konchenko P. S. Yuferov D. Fenske 《Journal of Structural Chemistry》2004,45(3):496-501
The crystal structures of three cluster compounds: [(µ-H)Fe2Mo(µ3-Te)(CO)8Cp*], [FeMo2(µ3-Te)(CO)7x Cp*2], and [FeMoW(µ3-Te)(CO)7CpCp*], where Cp = 5-C5H5, Cp* = 5-C5 (CH3)5, have been investigated. In the cluster with a tetrahedral {FeMo2Te} core, one can observe positional isomerism of the carbonyl and cyclopentadienyl ligands with respect to the plane through the Fe and Te atoms and the center of the Mo2bond, resulting in two mirror isomers in the racemic crystal. In the cluster with the {FeMoWTe} core, additional chirality causes the formation of four diastereoisomers. Earlier, the structure of the [FeMoW(µ3-Se)(CO)7Cp] cluster with Mo and W atoms coordinated to identical Cp-ligands has been structurally defined. In this crystal, statistical disordering of Mo and W over the metal positions is observed. In the [FeMo(Cp*)W(Cp)(µ3-Te)(CO)7] cluster studied here, the Mo and W atoms are coordinated to different cyclopentadienyl ligands. Due to this, two of four diastereoisomers were isolated as ordered racemic crystals; the other two are nonexistent for steric reasons.Original Russian Text Copyright © 2004 by A. V. Virovets, S. N. Konchenko, P. S. Yuferov, and D. FenskeTranslated from Zhurnal Strukturnoi Khimii, Vol. 45, No. 3, pp. 522–527, May–June 2004. 相似文献
870.
A. S. Saghiyan A. V. Geolchanyan L. L. Manasyan G. M. Mkrtchyan N. R. Martirosyan S. A. Dadayan T. V. Kochickyan V. S. Harutyunyan A. A. Avetisyan V. I. Tararov V. I. Maleev Yu. N. Belokon' 《Russian Chemical Bulletin》2004,53(4):932-935
An efficient method was developed for the asymmetric synthesis of (R)-S-(1,2,4-triazol-3-yl)cysteines by the addition of 3,4-disubstituted 1,2,4-triazole-5-thiols at the electrophilic C=C bond in a NiII complex of a Schiff base of dehydroalanine with (S)-N-(N-benzylprolyl)aminobenzophenone. The stereoselectivity of the formation of diastereomeric complexes with the (S,R) configuration under conditions of thermodynamic control of the nucleophilic addition exceeds 94%. Acid treatment of the reaction mixtures afforded enantiomerically pure (R)-S-hetarylcysteines (ee >98%). 相似文献