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71.
Francesco Demartin Fabrizia Fabrizi de Biani Cristina Femoni Maria Carmela Iapalucci Giuliano Longoni Piero Macchi Piero Zanello 《Journal of Cluster Science》2001,12(1):61-74
The [Ni36Pt4(CO)45]6- and [Ni37Pt4(CO)46]6- clusters have been obtained in mixture upon reaction in acetonitrile of [Ni6(CO)12]2- salts with K2PtCl4 in a 2.5:1 molar ratio. The two hexaanions were indistinguishable by spectroscopic techniques. Crystallization of their trimethylbenzylammonium salts led to crystals of composition 0.5[NMe3CH2Ph]6[Ni36Pt4(CO)45]-0.5[NMe3CH2Ph]6[Ni37Pt4(CO)46]·C3H8O, hexagonal,space group P63 (No. 173), a=17.853(9), c=27.127(13) Å, Z=2; final R=0.057. The metal core of the [Ni36Pt4(CO)45]6- anion consists of a Pt4 tetrahedron fully encapsulated in a shell of 36 Ni atoms belonging to a very distorted and incomplete 5 tetrahedron. The [Ni37Pt4(CO)46]6- hexaanion derives from the former by capping the unique triangular face of the metal polyhedron with an additional Ni(CO) fragment. The [Ni36Pt4(CO)45]6--[Ni37Pt4(CO)46]6- mixture is rapidly degraded to the known [Ni9Pt3(CO)21]4- cluster by exposure to carbon monoxide. Its reaction with protic acids initially affords the corresponding [H6-nNi36Pt4(CO)45]n--[H6-nNi37Pt4(CO)46]n- (n=5, 4) derivatives, and eventually leads to rearrangement to the known [H6-n Ni38Pt6(CO)48]n- species. Both [Ni36Pt4(CO)45]6--[Ni37Pt4(CO)46]6- and [HNi36Pt4(CO)45]5--[HNi37Pt4(CO)46]5- mixtures have been chemically and electrochemically reduced to their corresponding [Ni36Pt4(CO)45]n--[Ni37Pt4(CO)46]n- (n=7–9) and [HNi36Pt4(CO)45]n--[HNi37Pt4(CO)46]n- (n=6–8) mixtures. 相似文献
72.
Liquid chromatographic/electrospray ionization tandem mass spectrometric study of the phenolic composition of cocoa (Theobroma cacao) 总被引:2,自引:0,他引:2
Sánchez-Rabaneda F Jáuregui O Casals I Andrés-Lacueva C Izquierdo-Pulido M Lamuela-Raventós RM 《Journal of mass spectrometry : JMS》2003,38(1):35-42
Liquid chromatography coupled with ionspray mass spectrometry in the tandem mode (LC/MS/MS) with negative ion detection was used for the identification of a variety of phenolic compounds in a cocoa sample. Gradient elution with water and acetonitrile, both containing 0.1% HCOOH, was used. Standard solutions of 31 phenolic compounds, including benzoic and cinnamic acids and flavonoid compounds, were studied in the negative ion mode using MS/MS product ion scans. At low collisional activation, the deprotonated molecule [M - H](-) was observed for all the compounds studied. For cinnamic and benzoic acids, losses of CO(2) or formation of [M - CH(3)](-*) in the case of methoxylated compounds were observed. However, for flavonol and flavone glycosides, the spectra present both the deprotonated molecule [M - H](-) of the glycoside and the ion corresponding to the deprotonated aglycone [A - H](-). The latter ion is formed by loss of the rhamnose, glucose, galactose or arabinose residue from the glycosides. Different fragmentation patterns were observed in MS/MS experiments for flavone-C-glycosides which showed fragmentation in the sugar part. Fragmentation of aglycones provided characteristic ions for each family of flavonoids. The optimum LC/MS/MS conditions were applied to the characterization of a cocoa sample that had been subjected to an extraction/clean-up procedure which involved chromatography on Sephadex LH20 and thin-layer chromatographic monitoring. In addition to compounds described in the literature, such as epicatechin and catechin, quercetin, isoquercitrin (quercetin-3-O-glucoside) and quercetin-3-O-arabinose, other compounds were identified for the first time in cocoa samples, such as hyperoside (quercetin-3-O-galactoside), naringenin, luteolin, apigenin and some O-glucosides and C-glucosides of these compounds. 相似文献
73.
Cristina Giovannoli Gianfranco Giraudi Cinzia Tozzi Marcello Dolci 《Analytica chimica acta》2003,478(2):271-280
An enzyme-linked immunosorbent assay (ELISA) was used for the determination of fenoxycarb in apple leaf samples. Single step extraction procedures with phosphate-citrate buffered solution containing different amounts of methanol were tested showing that a solvent percentage of 20% (v/v) was the best condition, with recoveries between 85 and 100% in the working range of 25-500 μg kg−1 and a negligible matrix effect. The low detection limit reached, 1 μg kg−1 against 50 μg kg−1 for the recommended liquid chromatographic method, makes the ELISA more suitable for determinations of the fenoxycarb residues in apple leaf samples. The reliability of the ELISA was evaluated by assaying the insecticide in spiked and contaminated samples by three different approaches: direct determination, standard addition method with a calibration graph, and the dilution test. The corresponding coefficients of variation were, respectively, 11, 22 and 27%. The direct determination on the (1+1) diluted apple leaf extract was used to measure the insecticide residues in samples collected in the north-eastern Italian regions of Veneto and Trentino-Alto Adige. 相似文献
74.
Cristina Tealdi Lorenzo Malavasi Giorgio Flor 《Journal of solid state chemistry》2004,177(11):4359-4367
Atomistic computer simulation techniques have been used, for the first time, to reproduce the crystal structure of MgTa2O6 and to investigate the defect chemistry and dopant properties of this material. The calculated defect energetics suggest that the concentration of intrinsic atomic defects in this phase is insignificant and that the system is probably stable to both oxidation and reduction. Dopant solution energy versus ion size trends are found for both isovalent and aliovalent dopant incorporation at Mg and Ta sites. Divalent dopants (e.g. Ca, Cu) preferentially occupy the Mg site whereas dopants with higher charge (e.g. Sc, Zr, Nb) are more favorable on the Ta site. High migration activation energies (>2 eV) predict limited ionic conductivity in this material. 相似文献
75.
Cristina Rota Lino Liverani Franco Spelta Giuseppe Mascellani Aldo Tomasi Anna Iannone 《Research on Chemical Intermediates》2006,32(1):73-81
The use of low-molecular-weight heparins (LMWHs) has become common, since compared to unfractionated heparin (UFH), they have
a much longer plasma half-life and lower incidence of side effects. LMWHs are derived from the depolymerization of UFH, obtained
either chemically, physically or enzymatically. We employed electron spin resonance (ESR) spectroscopy to study the depolymerization
of UFH by copper in the presence of hydrogen peroxide. A stable nitroxide radical was detected. This could be generated by
the hydroxyl radical attack either to the N-SO−3 group or to free amino groups present in the UFH preparation. 相似文献
76.
Pinto FG Andrada D Magalhães CG Nunes BR de Amorim FR Franco MB Saint'pierre TD da Silva JB Curtius AJ 《Analytical and bioanalytical chemistry》2005,383(5):825-832
Different chemical modifiers for use with electrothermal atomic absorption spectrometry (ET AAS) were investigated in relation
to determining the selenium in human urine samples. The samples were diluted in a solution containing 1% v/v HNO3 and 0.02% m/v cetyltrimethylammonium chloride (CTAC). Studying the modifiers showed that the use of either Ru or Ir as the
permanent modifier gave low sensitivity to Se and the peak shape was very noisy, while Zr or Rh gave no peak at all. The same
occurred when Zr was used in solution. For mixtures of permanent modifiers, Ir plus Rh or Zr plus Rh gave very low sensitivity,
Zr plus Rh with co-injection of Ir in solution was also not efficient, Zr plus Rh in solution gave good sensitivity, but the
best results were obtained with a mixture of Zr and Rh as the permanent modifier and co-injection of Rh in solution. Using
this last modifier, the following dilutions with the HNO3 and CTAC were studied: 1:1, 1:2, 1:3 and 1:4. The best dilution was 1:1, which promoted good sensitivity and a more defined
peak shape and made it possible to correct for the background using a deuterium arc lamp. Under these conditions, a characteristic
mass of 26±0.2 pg was obtained for Se in aqueous solution. Six certified urine samples were analyzed using matrix matching
calibration and the measured concentrations were in agreement with the certified values, according to a t-test at the 95%
confidence level. Recovery tests were carried out and the recoveries were in the range 100–103%, with relative standard deviation
better than 9%. The limit of detection (LOD, 3 sd, n=10) was 3.0 μg L−1 in the sample. The treated graphite tube could be used for at least 600 atomization cycles without significant alteration
of the analytical signal. 相似文献
77.
Complete 1H and 13C NMR assignments of aurasperone A and fonsecinone A, two bis-naphthopyrones produced by Aspergillus aculeatus 总被引:1,自引:0,他引:1
Campos FR Barison A Daolio C Ferreira AG Rodrigues-Fo E 《Magnetic resonance in chemistry : MRC》2005,43(11):962-965
Complete assignments of 1H and 13C NMR chemical shifts of the polyketides aurasperone A and fonsecinone A were made by means of nuclear Overhauser enhancement and heteronuclear NMR correlation experiments. These compounds were isolated for the first time from Aspergillus aculeatus, an endophytic fungus obtained from leaves of Melia azedarach(Meliaceae). 相似文献
78.
Nieto-Oberhuber C López S Echavarren AM 《Journal of the American Chemical Society》2005,127(17):6178-6179
New Au(I) complexes with bulky, biphenyl phosphines are the most reactive catalysts for the cyclizations of enynes. 1,6-Enynes with an aryl ring at the alkyne give 2,3,9,9a-tetrahydro-1H-cyclopenta[b]naphthalenes by a 5-exo-dig cyclization followed by a Nazarov-type ring expansion. 1,8-Dien-3-ynes also cyclize by a 5-exo-dig pathway to form hydrindanes. 相似文献
79.
José R. Masaguer María Antonia Mendiola Cristina Molleda 《Transition Metal Chemistry》1985,10(10):387-389
Summary 2-Pyridylphenylacetonitrile (ppa) is oxidized by copper(II) halides in 1,2-dichloroethane to 1,2-dicyano-1,2-diphenyl-1,2-di(2-pyridyl)ethane (dcppe), yielding 41 complexes of dcppe with copper(II) dihalide, [CuX2(dcppe)4] (green). Nickel(II) and zinc(II) chlorides react with ppa giving complexes of a general formula [MCl2(ppa)2].Dcppe reacts with copper(II), zinc(II) chlorides and copper(II) bromide yielding complexes of formulae [CuCl2(dcppe)4] (yellow), [ZnCl2(dcppe)2] and [CuBr2(dcppe)]. No reaction is observed with cobalt(II) and nickel(II) chlorides. 相似文献
80.
Valeria Di Bussolo Giorgio Catelani Ettore Mastrorilli Cristina Di Bugno Raffaello Giorgi 《Tetrahedron: Asymmetry》1996,7(12):3585-3592
(±)-1-Cyclohexyl-c-2-hydroxymethyl-r-1-cyclohexanol 3, a precursor of the antimuscarinic drug Rociverine 1, was obtained diastereospecifically in very high yield, from the Grignard reaction between C6H11MgCl and an appropriately protected 2-(hydroxymethyl)cyclohexanone. The preparation of enantiomerically enriched cis diol (+)-(1R,2S)-3 and the corresponding 2-acetoxymethyl derivative (+)-(1S,2R)-12 was achieved by lipase PPL-catalyzed transesterification of racemic diol (±)-3. 相似文献