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71.
Bossée A Afonso C Fournier F Tasseau O Pepe C Bellier B Tabet JC 《Journal of mass spectrometry : JMS》2004,39(8):903-912
Peptide metallation with Cu2+ was explored in the negative ESI mode using an ion trap mass spectrometer. Under these conditions, the [(M-3H) + CuII]- species formed were investigated under low-energy collision-induced dissociation conditions. MS2 experiments indicate a very different behavior of CuII metallated complexes compared with [M-H]- species. CuII induces an easy loss of CO2 and specific side-chain cleavages (by radical losses) at the C-terminal residue, as observed previously by prompt 'in source' dissociation experiments. The loss of CO2 yields an unstable carbylide that leads to further dissociations involving the migration of a proton or a hydrogen radical (through the reduction of CuII). Multistage MS3 experiments were carried out to rationalize this behavior. Fragmentation pathways are proposed in order to explain the product ions observed. The side-chain radical loss at the C-terminus was demonstrated to be a consecutive process. Finally, evidence is provided that the specific side-chain cleavages can be used for the differentiation of Leu/Ile and Gln/Lys residues when they are located at the C-terminus. The existence of a zwitterionic form in the case of the anionic YGGFK-CuII complex is proposed. 相似文献
72.
Hélder A. Santos Elisabete S. Ferreira Elisa J. Pereira Carlos M. Pereira Prof. Kyösti Kontturi Prof. Fernando Silva Prof. 《Chemphyschem》2007,8(10):1540-1547
The interaction between glucose oxidase (GOx) and phospholipid monolayers is studied at the 1,2-dichloroethane/water interface by electrochemical impedance spectroscopy. Electrochemical experiments show that the presence of GOx induces changes in the capacitance curves at both negative and positive potentials, which are successfully explained by a theoretical model based on the solution of the Poisson-Boltzmann equation. These changes are ascribed to a reduced partition coefficient of GOx and an increase of the permittivity of the lipid hydrocarbon domain. Our results show that the presence of lipid molecules enhances the adsorption of GOx molecules at the liquid/liquid interface. At low lipid concentrations, the adsorption of GOx is probably the first step preceding its penetration into the lipid monolayer. The experimental results indicate that GOx penetrates better and forms more stable monolayers for lipids with longer hydrophobic tails. At high GOx concentrations, the formation of multilayers is observed. The phenomenon described here is strongly dependent on 1) the GOx and lipid concentrations, 2) the nature of the lipid, and 3) the potential drop across the interface. 相似文献
73.
Grez P Celedón C Molinari A Oliva A Orellana M Schrebler R del Río R Córdova R 《The journal of physical chemistry. B》2005,109(48):22920-22927
The interaction of the ethyl xanthate (EX) anion with a copper electrode in a borate buffer solution, pH 9.2, has been investigated by cyclic voltammetry (CV), electrochemical quartz crystal microbalance (EQCM), electrochemical impedance spectroscopy (EIS), and measurements of contact angle (CA) under controlled potential. The results obtained allow establishing that, in the potential range from -0.80 and -0.60 V, two parallel reactions were characterized. These reactions were the ethyl xanthate electroadsorption and the hydrogen evolution reaction (HER). This last reaction has not been described by previous authors. Besides, the EIS measurements show that the mechanism of the HER on copper electrodes is not affected by the presence of a ethyl xanthate species. The EQCM study shows that in the electrodesorption process the departure of each ethyl xanthate species from the copper electrode is accompanied with the simultaneous entry of four to five water molecules. This fact is in accordance with the number of copper atoms involved in the adsorption of one ethyl xanthate species. 相似文献
74.
A new one-step facile method for the synthesis of 1,12,3,4-tetrahydro5H-5-oxo-1,4-benzo-diuzepines is described. The method involves the addition of methyl anlhranilates to elhyl-enimine followed by intramolecular cyclizalion of the resulting intermediate compounds. Another attempted method starting from β-anilinoethylisocyanales is also described. 相似文献
75.
Coronado E Galán-Mascarós JR Martí-Gastaldo C Palomares E Durrant JR Vilar R Gratzel M Nazeeruddin MK 《Journal of the American Chemical Society》2005,127(35):12351-12356
The selectivity and sensitivity of two colorimetric sensors based on the ruthenium complexes N719 [bis(2,2'-bipyridyl-4,4'-dicarboxylate)ruthenium(II) bis(tetrabutylammonium) bis(thiocyanate)] and N749 [(2,2':6',2' '-terpyridine-4,4',4' '-tricarboxylate)ruthenium(II) tris(tetrabutylammonium) tris(isothiocyanate)] are described. It was found that mercury ions coordinate reversibly to the sulfur atom of the dyes' NCS groups. This interaction induces a color change in the dyes at submicromolar concentrations of mercury. Furthermore, the color change of these dyes is selective for mercury(II) when compared with other ions such as lead(II), cadmium(II), zinc(II), or iron(II). The detection limit for mercury(II) ions--using UV-vis spectroscopy--in homogeneous aqueous solutions is estimated to be approximately 20 ppb for N719 and approximately 150 ppb for N749. Moreover, the sensor molecules can be adsorbed onto high-surface-area mesoporous metal oxide films, allowing reversible heterogeneous sensing of mercury ions in aqueous solution. The results shown herein have important implications in the development of new reversible colorimetric sensors for the fast, easy, and selective detection and monitoring of mercuric ions in aqueous solutions. 相似文献
76.
Optimization of solid-phase clean-up prior to liquid chromatographic analysis of ochratoxin A in roasted coffee 总被引:2,自引:0,他引:2
An extraction and clean-up method for ochratoxin A (OA) in roasted coffee has been developed and the HPLC method optimized. An interfering compound with a similar retention time as OA was adsorbed by the aminopropyl (NH2) material at < or = 5% NaHCO3. Residual OA on the column was recovered by washing with the extraction solution followed with methanol. Fractions were mixed together for further clean-up with Ochratest immunoaffinity columns (IACs). Analysis by HPLC resulted in a well resolved OA peak and reduction in matrix interferences. Recoveries ranged from 72 to 84% and the detection limit was 1 ng/g. 相似文献
77.
Reactions of W(CO)(6) with formamidines contrast with those of Mo(CO)(6) and Cr(CO)(6) in that the former do not yield quadruply bonded dimetal species. From the reaction of W(CO)(6) with HDAniF (HDAniF = N,N'-di-p-anisylformamidine), several new ditungsten carbonyl compounds (W(2)(mu-CO)(2)(mu-DAniF)(2)(eta(2)-DAniF)(2) (1), W(2)(mu-CO)(2)(mu-DAniF)(2)(eta(2)-DAniF)(eta(2)-CH(2)DAniF) (2), and W(2)(mu-CO)(mu-CNC(6)H(4)OCH(3))(mu-DAniF)(2)(eta(2)-DAniF)(2) (3)) have been isolated and fully characterized. In 2, CH(2)DAniF represents a DAniF ligand in which a methylene group has been added to one of the nitrogen atoms. This ligand binds to the tungsten atom using a nitrogen and a carbon atom. Compound 1 has a tungsten-tungsten bond distance of 2.476(1) A and a planar W(2)(mu-CO)(2) core structure which has C(2)(h)() symmetry with short and long W-C bond distances (1.99(1) and 2.28(1) A, respectively). DFT calculations on a model of 1 indicate that (a) the C(2)(h)() instead of D(2)(h)() symmetry of the ditungsten core may be attributed to W --> CO pi back-bonding interactions and (b) the bond between the tungsten atoms may be formulated as a double bond. The new tetragonal paddlewheel compound W(2)(DAniF)(4) (4) and the edge-sharing bioctahedron W(2)(mu-O)(mu-NC(6)H(3)Cl(2))(mu-D(Cl)PhF)(2)(eta(2)-D(Cl)PhF)(2) (5) (D(Cl)PhF = N,N'-di-(3,5-dichlorophenyl)formamidinate) have also been prepared. 相似文献
78.
[reaction: see text] Direct asymmetric catalytic Michael reactions have been performed using chiral-amine/acid bifunctional catalysts. Performed with 0.3 equiv of (S)-(+)-1-(2-pyrrolidinylmethyl)pyrrolidine and 0.3 equiv of trifluoroacetic acid as the catalyst, the reaction of alpha,alpha-dialkylaldehydes with (E)-beta-nitrostyrene provided the alpha,alpha-dialkyl Michael products in up to 96% yield with up to 91% ee. With respect to enantioselectivity, l-proline was a poor catalyst of this class of Michael reactions. 相似文献
79.
Carlos Díaz 《Polyhedron》1985,4(7):1269-1270
The reaction of copper(II) perchlorate hexahydrate with a number of sulphur(II) compounds in acetonitrile as solvent were studied. It is found that SCl2, N,N′-thiobisamines S(NR2)2, ethoxythiomorpholineC2H5O-S-Nand pentacarbonyl (thiobismorpholine) chromium(O)[Cr(CO)5·S(NO)2]reduce Cu(II) with formation of the complex Cu[(CH3CN)4]CIO4 and SO2. 相似文献
80.
Michel Spiesser Robert P. Gruska S.N. Subbarao Carlos A. Castro Aaron Wold 《Journal of solid state chemistry》1978,26(2):111-114
Crystals of antimony-doped In2Se3 were grown by the Bridgeman method. This compound, whose composition is In1.8Sb0.2Se3, appears to be isostructural with In1.9As0.1Se3. The refined unit cell parameters are a = 3.97(1), c = 18.87(1) Å. Orthorhombic crystals of InSbSe3 were grown from an isothermal melt. The refined unit cell parameters are a = 9.43(1), b = 14.02(5), and c = 3.96(1) Å. These parameters agree with those determined for α-InSbSe3 by other studies. The observed densities measured by a hydrostatic technique are 5.98(3) g/cm3 for In1.8Sb0.2Se3 and 6.07(2) g/cm3 for InSbSe3. The room temperature dc resistivity for In1.8Sb0.2Se3 has been found to be 4.4 × 104 Ω-cm, whereas that of InSbSe3 has been found to be 15.2(1) Ω-cm. A resistivity versus temperature study has beenn carried out for InSbSe3 between 230 and 400°K. Optical studies indicate that In1.8Sb0.2Se3 is an n-type semiconductor with a band gap of 1.1 eV and InSbSe3 is a p-type semiconductor with a band gap of 0.92 eV. 相似文献