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111.
A comparison of different nebulisers for direct hyphenation of capillary and nano liquid chromatography (Cap-LC, Nano-LC) and quadrupole-based collision cell inductively coupled plasma mass spectrometry (CC-ICP–MS) for phosphorylation profiling of tryptic protein digests is described. Helium was used as cell gas and specially tuned instrumental conditions were used to achieve background minimisation at the mass of phosphorus, because of kinetic energy discrimination of the interfering polyatomic ions. The proposed set-up is based on a modified capillary electrophoresis interface and a home-made 4 mL spray chamber. It enables the use of gradient conditions with a highly concentrated organic mobile phase as often used in protein phosphorylation analysis, without the need to apply membrane desolvation for removal of the organic phase or further background minimisation. No significant signal suppression or other negative effects caused by the organic mobile phase occur, because of the low flow rates used in Cap-LC and the robust plasma conditions of the CC-ICP–MS instrument. A tryptic digest of beta-casein was investigated as model compound to demonstrate the applicability of the proposed set-up for phosphorylation profiling in protein analysis using quadrupole based collision-cell ICP–MS as phosphorus-specific detector. Detection limits for phosphorylated peptides down to the sub picomole level were obtained. As a complementary technique, electrospray ionisation tandem mass spectrometry (ESI–MS–MS) with data base searching was used for further characterisation of the phosphorylated peptides detected. 相似文献
112.
2-C5H5(CO)2[P(OMe)3]Mo(W)-substituted 4,4,5,5-tetramethyl-1,3,2-dioxarsolanes and -dioxaphospholanes (Ia–Ic) are obtained from C5H5(CO)3M derivatives via CO/P(OMe)3 exchange. In all cases the phosphite ligand appears trans to the σ-bonded arsenic heterocycle, which prefers a conformation with the transition metal group in an axial position. The dioxaphospholane-metal (Ia) undergoes isomerization with alkyl migration at 0°C, which due to stereochemical reasons can only occur by an intermolecular mechanism. 相似文献
113.
The products of decomposition of solutions of p-chlorobenzenediazonium tetrafluoroborate in aqueous buffer solutions (pH 9.0–10.3; ionic strength 0.1–0.5) at 20.0° have been analyzed quantitatively. Up to eleven low molecular weight compounds could be identified besides the major product, the complex polymeric diazo tar. The distribution of products is influenced by trace amounts of oxygen as well as by p-chlorophenol and the radical trapping reagent iodoacetic acid. Mechanisms of formation of the products are discussed. 相似文献
114.
Peter Roschger Werner Fiala Wolfgang Stadlbauer 《Journal of heterocyclic chemistry》1992,29(1):225-231
4-Chloro-3-nitro-2-quinolones 3 obtained from the 4-hydroxy quinolones 1 by nitration and chlorination, reacted with sodium azide to the 4-azido derivatives 4 which cyclized on thermolysis to yield the furoxanes 5 . Nucleophilic substitution reactions of 3 led to the 4-amino-, 4-fluoro- and 4-alkoxy-3-nitroquinolones 7, 8 and 9 , respectively. With thiols either 4-thio-3-nitro- 10 or 3,4-dithioquinolones 11 were obtained depending on the basic catalyst. 相似文献
115.
Qijin Chi Wolfgang Göpel Tautgirdas Ruzgas Lo Gorton Peter Heiduschka 《Electroanalysis》1997,9(5):357-365
The electrochemical properties of carbon paste electrodes (CPEs), including unmodified and modified with protein and polycations, were investigated by impedance spectroscopy (IS) using ferricyanide and ferrocene monocarboxylic acid (FcMA) as redox probes. Various electrochemical pretreatments were applied to the unmodified CPE. The heterogeneous charge transfer rate constant of ferro/ferricyanide couple is enhanced by 2 to 10 times compared with that obtained at untreated electrodes. It was found that for ferricyanide the more suitable pretreatments are successive cyclic voltammetric scans, cathodization and a square wave-like stepping rather than high-potential anodization. However, the pretreatment only exhibits a slight effect on the kinetics of FcMA. At the CPEs containing modifier, the electron transfer rate of the redox couple depends more on the pH of electrolyte solution if ferro/ferricyanide is used. The results can be explained by the differently charged states of the CPEs that were caused by the protonation or deprotonation of the modifiers in various pH solutions and demonstrate the importance of the electrostatic interaction on the kinetics of the highly polar species such as ferricyanide. The different adsorptive behavior of ferricyanide and FcMA is also discussed. 相似文献
116.
Natural irones from the essential oil of Iris rhizomes develop by oxidative degradation of C31-triterpenoids produced by the plant. Two enantiomeric forms of irones are found in Iris, oils of different origin. The optical properties and CD spectra of irones, dihydroirones and their C31-precursors are reported and their absolute stereochemistry is determined. 相似文献
117.
Chloro-dimethylaminosulfonium Salts. Preparation and I. R. Spectra By reaction of bis-dimethylamino-mono- resp. -disulfane with a mixture of chlorine/antimony(V) chloride the chloro dimethylaminosulfonium hexachloroantimonates(V) [(CH3)2N]2SCI⊕SbCl6? (I) and (CH3)2NSCI2⊕SbCl6? (II) are yielded. The i. r. spectra of these compounds were measured and assigned. 相似文献
118.
The goal of this work was the development of a novel type of heterogeneous catalyst, consisting of bare metal nanoparticles
on stainless steel foils, which can be shaped to any kind of architecture and, if necessary, heated electrically. Solutions
of pre-prepared, ligand protected and monodispersed gold, palladium, platinum and rhodium nanoparticles were sprayed onto
stainless steel foils, followed by the careful removal of the ligand molecules by an oxygen plasma treatment. Due to this,
bare particles become irreversibly fixed on the steel support. It could be shown that the original particle sizes do not change
during the plasma treatment. Foils, densely coated with the nanoparticles, were used for gas phase catalyses in a self-made
reactor at room temperature or at 60 °C. Hydrogenation of 1,3-butadiene at 15 nm Pd and 2 nm Pt, CO oxidation at 16 nm, 8 nm
and 1.4 nm gold and NO reduction with NH3 at 2 nm Rh particles were performed, indicating that the novel catalysts might in principle be applicable in technical processes
if the experimental conditions like form and temperature would be optimized.
Dedicated to Professor Dieter Fenske on the occassion of his 65th birthday. 相似文献
119.
Solution equilibrium studies on Cu(II)-, Ni(II)- and Zn(II)-N-Me-β-Alaninehydroxamic acid (N-Me-β-Alaha), -N-Me-α-alaninehydroxamic acid (N-Me-α-Alaha), -Imidazole-4-carbohydroxamic acid (Im-4-Cha), -N-Me-imidazole-4-carbohydroxamic acid (N-Me-Im-4-Cha) and -Imidazole-4-acetohydroxamic acid (Im-4-Aha) systems have been performed by pH-potentiometry, UV–Vis spectrophotometry, EPR, CD, ESI-MS and 1H NMR methods. According to the results: (i) the amino-N atoms are more basic in N-Me-α-Alaha and N-Me-β-Alaha than the hydroxamate function, but the trend is just the opposite between the imidazole-N(3) and hydroxamate. (ii) The metal ion anchor is always the hydroxamate part in the amino acid derivatives, while it is always the imidazole-N(3) in the studied imidazolehydroxamic acids. (iii) The three studied N-Me derivatives do not form metallacrowns. Only hydroxamate type chelate is formed with N-Me-β-Alaha, but with N-Me-α-Alaha a new type of coordination mode (via amino-N and hydroxamate-O) also exists. N-Me-Im-4-Cha also forms a dinuclear complex, [M2L3], with Cu(II) and Ni(II) (but not with Zn(II)). In this complex, one of the three ligands might bridge the two metal ions (five-membered hydroxamate-(O,O) plus five-membered (Nim, Ocarb) bridging bis-chelating mode), while each of the additional two ligands binds to one metal. (iv) The two studied N–H derivatives, having dissociable proton on the hydroxamic-N, are able to form metallacrown species. A pentanuclear complex, [M5L4H−4], is exclusively formed above pH 4 between Cu(II) and Im-4-Aha. Interestingly, this 12-metallacrown-4 type complex, although together with various mononuclear binding isomers, appears also with Ni(II) and Zn(II). Unfortunately, the complexes of Im-4-Cha are not soluble in water at physiological pH at all. 相似文献
120.
Wolfgang Marterer Horst Prinzbach Grety Rihs Jakob Wirz Jaques Lecoultre Edgar Heilbronner 《Helvetica chimica acta》1988,71(8):1937-1965
The propensity of the N?N bond to undergo photo [2 + 2] cycloadditions has been further explored. In the specifically designed 1,5-azo/enes 1–3 , no [2 + 2] cycloaddition has been observed upon either direct or sensitized excitation with light of various wave lengths at temperatures down to 77 K, in line with expectations based on X-ray ( 1 : d = 2.71 Å, ω = 129°) and PE measurements ( 1 : I1 = 8.00, I2 = 9.05 eV; 2 ; I1 = 8.00, I2 = 9.25eV). The steric/stereoelectronic demands for the participation of the N?N bond in pericyclic reactions are clearly more stringent than those for the C?C bond. 相似文献