Accurate mass measurements of positive ions in the desorption chemical ionization mode

Desorption chemical ionization mass spectrometry employing ammonia as the reagent gas has been extensively used to obtain molecular mass and structural information on a wide variety of compounds. Mass-deficient reference standards normally used for calibration purposes in mass spectrometry do not provide adequate mass spectra under ammonia chemical ionization conditions. In order to overcome this problem a mixture of ammonia and methane as reagent gases was employed. In high-resolution accurate mass measurement experiments, this gas mixture allows the simultaneous detection of mass spectra of perfluorokerosene adequate for calibration purposes and spectra containing molecular mass information of the analyte. A needle valve system was used to control the composition of the gas mixture introduced into the ion source. For positive-ion accurate mass measurements of higher masses (up to m/z = 2300), Fomblin 18/8 oil was successfully used as a reference standard under ammonia, methane and isobutane desorption chemical ionization conditions.     

Arsenic biomethylation by the microorganism apiotrichum humicola in the presence of l-methionine-methyl-d3

The microorganism Apiotrichum humicola (previously known as Candida humicola) grown in the presence of either arsenate, arsenite, methylarsonic acid or dimethylarsinic acid, produces arsenic-containing metabolites in the growth medium. When L-methionine-methyl-d₃ is added to the cultures, the CD₃ label is incorporated intact into the metabolites to a considerable extent to form deuterated dimethylarsenic and trimethyl-arsenic species, indicating that S-adenosylmethionine, or some related sulphonium compound, is involved in the biological methylation. Conclusive evidence of CD₃ incorporation in the arsenicals found in the growth medium was provided by using a specially developed hydride generation-gas chromatography-mass spectrometry system (HG–GC–MS).     

New Triterpenes from the Bark of Western White Pine (Pinus monticola DOUGL.)

Eleven new triterpenes with the lanostene-type skeleton were isolated from the benzene extract of western white pine bark. Their structures were determined mainly on the basis of physical and spectral data.     

Molar extinction coefficients of some carbohydrates in aqueous solutions

Molar extinction coefficients of some carbohydrates viz. l-arabinose (C₅H₁₀O₅), d-glucose (C₆H₁₂O₆), d-mannose (C₆H₁₂O₆), d-galactose (C₆H₁₂O₆), d(-) fructose (C₆H₁₂O₆) and maltose (C₁₂H₂₄O₁₂) in aqueous solutions have been determined at 81, 356, 511, 662, 1173 and 1332 keV by gamma ray transmission method in a narrow beam good geometry set-up. These coefficients have been found to depend upon the photon energy following a 4-parameter polynomial. These extinction coefficients for different sugars having the same molecular formula have same values varying within experimental uncertainty. Within concentration ranges studied, Beer-Lambert law is obeyed very well.     

Detection of lyso-platelet-activating factor by high-performance liquid chromatography after derivatisation with fluorescent fatty acids

Lyso-platelet-activating factor (lyso-PAF) was derivatised with 9-anthracenepropionic acid in the presence of dicyclohexylcarbodiimide, p-toluenesulfonic acid and 4-dimethylaminopyridine. The reaction yield exceeded 90% when the fatty acid was present in double molar amounts versus lyso-PAF. The procedure was equally effective in the derivatisation of other lysophospholipids. The derivatized phospholipids are detected by ultraviolet absorption (lambda = 253 nm) or fluorescence detection (using excitation at 254 nm and emission at 450 nm). The technique was applied successfully to the detection of lyso-PAF in complement activated rabbit plasma.     

Isolation and synthesis of glutamine and glutarimide derivatives fromCroton humilis

Extract ofCroton humilis L. were shown to contain N - [N - (2 - methylpropanoyl) -l - glutaminoyl] - 2 - phenylethylamine, N - [N - 2R - methylbutanoyl) -l - glutaminoyl] - 2 - phenylethylamine, 2 - [N- (2 - methylpropanoyl)] - N - phenylethylglutarimide and 2 - [N- (2R - methylbutanoyl)] - N - phenylethylglutarimide. Structural proof was based on acid degradation, spectral studies as well as the synthesis of N - [N- (2- methylpropanoyl) -l - glutaminoyl] - 2 - phenylethylamine and 2 - [N - (2 - methylpropanoyl] - N - phenylethylglutarimide.     

Synthesis of Novel Receptors From 7-Deoxycholic Acid and Studies on Their Cation Binding Properties

The synthesis and cation binding properties of chiral crown ethers derived from 7-deoxycholic acid along with their application in asymmetric Michael reaction are described.     

Ion-molecule reactions of dimethyl ether cations with polycyclic aromatic hydrocarbons in a quadrupole ion trap mass spectrometer

The reaction chemistry between dimethyl ether (DME) cations and polycyclic aromatic hydrocarbons (PAHs) was elucidated by isolating three different types of DME ions using a quadrupole ion trap and reacting them individually with neutral PAH molecules eluting from a gas chromatographic column. The results obtained show that the CH(2)OCH(3)(+) ion (m/z 45) reacts via adduct formation followed by elimination of CH(3)OH, the (CH(3))(2)OH(+) (m/z 47) ion serves as proton donor and the (CH(3))(3)O(+) ion (m/z 61) does not yield any reaction products. Copyright 1999 John Wiley & Sons, Ltd.     

离子液体作为溶剂/催化剂用于卤代烃对胺的选择性烷基化反应

在三乙胺存在下,在离子液体([bmim]I和[bmim]PF6)中进行了各种卤代烃对胺类化合物中氨基的选择性烷基化反应.反应在相对温和的条件下进行,转化率和选择性优异.离子液体可以回收并重复使用.