Pegamine: A new alkaloid fromPeganum harmala

Chemistry of Natural Compounds - The structure of pegamine has been established from its UV, IR, NMR, and mass spectra. 2. A fragmentation scheme for pegamine on mass spectrometry has been proposed.     

Efficient syntheses of 2,3-disubstituted natural quinazolinones via iridium catalysis

Natural products sclerotigenin, pegamine, deoxyvasicinone, mackinazolinone, and rutaecarpine were synthesized. Core quinazolinone structures were constructed via Ir catalysis.     

Two New Alkaloids from the Aerial Part of Peganum nigellastrum

Two new alkaloids, pegamine β‐D ‐glucopyranoside ( 1 ) and 2‐deoxypeganylacetic acid ( 2 ), together with the novel 3,4‐dihydro‐4‐hydroxynaphthalene‐2‐carboxylic acid ( 3 ), were isolated from the aerial part of Peganum nigellastrum. The structures of these compounds were elucidated on the basis of spectroscopic analyses, including 1D‐ and 2D‐NMR, and ESI‐MS/MS.     

A mass-spectrometric study of arnifolin, a new sesquiterpene lactone from Arnica montana and A. foliosa

Summary The mass spectra of arnifolin and [D]arnifolin have been obtained, and the fragmentation of arnifolin under the action of electron impact has been studied.A scheme of the fragmentation of arnifolin explaining the main peaks in its mass spectrum has been put forward. The mass spectrum agrees well with the structure established for this substance.All-Union Scientific-Research Institute of Medicinal Plants. Translated from Khimiya Prirodnykh Soedinenii, No. 5, pp. 587–590, September–October, 1971.     

Chemical ionization mass spectra of 2, 4, 6-trinitroaromatic compounds

The methane and isobutane chemical ionization mass spectra of ten 2,4,6-trinitroaromatic compounds have been recorded. The mass spectra contain intense [M + 1]⁺ ions and usually little fragmentation. However, in some cases major fragmentation processes have been observed. Some unusual adduct ions have been found with isobutane as the reagent and their temperature dependence has been studied.     

Effect of different arrangements of point source,aluminum absorber and detector on mass absorption coefficient of beta-particles

Summary The transmission of 0.766 MeV beta-particles emitted from ²⁰⁴Tl through aluminum has been investigated for different arrangements of point source, absorber and detector. In the first arrangement, the mass absorption coefficient (μ_m) has been measured as a function of the absorber to the source distance (H_AS), when the absorber foil was placed just above the window of a surface barrier solid state detector. In the second arrangement, the mass absorption coefficient has been measured as a function of the absorber to detector distance (H_AD), when the absorber foil was placed just on the source. The measured mass absorption coefficients of beta-particles have been compared to the values gained in a previous work.     

The structure of tetramycin,a new polyene macrolide antibiotic

The structure of the tetraene antifungal antibiotic tetramycin has been established by detailed studies of mass, ¹H and ¹³C NMR spectra as well as by chemical degradation. A newly developed mass analysis has been introduced for determining the carbon skeleton of the aglycone.     

Thermolysis and analysis of TDI char by supercritical methanol using TGA,DSC, IR and SEM

Journal of Thermal Analysis and Calorimetry - TDI's synthetic plant generates about 5 mass % of tar by phosgenation process, which has been currently a bottleneck needed to be broken through...     

Synthesis, characterisation and mass spectrometric fragmentation of O-(chlorodifluoroacylated) alcohols

An indirect and uncatalysed esterification of chlorodifluoroacetic acid with polyfluoro and hydrocarbon alcohols has been developed. The method which involves the reaction between sodium chlorodifluoroacetate and alcohols in dimethylformamide (DMF) is particularly facile with polyfluorinated alcohols resulting in esters in 71-85% yield. The esters have been characterised on the basis of ¹H and ¹⁹F NMR and mass spectral data. The electron impact (EI) mass spectrometric fragmentation of these polyfluorinated esters have shown some interesting features which have been substantiated by using tandem mass spectrometry.     

Photodegradation kinetics of aniline, 4-ethylaniline, and 4-chloroaniline in aqueous suspension of polycrystalline titanium dioxide

The photodegradation process of aniline, 4-ethylaniline, and 4-chloroaniline in aqueous suspension of irradiated TiO₂ (anatase) powder has been investigated. A batch photoreactor with immersed lamp irradiating in the near-UV region has been used for carrying out the reactivity experiments. For each substrate the influence of the initial concentration of organic compound and of pH on the degradation rate has been investigated. The main intermediates and the end products have been identified and determined, the total mass balance being satisfied. The kinetic modelling of the series of reactions occurring in the system has been satisfactorily carried out with a Langmuir-Hinshelwood rate law. The values of the parameters involved in the model have been also determined.     

Synthesis and Spectroscopic Characterization of a Complex of 1, 10‐Phenanthroline with Magnesium

The complex [Mg(1, 10‐phenanthroline)₃(NO₃)₂]·9H₂O has been synthesized. It forms crystals having the shape of sheaves with very thin filaments. The compound has been characterized by UV, IR, NMR and mass spectra. The UV and mass spectra are indicative of an electron density transfer from NO₃^— to Mg²⁺. On the base of the spectroscopic studies a model of the crystal structure has been proposed.     

Comparison of low-energy CAD spectra of sulphonium,ammonium and phosphonium cations,propene elimination from allyl-substituted oniums

The low-energy collision-activated dissociation of symmetrical n-butyl-substituted and of allyl-substituted onium cations has been recorded using fast atom bombardment ionization and a tandem mass spectrometry quadrupole mass spectrometer. Structure of the fragments and decomposition pathways have been ascertained using a multi-quadrupole MS/MS/MS triple analyser instrument. Whereas most sulphonium cations exhibit only heterolytic cleavages, fragmentation of ammonium and phosphonium is mainly homolytic. Allylic sulphonium, and to a lesser extent allylic ammonium, easily undergo propene elimination. This reaction, which does not occur in 1-propenyl oniums, might involve a McLafferty type rearrangement.     

Structure investigation of mesalazine drug using thermal analyses,mass spectrometry,DFT calculations,and NBO analysis

Mesalazine (MZ) drug has been used for several decades as a primary treatment for inflammatory bowel diseases. The drug was investigated using thermal analysis (TA) measurements and electron impact mass spectral fragmentation at 70 and 15 eV of electron energy. The optimum molecular geometry and the total energy of the neutral and the positively charged MZ molecules were calculated by density functional theory method with 6-311++G(d,p) basis sets. Stability of the molecules arising from hyperconjugative interactions, charge delocalization, and the natural atomic charges has been analyzed using natural bond orbital analysis. In electron ionization mass spectrometry, the primary rupture is due to successive loss of H₂O (OH from carboxyl and H from phenolic OH of the ring) and CO of the acetyl group. Thermogravimetric results have revealed two stages of mass loss at 75.3 and 25.3 % in ranges 225–350 and 350–650 °C, respectively. The first one may be due to successive losses of different groups or molecules with fast rate of decomposition. A comparison between MS and TA helped in selection the proper pathway representing the fragmentation mechanism of this drug.     

Reaction of tetraoxopyrrolo [2,3-d] pyrimidines,isatin analogues,with o-phenylenediamine

In the course of general studies on new antitumor tetracyclic intercalating agents, the condensation of o-phenylenediamine with two new tetraoxopyrrolo[2,3-d]pyrimidine derivatives has been carried out. The structure of the reaction products as arylketimines has been elucidated and mass spectral fragmentations are discussed.     

Fragmentation study of a 8-C-glycosyl isoflavone, puerarin, using electrospray ion trap time-of-flight mass spectrometry at high resolution

A mass spectrometry method that combines electrospray with an ion trap time-of-flight mass analyzer has been used to characterize puerarin (7,4'-dihydroxyisoflavone-8-C-beta-D-glucoside). MS(n) spectra (n 相似文献   

Separation of metal ions by capillary electrophoresis--diversity, advantages, and drawbacks of detection methods

Capillary electrophoresis (CE) has been applied to metal-ion analysis during the last 10 years. To improve sensitivity and selectivity different modes of detection have been adapted or developed. The selection of commercially available detection systems for metal-ion analysis is still primarily limited to UV-Vis detection, although other commercial systems, e.g. fluorescence, conductivity, or interfaces for coupling to mass spectrometry (MS) or inductively coupled plasma mass spectrometry (ICP-MS) are becoming available. High demands are made on any detector used in CE, because the analytical signal has to be extracted from less than 1 nL of sample, which corresponds to a total amount of < or = 10(-12) to 10(-15) mol analyte. This paper compares currently available and recently developed detection methods for CE as applied to the analysis of metal ions. Commercially available techniques, for example UV-Vis, fluorescence, or mass spectrometry, and other new detection methods including electrochemistry, radioactivity, and XRF, are discussed and future trends are anticipated.     

Quadrupole ion traps and trap arrays: geometry, material, scale, performance

Quadrupole ion traps are reviewed, emphasizing recent developments, especially the investigation of new geometries, guided by multiple particle simulations such as the ITSIM program. These geometries include linear ion traps (LITs) and the simplified rectilinear ion trap (RIT). Various methods of fabrication are described, including the use of rapid prototyping apparatus (RPA), in which 3D objects are generated through point-by-point laser polymerization. Fabrication in silicon using multilayer semi-conductor fabrication techniques has been used to construct arrays of micro-traps. The performance of instruments containing individual traps as well as arrays of traps of various sizes and geometries is reviewed. Two types of array are differentiated. In the first type, trap arrays constitute fully multiplexed mass spectrometers in which multiple samples are examined using multiple sources, analyzers and detectors, to achieve high throughput analysis. In the second, an array of individual traps acts collectively as a composite trap to increase trapping capacity and performance for a single sample. Much progress has been made in building miniaturized mass spectrometers; a specific example is a 10 kg hand-held tandem mass spectrometer based on the RIT mass analyzer. The performance of this instrument in air and water analysis, using membrane sampling, is described.     

Investigation of silyl-substituted alkylthioacetates by IR and UV spectroscopy,1H and29Si NMR,and mass spectrometry

Conclusions The IR, UV, NMR, and mass spectra of silyl-substituted alkylthioacetates have been investigated. Intramolecular coordination of the carbonyl group with the silicon atom has been shown to exist in molecules of trifluoroaeetylthiomethylsilane in the condensed state and in a polar solvent (acetonitrile).Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 10, pp. 2224–2228, October, 1985.     

Combinatorial chemistry of materials,polymers and catalysts

The need for new materials and catalysts has never been satisfied by conventional methods. Chemical diversity is much too large to be explored systematically. Combinatorial chemistry applied to the discovery of new materials and catalysts can provide new lead structures, which has already been demonstrated by pioneers in the field. Combinatorial chemistry is much more than just a multiplication of experiments. In order to provide the results expected, combinatorial chemistry requires the combination of library preparation, characterization, identification of the desired properties and retrievable collection of the accumulated data in an intelligent data base. The state of the art of combinatorial chemistry in materials, polymer and catalysis research is reviewed. We have been engaged in the manual and automated preparation of catalyst libraries by liquid phase techniques (sol‐gel‐process and hydrothermal synthesis) for a variety of applications. The chemical nature of the components prepared on the library is not only a product of the liquid phase reaction conditions, but also of the drying and calcination process. High‐throughput characterization of the library components is therefor as important as the identification of desired materials properties. Automated micro‐X‐ray‐fluorescence spectrometry with a commercial instrument has been used successfully to identify chemical compositions of library components. Automated microdiffraction has been used to characterize the microstructure of the materials prepared. For the sensitive detection of reaction energies on catalyst libraries emissivity corrected IR‐thermography has been developed. It is used to identify catalytic activity of library components through the heat of reaction with high efficiency. This method has been applied to total oxidation, selective oxidation and hydrogenation reactions. Although much slower, but more detailed information was obtained with spatially resolved mass spectrometry. In a simple set‐up product composition of selective oxidation reactions have been scanned with the help of a simple gas analyzer (quadrupole mass spectrometer). A remarkable discrimination of product selectivity was recorded on a diverse library containing amorphous microporous mixed oxide catalysts. With high resolution MS more difficult problems, such as the differentiation of products of the same unit mass, such as CO, N₂ and ethylene can be solved in high throughput modes. The selectivities observed correlate well with the behaviour of the materials under conventional reaction conditions.     

Tropylium,chlorine isotopic abundances,monomeric metaphosphate anion,and conestoga wagon theory

As I look back over a career in mass spectrometry, three high points stand out especially prominently. These are associated with (1) the tropylium model for the C_uH ₇ ⁺ ion in the mass spectra of toluene and other alkylbenzenes, (2) revision of the previously accepted value for the natural abundance of the chlorine isotopes, and (3) the first direct observation of the monomeric metaphosphate anion, which had been for a quarter of a century an elusive, suspected reaction intermediate. Studies of organic ions in the rarefied atmosphere of the mass spectrometer, where only unimolecular processes are allowed, have deepened my appreciation of the role and ubiquity of bimolecular processes in more conventional chemical contexts. Consideration of the two categories of molecular behavior has prompted me to seek and find, for a selected system in the mass spectrometer, parallels both in condensed-phase chemistry and, by an anthropomorphic extension, in human behavior.