Home About us Contact
|
Home About us Contact | ||
|
|
||
Mass Spectrometric Study (mass + spectrometric_study)
Kinds of Mass Spectrometric Study Selected AbstractsA Combined Gas-Phase Electron Diffraction/Mass Spectrometric Study of the Sublimation Processes of TeBr4 and TeI4: The Molecular Structure of Tellurium Dibromide and Tellurium DiiodideEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 33 2008Sergey A. Shlykov Abstract The sublimation processes of TeBr4 at 471(5) K and TeI4 at 373(5) K were studied with a combined gas-phase electron diffraction and mass spectrometric technique (GED/MS). The mass spectra and the analysis of the GED intensities showed that a contribution of 40(3) mol-% TeBr2, 59(3) mol-% Br2, and 1 mol-% TeBr4 was formed in the vapor over TeBr4(s). Solid tellurium tetraiodide decomposes to form I2(g) and Te(s). A very small contribution of 3.3,±,2.1 mol-% of gaseous TeI2 was also determined by both GED and MS. The "metallic" Te accumulated in the solid phase vaporizes at above ca. 670 K as the predominately Te2 molcular species. Refinement of the GED intensities resulted in rg(Te,Br) = 2.480(5) Ĺ and ,gBr,Te,Br = 99.0(6)° for TeBr2 and rg(Te,I) = 2.693(9) Ĺ and ,g(I,Te,I) = 103.1(22)° for TeI2. The small contribution of TeBr4 observed in the mass spectra of the vapor over TeBr4 could not be observed in the GED data. Geometric parameters and vibrational frequencies for the tellurium dihalides TeX2 with X = F, Cl, Br, and I were calculated with B3LYP, MP2, CCSD, and CCSD(T) methods by using aug-cc-pVTZ basis sets and various core potentials for the tellurium atom. Bonding properties in tellurium dihalides are discussed on the basis of natural bond orbital analyses. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source] Gas chromatography/mass spectrometric study of non-commercial C-4-substituted 1,4-dihydropyridines and their oxidized derivativesRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 24 2002C. López-Alarcón A gas chromatography/mass spectrometry (GC/MS) method for the qualitative and quantitative determination of the calcium-channel antagonists C-4-substituted 1,4-dihydropyridines, and their corresponding N-ethyl derivatives, is presented. Also, the electrochemical oxidation and the reactivity of the compounds with alkyl radicals derived from 2,2,-azobis-(2-amidinopropane) were monitored by GC/MS. Mass spectral fragmentation patterns for the C-4-substituted 1,4-dihydropy-ridine parent drugs were significantly different from those of their oxidation products, generated either by electrochemical oxidation or by reaction with alkyl radicals. However, for N -ethyl-1,4-dihydropyridine compounds it was not possible to detect the final products (pyridinium salts) using these experimental conditions. Copyright © 2002 John Wiley & Sons, Ltd. [source] Theoretical study of the microhydration of mononuclear and dinuclear uranium(VI) species derived from solvolysis of uranyl nitrate in waterJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 12 2010Milan On Abstract The structures and energetics of mononuclear and dinuclear uranium species formed upon speciation of uranyl(VI) nitrate, UO2(NO3)2, in water are investigated by quantum chemistry using density functional theory and the wavefunction-based methods (MP2, CCSD, CCSD(T)). We provide a discussion of the basic coordination patterns of the various mono- and dinuclear uranyl compounds [(UO2)m(X,Y)2m,1(H2O)n]+ (m = 1, 2; n = 0,4) found in a recent mass spectrometric study (Tsierkezos et al., Inorg Chem 2009, 48, 6287). The energetics of the complexation of the uranyl dication to the counterions OH, and NO3, as well as the degradation of the dinuclear species were studied by reference to a test set of 16 representative molecules with the MP2 method and the B3LYP, M06, M06-HF, and M06-2X DFT functionals. All DFT functionals provide structures and energetics close to MP2 results, with M06 family being slightly superior to the standard B3LYP functional. © 2010 Wiley Periodicals, Inc. J Comput Chem 2010 [source] Electron ionization mass spectrometric study of monomeric models of O -polysaccharides of Vibrio cholerae O:1, serotypes Ogawa and InabaJOURNAL OF MASS SPECTROMETRY (INCORP BIOLOGICAL MASS SPECTROMETRY), Issue 9 2003Vladimír Ková Abstract Fragmentation mechanisms of electron ionization (EI) mass spectrometry of the title compounds have been elucidated by high-resolution (HR) mass spectrometric measurements of the elemental composition and measurements of the metastable transitions (B2/E, CID). The experimental results were interpreted with the help of Mass Frontier 3.0 software, which aided the elucidation of fragmentation mechanisms and helped to deduce structures of the ions formed. Characteristic under the conditions of EI-MS measurement was the production of protonated adducts. Three distinct pathways observed include the formation of oxonium type ions, the conjugated transfer of electrons in the pyranose ring, and cleavage of the acylamide side chains. By applying the results obtained, the molecular mass, as well as the structures of both the saccharide and acylamide side chain involved in related substances, can be determined. Copyright © 2003 John Wiley & Sons, Ltd. [source] Electrospray ionization mass spectrometric study of end-groups in peroxydicarbonate-initiated radical polymerizationJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 18 2008Michael Buback Abstract Initiation by diethyl peroxydicarbonate (E-PDC), di- n -tetradecyl peroxydicarbonate (nTD-PDC), di- n -hexadecyl peroxydicarbonate (nHD-PDC), and di-2-ethylhexyl peroxydicarbonate (2EH-PDC) of free-radical polymerizations of methyl methacrylate in benzene solution was studied by end-group analysis via electrospray ionization mass spectrometry (ESI-MS). Unambiguous assignment of ESI-MS peaks allows for identification of the type of radical that starts chain growth. In case of initiation by dialkyl peroxydicarbonates with linear alkyl groups, almost exclusively alkoxy carbonyloxyl species, which are the primary fragments from initiator decomposition, occur as end-groups. With 2EH-PDC, however, both the primary 2-ethylhexoxy carbonyloxyl fragment and a second moiety, which is formed by decarboxylation of the 2-ethylhexoxy carbonyloxyl radical, are clearly observed as end-groups. The decarboxylation process is described by a concerted mechanism which involves a 1,5-hydrogen shift reaction. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 6071,6081, 2008 [source] Toward an "omic" physiopathology of reactive chemicals: Thirty years of mass spectrometric study of the protein adducts with endogenous and xenobiotic compoundsMASS SPECTROMETRY REVIEWS, Issue 5 2009Federico Maria Rubino Abstract Cancer and degenerative diseases are major causes of morbidity and death, derived from the permanent modification of key biopolymers such as DNA and regulatory proteins by usually smaller, reactive molecules, present in the environment or generated from endogenous and xenobiotic components by the body's own biochemical mechanisms (molecular adducts). In particular, protein adducts with organic electrophiles have been studied for more than 30 [see, e.g., Calleman et al., 1978] years essentially for three purposes: (a) as passive monitors of the mean level of individual exposure to specific chemicals, either endogenously present in the human body or to which the subject is exposed through food or environmental contamination; (b) as quantitative indicators of the mean extent of the individual metabolic processing which converts a non-reactive chemical substance into its toxic products able to damage DNA (en route to cancer induction through genotoxic mechanisms) or key proteins (as in the case of several drugs, pesticides or otherwise biologically active substances); (c) to relate the extent of protein modification to that of biological function impairment (such as enzyme inhibition) finally causing the specific health damage. This review describes the role that contemporary mass spectrometry-based approaches employed in the qualitative and quantitative study of protein,electrophile adducts play in the discovery of the (bio)chemical mechanisms of toxic substances and highlights the future directions of research in this field. A particular emphasis is given to the measurement of often high levels of the protein adducts of several industrial and environmental pollutants in unexposed human populations, a phenomenon which highlights the possibility that a number of small organic molecules are generated in the human organism through minor metabolic processes, the imbalance of which may be the cause of "spontaneous" cases of cancer and of other degenerative diseases of still uncharacterized etiology. With all this in mind, it is foreseen that a holistic description of cellular functions will take advantage of new analytical methods based on time-integrated metabolomic measurements of a new biological compartment, the "adductome," aimed at better understanding integrated organism response to environmental and endogenous stressors. © 2009 Wiley Periodicals, Inc., Mass Spec Rev 28:725,784, 2009 [source] High-temperature mass spectrometric study of the vaporization processes of V2O3 and vanadium-containing slagsRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 16 2010H. Wang A Knudsen effusion mass spectrometric method was used to study the vaporization processes and thermodynamic properties of pure V2O3 and 14 samples of vanadium-containing slags in the CaO-MgO-Al2O3 -SiO2 system in the temperature range 1875,2625,K. The system was calibrated using gold in the liquid state as the standard. Vaporization was carried out from double tungsten effusion cells. First it was shown that, in vapor over V2O3 and the vanadium-containing slags in the temperature range 1875,2100,K, the following vapor species were present: VO2, VO, O, WO3 and WO2, with the latter two species being formed as a result of interaction with the tungsten crucibles. The temperature dependencies of the partial pressures of these vapor species were obtained over V2O3 and the slags. The ion current comparison method was used for the determination of the V2O3 activities in slags as a function of temperature with solid V2O3 as a reference state. The V2O3 activity coefficients in the slags under investigation indicated positive deviations from ideality at 1900,K and a tendency to ideal behavior at 2100,K. It was shown that the V2O3 activity as a function of the slag basicity decreased at 1900,K and 2000,K and was practically constant in the slag melts at 2100,K. The results are expected to be valuable in the optimization of slag composition in high-alloy steelmaking processes as well as for their environmental implications. Copyright © 2010 John Wiley & Sons, Ltd. [source] High-temperature mass spectrometric study of the vaporization processes in the system CaO-MgO-Al2O3 -Cr2O3 -FeO-SiO2RAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 14 2009L. J. Wang Knudsen effusion mass spectrometry was used to study vaporization processes and thermodynamic properties of twenty samples of chromium-containing slags in the CaO-MgO-Al2O3 -Cr2O3 -FeO-SiO2 system in the temperature range 1850,2750,K. Tungsten cells were used and Cr2O3 solid was used as a reference material. The system was calibrated using liquid gold. As FeO was the first emanating vapor species, monitoring of the chromium-containing species could be carried out only after the complete vaporization of FeO. This, however, was found to have very little impact on the concentration of the slags investigated. During the measurements, the ion current intensities of CrO+ and CrO species in the mass spectra of the vapor over the CaO-MgO-Al2O3 -Cr2O3 -FeO-SiO2 samples were monitored and compared with those corresponding to solid Cr2O3. Data on the partial pressures of vapor species as well as the activities of Cr2O3 as a function of temperature were obtained. The results are expected to be valuable in the optimization of slag composition in high alloy steelmaking processes. Copyright © 2009 John Wiley & Sons, Ltd. [source] Electron ionization mass spectrometric study of N -benzyl- and N -nitrobenzyl-substituted derivatives of cytisine.RAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 2 2008First page of article [source] Post-source decay matrix-assisted laser desorption/ionization mass spectrometric study of tetracyclic 2,3-dihydro-1,5-benzothiazepinesRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 12 2004Sándor Kéki The fragmentation behavior of six tetracyclic 2,3-dihydro-1,5-benzothiazepine derivatives cationized with protons and silver ions under post-source decay (PSD) matrix-assisted laser desorption/ionization (MALDI) conditions is reported. The protonated adduct ions decompose into several structurally important fragment ions, including substituted cyclopropane and benzohydrothiazole cations. Elimination of Ag and H and/or AgH from the silver-cationized adduct ions of these ([M+Ag]+) compounds was observed. It was also found that [M+Ag]+ produced silver-depleted fragment ions exclusively. Based on the PSD results a fragmentation pathway is proposed for the [M+H]+ and [M+Ag]+ precursor ions. Copyright © 2004 John Wiley & Sons, Ltd. [source] In situ analysis of solvents on breath and blood: a selected ion flow tube mass spectrometric studyRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 5 2002Paul F. Wilson We report measurements of residual vapour levels of xylenes and trimethylbenzenes, present following a floor re-surfacing procedure, using the technique of selected ion flow tube mass spectrometry (SIFT-MS). A subject exposed to controlled amounts of xylene and mesitylene was monitored by direct breath exhalation over a 4-hour period after exposure to the volatile organic compounds (VOCs) had stopped. The headspace gases above 5-mL blood samples taken over this period were also monitored. The decays of the solvent levels with time were fitted to a two-compartment model with residence times for xylene and mesitylene of 0.37,h and 0.38,h, respectively (compartment one) and 2.5,h and 2.8,h, respectively (compartment two). Copyright © 2002 John Wiley & Sons, Ltd. [source] A mass spectrometric study of Al2O3 -SiO2 melts using a Knudsen cellRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 10 2001Johan Björkvall The thermodynamic activities of SiO2 in Al2O3 -SiO2 liquid slags were measured by the high-temperature Knudsen cell mass spectromeric method in the present work. The measurements were carried out in the temperature range 1863,2169,K. Tungsten crucibles were used to hold the slags. The system was calibrated using a CaF2 standard. The mass spectra obtained for pure SiO2 were in agreement with earlier data. The activities of silica, measured in the present work at 2150,K, show a slight negative deviation at very low alumina mole fractions which changed to a positive deviation at higher alumina contents. The activity values are in reasonable agreement with the assessment carried out by Hillert et al. The results were analysed on the basis of a slag model developed earlier at KTH, Stockholm. The present results are found to be compatible with the phase diagram proposed by Klug et al. Copyright © 2001 John Wiley & Sons, Ltd. [source] Electrospray ionisation mass spectrometric study of degradation products of quercetin, quercetin-3-glucoside and quercetin-3-rhamnoglucoside, produced by in vitro fermentation with human faecal floraRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 7 2001Ulla Justesen Eight phenolic compounds, obtained by in vitro fermentation of quercetin, quercetin-3-glucoside and quercetin-3-rhamnoglucoside were analysed by electrospray ionisation mass spectrometry (ESI-MS). Low-energy collision-induced dissociation tandem mass spectrometry (CID-MS/MS) was performed on the [M,,,H], precursor ions to obtain specific fragmentation. Typical fragmentation of the phenolic acids was loss of 44 (CO2) and 18 (H2O),u. Production of m/z 108 by loss of neutral radicals, e.g. HCO2, CH3 or HCO, was also favoured. Structures of the compounds, numbered 1,8, were suggested based on the fragmentation patterns. Copyright © 2001 John Wiley & Sons, Ltd. [source] | ||||||||||||||||||||||