bluuebunny/crossref_metadata_2025_split huggingface dataset:
Pyrolysis gas chromatography/mass spectrometry of polyvinylsilanes. Mass spectrometric characteristics of alkanes and alkenes containing two or more triorganosilyl substituents
Authors: Zaikin V. G. , Filippova V. G. , Semenov O. B. 
Published: May 2005

AbstractPyrolysis gas chromatography/mass Spectrometry was applied to the investigation of homopolymers obtained from trimethyl‐, n‐pentyldimethyl‐, n‐octyldimethyl‐ and trideuteromethyldimethyl‐vinylsilanes. The electron impact‐induced fragmentation of alkanes, alkenes and alkadienes containing two or more corresponding silyl substituents and resulting from pyrolysis of polymers was elucidated. The most characteristic fragmentation patterns of trimethylsilyl‐substituted compounds are due to the loss of HSi(CH3)3 and Si(CH3)4 from M+˙, the order of which depends on the presence or absence of a double bond in hydrocarbon chain. The same structural parameter determines the probability of the characteristic decomposition of n‐alkyldimethylsilyl‐substituted compounds through the loss of alkene and alkyl groups from the molecular ions.
Chemical ionization mass spectrometry of halogenoalkanes with tetramethylsilane as reagent gas
Authors: Chizhov Oleg S. , Kadentsev Valentin I. , Stomakhin Andrei A. 
Published: May 2005

AbstractChemical ionization mass spectra of halogenoalkanes (RX) obtained using tetramethylsilane as reagent gas show two major peaks corresponding to the cluster ion RX+SiMe3 and alkyl ion R+. Iodides exhibit the highest affinity toward the trimethylsilyl ion and produce the most stable silylated molecular ions, whereas bromides and especially chlorides are less reactive toward Me3Si+ ions and form less stable [M + SiMe3]+ ions.
Electron impact mass spectrometry of substituted benzyl(1‐allylcycloalkyl)amines and their cyclization products
Authors: Mikaya A. I. , Lantsetov S. V. , Kuznetsov V. V. , Varlamov A. V. , Prostakov N. S. 
Published: May 2005

AbstractElectron impact mass spectra have been measured for benzyl(1‐allylcycloalkyl)amines and α‐phenylethyl(1‐allylcycloalkyl)amines and for the spiro(benzo‐2‐azepine‐3,1′‐cycloalkanes) produced by their cyclization.
Computer processing and interpretation of mass spectral information. VIII—ariadna system
Authors: Sukharev Yu. N. , Nekrasov Yu. S. , Molgachova N. S. , Tepfer E. E. 
Published: May 2005

AbstractThe structure of a laboratory system for processing and interpreting mass spectral data intended to solve a wide range of analytical problems (determination of the composition and structure of molecules, isotopic analysis, etc) and research problems (study of the structure and reactivity of ions in the gas phase) is described and its functional possibilities are discussed. The basic software of the system includes both methods for calculation of elemental compositions of ions with the use of masses and amplitudes of isotopic peaks and methods for establishing spectralstructural correlations based on information theory and molecular graph theory.
Mass spectra of some per‐O‐benzoyl‐alditols and ‐aldobiitols
Authors: D'Accorso Norma B. , Thiel Inge M. E. 
Published: May 2005

AbstractElectron impact mass spectra of some per‐O‐benzoyl‐alditols and ‐aldobiitols are reported and the major fragmentation pathways are discussed.
Electron impact mass spectrometry of some unsubstituted and chlorine‐substituted bisnaphthalimides and related synthons
Authors: Krotz L. , Seraglia R. , Traldi P. , Guidugli F. , Kavka J. , Gaozza C. 
Published: May 2005

AbstractThe electron impact induced fragmentations of some unsubstituted and chlorine‐substituted naphthalimides and bisnaphthalimides are discussed in detail with the aid of B/E and B2/E linked‐scans for metastable ion analysis and collisional activation experiments. In the case of bisnaphthalimides the more important primary decomposition routes are related to cleavages of the alkyl chain.
Characterization of pyoverdins and their hydrolytic degradation products by fast atom bombardment and tandem mass spectrometry
Authors: Michels J. , Taraz K. 
Published: May 2005

AbstractAll types of pyoverdins (siderophores produced by Pseudomonas strains) have the following ‘chromophore’ substructure in common: (1S)‐5‐amino‐2,3‐dihydro‐8,9‐dihydroxy‐lH‐pyrimido[l,2‐α]quinoline‐1‐carboxyhic acid. Its hydrolysis product, (1S)‐2,3‐dihydro‐5,8,9‐trihydroxy‐lH‐pyrimido[l,2‐α]quinoline‐1‐carboxylic acid, has been isolated and analysed for the first time by means of fast atom bombardment (FAB) and tandem mass spectrometry. This allows the pyoverdin chromophore to be identified. It was established that the fragmentation of pyoverdin [M + H]+ ions under FAB conditions is initiated by a retro‐Diels‐Alder decomposition of the tetrahydropyrimidine ring of the chromophore moiety, contributing to the structure elucidation of pyoverdins.
Array detection of mass spectra, a comparison with conventional detection methods
Authors: Boerboom A. J. H. 
Published: May 2005

AbstractSensitivity, dynamic range, resolution, precision and response time of a channeltron electron multiplier array and of conventional detectors (Faraday cage, electron multiplier and photographic plate) are compared. The properties of the detection methods differ greatly and each method is superior in some aspect. Capabilities of channel plate detection and features of channel plate mass spectra are discussed.
Mass spectra of 5,5′‐(l,2‐ethanediyl)bis [3‐(aryl)‐l,2,4‐oxadiazoles]
Authors: Srivastava Rajendra M. , Nielsen Lawrence T. , da Silva Aníbal J. C. N. 
Published: May 2005

AbstractThe electron‐impact mass spectra of a series of bis [1,2,4‐oxadiazoles] are described.
Methylcyclopropane ion formation by elimination of water from n‐butanol and 2‐methylpropanol ions
Authors: Ahmed Mohammed S. , Hudson Charles E. , Giam C. S. , McAdoo David J. 
Published: May 2005

AbstractC4H8+˙ ions generated from ionized n‐butanol (a) and from ionized 2‐methylpropanol (b) were characterized by reaction of the daughter ions with ammonia in a Fourier transform mass spectrometer. Hydrogen transfers occur in a in the ratio five‐membered ring:six‐membered ring = 1:3.2. However, both hydrogen‐transfers are followed by the formation of ionized methylcyclopropane. Ionized methylcyclopropane is also produced on elimination of water from b.
Evidence for a double intramolecular trimethylsilyl rearrangement
Authors: Wood Karl V. , Rothwell Arlene P. , Scarpetti David , Fuchs Philip L. 
Published: May 2005

AbstractA double trimethylsilyl rearrangement ion, m/z 287, C6H5S(OSi(CH3)3)3, was observed in the isobutane chemical ionization mass spectrum of 3‐trimethylsilyl‐9‐(2‐trimethylsilylethylthio)‐1‐phenyl‐3‐phenylsulfonylnonane. The daughter mass spectrum of the protonated molecule produced the rearrangement ion, m/z 287, suggesting that the double trimethylsilyl rearrangement occurred intramolecularly.
Mass spectral fragmentation pattern of 3‐(2′‐hydroxyethyl)quinolin‐2(1H)‐one and its derivatives
Authors: Rajendran S. P. , Shanmugam P. 
Published: May 2005

AbstractFragmentation patterns resulting from electron impact ionization of 3‐(2′‐hydroxyethyl)quinolin‐2(1H)‐one, three of its monosubstituted derivatives and four of its disubstituted derivatives were studied. The molecular ion of quinolinone‐2‐etbanol undergoes initial fragmentation with the loss of OH·, H2O, CO, ·CHO, CH2O, CH2OH·, CH2CHOH and HCNO species. The [M – CHO]+ ion is tentatively suggested to have been formed by the expulsion of H· from the [M – CO]+· ion and the [M ‐ CHO]+ peak may be considered as diagnostic of a 2‐quinolone‐3‐ethanol.
Collision spectroscopy in isomer characterization: The case of (E)‐ and (Z)‐p‐nitrophenyldiazo tert‐butyl sulphides
Authors: Sottani Cristina , Mele Andrea , Favretto Donata , Traldi Pietro 
Published: May 2005

AbstractThe structural characterization of the E and Z isomers of p‐nitrophenyl‐diazo tert‐butyl sulphide has been achieved by means of different ionization methods (electron impact, fast atom bombardment, positive‐ion chemical ionization) and collision experiments performed under different kinetic energy regimes (high‐ and low‐energy collisions, angle‐resolved mass spectrometry and energy‐resolved mass spectrometry). The two compounds give rise to identical fragmentation patterns. Collision experiments, both at low energy and in the keV range at a scattering angle of 0°, in M+· species obtained by electron impact on the two isomers, do not show any significant differences; the same experiments performed with 8 keV ions at a scattering angle of 2° indicate a clear difference in the absolute abundances of the two main daughter ions. High‐energy collisions of MH+ ions obtained by fast atom bombardment lead to different spectra at both 0° and 2° scattering angles, proving that the energy deposition in the preselected species is an important parameter. Low‐energy collisions with argon of MH+ ions generated by positive‐ion chemical ionization (NH4+) give rise to almost identical energy‐resolved mass spectra, whereas the same experiments using helium as target gas lead to a clear distinction between the two isomers.
Pyrolysis/gas chromatography/mass spectrometry in the analysis of glycated poly‐L‐lysine
Authors: Lapolla Annunziata , Gerhardinger Chiara , Baldo Lorenzo , Fedele Domenico , Favretto Donata , Seraglia Roberta , Traldi Pietrc 
Published: May 2005

AbstractPyrolysis/gas chromatography/mass specfrometry was applied to the study of products arising from the interaction between glucose and poly‐L‐lysine. The comparison of pyrograms of control poly‐L‐lysine and glycated poly‐L‐lysine led to the identification of six different compounds, four of which were furan derivatives that can be considered as markers for advanced glycation processes.
Pyrolysis/gas chromatography/ion‐trap detection of polyphenols (vegetable tannins): Preliminary results
Authors: Galletti Guido C. , Reeves James B. 
Published: May 2005

AbstractTannins from sorghum grains with high and low tannin content, from grape skins and seeds and from apple pomace were analysed by pyrolysis/gas chromatography/ion‐trap detector mass spectrometry. Pyrolysis at 600°C produced catechol as a characteristic fragment of condensed tannins, and other phenolic compounds related to the lignified tissues. Catechol was also the main fragment in the pyrogram of catechin, a monomeric constituent of condensed tannins. Mass spectral data and relative quantifications of the pyrograms of several samples are provided. Quantitative data are discussed in terms of reproducibility and linearity of response and are compared with the results of a spectrophotometric assay for tannins.
Unimolecular chemistry of oxazole and isoxazole radical cations in the gas phase: Combined experimental and molecular orbital study
Authors: Flammang R. , Plisnier M. , Bouchoux G. , Hoppilliard Y. , Humbert S. , Wentrup C. 
Published: May 2005

AbstractMolecular radical cations of oxazole (1) and isoxazole (2) dissociate by losing carbon monoxide or a hydrogen atom, respectively. These fragmentations were examined by use of tandem mass spectrometry, flash vacuum pyrolysis and ab initiomolecular orbital calculations. A multi‐step mechanism is proposed which incorporates these new experimental and theoretical data. The case of methylated homologues of 1 and 2 is also considered.
Control of the regiospecific synthesis of dialkylpyrrolizidinones and their stereochemical behaviour using gas chromatography/mass spectrometry with chemical ionization
Authors: Lange C. , Provot O. , Mulheim C. , Celerier J.‐P. , Lhommet G. 
Published: May 2005

AbstractPyrrolizidine alkaloids were synthesized via the cyclization of an epoxide prepared from a lactam. The regiospecific control of this reaction is demonstrated using gas chromatography/mass spectrometry. Ammonia chemical ionization mass spectrometry permits the determination of the cis–trans stereochemistry of the final products.
Role of photoionization and photochemistry in ionization processes of organic molecules and relevance for matrix‐assisted laser desorption lonization mass spectrometry
Authors: Ehring H. , Karas M. , Hillenkamp F. 
Published: May 2005

AbstractThe ionization in ultraviolet laser desorption was investigated for a large number of small polar organic molecules which have a strong resonance absorption at the laser wavelength. In many cases, both positive‐ and/or negative‐ion mass spectra show strong signals of ion species which deviate from the simple scheme of even‐electron quasimolecular and fragment ion formation commonly expected for desorption techniques. These are radical cations and ion species formed by single and multiple hydrogen cleavage or addition. A model is proposed and discussed which explains these features assuming photoionization as the common initial ionization step followed by ion‐molecule reactions to the final product ions. The mass spectra of all compounds proved to function well in matrix‐assisted ultraviolet laser desorption/ionization show characteristic features indicative of their photochemical reactivity. This observation substantiates the hypothesis of tbe essential role of the matrix in analyte ionization.
Unimolecular dissociation of tert‐butyl methyl ether via an ion‐neutral complex
Authors: Beveridge William , Hunter John A. , Johnson Chris A. F. , Parker John E. 
Published: May 2005

AbstractAb initio calculations are presented representing the ionization of tertbutyl methyl ether and its subsequent fragmentation via loss of a methyl radical. This process is shown to proceed via an ion‐molecule complex, the nature of which is explored. The results obtained are found to be consistent with mass spectrometric evidence.
Quantum chemical study of the reaction of NH4+ with alkylmercury halides in the gas phase
Authors: Zagorevskii Dmitri C. , Nekrasov Yuri S. , Raevski Nikolai I. 
Published: May 2005

AbstractCalculations on the thermochemistry of reactions between NH4+ ions and EtHgX molecules (X = Cl, Br, I) were performed by the MNDO method. The calculations showed the possible existence of two stable isomers of composition [EtHgX, NH4]+ namely [EtHgX…︁HNH3]+ and [EtHg(NH3)XH]+. Protonation of EtHgX and of CH2CHHgX by NH4+ is characterized by high exothermicity.
Chemical ionization and electron impact mass spectra of S‐1‐chloroalkyl alkanesulfonothioates (thiosulfonates)
Authors: Freeman Fillmore , Keindl Monica C. 
Published: May 2005

AbstractThe chemical ionization (CI) and electron impact (El) mass spectra of six S‐1‐chloroalkyl alkanesulfonothioates (thiosulfonates) are reported.
Chemical ionization mass spectrometry of halomethanes with tetramethylsilane as reagent gas
Authors: Chizhov Oleg S. , Kadentsev Valentin I. , Stomakhin Andrei A. 
Published: May 2005

AbstractChemical ionization mass spectra of halomethanes measured using tetramethylsilane as reagent gas exhibit three major peaks corresponding to [M + SiMe3]+, [M − X]+ and (MeSi)2X+ ions (X = Cl, Br or I). Dihalomethanes CH2X2 form the most stable silylated molecular ions, whereas in the mass spectra of tetrahalomethanes (CX4) these ions have not been detected and the ions CX3+ are the most abundant. Production of bistrimethylsilyl‐halonium ions is the most pronounced process for haloforms (CHX3).
Formation of β‐distonic oxonium ions: Study of ROCH2CH2OR′ radical cations
Authors: Milliet Arielle , Sozzi Georges , Audier Henri E. 
Published: May 2005

AbstractRadical cations derived from the ethers ROCH2CH2OR′ (R, R′ = H, CH3, C25) were studied, since β‐distonic oxonium ions are often prepared from ionized ethers of glycol. The first step in the fragmentation is a 1,5‐transfer of an α‐hydrogen to oxygen of a terminal alkoxy group leading to a δ‐distonic oxonium ion. This step is thermo‐neutral and reversible in the ROCH2CH2OH radical cations and exothermic and irreversible in the dialkyl ether radical cations. Depending on R and R,′ these δ‐distonic oxonium ions fragment by three reactions: the loss of an alcohol or a water molecule, the formation of a β‐distonic oxonium ion ˙CH2CH2O(H)+R and a 1,4‐H migration between carbon atoms. Competition between these processes is discussed.
Direct chemical ionization mass silylated iridoid glucosides
Authors: Dyulgerov A. , Handjieva N. , Saadi H. , Popov S. , Baranovska I. 
Published: May 2005

AbstractThe direct chemical ionization mass spectra with isobutane of 14 silylated iridoid glucosides of different structural types were studied. The dependence of the intensity of different peaks on the structure and stereochemistry of the investigated compounds is discussed.
Mass spectra of synthesized mixed bromochloroacetic acids
Authors: Xie Yuefeng , Rajan R. V. , Reckhow David A. 
Published: May 2005

AbstractMass spectra of methyl esters of three common drinking water chlorination by‐products, bromodichloroacetic acid, dibromochloroacetic acid and tribromoacetic acid, are presented. The spectra are obtained in electron impact and chemical ionization modes, using a quadrupole mass spectrometer. Proposed fragment ion assignments are presented in detail. Fragment clusters were identified from their m/z values and confirmed with their relative isotope ratios. The detailed mass spectra presented are especially useful because standards for these drinking water contaminants are not yet commercially available.
Phenomenological models for matrix‐assisted laser desorption ion yields near the threshold fluence
Authors: Beavis Ronald C. 
Published: May 2005

AbstractPhenomenological models were proposed to explain the experimentally observed dependence of protein ion yields with laser fluence in matrix‐assisted laser desorption. Assuming that the illuminating laser had a Gaussian intensity profile at the sample being examined, it was possible to fit the experimental points with a model that only assumes a fluence threshold for ion production. No additional dependence of protein ion yield on illuminating fluence above the threshold value was necessary to explain the data.
Negative‐ion electrospray and fast atom bombardment mass spectrometry of esters of boron acids
Authors: Rose Malcolm E. , Wycherley Darren , Preece Steven W. 
Published: May 2005

AbstractIt is shown that both electrospray and fast atom bombardment mass spectrometry provide excellent negative‐ion mass spectra of the anionic esters of boric, boronic and borinic acids. For electrospray, contact of the esters with water causes some hydrolysis but, in most cases, spectra of the intact molecular anions are readily obtained. For fast atom bombardment, solvents that chelate with the boron esters must be avoided, Tetraethylene glycol diethyl ether, pentaethylene glycol dimethyl ether or hexaethylene glycol dimethyl ether are suitable solvents. Negative‐ion electrospray mass spectra showed few, if any, fragment ions, whereas fast atom bombardment generally produced abundant M− ions and several fragment ions of low abundance. It is shown that a simple reaction with dibenzene‐borinic acid converts diols such as monoglycerides and monoalkyl glyceryl ethers into anionic borinate esters as a pre‐ionization procedure for analysis by electrospray or fast atom bombardment mass spectrometry.
Determination of the double‐bond position in hexadecenols by mass spectrometry without prior chemical modification
Authors: Horiike Michio , Yuan Gu , Kim Chul‐Sa , Hirano Chisato , Shibuya Katsuhiko 
Published: May 2005

AbstractFourteen isomers of chemically unmodified hexadecenol were analysed by two types of quadrupole mass spectrometer, coupled with a gas chromatograph, for the location of the double‐bond position. A series of spectra were interpreted in terms of mass spectral patterns on a fuzzy classification, in which the intensity ratios of six diagnostic pairs of the predominant ions were preferred in devising similarity indices. The accuracy of the method in the location of double‐bond position was confirmed by testing with other series of spectra.
Low‐energy, low‐temperature mass spectra. Part 15: Electron ionization mass spectra of some monoterpene hydrocarbons
Authors: Brophy Joseph J. , Maccoll Allan 
Published: May 2005

AbstractThe electron ionization mass spectra of 19 monoterpenes are reported at 70 eV and ca. 500 K and at 12 eV and ca. 350 K. The former agree well with those published previously, whereas the latter show simplification, especially at low m/z values. Temperature has little effect on the limonene spectrum at electron energies of 12 or 70 eV. Variation of the electron energy at 350 K and 500 K has a marked effect. The effect of electron energy on the spectrum of myrcene is fairly small, apart from the decrease in the relative intensity (RI) of the molecular ion. In the cases of limonene and Δ‐2‐carene it is fairly large. A correlation is found between the 12 eV mass spectra and published linked scan spectra at constant B/E for some of the monoterpene hydrocarbons. The compounds are divided into three classes showing, respectively, low, medium and high fragmentation in their low‐energy mass spectra. The percentage fragmentation along with the ratios RI(m/z 121)/(m/z 93) serve in most instances to distinguish the terpene hydrocarbon.
Fragmentations and rearrangements of metastable [C2H5OS]+ ions
Authors: de Vries M. P. , Oudman D. , Weringa W. D. 
Published: May 2005

AbstractSeveral [C2H5OS]+ ions with different structures were generated from the appropriate precursors and their metastable ion spectra were determined. Deuterium labelled analogues of some of the [C2H5OS]+ ions were used to elucidate the nature of the observed fragmentations and their mechanisms. [C2H5OS]+ ions with different COS skeletons were found to give different fragmentation reactions. There are no indications for fast isomerization reactions leading to common intermediates before fragmentation. Most of the observed fragmentations can occur directly from the initial structures.
Ether and ester glucuronic acid conjugates of lacidipine metabolites: Mass spectrometric differentiation using thermospray and particle beam techniques
Authors: Rossato P. , Scandola M. , Pugnaghi F. , Grossi P. 
Published: May 2005

AbstractGlucuronic acid conjugates of Lacidipine metabolites were analysed by high‐performance liquid chromatog‐raphy/mass spectrometry with different ionization techniques, viz. thermospray and chemical ionization with a particle beam interface. Analyses were performed on bile samples collected from dogs after oral administration of 14C‐labelled Lacidipine. Phase II metabolites, originating from the conjugation with glucuronic acid of phase I metabolites containing free hydroxy or carboxylic functions, were isolated. Two types of glucuronides, with an ether or an ester bond, were characterized. They showed different mass Spectrometric behaviour owing to a specific interaction with the acetate in the mobile phase.
Dechlorination of polychlorinated biphenyls in electron impact mass spectrometry: Regioselective analysis using 35Ci‐labelled compounds
Authors: Lépine François L. , Milot Sylvain M. , Reimer Mark L. J. , Mamer Orval A. 
Published: May 2005

AbstractFour tetrachlorinated bipbenyls were chlorinated with 35Cl2 to yield seventeen polychlorinated biphenyls (PCBs) substituted once or twice with chlorine enriched in 35Cl. Gas chromatographic analysis of the mixtures allowed the identification of the labelled PCBs produced by comparison of their relative retention times with published values. This also permitted the assignment of the position of the labels in these molecules. Mass spectrometric determination of the 35Cl/35Cl ratio of the ions corresponding to successive dechlorination of these PCBs in positive‐ion electron impact (EI) allowed quantification of the residual 35Cl label in these ions. Chlorines in the ortho position are lost preferentially to those in meta or para positions. The first dechlorination reaction was found to be totally regioselective for at least two PCB congeners.