bluuebunny/crossref_metadata_2025 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

Pyrolysis 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

Chemical 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

Electron 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

The 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

Electron 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

The 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

All 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

Sensitivity, 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

The 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

C4H8+˙ 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

A 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

Fragmentation 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

The 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

Pyrolysis/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

Tannins 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

Molecular 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

Pyrrolizidine 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

The 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

Ab 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

Calculations 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

The 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

Chemical 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

Radical 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

The 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

Mass 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

Phenomenological 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

It 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

Fourteen 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

The 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

Several [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

Glucuronic 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

Four 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.
Conversion of acetamido‐ and nitro‐substituted ortho‐azidonitro derivatives of 2,3,4,5‐tetrahydrobenzo [b][1,4]dioxocin to the corresponding furoxans and furazans in the gas phase
Authors: Takakis Ioannis M. , Hadjimihalakis Phaedon M. , Gross Michael L. , Hayes Roger N. , Haas George W.
Published: May 2005

Electron impact ionization of the five isomeric 2,3,4,5‐tetrahydro‐9‐azido‐7,8‐dinitro‐, 2,3,4,5‐tetrahydro‐8‐azido‐7,9‐dinitro‐, 2,3,4,5‐tetrahydro‐8‐azido‐7,10‐dinitro‐, 2,3,4,5‐tetrahydro‐7‐azido‐8,9‐dinitro‐, 2,3,4,5‐tetrahydro‐7‐azido‐8,10‐dinitro‐ and the related 2,3,4,5‐tetrahydro‐7‐acetamido‐8‐azido‐9‐nitro‐, 2,3,4,5‐tetrahydro‐7‐acetamido‐9‐azido‐8‐nitro‐, 2,3,4,5‐tetrahydro‐9‐acetamido‐7‐azido‐8‐nitro‐, 2,3,4,5‐tetrahydro‐10‐acetamido‐7‐azido‐8‐nitrobenzo[b] [1,4]dioxocin derivatives furnished, after elimination of nitrogen, the corresponding nitro and acetamido dioxocino‐annelated benzofuroxans. Further loss of oxygen from the latter afforded the corresponding benzofurazans. It was shown in two cases that these processes occur primarily upon electron impact ionization, without excluding some small fraction undergoing a thermal degradation process. The proposed fragmentation patterns are supported by high‐resolution and mass‐analyzed ion kinetic energy spectroscopic data. Similar work on the unsubstituted 6,7‐dihydro[1,4]dioxino[2,3‐f]‐ and 7,8‐dihydro‐6H‐[1,4]dioxepino[2,3‐f]‐2,1,3‐benzoxa‐diazole 1‐oxide reveal that loss of oxygen from the molecular ion to furnish the corresponding benzofurazans is the result of electron impact ionization (at least in part).
Comparison between the mass spectrometric behaviour and condensed‐phase reactivity of products of addition of phthalimidesulphenyl chloride to aryl acetylenes
Authors: Capozzi G. , Menichetti S. , Nativi C. , Seraglia R. , Traldi P.
Published: May 2005

The electron impact‐induced mass spectrometric behaviour of six products of the addition of phthalimidesulphenyl chloride to aryl acetylenes was studied with the aid of daughter ion spectroscopy. The electron impact‐induced decomposition processes parallel those observed in the condensed phase. In particular for the diaryl adducts the formation of 3‐chlorobenzothiophene derivatives results in a highly favoured process under the two sets of operating conditions.
Identification of short‐chain α‐hydroxyaldehydes produced by lipid peroxidation in bovine liver
Authors: Loidl Angelika , Spiteller Gerhard
Published: May 2005

A method to detect short‐chain α‐hydroxyaldehydes in mammalian tissues is described. Aldehydes or their masked precursor molecules are converted into dithiolane derivatives. These are separated by thin‐layer chromatography and registered by multiple ion monitoring after trimethylsilylation. Fragmentation of 2‐(1′‐trimethylsilyloxy)‐1,3‐dithiolanes was studied by using electron impact ionization.
Electron‐impact‐induced Ortho effects in (O‐carboxyphenyl)diphenylphosphine
Authors: Srinivas R. , Rao G. K. Viswanadha , Ravinder V.
Published: May 2005

Proximity effects of the carboxyl group with the phosphorus atom in the molecular ion of (o‐carboxyphenyl)diphenylphosphine (1) leads to the loss of ĊHO to form the base peak at m/z 277, which is totally absent in the (m‐ and p‐carboxyphenyl)diphenylphosphines. The mechanism of the loss of ĊHO and the fragmentation of 1 was investigated in detail using metastable ion, collision‐induced dissociation and high‐resolution studies.
Reactivity of vinylamine radical cation with neutral olefins: An example of ‘ionic’ free‐radical chemistry in the gas phase
Authors: Bouchoux Guy , Penaud‐Berruyer Florence
Published: May 2005

Hydrogen atom abstraction and cycloaddition–cycloreversion reactions between ionized vinylamine and neutral olefins were studied in a Fourier transform ion cyclotron resonance spectrometer. The efficiencies of both processes are appreciably less than unity. The trend in reaction efficiencies is consistent with the presence of a substantial intrinsic barrier but interpretation based on constraints inherent to the approach of the reactants cannot be discarded. The regioselectivity observed during the cycloaddition–cycloreversion reactions closely parallels the nucleophilic attack of an olefin by a free radical. The thermochemistry of these reactions and partial potential energy surfaces were examined with the help of experimental data and molecular orbital calculations (MP2/6–31G*//3–21G).
Photoelectron spectra of the isomers of methoxypyridine
Authors: Dunne Simon J. , Summers Lindsay A. , von Nagy‐Felsobuki Ellak I.
Published: May 2005

The He I photoelectron spectra of 2‐, 3‐ and 4‐methoxypyridine are reported and interpreted in terms of a composite‐molecule model and ΔSCF/MP ionization energies. For pyridine, this ab initio method correctly locates the nitrogen lone‐pair molecular orbital with respect to experiment and shows quantitatively the importance of incorporating both correlation and relaxation effects. Comparison of experimental and ab initio ionization energies of the methoxypyridines with the semi‐empirical HAM/3 method further substantiates the utility of HAM/3 for the interpretation of photoelectron spectra.
Multiphoton excitation of ferrocene and vanadocene at 351 nm in comparison with 248 and 193 nm. Wavelength dependent competition between ionization and dissociation
Authors: Opitz Joachim , Bruch Detlev , von Bünau Günther
Published: May 2005

Multiphoton ionization of ferrocene and vanadocene upon nanosecond laser excitation at 351 nm is reported in comparison with results at 248 and 193 nm. A similar behaviour was found for both compounds at each wavelength. The excitation and fragmentation mechanism was elucidated by the determination of the number of absorbed photons for the ion formation and the analysis of the metastable ion decay. On biphotonic excitation at 248 nm extensive fragmentation of the neutral parent molecule to metal atoms is observed, followed by the ionization of these metal atoms after absorption of two further photons. In contrast, at 193 nm the molecular ion is formed after absorption of two photons and dominates the fragmentation pattern up to moderate laser intensities. At high laser intensities the metal ion, formed after resonant absorption of three photons, becomes prominent. At 351 nm the exclusive formation of molecular ions is observed only near the threshold of the laser intensity for ion detection. Metal ion formation prevails at higher laser intensities involving the absorption of five photons. Most likely this absorption mechanism is resonant.
Mass spectrometric study of some 2,3‐diaryl‐1,3‐thiazolidin‐4‐ones under electron impact
Authors: Woolston C. R. J. , Lee J. B. , Swinbourne F. J.
Published: May 2005

The mass spectral fragmentations of some 2,3‐diaryl‐1,3‐thiazolidin‐4‐ones were established by comparing spectra and by using exact mass measurements. The major fragment ions were identified and their relative importances related to substituent effects and bond strengths. Good correlations were observed between the relative abundances of some of the breakdown products and the Hammett σ constants of substituents in the aromatic rings.
Novel aryloxy migrations in substituted diphenyldithiocarbonates under electron impact conditions
Authors: Ramana D. V. , Mahalakshmi P. , George M.
Published: May 2005

Unusual expulsion of ‘SO’ was observed from the molecular ions of substituted diphenyldithiocarbonates under electron impact conditions. An initial aryloxy migration to sulphur followed by further rearrangement is proposed for this process, based on the substituent effects. The diarylthioketone radical–cation structure assigned for the [M – SO] ion was confirmed through the collision‐activated dissociation B/E linked‐scan spectra.
Organic cluster ions from continuous‐flow fast atom bombardment
Authors: Jarvis V. M. , Villanueva M. A. , Bostwick D. E. , Moran T. F.
Published: May 2005

Cluster ions from fast atom bombardment of liquid alcohols and nitriles were examined using a continuous‐flow technique. Protonated molecular MnH+ species are the dominant cluster ions observed in molecules of formula M. The abundances of the MnH+ cluster ions decrease monotonically with increasing n, and within a homologous series the MnH+ abundance diminishes more rapidly for higher molecular mass compounds. Reaction products (ROH)n(H2O)H+ and (ROH)n(ROR)H+ are observed also in the case of alcohols, and the ion abundances decrease with increasing n. Radiation damage yields fragment ions and ionic alkyl reaction products which are captured in solvent clusters. Semi‐empirical molecular orbital methods were used to examine the energetics of cluster ion formation and decomposition pathways. Metastable decomposition processes exhibit only evaporative loss of monomers, with the probability of loss increasing sharply with n. The evaporative ensemble model of Klots was used to predict the cluster size‐dependent trends of metastable dissociation processes observed for alcohol and nitrile cluster ions.
Substitution reactions in the secondary ion mass spectrometry of N‐methylpyridinium halides
Authors: Yoneda Michiaki , Tanizaki Ken , Tsujimoto Kazuo , Ohashi Mamoru
Published: May 2005

Secondary ion mass spectra of N‐methylpyridinium halides (C+X−, where C+ is a pyridinium cation and X− is a halogen anion) exhibit the C+ ions, a series of cluster ions ((C+)n(X−)n–1) and, furthermore, remarkable [CX – R]+ ions (R = H or Me). The mechanism of the formation of [CX – R]+ ions was investigated by the use of deuterated compounds and B/E and B2/E constant linked‐scan measurements. A possible explanation is proposed in which the ions are produced through substitution reactions between species constituting the C2X+ cluster ions in the gas phase.
Mechanism of production of ions in electrospray mass spectrometry
Authors: Ashton D. S. , Beddell C. R. , Cooper D. J. , Green B. N. , Oliver R. W. A.
Published: May 2005

A mechanism for the production of multiply charged molecular ion species in electrospray mass spectrometry (ES‐MS) is still required. A concise discussion of a recently published ionic solution equilibrium model offering a partial mechanism is presented. That publication proposed that the ion abundance–charge profile could be fitted by one or a series of superimposed Gaussian functions, in accord with a solution equilibrium model. It is shown that indeed a simulated mass spectrum based on a solution odel can compare well with the observed spectrum. However, some new and recently published experimental evidence is presented which shows that the ES mass spectra of many proteins give rise to multiply charged molecular ions which carry higher charges than those calculated by the model. Further, the ion abundance–charge profile is very sensitive to some experimental parameters, e.g. cone voltage; it does not necessarily reflect the solution or gaseous ion populations in the mass spectrometer source. Therefore, the concept that gaseous multi‐charged ions originate from equivalently charged solvated ions in electrically neutral solution must be treated with caution.
Negative‐ion fragmentation pathways in 2,4,6‐trinitrotoluene
Authors: Langford M. L. , Todd J. F. J.
Published: May 2005

The mass spectrum of 2,4,6‐trinitrotoluene vapour in air was recorded and the negative‐ion fragmentation pathways of the molecular anion were investigated down to the fourth generation. The dissociation of the parent anion led to the production of three fragment anions with masses 46, 197 and 210 u where the last two daughter ions initiated two entirely separate fragmentation pathways. These pathways were studied and the fragmentation mechanisms identified. The background negative‐ion mass spectrum, generated by the glow discharge ion source in the airstream which carries the sample vapour into the source, was examined in detail and an assignment of this mass spectrum is included.
Comparative investigations of the secondary ion emission of metal complexes under MeV and keV ion bombardment
Authors: Feld Herbert , Rading Derk , Leute Angelika , Benninghoven Alfred
Published: May 2005

A series of ionic and neutral Group VIII transition metal complexes with molecular masses up to 2500 u were analysed by time‐of‐flight secondary ion mass spectrometry (SIMS) and plasma desorption mass spectrometry (PDMS). The secondary ion emission, the secondary ion yields and the yield ratios Y(PDMS)/Y(SIMS) of 20 ionic and neutral metal complexes were determined. Both techniques generally provide both molecular and fragment ion information. Characteristic fragmentation patterns give useful data for structural characterization. Additionally, the stabilities of different secondary ion species were compared by their half‐lives. Both PDMS and SIMS are very sensitive, yielding optimum spectra from total sample sizes as low as 5 nmol, and the sample consumption is negligible.
Isomerization and isotope effects in sterically congested cluster ions
Authors: Szulejko J. E. , McMahon T. B.
Published: May 2005

The association reactions of methylated acetone with acetone and dimethyl ether were studied over an extended temperature range (30–250°C) by high‐pressure mass spectrometry. In addition, the association reactions of various deuterium‐substituted analogues of both the reactant ion and neutral molecules were investigated. Two distinct isomeric forms are apparent from the examination of the behaviour of the association equilibrium constant as a function of reaction temperature: (i) a low‐temperature, covalently bound isomer characterized by larger −ΔH° and −ΔS° values and significant equilibrium isotope effects on the entropy of association; and (ii) a high‐temperature, electrostatically bound isomer of lower −ΔH° and −ΔS° values and with insignificant equilibrium isotope effects. The equilibrium isotope effects and larger −ΔS° values are more pronounced for the methylated acetone–dimethyl ether adduct than for the less sterically congested methylated acetone‐acetone adduct. Molecular models of the low‐temperature isomers show severe restriction or complete loss of internal rotations and is the origin of the observed equilibrium isotope effects. No such phenomenon is expected or observed in the more loosely bound high‐temperature, electrostatic isomers. Potential energy surfaces for the transfer of methylcation from methylated acetone to a second acetone molecule and to dimethyl ether are proposed.
Dependence of benzyl alcohol loss onC‐terminal amino acid in tandem mass spectrometry ofN‐protected tripeptides
Authors: Schwartz Brenda L. , Erickson Bruce W. , Bursey Maurice M. , Marbury G. Dean
Published: May 2005

The effect of the basicity and chain length of theC‐terminal amino acid on the fragmentation ofN‐protected tripeptides was investigated with a hybrid tandem instrument. Positive‐ion unimolecular decomposition and colisionally activated decomposition studies on the [M + H]+ions of a series ofN‐benzyloxycarbonyl (Cbz or Z)‐protected tripeptides, Cbz–Gly–Leu–Xxx–OMe and Cbz–Gly–Pro–Xxx–OMe, where Xxx = Arg, Lys, Orn, Gln and Glu, indicate that substitution of leucine with proline at the second position in the tripeptides facilitates the loss of benzyl alcohol (108 u) from the precursor. Additionally, higher gas‐phase basicity and longer chain length of theC‐terminal side‐chain group promote the formation of the [M + H – 108]+ion.
Sequence‐ion studies in peptides: The generation of C″ ions—part 2
Authors: van Dongen W. D. , de Koster C. G. , Heerma W. , Haverkamp J.
Published: May 2005

The mechanism for the formation of Cx″‐type ions in which x ≤ n – 2, from protonated peptides containing n amino acids, produced under conditions of fast atom bombardment and collisional activation, was investigated. Comparison of the tandem mass spectra of the [M + H]+ ions of two model peptides (VGSE and AAA) with those of their corresponding [Md + D]+ ions, in which all exchangeable hydrogens are replaced with deuterium, revealed that in the case of VGSE the hydrogen atom from the hydroxyl group in the serine residue and/or from the amide group of the adjacent amino acid must be involved in the migration process which leads to the formation of C2″‐type ions. The second peptide (AAA) shows the exclusive transfer of the amide hydrogen atom in the formation of the C1″ ion. The mechanism differs from an earlier reported reaction channel which appeared to be applicable to the formation of C‐type ions. The most plausible neutral species which is eliminated in the formation process of the Cx″ ion from [M + H]+ is proposed on the basis of relative stability calculations.
Leucine and isoleucine in chemical ionization and plasma desorption mass spectrometry: A comparative study
Authors: Bouchoux Guy , Bourcier Sophie , Hoppilliard Yannik , Mauriac Christine
Published: May 2005

The NH3 and CH4 chemical ionization mass spectra of leucine and isoleucine are compared with their plasma desorption mass spectra. Mass‐analysed ion kinetic energy (MIKE) and collision‐induced dissociation (CID)/MIKE experiments are also presented and the mechanisms of the formation and dissociation of immonium ions [M – CO2H2]+ are discussed. A comparison between the various ionization techniques reveals that plasma desorption produces pseudo‐molecular ions whose internal energy lies between zero and 300 kJ mol−1.
Reaction of protonated acetaldehyde with methanol in the gas phase
Authors: König S. , Kofel P. , Reinhard H. , Sägesser M. , Schlunegger U. P.
Published: May 2005

The ion–molecule reactions between protonated acetaldehyde and methanol were explored on a quadrupole, quistor, quadrupole tandem mass spectrometer. In addition to proton transfer to methanol and subsequent methanol ionmolecule chemistry, the protonated acetaldehyde–methanol adduct and methylated acetaldehyde could be detected. Experiments with labelled counterparts showed that the formation of methylated acetaldehyde corresponds to substitution of the oxygen‐bound hydrogen of protonated acetaldehyde by the methyl group of methanol. The reaction rates involved and H–D exchange rates were determined.
Mass spectrometric studies of selected coumarins and psoralens. I—negative ions
Authors: Tkaczyk Martin , Zobel Alicja M. , Plomley Jeffry B. , March Raymond E.
Published: May 2005

An investigation of the negative‐ion chemistry of 13 coumarin and three psoralen compounds is reported. Negative‐ion chemical ionization was effected using O−˙ and OH− as the reagent ions; it was found that O−˙ leads preferably to [M – H + O]− whereas OH− mainly furnishes [M – H]−. The results of metastable anion fragmentation and collision‐induced dissociation of mass‐selected anions are presented.
Gas‐phase unimolecular chemistry of ethyl butyl ketone cations
Authors: Bouchoux Guy , Flammang Robert , Jaudon Pascale , Lefevre Odile
Published: May 2005

Mass spectra of the four isomeric ethylbutyl ketones, C2H5CO‐n‐C4H9 (1), C2H5CO‐iso‐C4H9 (2), C2H5CO‐sec‐C4H9 (3) and C2H5 CO‐t‐C4H9 (4), are reported. The structure of the fragment ions produced from precursors of both high and low internal energy were identified by collision experiments in a six‐sector mass spectrometer. Metastable molecular ions 1+˙ and 2+˙ behave identically in expelling CH3˙, C3H6 and C2H5˙ to produce the same fragment ions: [C2H5C(OH)CHCHCH3]+, [C2H5C(OH)CH2]+˙ and a mixture of [CHOHCHCHC2H5]+ and [CHOHCHC(CH3)2]+, respectively. The key isomerization step between 1+˙ and 2+˙ is a 1,2‐enol–olefin shift. Metastable molecular ions 3+˙ and 4+˙ give essentially ethene and ethyl losses, respectively; the fragment ions are [C2H5C(OH)CHCH3]+˙ and [t‐C4H9CO]+. Keto–enol isomerization also occurs to a significant extent for ions 1+˙ and 2+˙ and 3+˙. In contrast, 1,2‐ or 1,3‐ethylhydroxycarbene migrations are only marginal processes.
Structures and stabilities of C3H4O+˙ isomers: A G2 theoretical study
Authors: McKee Michael L. , Radom Leo
Published: May 2005

Six stable isomers andtwo transition structures were characterized on the C3H4O+˙ potential energy surface using the G2 procedure. Heat capacity corrections were made to allow the direct calculation of heats of formation at 298 K. The most stable isomer is the methylketene radical cation (1, ΔHf 298 = 797.0 kJ mol−1), followed by a distonic ion \documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\rm C}\limits^ \cdot {\rm H}_2 {\rm CH}_2 \mathop {\rm C}\limits^ +=\!={\rm O} $\end{document} (2), only 46.5 kJ Mol−1 higher in energy (ΔHf 298 = 843.5 kJ mol−1). Ionized cyclopropanone (7) represents a transition structure for exchange of terminal methylene groups in the distonic ion with a corresponding barrier of 57.6 kJ mol−1. There is amuch larger barrier (106.7 kJ mol−1) for the 1,2‐hydrogen migration in the distonic ion (2) to form the mor estabe ionized methylketene (I), while the fragmentation of 2 to C2H4+˙ + CO is highlyendothermic (by 113.1 kJ mol−1). The predicted ease of formation of the distonic ion on ionization of neutral cyclopropanone (7n) and the higher barrier for further reaction would suggest that ionized cyclopropanone should show reactivity characteristic of a radical as observed for ionized cyclobutanone. Three additional C3H4O+˙ isomers, hydroxyallene radical cation (3), acrolein radical cation (4) and oxetene radical cation (5), lie within 15 kJ mol−1 of one another in energy, while a cyclic form (6) of the distonic ion is much less stable. G2 heats of formation and adiabatic ionization energies were also calculated for four of the neutral C3H4O analogs. WHile the ionization energies are in good agreement with available experimental values, as are the heats of formation for acrolein (4n) and cyclopropanone (7n), the G2 heat of formation of methylketene (−65.1 ± 10 kJ mol−1) is almost 40 kJ mol−1 higher than the ‘standard’ value, which it is considered shoul dbe revised. Calculations iwth the G2(MP2) method, which is less computationally intensive than G2, yields of formation for the neutral and ionic species within 24 kJ mol−1 of the G2 values.
New [C2, H3, N, O]+˙ isomers: A metastable and collision‐induced fragmentation study
Authors: Hop Cornelis E. C. A. , Snyder David F.
Published: May 2005

Metastable and collision‐induced fragmentation in a masspsectrometer were used to characterize several [C2, H3, N, O]+˙ isomers. CO2 loss from ionized oxazolidine‐2,5‐dione yields the distonic ions H2CNHCO+˙ and HNCH2CO+˙ and not the cyclic isomer, . Kinetic energy relese measurement indicate that CO2 loss from the molecular ions is accompanied by a significant barrier for the reverse reaction. In this respect the behavior of oxazolidine‐2,5‐dione parallels that of the isoelectronic compound sucinic anhydride. O(H)CC(H)NH+˙ kions are generated via CO loss from 2(3H)‐oxazolone molecular ions. There is no evidence to support generation of the cyclic isomer, . For comparison, data wer obtained for the known isomers H3CNCO+˙, H3COCN+˙, H3CCNO+˙, HOCH2CH+˙ H2NCCOH+˙ H2N(H)CCO+˙ and H2CC(H)NO+˙. The H3COCN+˙ and H3CCNO+˙ structures were assigned to the m/z 57 fragment ions from methyl cyanoformate and acetohydroxamic acid, respectively.
A theoretical and experimental study of the structures and stabilities of the [C5H3]+ cation
Authors: Kompe Barbara M. , Peel J. Barrie , Traeger John C.
Published: May 2005

The structures and energies for 16 different [C5H3]+ isomers were geometry optimized from ab initio molecular orbital calculations. The global minimum on the [C5H3]+ surface at the MP3/6–31G* level was found to be the ethynyl cyclopropenylium cation (a), with a penta‐1,3‐diynylium structure (b) and a penta‐1,4‐diynylium structure (c) being 90 and 100 kJ mol−1 higher in energy, respectively. An isodesmic reaction was used to calculate a value of 1339 kJ mol−1 for the enthylpy of formation of b. Photoinization appearance energies were measured for the [C5H3]+ ions from penta‐1,3‐diyne, hexa‐2,4‐diyne and hexa‐1,5‐diyne as 11.66, 12.25 and 11.8 eV respectively The penta‐1,3‐diyne fragmentation was used to estimate an experimental enthalpy of formation for b of 1315 ± 2 kJ mol−1. There is some theoretical evidence that the penta‐1,3‐diyne fragmentation occurs without any significant reverse activation energy whereas both the hexa‐2,4‐diyne and hexa‐1,5‐diyne fragmentations involve excess energy.
Analysis of xanthates by negative‐ion fast atom bombardment mass spectrometry
Authors: Fourie L. , Kruger H. G.
Published: May 2005

A new technique using negative‐ion fast atom bombardment mass spectrometry for the analysis of xanthates and related compounds is described. Electron impact and positive‐ion fast atom bombardment mass spectrometry produced no structurally related fragment ions or observable molecular ions at the expected m/z values. It was demonstrated that negative‐ion fast atom bombardment ionization was the most suitable method of ionization for structure elucidation studies for the compounds described.