bluuebunny/crossref_metadata_2025_split huggingface dataset:
Electron impact ionization tandem mass spectrometry of glycosphingolipids. Part III. Study of the fragmentation modes of selected glycosphingolipids
Authors: Curtis Jonathan M. , Holgersson Jan , Derrick Peter J. , Samuelsson Bo E. 
Published: May 2005

AbstractResults are presented from a systematic study of the high‐energy tandem mass spectra (fragment ion spectra) of derivitized (permethylation followed by LiAlH4 reduction) porcine glycosphingolipids (GSLs) using a four‐sector mass spectrometer. The ions studied were the ammonium ions of the GSLs formed on loss of the sphingosine side‐chain following electron impact ionization. Fragment ion spectra are shown to provide structural data useful in identifying carbohydrate sequence, the location of hexosamine residues and the identification of fatty acid chain length. Differences between the fragment ion spectra of isomers differing in carbohydrate linkage position and stereochemistry were observed, but not easily predicted.
Calculation of ion composition in organic high‐resolution mass spectrometry
Authors: Ioffe B. V. , Vitenberg D. A. , Zenkevich I. G. 
Published: May 2005

AbstractThe theory of a method for the calculation of organic ion compositions is described. It is based on concepts of homologous groups and homologous increments of ‘mass defect.’ Unlike the common algorithms usually used for this purpose, the proposed method excludes the analysis and outcome of chemically unreal combinations of atoms. Reduction of the number of alternative compositions is discussed. The possibility of a single (non‐alternative) solution is considered in the case of additional information on the presence of functional groups containing nitrogen and/or oxygen and also aromatic fragments easily identified by their infrared spectra. The efficiency of the method is demonstrated with the help of new software for DEC‐ and IBM‐compatible computers.
Unprecedented double‐electron transfer to a triply charged cation: Reactions of C with anthracene, corannulene, benzo[rst]pentaphene and pyrene
Authors: Jahavery Gholamreza , Becker Hansjürgen , Petrie Simon , Cheng Pei‐Chao , Schwarz Helmut , Scott Lawrence T. , Bohme Diethard K. 
Published: May 2005

AbstractAn unprecented double‐electron transfer reaction has been observed between triply charged buckminsterfullerene, C, and the PAH molecules anthracene, corannulene, benzo[rst] pentaphene and pyrene at 294 ± 2 K in helium at 0.35 ± 0.01 Torr. The measurements were made with a selected‐ion flow tube (SIFT) apparatus. With anthracene, corannulene and pyrene double‐electron transfer was a minor channel (<5%): single‐electron transfer was the predominant channel. With benzo [rst] pentaphene, which requires the lowest energy for double ionization, single and double‐electron transfer proceeded in almost equal amounts.
Ion–neutral reorientation and unimolecular loss of alkanes from organic ions in the gas phase
Authors: Longevialle P. , Lefèvre O. 
Published: May 2005

AbstractThe loss of alkanes from ionized aliphatic alkanes, alcohols, ketones, ethers or amines takes place by a 1,2‐elimination involving a CC bond cleavage and the specific rearrangement of a hydrogen atom to the incipient radical. This reaction should normally occur within a limited distance between the reactant sites. This condition is accomplished with most probability during a concerted (or quasi‐concerted) mechanism, before the completion of the CC bond cleavage. The same reaction may also occur, however, in ion–neutral complexes, i.e. by a non‐concerted mechanism, after the CC bond cleavage is completed, provided that the probability is large enough for ion–neutral complexes to adopt suitable reactant configurations. This depends essentially on the proportion of possible reacting sites in the whole molecular ion.
Bimolecular reactions of distonic ions: Proton transfer and hydrogen atom abstraction with ˙CH2OH2+
Authors: Mourgues Philippe , Audier Henri Edouard , Leblanc Danielle , Hammerum Steen 
Published: May 2005

AbstractThe bimolecular reaction of ˙CH2OH2+ with a variety of neutral molecules in the gas phase were studied by Fourier transform ion cyclotron resonance experiments. The distonic ion is found to be considerably more acidic than protonated methanol; bracketing experiments provide a value of 695 ± 8 kJ mol−1 for the proton affinity of the conjugate base, the hydroxymethyl radical, Efficient hydrogen atom abstraction is only observed from neutral species less basic than ˙CH2OH. Transfer of CH to CS2, CH3I and C6H2F4 is observed.
H–D exchange at low energy in a collision cell between protonated aromatic hydrocarbons and D2O, CD3OD and C6D6
Authors: Stone John A. 
Published: May 2005

AbstractH–D exchange reations which occur between protonated molecules (mainly aromatic hydrocarbons) and deuterated neutrals (D2O, CD3OD and benzene‐d6) were studied using a hexapole collision cell. The efficiency of exchange is dependent on the proton affinity difference between aromatic and target molecules but the pattern of deuteration in the exchanged ions does not change as might be expected with collision gas pressure. The incident ion energy also has only a small effect on the pattern up to a certain value, but above that value no exchange occurs. It is suggested that ions which shows multiple exchange have the same distribution of transit times, independent of collision gas pressure and, within the above limits, of initial energy. The rate‐determining step is then exchange in an ion–molecule complex rather than collision rate.
O−˙ chemical ionization mass spectra of fluoroaromatic compounds
Authors: Merrett Kim , Young Alex. B. , Harrison Alex. G. 
Published: May 2005

AbstractThe O−˙ chemical ionization (CI) mass spectra of the mono‐ to pentafluorobenzenes, fluorotoluenes and fluoroanisoles were measured. For comparison, the O−˙ CI mass spectra of toluene (including deuterium‐labelled variants) and anisole were also measured. The major reaction channels of O−˙ with fluorobenzene involve H‐atom displacement and H abstraction. With increasing fluoring substitution H+ abstraction increases in importance. For the tri‐ and tetrafluorobenzenes H abstractions is important only when there are two hydrogen ortho to each other. Reaction channels which are unique to the fluoroaromatic molecules involve the formation of [M + O – HF]−˙, which, for polyfluoro compounds, fragments further by elimination of HF or CO. For the fluoroanisoles, formation of FC6H4O− and elimination of CH2O from [M – H]− and [M – 2H]−˙ are important reaction channels. The formation of [M + O – H]− by reaction of O−. with toluene is shown to involve specific displacement of a ring hydrogen, whereas the formation of [M – H]− involves primarily abstraction of a proton from the methyl group. By contrast, H abstraction is non‐specific and proceeds by three pathways: (i) abstraction of two hydrogens from the aromatic ring, (ii) abstraction of two hydrogens from the methyl group and (iii) abstraction of one hydrogen from each position; however, the resuls are not in accord with a random selection of hydrogens.
Measured and calculated double‐ionization energies of 2‐haloethanols
Authors: Seakins M. , Griffiths W. J. , Harris F. M. , Andrews S. R. , Parry D. E. 
Published: May 2005

AbstractDouble‐charge‐transfer spectroscopy was used to measure the double‐ionization energies of the 2‐haloethanols FCH2CH2OH, ClCH2CH2OH, BrCH2CH2OH and ICH2CH2OH; the values obtained were 30.1 ± 0.5, 28.1 ± 0.5, 27.6 ± 0.5 and 26.9 ± 0.5 eV, respectively. In addition, the energies were calculated using ab initio methods and the GAUSSIAN 90 program package. The measured and calculated values for FCH2CH2OH are in agreement, but for the three other molecules the calculated values are significantly lower than those measured. The discrepancies in the calculations are due mainly to the underestimation of correlation energies by the appropriate MP2 method, which becomes progressively worse with increasing number of electrons in the system.
The fast atom bombardment mass spectra of furyl and thienyl silanes and germanes in comparison with their electron impact mass spectra
Authors: Mažeika I. , Grīnberga S. , Gavars M. , Gaukhman A. P. , Erchak N. P. , Lukevics E. 
Published: May 2005

AbstractThe interaction of the π electron system of furyl and thienyl substituents with the silicon (or germanium) atom is less significant in fragmentation under fast atom bombardment than under electron impact. Under fast atom bombardment the primary fragmentation of the title compounds is determined by steric influence of the heteroaromatic substituents.
Electrospray mass spectrometry of pentacosasaccharides of blood group I‐activity and related compounds
Authors: Ii Tadashi , Ohashi Yoko , Matsuzaki Yuji , Ogawa Tomoya , Nagai Yoshitaka 
Published: May 2005

AbstractThe structural characterization of large synthetic oligosaccharides and related glycoconjugates performed by the use of electrospray ionization mass spectrometry (ESIMS) is described. The largest molecules described here are unprotected and protected pentaantennary pentacosasaccharides 2 and 5 with average molecular masses of 4441 and 9416, respectively. The straight‐chain neutral ceramide decasaccharide (d18:1/c24:0) 6 and the disialoganglioside GD2 (d18:1/c24:0) 7 were also successfully analyzed by ESIMS. In addition to exact mass determination, collision‐induced dissociation (CID) spectrometry of these compounds provided saccharide chain sequence information.
Growing protein‐doped sinapic acid crystals for laser desorption: An alternative preparation method for difficult samples
Authors: Xiang Fan , Beavis Ronald C. 
Published: May 2005

AbstractThis paper describes several protocols for growing large, protein‐doped 3,5‐dimethoxy‐4‐hydroxy‐trans‐cinnamic acid crystals. Examination of these crystals using laser desorption shows that the mass spectra obtained from the crystals can be useful for biochemical analysis. One particular crystal growing protocol allowed a non‐covalently bound heme group of horse muscle myoglobin to remain attached to the polypeptide following laser ablation and ionization. Crystals could be grown in solutions that contained involatile solvents that normally inhibit polypeptide ion production, such as glycerol. These crystals were protein doped and produced acceptable analytical mass spectra. The results suggest that some problems associated with the frequently used droplet‐drying method of sample preparation are caused by the changing concentration conditions present in drying solutions.
Various energy minima and corresponding fragmentation processes: Alkylsilanes
Authors: Vékey Károly , Paizs Béla , Somogyi Árpád , Knausz Dezsö , Pócsfalvi Gabriella 
Published: May 2005

AbstractFragmentation of alkylsilanes, in particular trimethylethylsilane, were studied by mass‐analysed ion kinetic energy (MIKE) and collision‐induced decomposition MIKE techniques. Ab initio and semi‐empirical molecular orbital calculations were applied to explain the main fragmentation processes. These calculations indicate that more than one minimum can be located on the potential energy surface of a given ground‐state molecule ion. These differ from each other mainly in the length of the silicon–carbon bonds. The structures can be adequately described as complexes of a trivalent silyl ion and an alkyl radical. Each of these complexes fragments by the loss of the weakly bound alkyl radical. The calculated energetics of these reactions were found to be in good agreement with the observed energy dependence of the mass spectra.
Acetone chemical ionization studies. VII‐acetylation of some aromatic compounds
Authors: Vairamani M. 
Published: May 2005

AbstractAcetone chemical ionization mass spectra of 14 monosubstituted aromatic compounds were studied. Benzene, toluene and halobenzenes give exclusively charge‐exchange spectra with very little fragmentation. Protonation is characteristic of compounds with higher proton affinities than acetone, with the exception of benzonitrile. Acetylation reactions are observed mainly with benzonitrile, phenol, anisole and aniline. The acetylation of phenol and aniline mostly occurs at the substitutent.
Structural studies of polyhydroxybis(tetrahydrofuran)acetogenins from Annona squamosa using the combination of chemical derivatization and precursor‐ion scanning mass spectrometry
Authors: Hirayama Kazuo , Akashi Satoko , Yuji Reiko , Niitsu Uno , Fujimoto Yoshinori 
Published: May 2005

AbstractThe structure of squamocin polyhydroxybis(tetrahydrofuran)acetogenin from Annona squamosa L., was characterized by a combination of the chemical derivatization and precursor‐ion scanning mass spectrometry. The lactone part of squamocin was modified with N,N‐dimethylethylenediamine in the vapour phase to afford a strong positive charge at one end of the skeleton. The derivative was ionized by fast atom bombardment (FAB), and the product ion spectrum from [M + H]+ and the precursor ion spectrum from the m/z 72 ion [CH2CHN+H(CH3)2] generated by low‐energy collision were acquired. The structure of the derivative could be characterized by the precursor‐ion spetrum from the m/z 72 ion, but little structural information could be obtained from the production spectrum from [M + H]+ of the derivative. By the attachment of a tertiary amino group to one end of the skeleton, charge‐remote fragmentation was facilitated and abundant and unique fragment ions were observed in the precursor‐ion spectrum. Structural characterization of six other isolated compounds was also carried out, and two novel compounds were found by this technique. A similar derivatization was applied in the peptide leu‐enkephalin, and full sequencing from the C‐terminus using precursor‐ion scanning from m/z 72 could be achieved.
1,2‐Versus 1,4‐reduction of α,β‐unsaturated carbonyl compounds in the gas phase
Authors: Ho Yeunghaw , Squires Robert R. 
Published: May 2005

AbstractThe regioselectivity involved in the gas‐phase hydride reduction of α,β‐unsaturated carbonyl compounds by pentacoordinate silicon hydride ions is investigated. The kinetics and product distributions of the reactions of acrolein, methyl vinyl ketone and cyclohex‐2‐enone with monoalkoxysiliconate ions of the general composition RSiH3(OR′)− were examined with the flowing afterglow–triple quadrupole technique. All three substrates react by hydride transfer and by formation of a siliconate adduct in which hydride reduction of the organic reactant has occurred. The structures of these adducts and the hydride transfer products were identified by various tandem mass spectrometric protocols, including analysis of competitive collision‐induced dissociation (CID) reactions and comparisons of CID spectra obtained from reference ions with known structures. 1,4‐Reduction forming an enolate ion product is found to be the dominant or exclusive process with all three substrates, i.e. acrolein (70 ± 5%), methyl vinyl ketone (72 ± 5%) and cyclohex‐2‐enone (100%). Comparisons are made between these gas‐phase results and the regioselectivity reported for analogous condensed‐phase reactions. The observed behavior is discussed in terms of the reaction thermochemistry.
Neutral counterparts of the C2H7O+ isomers
Authors: Sirois M. , George M. , Holmes J. L. 
Published: May 2005

AbstractThe neutral counterparts of the C2H7O+ isomers CH3O+ (H)CH3, CH3CH2OH2+ and \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm C}_2 \,{\rm H}_4 \,\, \cdot \cdot \cdot \mathop {\rm H}\limits^ + \, \cdot \cdot \cdot {\rm OH}_2 $\end{document} were studied by neutralization‐reionization mass spectrometry. Protonated dimethyl ether and its —O(D)+ analogue were produced by protonation (deuteration) of dimethyl ether and also generated as a fragment ion from (labeled) ionized CH3OCH2CH(OH)CH3 by loss of CH3CO⋅. It was observed that the dissociation characteristics of the ions and the stability of their neutral counterpart depended on the internal energy of the protonated ether ions. Stable neutral CH3Ȯ(H)CH3 was only produced from energy‐rich ions. The classical protonated ethanol ion CH3CH2OH2+ (a) was produced at threshold by the loss of CH3CO⋅. from ionized butane‐2,3‐diol. Mixtures of a with the non‐classical ion \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm C}_2 \,{\rm H}_4 \,\, \cdot \cdot \cdot \mathop {\rm H}\limits^ + \, \cdot \cdot \cdot {\rm OH}_2 $\end{document} (b) were produced by reaction of C2H5+ ions with H2O. As for the protonated ether, only high‐energy a and/or b ions yielded stable hypervalent radicals. It is suggested that the stable C2H7⋅O radicals are Rydberg states.
The ortho effect in the mass spectra of ortho/para isomers of bisphenol a derivatives and related compounds
Authors: Pleshkova Alexandra P. , Uspenskaya Marina N. , Volkovitch Sergei V. 
Published: May 2005

AbstractNew examples of the ortho effect in bisphenol A derivatives including interaction of the hydrogen of the ortho‐hydroxy group with the neighbouring aromatic ring have been observed. The characteristic ions [M  PhOH]+middot; (m/z = 134) and [M  CH3  PhOH]+ (m/z = 119) were shown to form through the hydrogen transfer from hydroxy and isopropyl groups, respectively. The spectra of cyclic derivatives having ortho‐hydroxy functions show [M  43]+, [M  C8H9O]+, m/z = 147, m/z = 135 and [M  C9H10O]+ ions. The proposed mechanims of the corresponding transformations were supported by mass spectra of deuterated analogues, methyl and trimethyl silyl ethers.
Influence of fluorine atoms on the electron impact and chemical ionization mass spectrometric fragmentation of methyl x‐deoxy‐x‐fluoro‐per‐O‐methyl‐β‐D‐galactopyranosides
Authors: Kováčik V. , Kováč P. 
Published: May 2005

AbstractFully methylated methyl x‐deoxy‐x‐fluoro‐β‐D‐galactopyranosides were studied using electron impact (EI) and chemical ionization (CI) mass spectrometry and by gas chromatography (GC)/mass spectrometry. Metastable daughter‐ and parent‐ion measurements and high‐resolution measurements were used to evaluate the fragmentation schemes. Both the presence and the position of the electronegative fluorine atom influences the fragmentation pathways of the permethylated compounds. The individual methyl x‐deoxy‐x‐fluoro‐per‐O‐methyl‐β‐D‐ galactopy‐ranosides have different GC retention times. This, together with the characteristic differences present in the EI or CI (methane or isobutane) mass spectra, allows the location of fluorine in these substances to be unambiguously determined.
Fingerprinting stereoisomers by survivor‐ion mass spectrometry
Authors: Gu Ming , Turecek Frantisek 
Published: May 2005

AbstractSurvivor‐ion mass spectrometry is used to distinguish stereoisomeric cis‐ and trans‐4‐methylcyclohexanol. The method involves producing ions by electron impact ionization and submitting them without mass selection to collisional neutralization and reionization, followed by selective monitoring of non‐dissociating ions. The differences in the electron impact mass spectra of the stereoisomers, due to the different fragment ion elemental compositions and structures, are highlighted by collisional neutralization with Xe, NO and CH3SSCH3, followed by reionization with oxygen. The differences in the survivor‐ion spectra are due to different neutralization efficiencies of the isobaric and isomeric ions produced by electron impact ionization, different stabilities of the intermediate neutral species, different reionization efficiencies and reionized ion stabilities. Neutralization‐reionization spectra of the C7H12+., C6H9+, C3H6O+. and C3H5O+ ions from stereoisomeric 4‐methylcyclohexanols are also reported.
Unimolecular reactions of \documentclass{article}\pagestyle{empty}\begin{document}$ ^ \cdot {\rm CH}_2 {\rm CH}_2 \mathop {\rm O}\limits^ + {\rm HCH}_2 {\rm CH}_2 {\rm CH}_3 $\end{document} βdistonic ion
Authors: Milliet Arielle , Lecarpentier Eric , Audier Henri‐Edouard 
Published: May 2005

AbstractThe β‐distonic ion \documentclass{article}\pagestyle{empty}\begin{document}$ ^ \cdot {\rm CH}_2 {\rm CH}_2 \mathop {\rm O}\limits^ + {\rm HCH}_2 {\rm CH}_2 {\rm CH}_3 $\end{document} has been shown previously to be an intermediate in the fragmentation of ionized ethyl propyl ether. The reactions of this ion (generated by fragmentation in the ion source of alkyl propyl ethers of glycol) were studied in this work. Labelling showed that this ion undergoes competing hydrogen transfers leading to a series of isomeric distonic ions. Each of them was submitted to an isotope effect.
Matrix influence on stability constants of 15‐crown‐5‐alkali metal complexes measured by liquid secondary ion mass spectrometry
Authors: Giraud Denis , Laprévote Olivier , Das Bhupesh C. 
Published: May 2005

AbstractThe liquid secondary ion mass spectra of 15‐crown‐5 in the presence of equimolecular mixtures of three alkali metal salts show large changes in the relative abundances of the 15‐crown‐5‐cation complexes formed, depending on the relative concentrations of ligand and salts. These variations are due either to various desorption rates of the cationized species or to different affinities of 15‐crown‐5 toward the alkali metal cations. An original method allowing discrimination between desorption and complexation effects on the relative abundance of ligand‐metal complex ions is described and can be applied for the calculation of their stability constants. The spectral data obtained using two different matrices demonstrate that the matrix polarity has a very important effect on the two parameters considered, i.e. the stability constants of the 15‐crown‐5‐cation complexes and their desorption rates.
Evaluation of fast atom bombardment mass spectrometric and low‐energy collisional activation tandem mass spectrometric data for the structural elucidation of bisbenzylisoquinoline alkaloids
Authors: Caldwell Gary W. , Masucci John A. , Wu Wu‐Nan 
Published: May 2005

AbstractThe fast atom bombardment (FAB) mass spectra and low‐energy collisional activation mass spectra of ions generated under FAB were investigated for twelve bisbenzylisoquinoline (BBI) alkaloids. The relative molecular mass of the free base and diquaternary BBI alkaloids can be obtained from FAB data. However, monoquaternary ammonium salts produce only an [M — X]+ ion and the relative molecular mass cannot be determined. For Type A (single ether linkage) BBI alkaloids, fragmentation occurs primarily from benzylic and ether cleavages. Thus, the total number of aromatic substituents (OH, OCH3 or OCH2O) can be determined for rings A‐B, C‐D, E and F. For Type B (two either linkages) BBI alkaloids, fragmentation occurs primarily from double benzylic cleavages. Hence only the total number of aromatic substituents can be determined for the upper half of the Type B BBI alkaloids, i.e. rings A‐B and C‐D. An unknown alkaloid was examined to illustrate the utility of the fragmentation schemes.
Gas‐phase studies on reductive cyclization to a benzotriazole derivative from its precursors by liquid chromatography/thermabeam tandem mass spectrometry
Authors: Kuila Debasish , Huang Sunkwei 
Published: May 2005

AbstractLiquid chromatography/Thermabeam mass spectrometry/mass spectrometry was carried out on the starting material, 2‐nitro‐2′hydroxy‐5′‐acetylazobenzene (1) and the intermediate N‐oxide (2) formed by dithionite reduction of the starting material (1). The mass spectra of (1) and the intermediate (2) showed an abundant fragment ion that corresponds to that of 2‐(2′‐hydroxy‐5′‐acetylphenyl)benzotriazole (3). These results show that 3 could be formed from both 1 and 2. The formation of 3 in the gas phase is analogous to the chemical reduction processes of the 2‐nitroazobenzene derivative 1 and the N‐oxide 2 in solution.
Fast atom bombardment mass spectrometric study of some unsaturated aryl C‐glycosides
Authors: Sinou Denis , Becchi Michel , Doyle Daves G. 
Published: May 2005

AbstractFast atom bombardment (FAB), FAB mass‐analysed ion kinetic energy (FAB MIKE) and collision‐activated dissociation (FAB CAD‐MIKE) mass spectra were obtained for two series of unsaturated anomeric aryl C‐glycosides. These tandem mass spectrometric techniques allowed the differentiation of the anomers by analysing either the [M + H]+ ion or the [M + met]+ ion (met=Li, Na).