bluuebunny/crossref_metadata_2025_split huggingface dataset:
Electron impact mass spectrometry of some macrocyclic and acyclic aldimines
Authors: Tamburini Sergio , Vigato Pietro A. , Traldi Pietro 
Published: May 2005

AbstractThe 70 eV electron impact mass spectra of some macrocyclic and acyclic aldimines, together with that of their synthon, are described and discussed with the aid of exact mass measurements, linked scans, deuterium labelling experiments and collisional experiments. The mass spectrometric behaviour of the acyclic compounds, not directly related to their structure, has been studied in detail with the aid of differential thermal analysis, which demonstrates the occurrence of pyrolysis.
Direct evidence for preformed ions of porphyrins in the solvent matrix for fast atom bombardment mass spectrometry
Authors: Musselman Brian D. , Watson J. Throck , Chang Chi K. 
Published: May 2005

AbstractThe observation that protonated molecules are present in solvents utilized for fast atom bombardment (FAB) mass spectrometric studies has been demonstrated using visible absorption spectrometry. Addition of porphyrins to thioglycerol, a solvent used for FAB analyses, results in partial protonation of the molecule. This reaction can be monitored by observing the shift in visible absorption maxima associated with the molecular transition from free base to protonated structure. A good correlation is observed between the degree of protonation indicated by the appropriate absorption bands and the abundance of the [M + H]+ ion in the FAB spectrum of the corresponding solution. Addition of certain non‐polar porphyrin molecules to thioglycerol does not result in the protonation of the molecule in solution; in these cases, analyses of the corresponding solutions by FAB do not yield [M + H]+ ions. Subsequent addition of trifluoroacetic acid to the solvent has proved sufficient to protonate the analyte molecule, as indicated by the visible absorption spectrum; FAB analyses of these non‐polar porphyins in acidified solvent result in the observation of [M + H]+ ions. These experiments demonstrate that analyses of these analyte molecules requires that they be present as ions in solution prior to analysis by FAB. This study provides experimental evidence for the presence of ions in solutions employed for FAB analysis, suggesting that these ions are essential for the generation of the protonated molecules observed during FAB mass spectrometric analyses.
The magic number nine‐atom alkali halide cluster ion. Is the nine‐atom planar structure the most stable?
Authors: Dunlap Brett I. , Campana Joseph E. 
Published: May 2005

AbstractThe question of whether the cubic structures proposed for the alkali halide cluster ions are the most stable has been re‐examined. Geometry/energy optimization calculations were performed on other candidate structures for the [M(MX)4]+ species. The square‐planar structure was found to be more than 3 eV lower in energy than a proposed quasi‐octahedral structure. The relative energies of the square‐planar and other structures for a series of nine‐atom alkali halide cluster ions are found to correlate with published experimental data.
Sulphonium ions: Collision‐activated dissociation using fast atom bombardment ionization and a triple quadrupole mass spectrometer
Authors: Mestdagh Hélène , Morin Nicole , Rolando Christian 
Published: May 2005

AbstractThe low‐energy collision‐activated dissociation of sulphonium cations, including symmetrical trialkyl R3S+, dimethylalkyl (CH3)2RS+, diphenylalkyl Ph2RS+ and cyclic (CH2)nS+R, has been recorded using fast atom bombardment ionization and a triple quadrupole mass spectrometer. The general trends are easy loss of sulphide to give [R]+, except for R  CH3, and loss of alkene to give protonated sulphide if β‐hydrogens are available. Loss of alkane, generally found in ammonium compounds, is not observed.
Intrinsic acidity and basicity of neutral and ionic species of some polyether‐ester compounds as shown by mass spectrometry
Authors: Podda Gianni , Corda Luciana , Maccioni Anna Maria , Traldi Pietro 
Published: May 2005

AbstractThe mass spectrometric behaviour of benzo‐[o]‐1,4,7,10,13‐pentaoxacycloheptadecane‐14,17‐dione (1), 3,6,9,12,15‐pentaoxabicyclo[15.3.1]heneicosa‐1(21),17,19‐triene‐2,16‐dione (2) and 1,15‐dioxo‐2,5,8,11,14‐pentaoxa[15](1,4)benzenophane (3) has been studied in detail with the aid of linked scans, mass‐analysed ion kinetic energy spectra, collisionally activated decomposition experiments, exact mass measurements and different ionization techniques (electron impact, positive and negative ion chemical ionization, charge exchange, electron attachment). The very low abundance of molecular ions and the presence of abundant [M + H]+ and [M – H]+ ions under electron impact conditions indicate the presence of acidic and basic sites in the molecular ions and neutral molecules, respectively.
High energy collisional spectroscopy of [RCOO]− anions from negative ion chemical ionization of fatty acid methyl esters
Authors: Bambagiotti A. Massimo , Coran Silvia A. , Vincieri Franco F. , Petrucciani Tiziano , Traldi Pietro 
Published: May 2005

AbstractSaturated and mono‐unsaturated fatty acid methyl esters as well as corresponding underivatized acids gave abundant carboxylate anions [RCOO]− under negative ion chemical ionization (OH− and NH2 −) and electron attachment conditions. B/E or mass‐analysed ion kinetic energy spectra of fragments arising from high energy collision activated dissociation (CAD) of these [RCOO]− species contained decisive information on the original structure of the neutrals. From an analytical point of view, the method can utilize the gas chromatographic mass spectrometric combination and, in the B/E mode, can be used in practice on any double‐focusing mass spectrometer.
Ion/molecule reaction inside the collision cell of a tandem quadrupole mass spectrometric system. 2. Energy dependence of ammonium ion formation
Authors: Schmit Jean‐Pierre , Beaudet Sylvie , Brisson Alain 
Published: May 2005

AbstractThe dependence of the protonation of neutral ammonia on the axial kinetic energy of protonated reactant ions has been studied in the gas phase, using various protonated carbonyl compounds, inside the collision cell of a tandem quadrupole mass spectrometric system. The hypothesis of two different and non‐competitive reaction channels has been proposed. The first is characterized by a very low (peaked at ±0.05 eVcm) and well‐defined axial kinetic energy of the reactant ion, while the second is more energy demanding (estimated threshold at ±0.2 eVcm) and expressed by a collisionally induced dissociation‐like energy curve. Fourier transform mass spectrometric experiments have shown that ammonium ion can be generated by direct proton exchange and fragmentation of the adduct ion obtained.
Mass spectral fragmentation pathways in nitroadamantanes. A tandem mass spectrometric collisionally induced dissociation study
Authors: Yinon J. , Bulusu S. 
Published: May 2005

AbstractA collisionally induced dissociation study of adamantane, 1‐nitroadamantane, 1,3‐dinitroadamantane and 1,3,5,7‐tetranitroadamantane was carried out using tandem high‐resolution mass spectrometry. Fragmentation pathways of the compounds were determined in the electron impact mode. It was found that the fragmentation of all three nitroadamantanes begins with the consecutive losses of the NO2 groups followed by fragmentation of the hydrocarbon structure.
Low energy, low temperature mass spectra. 6—A synoptic view
Authors: Maccoll Allan 
Published: May 2005

AbstractA review is presented of the low energy, low temperature mass spectra of a number of organic compounds, namely alkanes, alkanols, ethers, amines, alkanals, alkanones, alkanoic acids and alkanoic esters. The main fragmentation routes are described and the simplification of the mass spectra as compared with the 70 eV equivalents is emphasized.
Matrix effects in negative‐ion field desorption mass spectrometry
Authors: Röllgen F. W. , Dähling P. , Bramer‐Weger E. , Okuyama F. , Subhan M. 
Published: May 2005

AbstractThe negative ion mode of field desorption mass spectrometry is matrix dependent. The matrix is used to facilitate the desolvation of ions at field strengths below the onset of field induced electron detachment. The role of the matrix in the desolvation mechanism for negative ions is briefly described and the main properties of a matrix solution, such as viscosity, solubility for complex salts and acids, and adhesion to the emitter surface, on the ion formation are discussed. The application of matrix mixtures with strong adhesion to the emitter surface even at elevated temperatures and high field strengths are considered to be important for the further improvement of this ionization method.
A general soft ionization method for mass spectrometry: Resonance‐enhanced multi‐photon ionization of biomolecules
Authors: Grotemeyer Jürgen , Boesl Ulrich , Walter Klaus , Schlag Edward W. 
Published: May 2005

AbstractWe show here that ‘double‐barrelled’ laser desorption/resonance‐enhanced multi‐photon ionization mass spectrometry has many advantages over traditional single‐step desorption/ionization techniques, particularly if combined with Reflectron‐Time‐of‐Flight mass analysers. We demonstrate the effectiveness of this technique for large labile biomolecules, namely native chlorophylls, porphyrins and a peptide, as examples of structural and mass analysis.
Desorption ionization combined with tandem mass spectrometry: Advantages for investigating complex lipids, disaccharides and organometallic complexes
Authors: Cerny Ronald L. , Tomer Kenneth B. , Gross Michael L. 
Published: May 2005

AbstractCombining desorption ionization with tandem mass spectrometry overcomes the disadvantage of limited fragmentation accompanying desorption and permits mixtures of closely related substances to be investigated directly. These features of the combination are illustrated by completing the structure‐proof of a minor component of an ornithine‐containing lipid mixture isolated from Thiobacillus thiooxidans. The minor component is a homolog of the major constituent and differs from the principal component owing to the presence of a double bond in lieu of a cyclopropyl ring in one of the constituent fatty acids. Another feature of the combined method is the potentially complementary nature of collision‐activated dissociation spectra of protonated and cationized biomolecules. This is illustrated by the differences in the collision‐activated dissociations of the [M + Na]+ of sucrose, desorbed by field desorption, and [M + H]+, desorbed by fast atom bombardment. A third illustration is the application of field desorption and tandem mass spectrometry to an organometallic compound. The combined approach allows the ligands to be identified and the relative ligand binding energies to be approximated.
Fragmentations of protonated benzaldehydes via intermediate ion/molecule complexes
Authors: Filges U. , Grützmacher Hans‐Fr. 
Published: May 2005

AbstractIons ap and am corresponding to protonated p‐ and m‐methoxymethylbenzaldehydes have been generated in a mass spectrometer by electron impact fragmentation of the correspondingly substituted 1‐phenylethanols (1 and 2). Metastable ions ap and am (2nd FFR of a VG‐ZAB‐2F mass spectrometer) react by elimination of CH3OH, loss of HCOOCH3, formation of ions CH2=OCH3 and to a small extent by loss of CH2O and CH3OCH3, respectively. The mechanisms of these reactions have been studied by extensive D‐labelling, and it is shown that these fragmentations are initiated by a transfer of the proton located originally at the carbonyl group onto the aromatic ring. The formation of ions \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm CH}_2 = \mathop {{\rm OCH}_3 }\limits^ + $\end{document} and the loss of CH3OH occurs via π‐and σ‐complexes. The elimination of HCOOCH3 from ions ap and am corresponds to a functional group interaction between distal side chains and occurs via intermediate ion/molecule complexes formed by a protolytic cleavage of the formyl group. The loss of CH2O and CH3OCH3 proceeds also by intermediate ion/molecule complexes which are generated by a protolytic cleavage of the methoxymethyl side chain in ions ap and am.
Structure and formation of gaseous [C3H4N]+ ions
Authors: Heerma Wigger , Sarneel Maria M. , Dijkstra Geo 
Published: May 2005

Abstractmagnified imagegas phase has been established. This conclusion could be derived from a careful study of their collisional activation spectra, which show minor but characteristic differences. The ions studied were generated from various precursor ions in single or multiple fragmentation processes as well as via ion‐molecule reactions. Their heats of formation vary from 925 to 1085 kJ mol−1 according to MINDO/3 or from 925 to 1050 kJ mol−1 according to MNDO calculations.
Mass spectrometry of some dichloroacetamides of pharmacological interest. Evidence for an unusual skeletal rearrangement
Authors: Arlandini E. , Gioia B. , Pella E. , Tonani R. , Traldi P. 
Published: May 2005

AbstractThe mass spectrometric behaviour of six N‐(2‐ethoxyethyl)‐N‐p‐substituted benzyldichloroacetamides is described and discussed in detail with the aid of exact mass measurements, metastable analysis and mass‐analysed ion kinetic energy spectrometry. The presence of an unusual skeletal rearrangement is described.
Positive and negative ion fast atom bombardment mass calibration using concentrated H2SO4
Authors: Sharp Thomas R. 
Published: May 2005

AbstractConcentrated H2SO4 has proved to be an extremely useful calibrant for both positive ion and negative ion FAB mass spectrometry. It is a single compound, commonly found in any laboratory, and presents a clean, simple spectrum, with only approximately 100 peaks needed to achieve calibration up to at least m/z 1500.
Application of low energy CID in the determination of structures of [M – halogen]+ ions obtained from diethyl halosuccinates under electron impact
Authors: Weisz A. , Mandelbaum A. , Blum W. , Domon B. , Muller D. , Richter W. J. , Shabanowitz J. , Hunt D. F. 
Published: May 2005

AbstractLow energy collision induced dissociation (CID) spectra indicate that m/z 173 ions formed by the loss of a halogen atom from diethyl chloro‐ and bromo‐succinate under electron impact are mixtures of O‐protonated diethyl maleate (>90%) and fumarate (<10 %). Hydrogen migration precedes the C‐halogen bond cleavage in these cases. The low energy CID spectrum of the m/z 173 [MI]+ ion obtained from diethyl iodosuccinate shows that only a small fraction of the [MI]+ ions are the O‐protonated species formed by hydrogen migration. The results of this study demonstrate the potential of low energy CID in the determination of structure (including configuration) of gas phase ions.
Carbanion rearrangements. Collison induced dissociations of deprotonated alkyl acetoacetates
Authors: Eichinger Peter C. H. , Bowie John H. 
Published: May 2005

AbstractDeprotonation of methyl acetoacetate yields two enolate ions MeCOC̄HCO2Me (a) and C̄H2COCH2CO2Me (b). On collisional activation, ions a and b fragment differently. The major fragmentation of a is specific loss of MeOH through a four‐centred transition state to form −O(Me)CCCO. In contrast, ion b eliminates CH2CO to give −CH2CO2Me. Some rearrangement of b to a is also noted. Rearrangement of a to b is very minor under single collision conditions but at high collision gas pressure rearrangement of a to b is strongly promoted. Similar effects are observed in the collisional activation spectra of MeCOC̄(Me)CO2Me (c) and −CH2COC(Me)CO2Me (d). The loss of MeOH from (c) proceeds via a six membered transition state to −CH2COC(Me)CO; this is a stepwise process in which the deprotonation (step two) is not rate determining. A number of other decompositions occur, these have also been studied by deuterium labelling.
Reaction of ammonia with accelerated benzoyl ions under multiple‐collison conditions in a triple quadrupole instrument
Authors: White Earl L. , Tabet Jean‐Claude , Bursey Maurice M. 
Published: May 2005

AbstractThe reaction of benzoyl ion with ammonia in multiple‐collision conditions in the second quadrupole assembly of a triple quadrupole mass spectrometer at (laboratory) ion kinetic energies from 0 to 20 eV produced the even‐electron ions [C6H5]+, [C6H5NH3·(NH3)m]+ (m = 0, 1) and [C6H5CONH3·(NH3)n]+ (n = 0, 1, 2, 3) and the odd‐electron ions [C6H4NH3·(NH3)p]+· (p = 0, 1). Thermochemical information could not be obtained under multiple‐collision conditions: both exothermic and endothermic reactions were observed, with no translational‐energy onset measurable for the endothermic processes, nor decrease in the yield of the exothermic processes at high energies. The behaviour of cluster‐ion intensities as pressure varied was qualitatively as expected. There are pressure and energy regions where spectra change little; if this feature were to be general, it would point to some utility for these conditions in qualitative analysis.
Electron impact mass spectrometry of some macrocyclic polyether lactones
Authors: Podda Gianni , Corda Luciana , Anchisi Carlo , Pelli Beatrice , Traldi Pietro 
Published: May 2005

AbstractElectron impact mass spectrometry has been used together with linked scans, exact mass measurements and mass‐analysed ion kinetic energy spectrometry to study nine inacrocyclic polyether lactones in detail. The presence of abundant hydrogenated oxirane ions has been observed for all the compounds examined, and confirmed by kinetic energy release measurements.
On the unimolecular loss of acetylene from metastable C11H9]+ ions
Authors: My Nguyen Kieu , Schwarz Helmut 
Published: May 2005

AbstractExtensive 13C labelling experiments demonstrate that loss of acetylene from metastable [C11H9]+ ions is a complex process, which can be described quantitatively in terms of a four‐parameter model. The major reaction path (77.8%) involves scrambling of all 11 carbon atoms. Insight into the reaction details is provided neither by the kinetic energy release associated with the reaction [C11H9]+ → [C9H7]+ + C2H2 nor by the analysis of the collisional activation mass spectra of the resulting [C9H7]+ ions.
Fractional mass values of large molecules
Authors: Pomerantz Steven C. , McCloskey James A. 
Published: May 2005

AbstractFrom the standpoint of relative molecular mass (RMM) determination by mass spectrometry, the average relative molecular masses of organic molecules in the range over 2000 daltons are significantly influenced both by the fractional masses of the constituent elements and by natural variations in isotopic abundance. Differences between monoisotopic RMM and relative atomic mass (RAM) based RMM tend characteristically to differ between major classes of biomolecules primarily because of molar carbon content, the difference between polypeptides and nucleic acids being about 4 daltons at Mr = 25 000. Considering terrestrial sources alone, variations in the isotopic abundance of carbon lead to differences of about 10–25 ppm in average molecular mass, which is significant with respect to present mass measurement capability in the region up to several thousand daltons. Comments are made concerning the calculation of average RMM values horn isotopic probability profiles versus those from RAMs.
Gas‐phase derivatization of [C3H5]+ ions using tandem mass spectrometry methods A13C labelling study
Authors: My Nguyen Kieu , Schilling Marita , Schwarz Helmut 
Published: May 2005

AbstractThe study of specifically 13C‐labelled precursors sheds further light on the gas‐phase chemistry of allyl and 2‐propenyl cations. It is demonstrated that both species are formed from allyl and 2‐propenyl bromide upon 70 eV electron impact ionization without skeletal reorganization. Gas‐phase derivatization of the [C3 H5]+ ions with benzene facilitates, as suggested and observed earlier, the distinction of the two isomers using collision‐induced dissociation of the Wheland complexes (or isomers thereof). The 13C labelling data clearly demonstrate that 64% of allyl cations survive the derivatization while 36% isomerize to 2‐phenylpropyl cations; the latter are also formed via the reaction of 2‐propenyl cation with benzene, protonation of α‐methylstyrene and water loss from protonated 2‐phenyl‐2‐propanol, respectively. Unimolecular loss of C2H4 from protonated allylbenzene proceeds via two competing reaction channels: one involves heterolysis of 1‐phenylpropyl cations (∼30%); the major pathway (∼70%), however, involves decomposition via propylene benzenium ions.
Stereochemical applications of mass spectrometry 4. Energy‐resolved study of the fragmentation of esters of maleic and fumaric acids
Authors: Harrison Alex G. , Nacson Sabatino , Mandelbaum Asher 
Published: May 2005

AbstractThe fragmentation of the dimethyl and diethyl esters of maleic and fumaric acids have been studied as a function of the internal energy of the molecular ions using charge exchange techniques and metastable ion studies in combination with isotopic labelling. The dimethyl ester molecular ions show distinctive behaviours at both low and high internal energies, indicating that interconversion of the molecular ions does not occur. The fumarate molecular ion fragments by elimination of CH2O and (CO2 + CH3) in the metastable ion time‐frame, while the maleate ester fragments primarily by loss of CH3O. At higher internal energies both molecular ions fragment primarily by loss of CH3O but the fragment ion from the maleate ester shows a greater stability, presumably because it assumes the cyclic cationated maleic anhydride structure. The diethyl maleate and diethyl fumarate molecular ions show identical metastable ion characteristics; in addition the [COS]+· charge exchange mass spectra are very similar. These results indicate that low‐energy molecular ions interconvert. At higher internal energies interconversion does not occur, and, although both moiecular ions fragment by loss of C2H5O, the resultsint fragment ions show different stabilities and fragmentation reactions.
A study of the electron capture induced decompositions and charge separation reactions of the doubly charged isomeric ions of the methylpyridines and aniline
Authors: Curtis J. M. , Vékey K. , Brenton A. G. , Beynon J. H. 
Published: May 2005

AbstractThe doubly charged isomeric ions [C6H7N]2+ formed from 2‐, 3‐ and 4‐methylpyridine and aniline were investigated via their unimolecular charge separation reactions and by electron capture induced decompositions (ECID). The ECID spectra were compared with the collision induced decomposition (CID) spectra of the singly charged ions in an attempt to investigate the structure of the doubly charged ions. The four isomers could be unambiguously identified by their unimolecular charge separations. These differences were greater than in the mass spectra, ECID spectra or CID spectra of singly charged ions.