bluuebunny/crossref_metadata_2025_split huggingface dataset:
A photoionization study of [C4H7]+ ions in the gas phase
Authors: Traeger John C. 
Published: May 2005

AbstractThe ionization and [C4H7]+ appearance energies for a series of C4H7CI and C4H7Br isomers have been measured by dissociative photoionization mass spectrometry. Cationic heats of formation, based on the stationary electron convention, are derived. No threshold ion is observed with a heat of formation corresponding to the trans‐1‐methylallyl cation, although there is evidence for formation of the less stable cis isomer. A 298 K heat of formation of 871 kJ mol−1 is obtained for the cyclopropylcarbinyl cation, with the cyclobutyl cation having a higher value of 886 kJ mol−1. At the HF/6‐31G** level, ab initio molecular orbital calculations show the 2‐butenyl, isobutenyl and homoallyl cations to be stable forms of [C4H7]+, being less stable than the trans‐1‐methylallyl cation by 101 kJ mol−1, 159 kJ mol−1 and 164 kJ mol−1, respectively. However, threshold formation is not observed for any of these ions, the fragmentation of appropriate precursor molecules producing [C4H7]+ ions with lower energy structures.
New explorations of in situ reactions of boron‐containing compounds during fast atom bombardment mass spectrometry
Authors: Rose Malcolm E. , Webster Matthew J. 
Published: May 2005

AbstractVarious reactions, intentional or unwanted, between several types of boron‐containing compound and multifunctional nucleophilic substrates occurring on the probe tip can be examined in situ by negative‐ion fast atom bombardment mass spectrometry (FABMS). Unwanted reactions of spiroborates with common liquid matrices can be avoided by using tetraethylene glycol diethyl ether as solvent for FABMS. Even so, the components of mixtures of spiroborates undergo ligand exchange with each other. Different orientations of hydroxy groups in isomeric diols, hydroxyacids and dicarboxylic acids can be differentiated by reaction on the probe tip with trialkyl borates, producing negatively charged spiroborates, or preferably with dibenzeneborinic acid ethanolamine complex. Successful reaction in the latter case can be assessed by observing the eliminated ethanolamine by positive‐ion FABMS and formation of the corresponding negatively charged borate in the negative‐ion mode. Potential applications of this methodology are discussed.
Mass spectrometric fragmentation patterns of isomeric 5‐methyl‐3‐alkyl‐2‐alkenylpyrazines
Authors: Brophy Joseph J. , Sun Chang‐Ming , Tecle Berhane , Toia Robert F. 
Published: May 2005

AbstractThe detailed mass spectral fragmentation pathways of a series of both naturally occurring and synthetic 5‐methyl‐3‐alkyl‐2‐aIkenylpyrazines have been elucidated with the aid of deuterium labels placed specifically in the alkenyl side‐chain. The influence on the fragmentation pattern of the stereochemistry of the alkenyl group as well as the relative placement of the groups on the pyrazine nucleus have also been evaluated. This provides information of some diagnostic value in the assignment of structures by mass spectrometry to new compounds within this class.
Skeletal rearrangement for water loss from molecular protonated ions of t‐butoxycyclohexane
Authors: Diakiw Vladimir , Gordon Patrick M. , Kingston Eric E. , Shannon James S. , Lacey Michael J. 
Published: May 2005

AbstractIsotopic labelling and chemical substitution support the proposition that the skeletal rearrangement for water loss from molecular protonated ions of t‐butoxycyclohexane involves competition between three reaction pathways. The principal reaction pathway (83%) involves migration of the t‐butyl group to the 2‐(6‐) position of the cyclohexyl ring with reciprocal hydrogen transfer. A second reaction pathway (12%) involves ring contraction followed by reciprocal exchange of the t‐butyl group with the 2‐(5‐) hydrogen atom of the nascent cyclopentyl ring. The third reaction pathway (5%) involves rearrangement of a proton‐bound complex to permit ipso attack by isobutene. Stereospecific substitutions indicate that the principal reaction pathway is susceptible to 1,3‐diaxial interactions.
Negative‐ion‐negative‐ion neutralization‐reionization (−NR−)
Authors: McMahon Adam W. , Chowdhury Swapan K. , Harrison Ale X. G. 
Published: May 2005

AbstractThere are four neutralization‐reionization processes which can be studied. In the first two, gaseous cations are collisionally reduced and the resulting fast neutrals are either oxidized by collisional electron removal (NR) or reduced further by collisional electron attachment (NR−). In the third and fourth processes, gaseous anions are collisionally oxidized and the resulting fast neutrals are either oxidized further by collisional electron removal (−NR) or reduced by collisional electron attachment (−NR−). These four processes are illustrated briefly using the interrelated species [SF5]+ and [SF5]−. Negative‐ion‐negative‐ion neutralization‐reionization (−NR−) processes are illustrated for [CH3O]−, [C2H5O]−, [CO3]− and [HCO3]− and compared with −NR processes. In addition, collisional electron attachment ionization of fast neutrals formed in unimolecular fragmentation of cations is illustrated. The −NR− studies of [CO3]− and [HCO3]− show that both CO3 and HCO3 are stable neutral species with lifetimes greater than 0.7 μs.
Neutralization‐reionization study of C6H6O isomers
Authors: Turecek Frantisek , Drinkwater Donald E. , Maquestiau Andre , McLafferty Fred W. 
Published: May 2005

AbstractNeutralization‐reionization (+NR+) mass spectrometry is employed to examine the behavior of C6H6O isomers in the gas phase. Phenol and cyclohexa‐2,4‐dienone are found not to interconvert following neutralization with mercury of their corresponding cation radicals at 9.9 keV kinetic energy. A very low extent of isomerization is observed following collisional activation of fast C6H6O neutrals with helium. The +NR+ and collisionally activated dissociation spectra, the latter obtained at unit mass resolution, are used to identify these [C6H6O]+ ˙ isomers. Hexa‐1,3,5‐trienal is found to cyclize spontaneously to cyclohexa‐2,4‐dienone during attempted pyrolytic preparation. The thermochemistry of these C6H6O molecules and cation radicals is discussed on the basis of experimental data and MNDO calculations.
Kinetics of acrylamide/glutathione binding by fast atom bombardment and thermospray mass spectrometry
Authors: Harrison M. E. , Baldwin M. A. 
Published: May 2005

AbstractThe kinetics of the binding of the neurotoxin acrylamide to the cysteine residue of glutathione has been studied. At 37 °C and pH 7.3 the second order rate constant has been determined to be 0.72 ± 0.06 mol−1 dm3 min−1 by thermospray mass spectrometry. The critical energy at pH 11.5 measured over the temperature range 10–37°C by fast atom bombardment mass spectrometry was measured as 24.6 kJ mol−1.
Laser Desorption electron impact mass spectrometry: Studies of ion radical fragmentation mechanisms and hydrogen/deuterium rearrangement in time‐resolved experiments
Authors: Fenselau Catherine , Emary W. Bart , Cotter Robert J. 
Published: May 2005

AbstractLaser desorption of neutral molecules followed by electron impact ionization is shown to produce gaseous ion radicals that undergo fragmentation analogous to that observed with electron impact and field ionization. Spectra were measured of heptanal and four deuterium‐labeled analogs regenerated from bisulfite derivatives, and compared with electron impact, chemical ionization and field ionization spectra published previously. Lifetimes of desorbed neutral molecules and of ions were found to influence the fragmentation process as reflected in isotope patterns. This is explained on the basis of internal energies.
Mass spectrometry of pancuronium bromide and related quaternary ammonium steroids using the moving belt LC/MS interface
Authors: Baker Timothy R. , Vouros Paul , Martyn Jeevendra A. J. 
Published: May 2005

AbstractPancuronium and vecuronium are members of a series of quaternary ammonium steroids used as neuromuscular blocking agents in anesthesiology. In this study the mass spectrometric properties of these bromide salts are examined and spectral features which permit their differentiation are evaluated. The relative merits of chemical ionization and fast atom bombardment using the moving belt liquid chromatography/mass spectrometry interface have been investigated. Fragmentation pathways for both ionization methods were determined with deuterium labeling and linked‐scan techniques. Cleaner spectra can be obtained via the matrix‐free belt introduction system as compared to conventional fast atom bombardment.
Gas chromatography/electron impact mass spectrometry applied to the differentiation of the positional isomers of long‐chain n‐alkylcyclohexanones
Authors: Rontani J.‐F. , Giusti G. 
Published: May 2005

AbstractThe influence of n‐butyl group position upon the fragmentation behavior of the three isomeric n‐butylcyclohexanones was studied. The different fragmentation processes are described and have been applied to the differentiation of the positional isomers of long‐chain n‐alkylcyclohexanones. In the case of the 4‐n‐alkyl isomers, an interesting mechanism involving a recyclization is proposed and substantiated by deuterium labelling.
FAB and chemical ionization in the production of [M+ H]+ and [M− H]− species from 2‐aryl‐2‐methyl‐1,3‐dithianes
Authors: Sturaro Alberto , Traldi Pietro , Paradisi Cristina 
Published: May 2005

AbstractThe unimolecular fragmentations of [M + H]+ and [M – H]− ions from four 2‐aryl‐2‐methyl‐1,3‐dithianes are described and clarified with the aid of deuterated derivatives. Comparison of the MIKE spectra of [M + H]+ species obtained under chemical ionization and fast atom bombardment (FAB) conditions reveals differences which are attributed to the different energetics involved in the two ionization processes. It is suggested that FAB is a ‘softer’ ionization technique but, at the same time, it provides, for the possibility of solvation, reaction sites not available in gas‐phase protonation. [M – H]− species and anionic fragments thereof were generally not obtained under FAB(−) conditions. [M – H]− ions are readily produced in gas‐phase reactions with OH− via proton abstraction from C(4) or C(5), and from the 2‐methyl substituent; and they fragment according to several reaction pathways.
Structural characterization of organic molecules by negative ions in laser microprobe mass spectrometry. Part 1—Neutral compounds
Authors: Van Vaeck L. , Bennett J. , Van Epsen P. , Schweikert E. , Gijbels R. , Adams F. , Lauwers W. 
Published: May 2005

AbstractLaser microprobe mass spectrometry (LMMS) has been used to systematically study polyfunctional molecules, covering a wide range of structure and polarity. The knowledge about the mechanisms actually involved for desorption and ionization (DI) of organics by laser microbeam irradiation of solid samples at high‐power density is rather limited. Therefore we have elaborated a set of tentative hypotheses about DI in LMMS, permitting consistent rationalization of detected signals. The technique apparently combines desorption under mild conditions, shown by the release of intact thermolabiles, with extensive fragmentation. Structural data are typically distributed between cations and anions. Interpretation of negative‐ion detection mode mass spectra often represents intricate problems, partly due to the lack of sustaining background information from conventional mass spectrometry. Selected examples are presented to illustrate the occurrence of electron capture ionization, the role of heteroatoms in the formation of negative ions and the tendency to undergo complex skeletal rearrangements. Although LMMS was originally aimed at microprobe applications, it has been found to be a valuable tool in organic mass spectrometry.
Chemical ionization and collisional activation spectra of α,β‐unsaturated nitriles
Authors: Madhusudanan K. P. , Murthy V. S. , Fraisse D. 
Published: May 2005

AbstractA study of the chemical ionization (CI) and collisional activation (CA) spectra of a number of α, β‐unsaturated nitriles has revealed that the even‐electron ions such as [MH]+ and [MNH4]+ produced under chemical ionization undergo decomposition by radical losses also. This results in the formation of M +˙ ions from both [MH]+ and [MNH4]+ ions. In the halogenated molecules losses of X˙ and HX compete with losses of H˙ and HCN. Elimination of X˙ from [MH]+ is highly favoured in the bromoderivative. The dinitriles undergo a substitution reaction in which one of the CN groups is replaced with a hydrogen radical and the resulting mononitrile is ionized leading to [M  CN + 2H]+ under CI(CH4) or [M  CN + H + NH4] and [M  CN + H + N2H7]+ under CI(NH3) conditions.
Rearrangements in aryl substituted α, β‐unsaturated nitriles. A collisional activation study
Authors: Madhusudanan K. P. , Murthy V. S. , Fraisse D. 
Published: May 2005

AbstractThe rearrangement reactions following electron ionization in a number of aryl substituted conjugated nitriles have been studied using labelled compounds and collisional activation (CA) spectroscopy. The results indicate that α‐phenyl cinnamonitriles and 9,10‐dihydro‐9‐cyanophenanthrene rearrange to a common intermediate which loses CH3˙ or CH2CN˙ to give the ions at m/z 190 and 165. The CA spectrum of the deuterated analogue (compound 2) shows that there is a complete hydrogen scrambling prior to the loss of the CH3˙ radical. The fluoroderivatives (compounds 5 and 6) behave similarly to the parent nitrile. The introduction of chlorine or bromine into the aromatic ring alters the fragmentation pattern and the only favoured decomposition pathway is the loss of a halogen radical. The CA spectra of the doubly charged ions at m/z 102 and 88 are also discussed. The CA spectrum of the M +˙ ion 1,1‐dicyano‐2‐phenyl ethylene is characterized by the presence of a rearrangement ion atm/z 103 (PhCN+ ˙).
Fragmentation of 1‐aryl‐5‐(2‐dialkylaminovinyl)‐1H‐tetrazoles upon electron impact
Authors: Herrmann Michael , Fischer Gerhard W. 
Published: May 2005

AbstractThe mass spectrometric behaviour of 1‐aryl‐5‐(2‐dialkylaminovinyI)‐lH‐tetrazoles was studied, especially 1‐phenyl‐5‐(2‐dimethylaminovinyl)‐l H‐tetrazole as a typical example of D‐ and 15N‐labelled derivatives revealed a rearrangement via a carbodiimide‐like intermediate ion.
Influence of reversed‐ and normal‐phase liquid chromatographic eluents in the fragmentation of selected chlorinated herbicides in thermospray liquid chromatography‐mass spectrometry
Authors: Barceló Damià 
Published: May 2005

AbstractThe effect of two completely different mobile phase compositions, reversed‐phase acetonitrile‐water + ammonium acetate and normal‐phase cyclohexane, were compared in filament‐on thermospray liquid chromatography‐mass spectrometry (LC‐MS) for the determination of selected chlorinated herbicides such as chloroatrazines and chlorinated phenoxyacetic acids. By using acetonitrile‐water + 0.05 M ammonium acetate mixtures in positive ion mode thermospray LC‐MS, the chloroatrazine herbicides showed the acetonitrile adduct ion [M + (CH3CN)H]+ as the base peak, whereas the chlorinated phenoxyacetic acids showed no signal. In contrast, when cyclohexane, which is reported for the first time as an eluent in the thermospray technique, was used as the mobile phase the chlorinated phenoxyacetic acid herbicides exhibited [M – H]+, [M – Cl]+ and M+˙ as the main ions.Negative ion mode thermospray LC‐MS showed [M – H]− as the base peak for the chloroatrazines in the different mobile phases, whereas the chlorinated phenoxyacetic acids exhibited [M + H]−, [M + Cl]− or [M – HCl]− as the base peaks in cyclohexane and [M + acetate]− in acetonitrile‐water‐ammonium acetate.
Electron impact induced fragmentation of β‐allenic and γ‐acetylenic alcohols
Authors: Arseniyadis Siméon , Maquestiau André , Flammang Robert , Guenot Pierre , Carrié Robert 
Published: May 2005

AbstractThe main fragmentation pathway of ionized hydroxyallenes (1) consists of a methyl loss. Extensive deuterium‐labelling experiments indicate that the terminal allenic carbon is implied in this fragmentation. Collisional activation spectra indicate a propenyl‐acylium structure (a) for these [M – CH3]+ ions which can originate from a 1,4‐hydroxyl migration followed by hydrogen rearrangements. Isomeric hydroxyacetylenes (2) behave similarly, also giving rise, by methyl loss, to acylium ions a. It is proposed that 2+ ˙ is irreversibly isomerized into 1+ ˙ by a 1,3‐hydrogen transfer ‘catalysed’ by the hydroxy group. The proposed internal proton‐bound complex justifies also the easier loss of water from 2+˙. Ethyl loss is also a prominent fragmentation for the hydroxyallene and hydroxy‐acetylene homologues.
The unimolecular fragmentation of steroidal amides under electron impact. The role of intermediary ion‐neutral complexes
Authors: Longevialle Pierre , And Guy Bouchoux , Hoppilliard Yannik 
Published: May 2005

AbstractThe neutral fragment produced in the main decomposition process of 3‐amido steroids after electron impact is shown, by thermochemical arguments, to have the amide structure rather than enolamide as would be expected from a simple McLafferty rearrangement. It is proposed that the enolamide to amide tautomerization takes place during the decomposition process involving ion‐neutral complexes, and is responsible for the lack of regioselectivity in the origin of the hydrogen transferred. An energy barrier of unknown origin is shown to exist in the formation of the accompanying [amide + H]+ ion.
Characteristic fragmentations of peptide derivatives containing proline in negative‐ion fast atom bombardment mass spectrometry
Authors: Tsunematsu Hideaki , Nakashima Shizuko , Yamamoto Magobei 
Published: May 2005

AbstractFragmentations of N‐benzyloxycarbonyl‐protected tripeptide ethyl esters containing proline were compared with those of the corresponding peptide derivatives not containing proline in negative‐ion fast atom bombardment mass spectrometry. The fragment ion [M – 109]− due to loss of the benzyloxy group followed by dehydrogenation from the peptide molecule was the base peak in the negative‐ion mass spectra for the peptides not containing proline, whilst it was a very weak fragment ion or not observed at all in those for the peptides containing proline. These results suggest that the fragmentations of the peptide derivatives in negative‐ion fast atom bombardment mass spectrometry depend on the conformational difference of the peptide derivatives owing to the existence of proline in the derivative.
MNDO study of fragmentations in mass spectrometry. Part I. The geometry and electron structure of [C3H6O] + ˙ systems and [C2H3O]+ ions
Authors: Hrušák Jan , Tkaczyk Martin 
Published: May 2005

AbstractMNDO calculations of [C3H6O]+ ˙ predict the parallel existence of both structures of radical cations of acetone (1) and propen‐2‐ol (2) in electron ionization spectra. The calculated heats of formation of 1+ ˙ (ΔHfMNDO = 783.2 kj mol−1) and of 2+ ˙ (ΔHfMNDO = 649.8 kJ mol−1) are in very good agreement with the experimental results. A comparison with the results of ab initio calculations (3–21 G and 6–31 G) and experimental data for the individual structures of the main fragment [C2H3O]+ demonstrates a sufficient accuracy of MNDO results, suggesting the possibility of applying the method also in other cationic systems, especially in larger ones.
Chemical ionization mass spectrometry with amines as reactant gases. VII—Amine chemical ionization mass spectrometry of some iridoid and secoiridoid glucosides
Authors: Mollova N. N. , Handjieva N. V. , Popov S. S. 
Published: May 2005

AbstractThe chemical ionization mass spectra of iridoid glucosides of the loganin type and secoiridoid glucosides of the gentiopicroside type were investigated. Triethylamine, diethylamine, ethylenediamine and ammonia were used as reactant gases. The possibilities of establishing the relative molecular masses and the masses of both the sugar residue and the aglycone and some structural and stereochemical features are discussed.
Electron ionization mass spectra of novel 2,3:4,5‐bis‐O‐(1‐methylethylidene)‐β‐D‐fructopyranose derivatives and related sugar sulfamates
Authors: Caldwell Gary W. , Sorgi Kirk L. , Scott Lorraine , Maryanoff Bruce E. , Maryanoff Cynthia A. , Masucci John A. , Nortey Samuel O. , Sisco William R. , Micheel Arthur , Ko Chan‐Yan 
Published: May 2005

AbstractThe electron‐impact (EI) mass spectral fragmentation of ten bis‐O‐ (1‐methylethylidene)fructopyranose derivatives and three related sugar sulfamates were investigated. In particular, 2,3:4,5‐bis‐O ‐ (1‐methylethylidene)‐β‐D‐fructopyranose sulfamate (topiramate), a potent anticonvulsant, was examined in greater detail. The fragmentation of the 2,3:4,5‐bis‐O‐(1‐methylethylidene) fructopyranose derivatives in general was not very dependent on the nature of substitution; the mechanisms of the common and unique fragmentation patterns are presented. These compounds showed characteristic peaks at m/z [M – 15]+, [M – 15 – 58]+, [M – 15 – 58 – 60]+, [M  CH2X]+ and [M  CH2X – 58]+ where X = OSO2NR2 (R  H, CH3, and/or Ph), OC (O)NHR, NH2, CI and OH. The fragmentation of isomeric bis‐O‐(1‐methylethylidene) derivatives of aldopyranose, ketopyranose and ketofuranose sulfamates was also investigated. The results indicate that isomeric sugar sulfamates can be easily distinguished in the EI mode. Key fragmentation pathways are discussed for these compounds.
Obtaining structural information on perfluorocarbons by mass spectrometry II‐charge‐exchange method
Authors: Huang Sunkwei 
Published: May 2005

AbstractStructural and molecular ion information on perfluorocarbons (PFCs) can be obtained by charge‐exchange reactions of nitrogen or oxygen radical cations with PFCs; such information usually cannot be obtained by the electron impact or negative ion chemical ionization methods. Charge‐exchange reactions occurred when 0.5‐1.0 Torr (1 Torr as 133.3 Pa) of nitrogen, air or other gases was introduced into the chemical ionization source of a mass spectrometer, with electron energies ranging from 55 to 230 eV. Changing the repeller voltages and electron energies had little effect on the appearance of charge‐exchange mass spectra of PFCs. However, when air or nitrogen was introduced in the direction opposite to sample flow, more intense molecular ions and/or higher mass fragment ions were obtained at the cost of a small loss of sensitivity. The charge‐exchange mass spectrum of perfluoro‐1,3‐dimethyladamantane is very similar to the high‐energy collisionally induced dissociation spectrum of its molecular radical cation. This technique provides an important validation tool without the use of tandem mass spectrometry for the structure determination of PFC isomers.
Formation of negative ions of monosubstituted group VIB pentacarbonyls during fast atom bombardment mass spectrometry
Authors: Van Breemen Richard B. , Martin LeRoy B. , Schreiner Anton F. 
Published: May 2005

AbstractThe first negative‐ion fast atom bombardment mass spectra of a related series of monosubstituted Group VIB transition metal pentacarbonyls, M(CO)5L (M = Cr), Mo or W and L = P(Ph)3, As(Ph)3 or Sb(PH)3), have been obtained. Instead of molecular ion radicals, pseudomolecular adduct ions, [M + H]− and [M + 15]−, were detected, with the hydride species being much more abundant. High‐resolution measurements and comparison of observed isotope clusters with computer‐generated theoretical isotope patterns confirmed that ionization occurred by several mechanisms, including electron capture, charge dissociation and formation of adducts with charged species. Fragmentation consisted primarily of elimination of neutral ligands, i.e. ([MH ‐ L]−, [MH ‐ CO]−, [MH ‐ 2CO]−, etc. B/E and constant neutral loss linked scanning with collisional activation were used to confirm fragmentation pathways and characterize the site of hydride attachment on the transition metal complex. The information obtained demonstrates the utility of fast atom bombardment mass Spectrometry in the analysis of metal carbonyls.