bluuebunny/crossref_metadata_2025_split huggingface dataset:
Gas chromatographic/mass spectrometric analysis of cembrenoid diterpenes in kerogen from a lacustrine sediment
Authors: Barakat Assem O. , Rullkötter Jürgen 
Published: May 2005

AbstractAlkaline hydrolysis of kerogen from a Miocene lacustrine sediment (Nördlinger Ries, southern Germany) afforded a series of cembrenoid diterpenes characterized by a 14‐membered ring system together with a second, probably related, series of yet unidentified structure. This is the first report of the occurrence of these compounds in fossil organic matter. The interpretation of cembrenoids as molecular markers of arid or semiarid climate is consistent with other information about the depositional environment of the former Nördlinger Ries crater lake.
Chemical reactions at interfaces: Hydrogen–deuterium exchange using a solid ND4Cl matrix in molecular secondary ion mass spectrometry
Authors: Hand Owen W. , Ranasinghe Asoka , Cooks R. Graham 
Published: May 2005

AbstractOrganic compounds containing active hydrogens (e.g. imino, amino, carboxylic acid and hydroxy functional groups) undergo hydrogen–deuterium (H–D) exchange reactions in the course of argon ion bombardment in molecular secondary in mass spectrometry (SIMS) when examined as solids in solid ND4Cl matrix. The positive‐ion SIMS spectra of non‐ionic compounds (M) display ions resulting from exchange of active hydrogens in both the deuterated ((M + D)+) and cationized ((Ag + M)+ and (C+ + M)+) forms, while ionic compounds display exchange products in the intact cation (C+, where C = cation). Analogous H–D exchange is observed in the negative SIMS spectra of compounds bearing active hydrogen atoms. The fact that the exchange reactions are dependent on the primary ion dose demonstrates that they occur in the energized sample and not prior to ion bombardment. Information on the mechanisms of interfacial reactions, insights into the SIMS mechanism and confirmation of the number of acidic hydrogens in non‐volatile organic ompounds are revealed by this experiment.
Comparative study of Møller–Plesset perturbation theory and configuration interaction theory for the structure of the N4+ cation
Authors: Kemister Gary , Peel J. Barrie 
Published: May 2005

AbstractA theoretical study of the ground electronic state of N4+, the dimer ion of N2, has shown, in agreement with other studies, that the Møller–Plesset perturbation expansion for open‐shell molecular species is unstable and divergent when used with certain spin‐contaminated UHF reference wavefunctions. This failure is more serious than in the earlier studies, which noted that the breakdown occurred for the extended bond lengths descriptive of potential energy curves of diatomic systems. In this study the breakdown occurs for the potential energy surface of N4+ close to the global minimum structure, which is incorrectly determined as corresponding to a trans‐planar geometry. In comparison variational configuration interaction procedures represented by the CISD and QCISD methods are clearly superior in the case of N4+, with both yielding the correct linear geometry. The QCISD calculation provides a calculated antisymmetric vibration frequency which is in good agreement with, and hence confirms, the assignment of the neon‐matrix infra‐red spectrum attributed to the N4+ species. The search for a bound excited electronic state of N4+ was partly successful in that a configuration of rectangular geometry shows properties in fair agreement with experimental results.
Negative‐ion mass spectrometric study of ion‐pair formation in the vacuum ultraviolet. VII—SO2 → O− + SO+, O− + S+ + O
Authors: Mitsuke Koichiro , Suzuki Shinzo , Imamura Takashi , Koyano Inosuke 
Published: May 2005

AbstractIon‐pair formation from photoexcitation of SO2 was studied by negative‐ion mass spectrometry using synchrotron radiation in the 15–35 eV photon energy range. Negative ions O− from SO2 were observed. The appearance energy in the photodissociation efficiency curve for O− is in good agreement with the thermochemical threshold of 14.49 eV for the formation of O−(2Pu) + SO+(X̃2Π). Three vibrational progressions in the efficiency curves are assigned as resulting from predissociation of the s‐type Rydberg states converging to SO2+(D̃2A1). The O− efficiency rises markedly at wavelengths of 622 and 570 Å. These onsets are attributed to formation of triplets of fragments: O−(2Pu) + S+(4Su) + O(3Pg) and O−(2Pu) + S+(2Du) + O(3Pg).
A kinetic approach to the proton affinities of amine bases
Authors: Li Xiaoping , Harrison Alex. G. 
Published: May 2005

AbstractThe fragmentation of proton‐bound clusters [B1—H—B2]+ of amine bases B1 and B2 were studied at collision energies of 10–50 eV in the quadrupole collision cell of a hybrid tandem mass spectrometer. The relative abundances of the fragment ions B1H+ and B2H+ were correlated with the proton affinities of the amines. The proton affinities of 21 amines are reported based on the expanded proton affinity scale of Meot‐Ner and Sieck [J. Am. Chem. Soc. 113, 4448 (1991)]. It is found that the fragmentation of mixed proton‐bound clusters of α‐amino acids and amines can be used to establish the proton affinities of simple amino acids such as glycine, alanine, valine, leucine and phenylalanine. However, low values are obtained by this method for the proton affinities of amino acids containing a functional group (additional to the carboxyl group) capable of stabilizing the protonated species by intramolecular hydrogen bonding.
Collision‐induced decomposition of large organic ions and inorganic cluster ions. Effects of pressure on energy losses
Authors: Bradley Caroline D. , Derrick Peter J. 
Published: May 2005

AbstractTranslational energy losses ΔE in keV‐collisions have been determined for peptide ions and for caesium iodide cluster ions subsequently decomposing to specific fragment ions, and the dependences of these energies upon transmission have been investigated. Parent ions decomposing to certain fragment ions exhibit energy losses which are independent of transmission, while parent ions associated with other fragment ions show strong dependence of energy loss upon transmission. These findings are interpreted in terms of energy redistributions of tens of eV taking place in single collisions via direct momentum‐transfer.
Stereochemically controlled decomposition of silver‐cationized methyl glycosides
Authors: Berjeaud Jean‐Marc , Couderc François , Prome Jean‐Claude 
Published: May 2005

AbstractSilver ion adducts of several methyl glycopyranosides were generated by fast atom bombardment of 1:1 mixtures of the glycosides with silver nitrate. The unimolecular decompositions of [M + Ag]+ ions showed dramatic differences related to the relative positions of both the hydroxyl group on C(2) and the anomeric methoxyl group. When these groups were in the cis position, methanol was exclusively expelled. When they were in the trans position, silver hydride was preferentially lost. The stereoselective elimination reaction is proposed to proceed through a five‐membered silver‐containing intermediate complex, from the oxygen on C(2) to the anomeric substituent (methoxyl group or hydrogen atom).
Behaviour of salts of very strong proton‐sponge bases in the gas phase: Extended proximity effects and maintenance of the hydrogen bridge under soft ionization. An electron impact and liquid secondary ion mass spectrometric/collision‐induced dissociation tandem mass spectrometric study
Authors: Rentzea Marina , Kühn Fredy , Staab Heinz A. 
Published: May 2005

AbstractThe liquid secondary ion mass spectrometry and electron impact ionization fragmentation pathways of 1,9‐bis(dimethylamino)‐2,8‐dimethoxy‐dibenzofuran (1), a new proton‐sponge base with increased steric compression (buttressing) and much higher basicity (pKa = 14.3), and of its monoprotonated (2) and monodeuterated (3) salts were invetigated in a collision‐induced dissociation (CID) tandem mass spectrometric study supported by unimolecular linked scans at constant B/E, CID mass‐analysed ion kinetic energy spectra and accurate mass measurements. They show an ‘extended’ proximity effect, involving the stepwise participation of all the four functional groups, in addition to the ‘normal’ proximity effect involving loss of Me2NH and H˙. The behaviour of 1 appears to differ in some ways from that of its protonated (2) or deuterated (3) salts. The unprecedented observation of the maintenance of the hydrogen (or deuterium) bridge under soft ionization in the salts of very strong proton‐sponge bases, which show buttressing effects in solution, is strong experimental support for the conservation of these buttressing effects in the gas phase, where the protonated (or deuterated) cations of salts such as 2 (or 3) are very stable, H+ (or D+) being completely ‘sequestered.’
Reaction dynamics of the dichlorocarbene anion using tandem mass spectrometry
Authors: Leyh Bernard , Mélon Pierre 
Published: May 2005

AbstractThe dissociation dynamics of CCl2− anions were studied under various internal energy conditions. This study involved the measurement of daughter‐ion spectra and branching ratios and of the amount of kinetic energy released (KER) on the fragments. The competition between C and Cl loss for CCl2− ions created by any of the following sequence of processes:
equation image
was particularly investigated. For process (1), the amount of fragmenting CCl2− ions is 8–10 times larger with Kr than with Xe or C6H6. The KER for Cl loss is smaller than 0.20 eV with the three target gases used. For the loss of C, the KER is much larger (0.7 eV). This KER is, however, equal to 0.21 eV for the collisionally activated C loss in process (2). For this latter process, the C loss vs. Cl loss branching ratio decreases with increasing internal energy. The KERs measured for process (3) are very similar to those obtained for process (1). It is suggested that repulsive or slightly bound excited states which correlate directly to the Cl2− (X2Σu+) + C asymptote and which are vibronically coupled to the ground state play an important role in these dissociation processes.
Hybrid tandem mass spectrometry of electrospray‐produced peptide ions
Authors: Tomer Kenneth B. , McGown Steven R. , Deterding Leesa J. 
Published: May 2005

AbstractThe collision‐induced decomposition spectra of electrospray‐produced molecule ions were investigated on a hybrid tandem mass spectrometer. The molecular mass of the peptides investigated ranged from m/z 409 (as the singly protonated molcule ion) to 1758 (as the singly, doubly and triply protonated molecules). The effect of changing the center‐of‐mass collision energy by changing either the laboratory collision energy or the mass of the target gas was investigated. The spectra of all ions investigated showed a large number of sequence ions representative of the peptides' structures.
Is droplet evaporation crucial in the mechanism of electrospray mass spectrometry?
Authors: Siu K. W. M. , Guevremont R. , Le Blanc J. C. Y. , O'Brien R. T. , Berman S. S. 
Published: May 2005

AbstractEvaporation of solvent from charged droplets was found not to be a prerequisite to ion desorption in electrospray mass spectrometry. Evidence of evaporation was absent in an examination of the electrospray mass spectral profiles of cytochrome c and myoglobin in 0.2% acetic and propionic acid solutions; the pHs of these two acid solutions are expected to change in opposite directions with evaporation. The results strongly suggest that ions, as observed in electrospray mass spectrometry, are desorbed from solutions that have undergone minimal evaporation, in other words, at the beginning rather than later parts of the electrospray process. It is speculated that ions are desorbed directly from the solution‐air interface at the needle tip.
Determination of collision‐induced dissociation mechanisms and cross‐sections in organophosphorus compounds by atmospheric pressure ionization tandem mass spectrometry
Authors: Harden Charles S. , Snyder A. Peter , Eiceman Gary A. 
Published: May 2005

AbstractNineteen organophosphorus compounds (OPCs) of the generic classes (dialkyl alkyl′‐phosphonates (twelve compounds) and tri‐alkyl phosphates (seven compounds) were investigated by atmospheric pressure ionization (API) tandem mass spectrometry (MS/MS). All OPCs showed consistent and comparable collision‐induced dissociation (CID) pathways allowing for a generalized scheme for dissociation. When the alkyl groups are equal to or larger than ethyl, CID mechanisms are dominated by McLafferty rearrangements and neutral losses are stable molecules in all cases except cleavage of PC or OC bonds to form alkyl fragment ions. CID cross‐sections for the OPCs were determined with excellent reproducibility and a good correlation was found with a simple model. Inferences with respect to ionic structures were made from observed trends in the cross‐section measurements. Limitations in API‐MS/MS instruments of this design are found in the energy distribution of the ionization and ion sampling events.
Structural characterization of reactive dyes using liquid secondary ion mass spectrometry/tandem mass spectrometry
Authors: Richardson Susan D. , Thruston Alfred D. , McGuire John M. , Weber Eric J. 
Published: May 2005

AbstractReactive Blue 19 (RB 19), its reactive form (RB 19‐VS) and its hydrolyzed form (RB 19‐OH) were examined using liquid secondary ion mass spectrometry/tandem mass spectrometry (LSIMS/MS/MS) in the negative‐ion mode under low‐energy collision conditions (240–300 eV). Structurally characteristic fragment ions were obtained, none of which has been previously reported for these reactive dyes. Among the ions obtained were SO3− ions, ions due to central amino cleavage and reactive group cleavage, and ions due to loss of SO3 and SO2. Possible pathways for the formation of product ions are proposed. The structural information obtained should help to characterize and identify reactive dyes better.
Electron impact mass spectra of synthetically modified milbemycins
Authors: Jones M. T. , Millen W. G. , Thomson M. L. 
Published: May 2005

AbstractThe potent endectocide 23‐(O‐methyloximino)‐F28249α and related compounds were identified and characterized by mass spectrometry. The fragmentation pathway of 23‐(O‐methyloximino)‐F28249α was identified by its high‐resolution mass spectrum and the electron impact unit mass spectra of its homologs. This fragmentation pathway is presented and discussed.
Gas‐phase oxirane addition to acylium ions on reaction with 1,3‐dioxolanes elucidated by tandem and triple stage mass spectrometric experiments
Authors: Eberlin Marcos N. , Cooks R. G. 
Published: May 2005

AbstractAcylium ions containing a variety of substituents all undergo an unprecedented reaction with 1,3‐dioxolanes which gives rise to a cyclic, resonance‐stabilized oxonium ion, formally the product of oxirane (C2H4O) addition to the reagent ion. The structure for the ion–molecule product is supported by multiple‐stage mass spectrometric experiments, performed in a pentaquadrupole mass spectrometer, which show the expected fragmentation by C2H4O loss to yield the original reactant acylium ions. The oxonium ions are formed in relatively high abundance in many cases and are observed even when proton‐transfer reactions would be expected to occur competitively owing to the acidity of some of the acylium ions studied. This ion–molecule reaction is proposed to serve as a general method for identification and/or trapping of ions of the whole acylium ion class and also for the gas‐phase generation of the oxonium ions. The reaction with 1,3‐dioxolane is also useful in distinguishing the most stable C2H3O+ ion, the acetyl cation, from its two stable isomers, O‐protonated ketene and the oxiranyl cation. The thioacetyl cation, the only sulfur analog investigated, also reacts with dioxolane to form the corresponding oxirane addition product, indicating that the C2H4O addition reaction occurs and that it may be useful for identification of the thioacylium class and for the gas‐phase generation of sulfur analogs of oxonium ions.
Identification of Diels–Alder regioisomers by mass spectrometry coupled with theoretical calculations
Authors: Cativiela C. , García J. I. , Garín J. , Mayoral J. A. , Orduna J. , Salvatella L. 
Published: May 2005

AbstractDifferences in the mass spectra of Diels–Alder cyclohexene regioisomers are explained with the aid of a simple model based on the relative stability differences of the open‐chain structures resulting from the alternative cleavage of the C(1)–C(2) and the C(5)–C(6) bonds of the 1‐substituted cyclohexene ring. Theoretical SCF‐MO calculations at a semi‐empirical level proved to be useful tools for determining the relative stabilities of these open‐chain radical cation structures and hence in the interpretation of mass spectra and the correct assignment of regioisomer structures from these spectra.
A fast atom bombardment mass spectrometric study of room‐temperature 1‐ethyl‐3‐methylimidazolium chloroaluminate(III) ionic liquids. Evidence for the existence of the decachlorotrialuminate(III) anion
Authors: Abdul‐Sada Ala'a K. , Greenway Anthony M. , Seddon Kenneth R. , Welton Thomas 
Published: May 2005

AbstractPrevious studies of 1‐ethyl‐3‐methylimidazolium chloride–aluminium(III) chloride ([emim]Cl–AlCl3) ionic liquids have been hampered by significant contamination of these liquids by oxide impurities. Treatment of these liquids with phosgene removes the oxide impurities, and the use of a specially constructed sample inlet system for air‐sensitive materials permitted them to be studied by fast atom bombardment mass spectrometry. The ions Cl−, [Cl2]−, [AlCl4]−, [Al2Cl7]−, [emim]+ and [(emim)2X]+ (X = Cl or AlCl4) were observed for the basic ionic liquid. In addition, the anion [Al3Cl10]− was observed for the acidic composition. Within the mass spectrometer, the hydrolyses of [Al3Cl10]− to produce [Al3Cl8O]− and of [Al2Cl7]− to produce [Al2Cl5O]− were observed. Comparison of these results with published 17O NMR data suggests that the primary hydrolysis products in acidic ionic liquids are [Al3Cl8O]− and [Al2Cl5O]− and that the principal secondary hydrolysis product is [Al2Cl6(OH)]−.
Characterization of positional and anomeric isomers of methyl 2‐O‐ and 3‐O‐sulfo‐D‐glucopyranosiduronic acids and methyl 2‐O‐ and 3‐O‐sulfo‐D‐glucopyranosides by secondary ion mass spectrometry
Authors: Ii Tadashi , Okuda Satoshi , Hirano Takashi , Tsujimoto Kazuo , Ohashi Mamoru 
Published: May 2005

AbstractSecondary ion mass spectrometry (SIMS) of anomeric pairs of methyl 2‐O‐ and 3‐O‐sulfo‐D‐glucopyranosiduronic acids and methyl 2‐O‐ and 3‐O‐sulfo‐D‐glucopyranosides show the deprotonated molecule in the negative‐ion mode and ammoniated and sodiated molecules in the positive‐ion mode. The four isomers were distinguished from each other by linked scanning at constant B/E in negative‐ and positive‐ion SIMS, which gave information characteristic of the position of the sulfate group and even the configuration of the anomeric methoxy group. The main fragmentation processes correspond to the loss of methanol and the elimination of SO3.
Electron impact‐induced fragmentation of 2,1‐benzisothiazoline 2,2‐dioxide
Authors: Danikiewicz Witold , Wojciechowski Krzysztof , Fokkens Roel H. , Nibbering Nico M. M. 
Published: May 2005

AbstractThe electron impact‐induced fragmentation patterns of 2,1‐benzisothiazoline 2,2‐dioxide nitro derivatives were studied. The rationalizations proposed for the fragmentations are supported by accurate mass measurements, daughter ion (mass analysed ion kinetic energy and B/E linked‐scan), parent ion, and constant neutral loss spectra in metastable and collision‐induced dissociation modes and deuterium labelling.
Unimolecular fragmentations of long‐chain aliphatic iminium ions
Authors: Gross Jürgen H. , Veith Hans H. 
Published: May 2005

AbstractThe metastable ion characteristics of N‐alkyl‐N‐methylmethyleneiminium ions (\documentclass{article}\pagestyle{empty}\begin{document}$ {\rm H}_2 {\rm C}=\!=\mathop {\rm N}\limits^ + ({\rm CH}_3){\rm R} $\end{document}, R = n‐CmH2m + 1, m = 3, 4, 5, 6, 8, 10, 14, 18) are reported and discussed. For R = n‐propyl, alkene loss by onium reaction and alkene loss by McLafferty rearrangement occur, whereas for the higher homologues only the latter reaction is observed. As a result of 2H and 13C labelling experiments, the mechanism of alkene loss by γ‐H transfer and β‐cleavage does not change with increasing chain length and the iminium ions do not isomerize prior to decomposition, neither by H–D scrambling nor by carbon skeleton rearrangement. Whereas the sequence of elementary steps during fragmentation is not affected, the energetics of the reaction change as the chain length increases. Resulting from thermodynamic estimations, the enthalpy of reaction ΔHr, critical energy E0 and reverse critical energy E0r diminish markedly as R increases from n‐propyl to n‐octadecyl. The knowledge of the reaction energetics including kinetic energy release data allows information about partitioning of excess energy into internal and translational degrees of freedom to be deduced.
Collision‐induced dissociation of glycoside–alkali metal adduct ions in fast atom bombardment mass spectrometry
Authors: Takayama Mitsuo 
Published: May 2005

AbstractThe collision‐induced dissociation (CID) spectra of glycoside–alkali metal adduct ions [M + C]+ (C = Li, Na, K and Rb) produced under fast atom bombardment (FAB) conditions are reported. The results obtained suggested that the CID spectra of the [M + C]+ ions of some flavonoid glycosides reflect the coordination structures because the CID patterns generally changed with the metal cation size. In diglycosides, the CID spectra showed that the relatively small cations Li+ and Na+ rather bind to the sugar moiety, whereas the large cations K+ and Rb+ rather bind to the aglycone moiety. In monoglycosides, the cations C+ rather bind to the aglycone moiety. It was concluded that the CID technique combined with FAB is useful for the structural elucidation of [M + C]+ ions and, in principle, the CID spectra reflect the coordination structures in the gas phase.
Identification of cyclic nucleotide derivatives synthesized for radioimmunoassay development by fast atom bombardment with collision‐induced dissociation and mass‐analysed ion kinetic energy spectroscopy
Authors: Newton Russell P. , Evans Andrea M. , Hassan Hamed G. , Walton Terence J. , Brenton A. Gareth , Harris Frank M. 
Published: May 2005

AbstractThe syntheses of 2′‐O‐succinyl, 2′‐O‐succinyltyrosinyl methyl ester and 2′‐O‐succinyliodotyrosinyl methyl ester derivatives of a cyclic nucleotide, derivatives necessary for the successful development of a specific radioimmuno‐assay, are described. Fast atom bombardment with collision‐induced dissociation and mass‐analysed ion kinetic energy spectroscopy were used to verify the positions of substitution and the retention of the 3′,5′‐cyclic phosphate moiety. Comparison of spectra produced after different iodination times permitted the optimization of the reaction conditions.
Surface‐induced ion neutralization with high energy deposition
Authors: Chorush Russell A. , Vidavsky Ilan , McLafferty Fred W. 
Published: May 2005

AbstractIon‐to‐neutral conversion at surfaces is found to be complementary to that with gas‐phase targets for neutralization–reionization mass spectrometry and to yield high‐energy neutral species. With an Ag surface deposited on an in‐line Si substrate, neutralization–reionization efficiencies of 0.01% are achieved using 9.8 keV CH, with the neutral CH4 receiving a median internal energy of 14 eV; with a conventional target of K vapor, the efficiency is 0.4% with a neutral energy of 8.2 eV expected from their ionization energy difference. The energy deposition can be increased by increasing the potential that deflects ions into the surface; in this way ∼15% of CH4 neutral species can be given >20 eV of internal energy. Product abundances from CH4 dissociation provide a useful estimate of the distribution of energy values deposited in neutralization.