bluuebunny/crossref_metadata_2025_split huggingface dataset:
Collision‐Induced consecutive dissociation reactions of the monocarboxylate anions generated from the dimethyl and diethyl esters of glutaric acid and its 3,3‐dimethyl analogue
Authors: Maas Wilfried P. M. , Nibbering Nico M. M. 
Published: May 2005

AbstractThe collision‐induced dissociation reactions of the monocarboxylate anions, generated from the dimethyl and diethyl esters of glutaric acid and its 3,3‐dimetbyl analogue in a chemical ionization source, were studied as a function of the potential applied to the collision cell in combination with 2H labelling experiments. It was shown that many of the product anions are formed in consecutive steps. The mechanisms associated with these steps appear to be initiated by a functional group interaction between the carboxylate anion and the ester group, 1,5‐hydrogen migrations both to the carboxylate anion and the uncharged ester group and charge remote fragmentation. In one of the collision‐induced dissociation channels a methyl anion is generated as a granddaughter product anion, which contains the hydrogen atoms exclusively originating from positions 2 and 4 as shown by the applied 2H labelling.
Field desorption mass spectrometric analysis of mixtures of surfactants and inorganic salts
Authors: Zhu Peifen , Su Keman 
Published: May 2005

AbstractA field desorption mass spectrometric method is proposed for the analysis of mixtures of surfactant and inorganic salts. Different compounds in the mixture are determined with different heating currents and distinguished on the basis of the exterior character of the mass spectrum. The effectiveness of the method is demonstrated with known mixtures of surfactants and inorganic salts. Two unknown additives for electric tin plating were tested with the method.
Unimolecular reactions of the isolated immonium ions CH3CH = NH+C4H9, CH3CH2Ch = NH+C4H9 and (CH3)2C = NH+C4H9
Authors: Bowen Richard D. , Colburn Alex. W. , Derrick Peter J. 
Published: May 2005

AbstractThe reactions of ten metastable immonium ions of general structure R1R2CNH+C4H9 (R1 = H, R2 = CH3, C2H5; R1 = R2 = CH3) are reported and discussed. Elimination of C4H8 is usually the dominant fragmentation pathway. This process gives rise to a Gaussian metastable peak; it is interpreted in terms of a mechanism involving ion‐neutral complexes containing incipient butyl) cations. Metastable immonium ions ontaining an isobutyl group are unique in undergoing a minor amount of imine (R1R2CNH) loss. This decomposition route, which also produces a Gaussian metastable peak, decreases in importance as the basicity of the imine increases. The correlation between imine loss and the presence of an isobutyl group is rationalized by the rearrangement of the appropriate ion‐neutral complexes in which there are isobutyl cations to the isomeric complexes containing the thermodynamically more stable tert‐butyl cations. A sizeable amount of a third reaction, expulsion of C3H6, is observed for metastable n‐C4H9 +NHCR1R2 ions; in contrast to C4H8 and R1R2CNH loss, C3H6 elimination occurs with a large kinetic energy release (40–48 kJ mol−1) and is evidenced by a dish‐topped metastable peak. This process is explained using a two‐step mechanism involving a 1,5‐hydride shift, followed by cleavage of the resultant secondary open‐chain cations, CH3CH+ CH2CH2NHCHR1R2.
Electron impact excitation of ions from larger organic molecules
Authors: Wang Bing‐Huang , McLafferty Fred W. 
Published: May 2005

Abstract[M + Na]+ ions (m/z 1164) from gramicidin S can be dissociated in a Fourier‐transform mass spectrometer with ∼ 85% efficiency using a 50 μA beam of 70 eV electrons for 500 μs. Although the fragment ions are smaller, on average, than those from collisionally activated dissociation or 193 nm photodissociation, these also provide extensive sequence information.
Role of molecular oxygen in fragmentation processes of abscisic acid methyl ester in electron capture negative ionization
Authors: Heath Timothy G. , Gage Douglas A. , Zeevaart Jan A. D. , Watson J. Throck 
Published: May 2005

AbstractIon‐molecule reactions with oxygen promote fragmentation in the electron capture negative ionization mass Spectrometry of methylated abscisic acid. It is shown that low‐energy collisions of the molecular anion (m/z 278) with O2 in the center quadrupole of a triple quadrupole mass spectrometer result in the formation of an adduct ion which subsequently fragments to yield two prominent ions, one at m/z 141 which contains the side‐chain and a second at m/z 152 which includes the ring. Two minor products are represented by peaks at m/z 179 and 136. These ion‐molecule reactions can also occur in the ion source when oxygen is present, which may cause fluctuations in relative intensities of the fragment ion peaks. The principal fragments of mass 141 and 152, and also those of mass 179 and 136, do not form in the absence of O2. Product ion mass spectra following collisions of M−· with 18O2 in the center quadrupole show that the side‐chain fragment ion shifts from m/z 141 to m/z 143, indicating retention of an oxygen atom from the gas‐phase reaction with molecular oxygen. It is proposed that on reaction with oxygen, a peroxy radical anion intermediate at m/z 310 is formed which then fragments to yield an enolate anion (m/z 141) or a quinone‐like radical anion (m/z152). The induced fragmentations of the 2‐cis and 2‐trans isomers of methylated abscisic acid appear to be identical. Analysis of isotopically labeled compounds of both abscisic acid and structurally similar metabolites reveal that oxygen‐activated fragmentation in these selected cases provides diagnostic ions which allow one to determine the position(s) of isotopic enrichment in the molecule.
The acid effect in fast atom bombardment
Authors: Shiea Jentaie , Sunner Jan 
Published: May 2005

AbstractThe effects on fast atom bombardment (FAB) mass spectra of analyte bases in glycerol on adding acids were investigated. The MH+ ion intensity usually increased but sometimes decreases were also found. For the practical use of FAB, it is importaat to clarify the reasons for this acid effect. By critical evaluation, a variety of different explanations were found, e.g. changes in solubility, surface activity, volatility, radiation‐induced chemistry and desorption energetics. No unambiguous examples of efficient preformed ion formation were found. However, it is still possible that preformed ion formation may be important in the uppermost surface layer. The mechanistic implications of these findings are briefly discussed.
Mass spectra of liquid crystals. V.—cyclohexyl and phenyl esters of cyclohexanecarboxylic and benzole acids
Authors: Leclercq P. A. , van den Bogaert H. M. 
Published: May 2005

AbstractThe 70 eV electron impact mass spectra of 38 cyclohexanecarboxylate and 15 benzoate derivatives are presented. This part includes data on six substituted cyclohexyl and 47 derivated phenyl esters, including eleven alkoxyphenyl and 17 dicyanoalkoxypnenyl esters. Based on the observed peak shifts by various substituents, the elemental formulae of the main fragment ions are rationalized.
Structural study of Mn(III)‐tetraarylporphyrin complexes by fast atom bombardment mass spectrometry
Authors: Rubino F. M. , Mascaro P. , Banfi S. , Quici S. 
Published: May 2005

AbstractA series of 27 Mn(III)‐tetraarylporphyrins bearing heterogeneous substituents on the phenyl rings at the meso positions were subjected to positive ion fast atom bombardment mass spectrometry The source spectra yielded the molecular ion and a few peaks confirmative of the chemical structure. Major processes were hydrogenolytic loss of the aryl rings or of their substituents. Molecules carrying a side‐chain underwent loss of the chain either as a solution process (amide linkage) or as a gas‐phase process (phenolic ether linkage). Collisionally activated dissociation mass‐analysed ion kinetic energy spectroscopy allowed discrimination between the two types of fragmentation processes and some other previously unreported gas‐phase reaction channels to be recognized.
Thermal denaturation of some proteins and its effect on their electrospray mass spectrat
Authors: Blanc J. C. Y. Le , Beuchemin D. , Siu K. W. M. , Guevremont R. , Berman S. S. 
Published: May 2005

AbstractThe effects of beat on the electrospray mass spectra of eight globular proteins in solution were studied. These ranged from hardly noticeable to a dramatic shift in the mass spectrometric profile and a concomitant increase in ion abundance. This change is believed to be the result of thermal denaturation of the protein species in solution resulting in a transition from a more compact to a less compact conformation. We accounted for this transition by means of a recently proposed model based on aqueous solution acid/base equilibria. For cytochrome c, profiles calculated by means of this model agree well with experimental data. The ΔH of the denaturation reaction of cytochrome c in aqueous solution containing 0.2% acetic acid was calculated from experimental data to be 103.8 ± 9.2 kJ mol−1, in good agreement with previous measurements.
Electron impact, chemical ionization and negative chemical ionization mass spectra, and mass‐analysed ion kinetic energy spectrometry–collision‐induced dissociation fragmentation pathways of some deuterated 2,4,6‐trinitrotoluene (TNT) derivatives
Authors: Yinon Jehuda , Fraisse Daniel , Dagley Ian J. 
Published: May 2005

AbstractMass‐analysed ion kinetic energy spectrometry (MIKES) with collision‐induced dissociation (CID) has been used to study the fragmentation processes of a series of deuterated 2,4,6‐trinitrotoluene (TNT) and deuterated 2,4,6‐trinitrobenzylchloride (TNTCI) derivatives. Typical fragment ions observed in both groups were due to loss of OR′ (R′ = H or D) and NO. In TNT, additional fragment ibns are due to the loss of R2′O and 3NO2, whilst in TNTCI fragment ions are formed by the loss of OCI and R2′OCI. The TNTCI derivatives did not produce molecular ions.In chemical ionization (Cl) of both groups. MH+ions were observed, with [M – OR′]+fragments in TNT and [M – OCI]+fragments in TNTCI. In negative chemical ionization (NCI) TNT derivatives produced M−′, [M–R′]−, [M–OR′]−and [M–NO]−ions, while TNTCI derivatives produced [M–R]−, [M–Cl]−and [M – NO2]−fragment ions without a molecular ion.
Alkene loss from metastable methyleneimmonium ions: Unusual inverse secondary isotope effect in ion‐neutral complex intermediate fragmentations
Authors: Veith Hans J. , Gross Jürgen H. 
Published: May 2005

AbstractThe mechanism of propene elimination from metastable methyleneimmonium ions is discussed. The first field‐free region fragmentations of complete sets of isotopically labelled methyleneimmonium ions (H2C = \documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\rm N}\limits^{\rm +} $\end{document}+R1R2: R1 = R2 = n‐C3H7; R1 = R2 = i‐C3H7; R1 = n ‐C3H7; R2 = C2H5; R1 = n‐C3H7; R2 = CH3; R1 = n‐C3H7; R2 = H) were used to support the mechanism presented. The relative amounts of H/D transferred are quantitatively correlated to two distinct mathematical concepts which allow information to be deduced about influences on reaction pathways that cannot be measured directly. Propene loss from the ions examined proceeds via ion‐neutral complex intermediates. For the di‐n‐propyl species rate‐determining and H/D distribution‐determining steps are clearly distinct Whereas the former corresponds to a 1,2‐hydride shift in a 1‐propyl cation coordinated to an imine moiety, the latter is equivalent to a proton transfer to the imine occurring from the 2‐propyl cation generated by the previous step. For the diisopropyl‐substituted ions which directly form the 2‐propyl cation‐containing complex, the rate‐determining hydride shift vanishes. The 2‐propyl cation‐containing complex can decompose directly or via an intermediate proton‐bridged complex. Competition of these routes is not excluded by the experimental results. Assuming a 2:1:3 distribution, a preference for the α‐ and β‐methylene of the initial n‐propyl chain as the source of the hydrogen transferred is detected for n‐propylimmonium ions containing a second alkyl chain R2. This preference shows a clear dependence on the steric influence of R2. During the transfer step isotopic substitution is found to affect the H/D distribution strongly. For the alternative route of McLafferty rearrangement leading to C2H4 loss, specific γ‐H transfer is observed.
Is the McLafferty rearrangement of ketones concerted or stepwise? The application of kinetic isotope effects
Authors: Stringer Michael B. , Underwood Dennis J. , Bowie John H. , Allison Colin E. , Donchi Kevin F. , Derrick Peter J. 
Published: May 2005

AbstractIntramolecular 13C and 2H isotope effects have been measured for unimolecular losses of ethene (the McLafferty rearrangement) from metastable molecular ions of 2‐ethyl‐1‐phenylbutanl‐1‐one, 3‐ethylpentan‐2‐one and heptan‐4‐one. Primary and secondary deuterium isotope effects are observed at the γ‐(terminal) and β‐positions, respectively. Large primary 13C isotope effects occur at β‐positions and for the y positions of γ‐ethylpentan‐2‐one and heptan‐4‐one. The carbon isotope effects in the cases of the doubly isotopically labelled CH3COCH(C2H5)(13CH2CH3) and CD3COCD(C2D5)(13CD2CD3) are 1.17 (±0.01) and 1.04 (±0.01), respectively. All of these isotope effects are consistent with a stepwise mechanism in which more than one step is rate determining.
Structural characterization of sulfonated azo dyes using liquid secondary ion mass spectrometry/tandem mass spectrometry
Authors: Richardson Susan D. , McGuire John M. , Thruston Alfred D. , Baughman George L. 
Published: May 2005

AbstractEight monosulfonated and disulfonated azo dyes were analyzed using liquid secondary ion mass spectrometry/tandem mass spectrometry, in the negative ion mode, under low‐energy collision conditions (110–150 eV). Many structurally characteristic fragment ions were obtained, several of which have not been reported previously using other mass spectrometric techniques. Among the structurally important ions observed were those due to loss of SO2, SO3 and various aromatic substituents, such as NO2 and NHCOCH3. Losses of N2 were also proposed. In addition, product ions due to cleavage at the azo linkage were observed, and also SO3− and HSO3− ions. Several of the azo cleavage product ions detected did not contain sulfonate groups. Possible pathways for the formation of product ions are proposed. The structural information obtained should help to better characterize and identify sulfonated azo dyes in the future.
Experimental aspects of the collision‐induced decomposition of ions in a four‐sector tandem mass spectrometer
Authors: Bordas‐Nagy Jozsef , Despeyroux Dominique , Jennings Keith R. , Gaskell Simon J. 
Published: May 2005

AbstractThe collision‐induced decomposition (CID) of ions in the collision cell of a four‐sector tandem mass spectrometer (EBEB) was studied as a function of cell potential and collision gas over the mass range 246–1847. When the cell is at a potential of 2 kV or greater above earth, the loss of light ions by scattering is negligible and the detection sensitivity for light ions increases owing to their being reaccelerated on leaving the cell. The CID spectra given by helium and argon are very similar for ions derived from samples of m/z ⩽ 1000 but at higher masses argon is the more efficient collision gas.
Gas‐phase reactions of C3Hn+ ions
Authors: Prodnuk Stephen D. , Grocert Scott , Bierbaum Veronica M. , DePuy Charles H. 
Published: May 2005

AbstractThe kinetics and reactivity of linear C3H+ and cyclic and linear isomers of C3H2+ and C3H3+ were studied in a tandem flowing afterglow‐selected ion flow tube (FA‐SIFT). The C3Hn+ ions represent possible ionic precursors to neutral cyclopropenylidene, c‐C3H2, a molecule that has been found to be one of the most common species in interstellar space. Accordingly, rate coefficients and product branching ratios were measured for reactions of each ion with a variety of organic and inorganic compounds, with particular (but not exclusive) attention to neutral species likely to be present in the interstellar medium. The chemistry of C3H+ is found to be dominated by oxygen abstraction reactions to produce the relatively stable HC3O+ ion, and by reactions in which C2H2 or CO are eliminated. Cyclic and linear isomers of C3H2+ readily abstract H atoms to produce the stable cyclic or linear C3H3+ ions, presumably the ionic precursors to interstellar C3H2. C3H3+ ions react predominantly by clustering with the neutral reagent in three‐body association reactions. C3H3+ also proton transfers to several species to produce directly neutral C3H2.
Ion—neutral complex intermediate for loss of water from fatty acid carboxylates
Authors: Jensen Nancy J. , Haas George W. , Gross Michael L. 
Published: May 2005

AbstractFatty acid carboxylates desorbed into the gas phase by fast atom bombardment (FAB) undergo both metastable‐ion and collisionally activated dissociation (CAD) to eliminate water. Upon CAD, the water elimination competes with charge‐remote fragmentation. Deuterium labeling results are in accord with the elimination occurring via an ion‐neutral complex involving hydroxide ion and neutral ketene. Evidence that the precursor of the ion‐neutral complex is the enol form of the carboxylate was obtained by forming the enolate directly by decarboxylation of appropriate dicarboxylic acids. The [M  H  CO2]− ions of these species undergo a more facile elimination of water than do carboxylates desorbed directly upon FAB.
The barrier to methane elimination from ionized butan‐2‐one: Theory and experiment
Authors: Hudson Charles E. , Ahmed Mohammed S. , Olivella Santiago , Giam C. S. , McAdoo David J. 
Published: May 2005

AbstractExperimental and theoretical approaches are used to characterize the losses of methyl and methane from ionized butan‐2‐one (a). Formation of a with an energy content near its dissociation threshold by charge exchange demonstrates that even very close to the threshold, methane elimination competes poorly with methyl loss. The fragmentations of a generated by reaction of CH3CH3 with CH2CO+˙ support this conclusion. Ab initio calculations were used to locate a transition state for methane elimination from a though the ion‐neutral complex [CH3CH2CO+ ˙CH3]. These calculations place the top of the barrier to methane elimination 6–7 kJ mol−1 above the threshold for methyl loss and the products of methane elimination about 35 kJ mol−1 below that threshold. This barrier prevents methane elimination from competing strongly with methyl loss. A binding energy of 18 kJ mol−1 was obtained for the complex [CH3CO+ ˙CH2CH3]. The difference between the theoretical energies for the products of methane and methyl loss obtained by including electron correlation are in good agreement with experimental results. However, the calculated difference [ΔHf(CH3CH2CO+) + ΔHf(˙CH3)] minus ΔHf(a) was 23.1 kJ mol−1 smaller than the experimental difference. Although there is clearly a barrier to the H transfer in the elimination of methane from a, whether that transfer takes place by surmounting the barrier or by tunneling through it cannot clearly be determined owing to uncertainties in the barrier height.
Calibration of ion spray mass spectra using cluster ions
Authors: Anacleto J. F. , Pleasance S. , Boyd R. K. 
Published: May 2005

AbstractMass calibration for ion spray mass spectrometry can be achieved by using cluster ions formed by flow injection of solutions of alkali metal salts in aqueous acetonitrile into the liquid flowing to the ion spray needle. Source contamination is thereby reduced to a minimum. For quadrupole mass analyzers, sodium iodide provides an ideal compromise between undesirable spectral complexity and spacings between calibrant mass peaks sufficiently close that interpolation errors are negligible. When much closer spacings are required, protonated water clusters provide an excellent calibration up to about m/z 1000. If higher mass ranges are required with a large number of calibrant peaks, a solution of mixed alkali metal iodides does provide the expected spectra but intensities are poor at higher m/z values. For liquid chromatography with on‐line mass spectrometry (LC/MS) the mass calibration may be checked without changing the mobile phase by post‐column flow injection of a cesium carbonate solution, since the carbonate anion is wholly displaced by the anion of the mobile phase acid modifier, resulting in no mixed clusters. The metal salt calibrants have the additional advantage of being useful over a wide range of tuning parameters in the atmospheric pressure ionization source, covering those appropriate to both relative molecular mass determinations of large proteins and to LC/MS of small analyte species.
Plasma desorption mass spectrometry of non‐molecular materials: Positive and negative ions formed from [Cd(SC6H4‐2‐CH3)2]∞
Authors: Craig A. Grey , Kinny David , Garbutt Robert , Dance Ian G. , Derrick Peter J. 
Published: May 2005

AbstractBoth positive and negative plasma desorption mass spectra of the three‐dimensionally non‐molecular material [Cd(SC6H4‐2‐CH3)2]∞ contain fragment ions directly related to the lattice structure of the material. Fragment ions are observed which correspond with [CdSC7H7]+˙ and [CdS2C7H7]−˙ which do not involve proton transfer reactions. In contrast, a fragment ion [CdS2C14H13]−˙ would appear to involve a deprotonation reaction. The scarcity of protonated positive ion fragments may be a consequence of the sample structure and/or constraints of the analysis system.
Mass spectrometric study of structure and stereochemistry of some stereoisomeric furanosidic derivatives
Authors: Borges C. , Ferreira M. A. Almoster , Jennings K. R. 
Published: May 2005

AbstractA mass spectrometric study of eight new carbohydrate derivatives has been carried out to determine the influence of structure on the fragmentation mechanisms of stereoisomers. Results indicate that the relative intensities of peaks due to fragment ions of each pair of isomers are sometimes very different, especially those observed in the collision‐induced decomposition mass spectra of [MH]+ ions. Metastable decompositions related to identical fragmentation processes of two isomers release different amounts of kinetic energy, however. It is usually observed that the kinetic energy released is larger for the S‐configuration than for the R‐configuration of the two epimers of a particular species.
Studies on structure characterization of tryptophan melanin: Comparison between filament and curie‐point pyrolysis gas chromatography/mass spectrometry
Authors: Vèkey Karoly , Tamás József , Somogyi Arpád , Bertazzo Antonella , Costa Carlo , Allegri Graziella , Seraglia Roberta , Traldi Piero 
Published: May 2005

AbstractStructural studies of a synthetic melanin, obtained by means of performic acid oxidation of tryptophan, were carried out by pyrolysis gas chromatography/mass Spectrometry (Py‐GC/MS). To identify the best pyrolysis conditions, both Curie‐point pyrolysis and filament pyrolysis were employed and the effects of pyrolysis temperatures and times were studied. Using the first approach, various compounds were identified: toluene, ethylbenzene, styrene, indole, methylindole, ethylindole, phenol, cresol and ethylphenol. Using filament pyrolysis some interesting differences could be observed. Whereas toluene, ethylbenzene, phenol, cresol and methylindole were found, neither indole nor ethylindole was detected. Instead, new pyrolysis products were evident, such as methylpyrrole and indolin‐2‐one. Hence filament pyrolysis seems to activate different thermal decomposition pathways of the melanin under study. It is suggested that tryptophan melanin is a polymer containing indole and hydroxyindole derivatives as subunits.