bluuebunny/crossref_metadata_2025_split huggingface dataset:
Collision‐activated dissociation mass spectra of crown ethers, perfluorinated crown ethers and related macrocycles
Authors: Maleknia Simin , Liou Chien‐Chung , Brodbelt Jennifer 
Published: May 2005

AbstractThe collision‐activated dissociation (CAD) mass spectra for a series of crown ethers, perfluoro crown ethers, cryptands and several dicyclohexano substituted crown ethers are reported. The CAD spectra were acquired with a triple quadrupole mass spectrometer, and in some cases spectra were recorded as a function of collision energy. In general, the protonated crown ethers dissociate via a series of losses of C2H4O units. The perfluoro crown ethers dissociate predominantly via losses of C2F4O units. The dicyclohexano ethers fragment in analogous ways in conjunction with cleavage of the cyclohexano rings. CAD spectra are also reported for acyclic ether systems.
Energy disposal in gas‐phase nucleophilic displacement reactions
Authors: Vanorden Steven L. , Pope R. Marshall , Buckner Steven W. 
Published: May 2005

AbstractThe partitioning of reaction exothermicity into relative translational energy of the products of gas‐phase SN2 (F− + CH3Cl) and nucleophilic aromatic substitution (F− + C6H5Cl) reactions has been investigated using kinetic energy release Fourier transform ion cyclotron resonance spectroscopy. The chloride product ion is observed to be highly translationally excited for the SN2 reaction, indicating a cold internal energy distribution for the products. For the chlorobenzene reaction the products are not generated with large translational energies. The results are compared with a statistical model. Ion‐intensity profiles for the CH3Cl reaction deviate significantly from the statistical model whereas the chlorobenzene results are consistent with this model. The kinetic energy release for the CH3C1 reaction is compared with energy‐disposal results for the photodissociation and dissociative electron‐attachment processes of halomethanes. In all three cases a node in the molecular orbital between the carbon atom and the departing halogen results in a repulsive energy release. Ion‐retention curves for the nucleophilic aromatic substitution reaction are consistent with the existence of a long‐lived ion‐dipole complex on the exit channel for this reaction.
Loss of CO from the molecular ions of o‐, m‐ and p‐anisoyl fluorides, CH3OC6H4COF, with fluorine atom migration
Authors: Tajima Susumu , Tobita Seiji , Mitani Motohiro , Akuzawa Kazuko , Sawada Hideo , Nakayama Masaharu 
Published: May 2005

AbstractLoss of CO from the molecular ions ([CH3OC6H4COF]+˙) of o‐, m‐ and p‐anisoyl fluorides has been investigated by mass‐analysed ion kinetic energy (MIKE) spectrometry. This reaction involves fluorine atom migration from the carbonyl group to the benzene ring.In the cases of o‐ and p‐anisoyl fluorides, the fluorine atom migrates via a three‐membered transition state to form the molecular ions ([CH3OC6H4F]+˙) of o‐ and p‐fluoroanisoles, respectively. On the other hand, in the case of m‐anisoyl fluoride, the fluorine atom migrates from the carbonyl group to the benzene ring via a three‐ or four‐membered transition state.
Alkane loss from collisionally activated alkylmethyleneimmonium ions
Authors: Veifth Hans J. , Gross Jürgen H. 
Published: May 2005

AbstractThe collision‐induced dissociation (CID) spectra of five alkylmethyleneimmonium ions (H2C‐N+R1R2, (a) R1 = R2 = C2H5, (b) R1 = n‐C3H7, R2 = H, (c) R1 = n‐C3H7, R2 = CH3, (d) R1 = n‐C3H7, R2 = C2H5, (e) R1 = R2 = n‐C3H7) are reported and discussed in terms of the mechanism of alkane loss. The most abundant alkane losses result from 2‐azaallylic bond cleavages within R1 and R2 leading to daughter ions of m/z 84. Ion d (R1 = n‐C3H7, R2 = C2H5) was chosen for a deuterium‐labelling study because it exhibited methane loss nearly free from interferences with other fragmentations. The methane lost consists to a great extent (95%) of the methyl moiety of R2. Whereas the methyl moiety obviously stays intact during the fragmentation process, the hydrogen additionally needed originates from all positions of R1 and the double‐bonded methylene in an approximately random distribution, suggesting extensive hydrogen migrations preceding the transfer step.
Selective isotopic exchange of polyfimctional ions in tandem mass spectrometry: Methodology, applications and mechanism
Authors: Ranasinghe Asoka , Cooks R. Graham , Sethi Satinder K. 
Published: May 2005

AbstractIsotopic exchange of mass‐selected odd‐ and even‐electron molecular ions of aromatic compounds upon collision with deuterated gases was investigated as a function of reagent gas, interaction time and collision energy. Use of ND3 as reagent allows exchange of all active hydrogens for the compound types studied, providing a count of the total number of active hydrogens present in the analyte. CH3OD exchanges specific types of active hydrogens, such as phenolic and carboxylic hydrogens, without exchanging amino hydrogens. This selectivity assists in the identification and enumeration of different types of active hydrogens present in polyfunctional compounds. The H–D exchange patterns serve to differentiate isomeric aromatic compounds containing methoxy, amino, hydroxy and carboxylic acid substituents. Trapping of mass‐selected ions in the collision region of a triple quadrupole mass spectrometer greatly enhances the degree of H–D exchange, thereby facilitating determination of the number of active hydrogens in the analyte. Triple stage mass spectrometric experiments, performed in a pentaquadrupole mass spectrometer, help elucidate the exchange process. Isotopic exchange in the collision region of a tandem mass spectrometer also provides insights into the site of protonation in molecules containing several functional groups. The proximity of the functional groups and the proton affinity difference between the analyte and the reagent gas are important factors in site‐specific H–D exchange in polyfunctional compounds. An investigation of the effects of collision energy reveals that cluster ion formation plays a major role in the exchange mechanism operating in the triple quadrupole and that H–D exchange, ion‐molecule adduct formation and endothermic fragmentation are competitive reaction channels.
Electron impact mass spectra of some acridones substituted with hydroxyl, methoxyl, alkyl and alkenyl groups
Authors: Lin Shaw‐Tao , Wu Tian‐Shung , Furukawa Hiroshi 
Published: May 2005

AbstractForty‐four acridones were examined by mass Spectrometry. The fragmentations were studied, and included cleavage of the carbonoxygen bond of methoxyl groups, cleavage of the carbon–carbon bonds of γ,γ‐dimethylpyranyl groups, cleavage of isoprenyl groups and the formation of doubly charged molecular ions and daughter ions. The tendency for fission of carbonoxygen bond in the methoxyl group for acridones is about 300 : 200 : 8 : 1 for the C(2), C(4), C(5) and C(6) positions, respectively. The isoprenyl group is very sensitive to its position in fragmentation, and mass Spectrometry can be a powerful aid in distinguishing between C(2)‐ and C(4)‐isoprenyl isomers.
Electron impact mass spectrometry of ethyl esters of halogenated acetic acids
Authors: Catinella Silvia , Favretto Donata , Traldi Pietro , Bravo Pierfrancesco , Viani Fiorenza 
Published: May 2005

AbstractThe behaviour of a series of differently halogenated acetic acid ethyl esters was studied using electron impact and metastable ion techniques. The presence of different halogens strongly influences the fragmentation pathways and also the kinetic energy release values associated with some decomposition routes. By mass‐analysed ion kinetic energy spectrometry, a composite metastable peak was detected for the transition CF2BrCO+ → CF2Br+, and rationalized on the basis of two different structures for the precursor ion.
Boundary effects and collisional activation in a quadrupole ion trap
Authors: Paradisi Cristina , Todd J. F. J. , Traldi Pietro , Vettori Umberto 
Published: May 2005

AbstractThe effects of storing ions at different values of the stability parameters az and qzwere studied in a quadrupole ion trap, using helium or argon as buffer. A region was localized near the boundaries of the stability diagram in which the ions experience an increase in their kinetic energy. This is reflected in the occurrence both of fragmentation due to collisional activation and of a certain extent of ion loss due to unstable trajectories. The results of this excitation, referred to as ‘boundary effects,’ depend on the specific qzat which the ion storage is performed and on the buffer gas used, and point to a simpler means of obtaining tandem mass spectra with the ion trap without the need to apply resonant tickle voltages between the end ‐cap electrodes.
Differentiation of anomeric C‐glycosides by mass spectrometry using fast atom bombardment, mass‐analysed ion kinetic energy and collision‐activated dissociation
Authors: Brakta Mohamed , Chaguir Brahim , Sinou Denis , Banoub Joseph , Becchi Michel 
Published: May 2005

AbstractPositive‐ion fast atom bombardment mass spectrometry appears to be a useful method for the differentiation of anomeric C‐glycosides. The mass‐analysed ion kinetic energy (MIKE) and collision‐activated dissociation (CAD) MIKE spectra of selected positive ions can be used as fingerprints of the α‐ or β‐anomers. The main fragmentation routes and particularly the formation of the [M − H]+ ion and the [M + H − PhCH2OH]+ ion were traced for each anomer.
Bimodal internal energy distribution as a consequence of Cul‐de‐sac isomerization reactions
Authors: Hammerum Steen , Vulpius Tore , Audier Henri‐Edouard 
Published: May 2005

AbstractA simple model is developed to examine the internal energy distribution for metastable ions and the probability of reaction in the field‐free regions of sector mass spectrometers in systems where the reactant ions in the ion source react by dissociation in competition with reversible isomerization to non‐dissociating species. The internal energy distribution for the reacting ions is strongly dependent on whether dissociation is preceded by isomerization and back‐isomerization, and it is shown that a range of reasonable combinations of rate constants for the forward and reverse isomerization result in a bimodal distribution of the internal energy for the ions that dissociate in the field‐free regions. The isomerization effectively provides a kinetic reservoir of higher energy reactant ions. The reaction probability of the metastable ions varies strongly with internal energy, and the back‐isomerized ions may in some instances be responsible for most of the reactions observed. A bimodal energy distribution will give rise to composite metastable peaks even though neither non‐statistical behavior nor multiple reaction channels are involved.
Competing oxygen transfers from nitro group to sulphur and allenic double bonds in allenyl o‐nitrophenyl sulphides on electron impact
Authors: Ramana D. V. , Ramakrishna N. V. S. 
Published: May 2005

AbstractInteresting oxygen transfers from the o‐nitro group to allenic carbons were observed in allenyl o‐nitrophenyl sulphides under electron impact conditions giving rise to abundant fragment ions at m/z 151, 138 and 136. However, a similar oxygen transfer to the sulphur leads to another intense ion at m/z 145. The proposed fragmentation pathways and the ion structures were established through high‐resolution data, collision‐activated dissociation mass‐analysed ion kinetic energy and B/E linked‐scan spectra.
Effect of structure on the electron‐capture negative ionization mass spectrometric response of steroids
Authors: Mayer Helen K. , Reusch William , Watson J. Throck 
Published: May 2005

AbstractThe key to enhanced electron‐capture negative ion mass spectrometry (ECNI‐MS) response of ketosteroids is extensive α,β‐unsaturation. Combinations of double bonds, carbonyl groups, epoxides and halogens within a steroid nucleus were correlated with their ECNI responses. The greatest ECNI responses result from extensive conjugation, such as the linearly conjugated 4‐ene‐3,6‐dione system and the cross‐conjugated 1,4‐diene‐3,11‐dione system. In general, an epoxy ketosteroid has a relative response 40 times greater than that of its corresponding enone. In an α‐halo ketone, an axial halogen substitution will increase the relative response by an order of magnitude, but an equatorial halogen substituent will not affect the response. The fragmentation of ketosteroids as related to ECNI response is discussed.
Reactivity of electron impact ionized large‐ring cycloalkylamines. Loss of CnH2n + 1. Alkyl radicals from long‐chain aliphatic compounds with a terminal enamine or ester function (lipids)
Authors: Lefèvre O. , Mollova N. , Longevialle P. 
Published: May 2005

AbstractLarge‐ring Cycloalkylamines rearrange after electron impact ionization into long‐chain enamines. A general mechanism is proposed for their fragmentation, and a parallel is established with the fragmentation of long‐chain esters (lipids). It is shown that the parent ions rearrange into a series of interconverting branched onium ions from which alkyl radicals are lost. The mechanism of the interconversion is discussed.
Electron impact fragmentation of pyranocoumarin derivatives. Tandem mass spectrometric study of abundant singly and doubly charged fragment ions at high and low collision energy
Authors: Rubino F. M. , Mascaro P. , Palmisano G. , Appendino G. , Cravotto G. , Tagliapietra S. , Nano G. M. 
Published: May 2005

AbstractA series of novel pyranocoumarin derivatives were analysed by electron impact mass spectrometry and tandem mass spectrometry at low aud high collision energy. The collision‐induced decomposition tandem mass spectra of the [M  CH3]+ ions yielded several structurally valuable fragments and those of the [M  CH3]2+ ions allowed some charge‐separation reactions to be recognized.
Chemical ionization and electron impact mass spectra of symmetrical S‐alkyl alkanesulfonothioates (thiosulfonates)
Authors: Freeman Fillmore , Keindl Monica C. 
Published: May 2005

AbstractThe chemical ionization (CI) and electron impact (EI) mass spectra of eight symmetrical S‐alkyl alkanesulfonothioates (thiosulfonates) are reported.
Fragmentation selectivity in electron impact ionization mass spectra of substituted dimethoxybenzenes
Authors: Nakata Hisao , Jitsukawa Fumie , Toyama Hitomi , Kato Yuko 
Published: May 2005

AbstractSeveral 1‐X‐sabstitirted‐3‐methoxy‐4‐trideuteromethoxybenzens were synthesized and their electron impact ionization mass spectra were measured with an ionizing energy of 20 eV. From the peak intensity ratio of [M  CD3 ] and [M  CH3] the fragmentation‐directing ability of the substituent X was evaluated. The most powerful group was found to be NH2, which expelled a methoxy methyl group only from its para position. The CH3 group and four halogen atoms, F, Cl, Br and I, exerted a moderate effect Electron‐withdrawing groups such as NO2, CHO and CN had only a little influence on the fragmentation selectivity. These results were interpreted in terms of the effect of X on the distribution of both the unpaired electron and the positive charge in the molecular ion.
In situ N‐phosphorylation of oligopeptides for fast atom bombardment mass spectrometry
Authors: Yang Hou‐Jun , He Mei‐Yu , Ye Yun‐Hua , Zhao Yu‐Fen 
Published: May 2005

AbstractPositive ion fast atom bombardment mass spectrometry (FABMS) of in situ N‐phosphorylated oligopeptides showed intense quasi‐molecular ions together with the successive alkene loss fragment ions, which afford multiple checks of the unequivocal reality of the relative molecular mass of the tested samples. More interesting, in a novel cleavage pattern only the N‐phosphoryl fragment ions gave intense peaks, the C‐terminal series ions being suppressed. For each of the N‐terminal ions, losses of alkenes also occur to provide multiple checks for the existence of these ions. The FABMS of the in situ N‐ phosphorylated oligopeptides might provide an easily accessible routine method for peptide sequencing.
Internal energy deposition in doubly charged tungsten hexacarbonyl on charge exchange at high energy with atomic and molecular targets
Authors: Susič R. , Lu L. , Riederer D. E. , Žigon D. , Cooks R. G. , Ast T. 
Published: May 2005

AbstractCharge exchange of W(CO) in the course of 7 keV collisions with various targets results in singly charged ions which are highly internally excited. The distribution of internal energies estimated by the degree to which consecutive fragmentations by CO loss occur is broad and includes very high energies (up to 15 eV). This result is inconsistent with exclusive operation of long‐range electron transfer e.g. by either a curve crossing or Demkov mechanism; rather it suggests that direct excitation to a high‐energy repulsive state of the products also occurs perhaps by an electronic excitation mechanism. The nature of the internal energy distribution suggests mechanistic analogies with simple collisional activation. Different target gases give rise to different average internal energy depositions monatomics and diatomics yielding higher energy depositions than do polyatomic targets. There is an approximate correlation between energy deposition and target ionization energy which is consistent with the proposed excitation mechanism considering the shapes of the potential energy surfaces. When the detailed internal energy distributions are compared characteristic differences are seen for individual targets. The efficiencies of the various targets at producing charge exchange were also compared. Large differences were found with the polyatomic targets having the greatest efficiencies. In addition a rough correlation was observed between the extent of charge exchange and target ionization energy and this is interpreted in terms of greater contributions from the long‐range electron transfer process for targets of lower ionization energy. All the results are also consistent with contributons from more violent collisions which involve electron transfer at relatively small internuclear distances where the shapes of the potential surfaces are strongly dependent on distance.
Reactive collisions in quadrupole cells. Part I. Reaction of [CH3NH2]+˙ with the isomeric butenes and pentenes
Authors: Usypchuk Laurie L. , Harrison Alex. G. , Wang Jianyao 
Published: May 2005

AbstractThe reactions of mass‐selected [CH3NH2]+˙ ions with the isomeric butenes and pentenes were studied at low collision energies in the radiofrequency‐only quadrupole collision cell of a hybrid BEqQ tandem mass spectrometer. Characteristic iminium ions arising by addition of the methylamine to the olefin followed by fragmentation are observed for but‐1‐ene pent‐1‐ene and 3‐methylbut‐1‐ene. However, for but‐2‐ene pent‐2‐ene 2‐methylpropene 2‐methylbut‐1‐ene and 2‐methylbut‐2‐ene the major reaction channel of [CH3NH2]+˙ is charge exchange to form the olefinic molecular ion. The isomeric olefins are characterized to a considerable extent by the characteristic ion–molecule reactions that these molecular ions undergo with the neutral olefin.
Preservation of non‐covalent associations in electrospray ionization mass spectrometry: Multiply charged polypeptide and protein dimers
Authors: Smith Richard D. , Light‐Wahl Karen J. , Winger Brian E. , Loo Joseph A. 
Published: May 2005

AbstractThe ‘softness’ of the electrospray ionization (ESI) method provides a direct link between solution chemistry and the inherent gas‐phase environment of mass Spectrometry. Available results related to the preservation of non‐covalent associations into the gas phase after ESI are reviewed. These associations include the possible retention of elements of higher order protein structure, non‐covalent polypeptide–heme associations and enzyme complexes. Experimental results are presented showing that non‐covalently bound polypeptide and protein dimer ions are relatively common as low level contributions to ESI mass spectra. It is argued that these dimers are reflective of multimeric species in solution since Coulombic barriers preclude dimerization after ESI although uncertainty remains regarding whether they exist prior to the formation of highly charged droplets. The dissociation of dimers is facile and for proteins can yield monomers having a broad distribution of charge states. The detection of non‐covalently associated dimers requires gentle ESI mass spectrometer interface conditions, yielding relatively low levels of internal excitation. Under such conditions incomplete molecular ion desolvation can result in experimental artifacts for tandem mass spectrometric experiments. ESI mass Spectrometry may have broad potential for the study of noncovalent liquid phase associations.
Negative‐ion fast atom bombardment mass spectra of some bisanionic hypervalent germanium, silicon and titanium salts
Authors: Cerveau G. , Chuit C. , Reye C. , Aubagnac J.‐L. 
Published: May 2005

AbstractNegative‐ion fast atom bombardment mass spectra of hypervalent germanates silicates and titanate with the use of two matrices, glycerol and m‐nitrobenzyl alcohol, were studied. In the case of germanates a complete reaction of the studied anion with glycerol is observed, so it is impossible to use such a matrix to identify these compounds. The use of m‐nitrobenzyl alcohol allows spectra to be obtained that are significant with respect to the structure for all the studied compounds. However, for each compound a partial reaction of this matrix is observed. Further, in the case of doubly charged anions, the adduct ion obtained with an alkali metal cation does not show glycerol reactivity whereas such reactivity occurs from the adduct ion obtained with proton.
Stereochemical effects in the mass spectra of some cyclopropylsilanes explained by the MNDO molecular orbital method. I. Silicon‐oxygen interactions
Authors: Vékey Károly , Somogyi Árpád , Tarnás József , Pócsfalvi Gabriella 
Published: May 2005

AbstractLarge differences have been found between the mass spectra of cis‐ and trans‐1‐carbomethoxy‐2‐trimethylsilylcyclopropane. To help in explaining these differences, quantum chemical calculations were performed by the MNDO method on the neutral molecules, on the vertical and adiabatic molecular ions and also the [M – methyl]+ ions. To evaluate the results, heats of formation, bond orders, molecular geometry, spin and charge densities and orbital coefficients were used. These indicate the formation of a very strong bonding interaction between silicon and oxygen in the molecular ion of the cis but not the trans isomer, leading to spontaneous methyl loss and a stabilization energy of ∼ 2.6 eV.
Electron impact mass spectrometry of [C7H8N]+ and [C6H7]+ and [C6H7]+ fragment ions produced from o‐toluidine and N‐methylaniline
Authors: Selim Ezzat T. M. , Rabbih M. A. , Fahmey M. A. 
Published: May 2005

AbstractAn energetic study of the production of [C7H8N]+ and [C6H7]+ fragment ions from o‐toluidine and N‐methylaniline is reported. The mechanisms for the formation of the ions are suggested. Metastable peaks associated with the formation and fragmentation of reactive [C7H8N]+ and [C6H7]+ ions were detected and kinetic energy released were determined. The results indicate that the [C7H8N]+ ion is formed at threshold from o‐toluidine with an aminotropylium structure whereas for N‐methylaniline the ion is formed with anN‐phenylmethaniminium structure. [C6H7]+ ions are believed to be formed at threshold from the two precursors with a protonated benzene structure.