bluuebunny/crossref_metadata_2025_split huggingface dataset:
Differentiation of isomeric 5‐ and 7‐oxo derivatives of tetrahydrothiazolo[3,2‐a]pyrimidine by electron impact mass spectrometry
Authors: Jeanneau‐Nicolle Edwige , Bosso Claude , Benoit‐Guyod Martine , Leclerc Gérard 
Published: May 2005

AbstractThe electron impact mass spectra of two series of 5‐oxo‐tetrahydro‐5H‐thiazolo [3,2‐a]pyrimidine‐6‐ethylcarboxylates and 7‐oxo‐tetrahydro‐7H‐thiazolo [3,2‐a]pyrimidine‐6‐ethylcarboxylates were measured and fragmentation patterns examined. Structures were assigned from analysis of oxo molecular ion fragmentations. Compounds of the 5‐oxo series gave an [M – CO2C2H5]+ fragmentation whereas compounds of the 7‐oxo series gave three characteristic cleavages. This decomposition was confirmed for one pair of isomers by high‐resolution mass spectrometry and unimolecular mass‐analysed ion kinetic energy spectrometry. Electron impact mass spectrometry is a convenient method for assigning structures of 5‐ and 7‐oxo regioisomers of tetrahydrothiazolo[3,2‐a]pyrimidine‐6‐carboxylates.
Characterization of titanocenium and titanocene by tandem mass spectrometry
Authors: Zagorevskii Dmitri V. , Holmes John L. 
Published: May 2005

AbstractTandem mass spectrometric techniques were used for the characterization of gas‐phase titanocenium ions. Decomposition of metastable and collisionally activated C10H10Ti+˙ ions involved cyclopentadienyl–metal bond rupture, acetylene loss and dehydrogenation as the prominent processes. The intermediate formation of titanium (di)hydride complexes was proposed to explain the selective H2 molecule loss. The neutralization–reionization mass spectrum showed a very abundant recovery signal, indicating a high stability for the neutral gas‐phase C10H10Ti species.
Structural characterization of mono‐ and bisphosphonium salts by fast atom bombardment mass spectrometry and tandem mass spectrometry
Authors: Claereboudt J. , Baeten W. , Geise H. , Claeys M. 
Published: May 2005

AbstractPositive‐ion fast atom bombardment (FAB) mass spectra are reported for a representative series of mono‐ and bisphosphonium halides derived from triphenylphosphine. The mass spectra of the monoalkyltriphenylphosphonium salts typically contain abundant intact cations that can be used to establish the cationic relative molecular mass and diagnostic fragment ions that allow the characterization of structural subgroups. Depending on the functional group substitution on the alkyl group, additional fragment ions are observed which are formed by loss of small neutral molecules from the intact cation and that can be used for the differentiation of isomeric phosphonium salts. Molecular dication are typically observed in the FAB mass spectra of the bisphosphonium salts when they are analysed in 3‐nitrobenzyl alcohol. In addition, production of singly charged ions by clustering with a counter ion, decomposition involving removal of one of the charge centres and one‐electron reduction are generally observed. Structurally diagnostic fragments are also obtained. The fragmentation pathways of the ions derived from the phosphonium salts were elucidated by precursor ion and product ion tandem mass spectrometric experiments. For the phosphonium salts containing a long‐chain hydrocarbon alkyl group, high‐energy collision‐induced decomposition of the intact cation is needed to obtain unambiguous structural information.
Mass spectrometry and pyrolytic decomposition of 2‐amino‐3′,4′,6‐trisubstituted isoflavones
Authors: Hu Peifeng , Li Yongfu , Lu Yongquan , Pihlaja Kalevi 
Published: May 2005

AbstractThe 2‐aminoisoflavones studied exhibited some familiar fragmentation pathways, such as the formation of the retro‐Diels–Alder ions. However, substitutions at C(2), C(3′), C(4′) and C(6) induced some specific decompositions of both mass spectrometric and pyrolytic origin. Pyrolytic decompositions reverse to the Mannich reaction occurred with all compounds to variable extents. The three compounds with the (Me)2NSO2 substitution at C(6) exhibited another type of pyrolytic reaction, namely the formation of products corresponding to ions of m/z 272, 300 and 314, depending on the type of substitution at C(3′). The occurrence of an interesting ‘ortho effect’, the elimination of the elements of CH3O from C(3′) and C(4′), was also established.
Novel proximity effects and Ortho interactions in 2,2′‐disubstituted diphenylamines on electron impact
Authors: Ramana D. V. , Mahalakshi P. 
Published: May 2005

AbstractUnexpected ejections of CH3NO2/[˙CH3 + ˙NO2], N2O4/[˙NO2 + ˙NO2] and CH3OCH3/[˙CH3 + ˙OCH3] were observed from the molecular ions of 2‐methoxy‐2′‐nitrodiphenylamine, 2,2′‐dinitrodiphenylamine and 2,2′‐dimethoxydiphenylamine, respectively, under electron impact conditions owing to proximity effects. In other competing fragmentation pathways, novel proximity effects triggered by the ortho interactions leading to the unusual eliminations of [˙CH3 + H2O] from M+˙ of 2‐methoxy‐2′‐nitrodiphenylamine and HNO3/[˙NO2 + ˙OH] from M+˙ of 2,2′‐dinitrodiphenylamine were observed. Evidence for the interpretation of the main fragmentation pathways was obtained from the metastable ion spectra and high‐resolution mass spectrometry. Confirmation of the structures assigned to the ions was provided by collision‐activated dissociation mass‐analysed ion kinetic energy spectra.
Energy dependence of rearrangements of an N‐terminal protecting group in tandem mass spectrometry of protonated tripeptides containing C‐terminal arginine
Authors: Schwartz Brenda L. , Erickson Bruce W. , Bursey Maurice M. , Marbury G. Dean 
Published: May 2005

AbstractThe types and intensities of tandem mass spectrometric products of side‐chain interactions were investigated with a hybrid tandem instrument. Positive‐ion unimolecular decomposition and collisionally activated decomposition studies were conducted on the [M + H]+ ions of two N‐benzyloxycarbonyl (Cbz or Z)‐protected tripeptides, Cbz‐Gly‐Leu‐Arg‐NH2 and Cbz‐Gly‐Pro‐Arg‐NH2. The loss of benzyl alcohol (108 u) and the formation of other significant product ions and their dependence on collision energy and gas pressure suggest reaction between both ends of the molecule. Replacement of leucine with proline at the second position in the tripeptide produces a very intense [M + H − 108]+ ion and fewer lower mass fragment ions in the tandem mass spectra for Cbz‐Gly‐Pro‐Arg‐NH2 than in those for Cbz‐Gly‐Leu‐Arg‐NH2.
Addition of alkenes to phenyl‐substituted enol radical cations, C6H5C(OH)CHR+˙
Authors: Mourgues P. , Denhez J. P. , Audier H. E. , Hammerum S. 
Published: May 2005

AbstractThe addition‐fragmentation reactions of phenyl‐substituted enol radical cations, C6H5C(OH)CHR+˙ (R = H, CH3), with alkenes were studied by Fourier transform ion cyclotron resonance spectroscopy. These reactions (involving both labelled and unlabelled reactants) were compared with the unimolecular reactions of aromatic ketone molecular ions and related species that give rise to C6H5C(OH)CHR+˙ and alkene products. It is shown that the phenyl‐substituted enol ions react with alkenes by CC bond formation leading to an intermediate γ‐distonic ion; the reactions are not accompanied by cyclization to cyclobutanol intermediates.
Gas‐phase bimolecular chemistry of isomeric cyclic ethylenehalonium and α‐haloethyl cations
Authors: Heck Albert J. R. , de Koning Leo J. , Nibbering Nico M. M. 
Published: May 2005

AbstractThe gas‐phase bimolecular chemistry of C2H4X+ (X = F, Cl, Br) cations was studied using Fourier transform ion cyclotron resonance mass spectrometry (FT‐ICR‐MS). The results support earlier suggestions that at least two isomers of the halonium ions C2H4X+ (X = Cl, Br) exist, but no experimental evidence was found for the possibility of more than one stable isomer for C2H4F+. It is shown that the cyclic ethylenehalonium and α‐haloethyl cations react differently with various substrates. The probe reactions used to characterize the two isomers were hydrogen–deuterium exchange with deuterium oxide and reactions with benzene, alkenes and vinyl ethers. It was found that the α‐haloethyl cations react as proton donors and/or electrophiles, whereas the cyclic ethylene‐chloronium and ethylenebromonium ions react as electrophile and/or as haloganyl cation donors in reactions with alkenes and vinyl ethers.
Cyclization of α‐substituted α,ω‐diphenylalkyl carbenium ions: Reactivity of α‐trifluoromethylbenzyl cations vs. α‐methylbenzyl cations
Authors: Sürig T. , Grützmacher H.‐Fr. , Bégué J.‐P. , Bonnet‐Delpon D. 
Published: May 2005

Abstract1‐(n‐Phenylalkyl)‐1‐trifluoromethylbenzyl cations and the α‐CH3‐substituted analogues were generated from the corresponding protonated benzyl alcohols by loss of H2O during chemical ionization (CI). The unimolecular reactions of these ions and of their derivatives specifically deuterated at the 1‐phenyl group were studied using the CI (methane) and CI (isobutane) mass spectra and the mass‐analysed ion kinetic energy spectra. The characteristic reaction giving rise to abundant ions in all the spectra is the elimination of C6H6 initiated by an electrophilic attack of the benzyl cation on the remote phenyl group. The α‐CH3‐ and α‐CF3‐substituted benzyl cations respond differently to the effect of internal excess energy on the intensity of the benzene elimination process and on the H–D exchange accompanying this process of the deuterated ions. This different reactivity of both series of ions demonstrates unambiguously that the α‐CF3‐substituted benzyl cations correspond to destabilized benzyl cations exhibiting the particular reactivity of ‘hot’ carbenium ions in the gas phase.
Electron impact fragmentation of binuclear crown ethers
Authors: Gren A. I. , Mazepa A. V. , Timofeev O. S. 
Published: May 2005

AbstractIt is shown that fragmentation under electron impact of binuclear crown ethers is similar to those for crown ethers with the general formula 3n‐crown‐n‐n except for the formation of fragment ions with mass numbers reflecting the ring sizes in binuclear crown ether molecules. The formation of these ions occurs with hydrogen atom migrations in CH…︁O interactions between atoms from different rings determined in the crystal state.
Study of transition‐state methods in the calculation of vertical ionization potentials by local density approximation
Authors: Duffy Patrick , Chong Delano P. 
Published: May 2005

AbstractThe vertical ionization potentials of nine small molecules were computed by the deMon density functional program and different versions of the transition‐state method and the results were compared with earlier calculations and with experiment. The average absolute deviation of the 38 computed ionization potentials of the valence electrons of nine small molecules from experiment is 0.4 eV, which compares well with previous ab initio post‐Hartree–Fock and semi‐empirical HAM/3 calculations. The efficient methods were then used to calculate 68 ionization potentials of sixteen 22‐electron molecules, with results of similar quality.
Molecular fragmentation patterns of carbon dioxide at very high internal energies
Authors: Svensson A. , Bordas J. , Hughes E. A. , Mant G. 
Published: May 2005

AbstractIon–ion coincidence measurements following K‐shell absorption in the carbon dioxide molecule were performed by applying time‐of‐flight mass spectrometry in conjunction with monochromatic synchrotron radiation and electron impact. Identification of particularly sensitive electronic transitions and the consecutive molecular fragmentation in real time was performed. Analysis of coincidence recordings from decomposition of carbon dioxide reveals one distinct pathway in which three cations are formed following excitation of oxygen Is electrons.
Multi‐electron‐capture processes by C4+ from CH4, C2H6, C3H8 and n‐C4H10 in the energy range 0.7–400 eV u−1
Authors: Soejima K. , Okuno K. , Kaneko Y. 
Published: May 2005

AbstractCharge‐changing cross‐sections σ43, σ42 and σ41 of C4+ injected into CH4, C2H6, C3H8 and n‐C4H10 were measured in the energy range 0.7–400 eV u−1. A tandem mass spectrometer system with an ion source of the EBIS type (Mini‐EBIS) and a collision cell consisting of an octupole ion beam guide was used. It is a significant feature that both the magnitude and energy dependence of the cross‐sections obtained showed very little target dependence for all the hydrocarbon targets studied. Another feature is that σ41 is very close to σ42, and they become flat at low energy, in contrast to the case with an argon target which was studied as a reference. This implies that multi‐electron‐capture processes become dominant in low‐energy collisions with hydrocarbon molecules.
The reaction of germyl ions with ethylene
Authors: Lim K. P. , Lampe F. W. 
Published: May 2005

AbstractThe reactions of [GeH3]+ ions with C2H4 and C2D4 have been studied in a tandem mass spectrometer over a pressure range of 1–20 millitorr and over an energy range of 1–9 eV (LAB). The predominant reaction of an initial [GeC2H7]+ collision complex is back‐reaction to reactants. However, stabilized adduct ions [GeC2H7]+ and their daughter decomposition products [GeC2H5]+ are observed in increasing amounts as the pressure of C2H4 is increased. It is proposed that the structures of these product ions are [CH3CH2GeH2]+ and [CH2CHGeH2]+, respectively. The hydrocarbon ions [C2H5]+ and [C2H3]+ are observed as products of endothermic reactions of ground electronic state [GeH3]+ ions with C2H4; these same ions along with [C2H4]+ and [C2H2]+ are observed as products of exothermic reactions of an electronically excited state of [GeH3]+ present in the ion beam.
Time‐dependent mass spectra and breakdown graphs. 16–The methylnaphthalenes
Authors: Gotkis I. , Lifshitz C. 
Published: May 2005

AbstractTime‐resolved photoionization efficiency (PIE) curves were measured for [C11H10]+ and [C11H9]+ for 1‐ and 2‐methylnaphthalene and for the ion–molecule reaction product [C12H11]+. PIE curves were modelled by k(E) dependences via RRKM/QET calculations based on a model by Huang and Dunbar, with a critical energy E0 = 2.41 eV and a 1000 K activation entropy ΔS‡ = −13.3 eu. Kinetic shifts are much higher than for the analogous H˙ loss reaction in toluene. The crossover shift in the breakdown graphs between 24 μs and 40 ms is 1.45 eV; the conventional shift is 2.05 eV and the intrinsic shift, due to radiative decay in the infrared, is 1.1 eV. The heat of formation of [C11H9]+ is deduced to be ΔHf298(C11H9+) ≤ 890 ± 20 kJ mol−1. The [C11H9]+ population contains at least 20% of methylnaphthylium, the rest being benzotropylium.
Application of B–E time‐of‐flight mass spectrometry to the detection of high‐energy neutral atoms following the photoexcitation of Ar
Authors: Smith J. A. , Winkel J. F. , Stace A. J. , Whitaker B. J. 
Published: May 2005

AbstractA novel instrument which combines high‐resolution double‐focusing mass spectrometry with time‐of‐flight detection was applied to the study of cluster ion photofragmentation. Using this apparatus, kinetic energy measurements were made on neutral photofragments following the excitation of Ar at 532 nm. The results show that one and possibly two argon atoms with high centre of mass kinetic energies emerge from the cluster within a few picoseconds of the photon being absorbed.
Formation and reactivity of metal carbonyl anions in the gas phase
Authors: van den Berg Klaas Jan , Ingemann Steen , Nibbering Nico M. M. 
Published: May 2005

AbstractThe reactions of metal carbonyl anions (M(CO)n−; M = Cr, Mn and Fe; n = 1–3) with n‐heptane, water and methanol were studied with use of a Fourier transform ion cyclotron resonance (FT‐ICR) mass spectrometer equipped with an external ion source. The M(CO)n− ions were formed in the FT‐ICR cell by collision‐induced dissociation of the most abundant primary ion generated by electron impact of the appropriate metal carbonyl compound present in the external ion source. The M(CO)n− ions were allowed subsequently to undergo non‐reactive collisions with argon in order to remove possible excess internal/translational energy prior to the ion/molecule reaction. Only the Cr(CO)3−, Mn(CO)3− and Fe(CO)2− ions react with n‐heptane. This reaction proceeds by loss of H2 from the collision complex and the Cr(CO)3− and Fe(CO)2− ions react about three times more efficiently than the Mn(CO)3− ion. With water, Mn(CO)− and Fe(CO)3− are unreactive, whereas the other ions react by loss of one or two CO molecules from the collision complex. The rate of the reaction with water decreases in the order Cr(CO)3−, Fe(CO)2−, Cr(CO)2−, Fe(CO)−, Mn(CO)3− and Mn(CO)2−. With methanol, the Cr(CO)2− ion reacts by loss of two CO molecules from the collision complex, whereas loss of one CO molecule and elimination of CO + H2 occur in the reaction with Cr(CO)3−. Competing loss of CO and one or two H2 molecules occurs in the reactions of Mn(CO)3− and Fe(CO)2− with methanol. The rate of the reaction with methanol decreases in the order Cr(CO)3−, Fe(CO)2−, Cr(CO)2− and Mn(CO)3−.
Behaviour of methyl red under fast atom bombardment conditions
Authors: Florêncio M. Helena , Heerma Wigger 
Published: May 2005

AbstractThe influence of the pH, the nature of the matrix and the presence of a surfactant on the positive‐ and negative‐ion abundances in the molecular mass region in the fast atom bombardment (FAB) mass spectra of methyl red was investigated. A small but significant pH effect was observed which was attributed to the non‐ or at the most low surface‐active character of the intact methyl red molecule. As expected, the more basic the solution, the less protonated molecules with respect to M+˙ are observed and in the negative‐ion mode less [M + H]− and more [M – H]− ions with respect to M−˙ were found. In contrast to neutral solutions, both acidic and basic solutions give a long‐lasting stable response of all methyl red ions. For dyes with a moderately negative redox potential such as methyl red, beam‐induced redox reactions seem to play a role in the ionization process, the neutral medium offering the best conditions for reduction processes. The ion intensities in the molecular mass region depend on the nature of the matrix. Protonation of the molecule has been found to be more effective in glycerol than in 3‐nitrobenzyl alcohol; the former also appears to offer the best conditions for reduction processes. Anionic and cationic surfactants effectively suppress the contribution of ions from glycerol in both positive‐ and negative‐ion spectra and generally promote the formation of analyte ions at the surface. The most important effect of the surfactant in a neutral medium seems to be the promotion of a regular transport of ions and molecules to the surface, which permits the creation of stable ion currents, instead of an unstable ion beam if the surfactant is absent. Moreover, when the surfactant is present an increase of the sample ion abundances is observed. Redox reactions involving molecules and molecular ions and also molecules and preformed ions in the solution, brought to the surface by micelles, have been proposed to give some contribution for the small but significant enhanced abundance of [M + nH]+ (n > 1) ions with respect to [M + H]+ ions, in the presence of a surfactant. The results have been rationalized in terms of the surface phenomena while the important role of surfactants for obtaining better FAB mass spectra is emphasized.
Mechanism for dehalogenation reactions in fast atom bombardment mass spectrometry
Authors: Musser Steven M. , Kelley James A. 
Published: May 2005

AbstractThe mechanism of a dehalogenation reaction that occurs during fast atom bombardment (FAB) mass spectrometry was examined using halogenated nucleosides as model compounds. For aglycone‐halogenated nucleosides, an inverse linear relationship exists between the extent of FAB dehalogenation and the calculated electron affinity of an individual nucleoside. The degree of dehalogenation for a given nucleoside also varies inversely with the calculated electron affinity of most FAB matrices. The observed dehalogenation reaction can be completely inhibited when matrices with positive electron affinities, such as 3‐nitrobenzyl alcohol and 2‐hydroxyethyl disulfide, are used. High‐performance liquid chromatographic analysis of the bulk glycerol matrix following exposure to the FAB beam indicates measurable amounts of dehalogenated product, suggesting that this reaction occurs in the condensed phase prior to gas‐phase ion formation. A dehalogenation mechanism involving thermal electron capture and subsequent negative charge stabilization is consistent with these observations.
Concerted chain isomerization in protonated alkylbenzenes
Authors: Denhez J. P. , Audier H. E. , Berthomieu D. 
Published: May 2005

AbstractThe first step in the unimolecular reaction of metastable protonated alkylbenzenes is the stretching of the C(benzene)—C(α) bond. Therefore, the intermediacy of a π‐complex [C6H6, alkyl+] has often been proposed. In this work, the kinetic energy releases associated with the [tert‐alkyl]+ product were measured for a large number of [C6H6–CnH] (n > 3) ions. At least for β‐branched alkylbenzenes, it is shown that the chain isomerization which occurs prior to dissociation involves neither the [C6H6, CnH] π‐complex nor a [C6H7+, alkene] ion–neutral complex. The data are explained by a concerted process in which the stretching of the C(benzene)—C(α) bond is accompanied by the migration of the tertiary β‐hydrogen from C(β) to C(α).
Studies on the complexation of polyols and carbohydrates with excess borate using thermospray mass spectrometry
Authors: Lipták Miklós , Dinya Zoltán , Herczegh Pál , Jekő József 
Published: May 2005

AbstractComplex formation between different polyols, carbohydrates and borate was studied by thermospray mass spectrometry. The analytes were dissolved in 0.1 M ammonium borate buffer and introduced through a standard thermospray interface into a quadrupole mass spectrometer. The formation of various complexes which gave rise to relatively abundant ions in the thermospray spectra was observed. A correlation has been found between the relative intensities of these ions and the orientation of the hydroxyl groups involved in the complexation.
Mass spectrometric investigation of polyfluorinated C60. Evidence for the existence of C60F2n (n = 0–30)
Authors: Chowdhury Swapan K. , Cameron Stephen D. , Cox Donald M. , Kniaz Krzysztof , Strongin Robert A. , Cichy Maria A. , Fischer John E. , Smith Amos B. 
Published: May 2005

AbstractElectron‐capture negative ion chemical ionization (EC‐NICI) and field desorption (FD) mass spectrometric techniques were utilized to examine polyfluorinated C60. Two different samples from the same preparation, one prior to sublimation and the other sublimed material, were investigated. From the raw non‐sublimed product in EC‐NCI six series of ions corresponding to different numbers of attached oxygen atoms were obtained, which are represented by the formula [C60F2nOm]−, where n ranged from 0 to 30 and m from 0 to 5. The sublimed material in EC‐NICI produced the same six series of ions with up to 48 fluorine atoms attached to C60. The field desorption of the same sample produced similar results, but the signal‐to‐noise ratios of the spectra were low. Both samples, in the two different techniques examined, yielded C60F60 ions with only an even number of fluorine atoms attached. The present investigation, for the first time, provides direct experimental evidence for the existence of higher fluorinated C60 up to C60F60 and multiple oxides of polyfluoro‐C60 with up to five oxygen atoms attached.
Fragmentation pathways of isomeric dodecenols studied by electron impact mass spectrometry
Authors: Yuan Gu , He Meiyu , He Xiaoran 
Published: May 2005

AbstractElectron impact‐induced fragmentations of isomeric dodecen‐1‐ols were investigated using mass‐analysed ion kinetic energy (MIKE) spectrometry and high‐resolution data. The principal fragmentation pathways of the positional isomers studied are dominated by the CC double bond and involve migration and radical‐site rearrangements along the carbon chain with the aid of consecutive rearrangements of hydrogen atoms.