bluuebunny/crossref_metadata_2025_split huggingface dataset:
Anomalies in the molecular ion region in the electron impact mass spectra of α‐ and β‐hydroxyesters
Authors: Konopski Leszek 
Published: May 2005

AbstractIn the electron impact mass spectra of some alkyl α‐ and β‐hydroxyesters (introduced using the gas chromatography/mass spectrometry (GC/MS) technique), the absence of the molecular ion M+· and the presence of the [M + 1]+ ion instead is observed. This phenomenon is especially characteristic of C3C6 glycolates and diethyl malate, and is due to chemical auto‐ionization—ion‐molecule reactions in the high concentration gradient at the top of the GC peak. The existence of the [M  2]+·, [M −1]+ and M+· ions in the mass spectra of other β‐ and α‐hydroxyesters is discussed.
The loss of water from ionized heptanols in the gas phase
Authors: Haib J. , Stahl D. 
Published: May 2005

AbstractThe mechanism of water loss from the 1‐beptanol molecular ion was studied by using a set of deuterium 1‐heptanols labelled at each position of the chain. The carbon‐bound hydrogen atom lost in the water comes mainly from C(4) (69%) but also from C(2) and C(3) (10 and 13%, respectively), and from C(5) and C(6) (5 and 4%, respectively). No measurable contribution by an H atom from C(7) and C(l) was found. The structure of the resulting [C7H14]+· ion was studied by using the MIKE and CAD/MIKE techniques applied to unlabelled, and 2H and 13C labelled compounds and by ionization energy and appearance energy measurements.The results clearly indicate that at the onset of the reaction, the [C7H14]+· ion formed has the propylcyclobutane structure. At 70 eV electron energy, the [C7H14]+· ion formed is indistinguishable from molecular ions of heptenes.
Mass spectral fragmentation pathways in aminonitrobenzenes. A mass spectrometry/mass spectrometry collision‐induced dissociation study
Authors: Yinon Jehuda 
Published: May 2005

AbstractA collision‐induced dissociation (CID) study of a series of aminonitrobenzenes was carried out using a tandem BB mass spectrometer. Fragmentation pathways were determined in the electron impact mode. Loss of NO· was found to be a major decomposition process. Peaks formed by this process were ‘dished’ in compounds having a nitro group para or ortho to an amino group and Gaussian peaks for compounds having a nitro group meta to an amino group. This loss of NO· with formation of dished peaks occurred for both unimolecular and collision‐induced dissociation pointing to a similar process for both modes of dissociation involving large kinetic energy release.Loss of OH·, due to an ortho effect, was a major decomposition route only in a compound having two nitro groups ortho to the amino group, whilst in other compounds where a nitro group was ortho to an amine this process was smaller because of competitive decomposition processes.Loss of NO2· was a major decomposition route in most compounds and it preceded the cleavage of the aromatic ring.
Electron impact and chemical ionization mass spectra of norbornane/ene di‐exo and di‐endo‐fused 1,3‐oxazin‐2(1H)‐ones and 1,3‐oxazine‐2(1H)‐thiones
Authors: Partanen Tuula , Vainiotalo Pirjo , Stájer Géza , Bernáth Gábor , Pihlaja Kalevi 
Published: May 2005

AbstractMass spectral fragmentations of four norbornane/ene di‐exo‐ and di‐endo‐fused 1,3‐oxazin‐2(1H)‐ones and four 1,3‐oxazine‐2(1H)‐thiones were examined by means of metastable ion analysis, the collision‐induced dissociation technique and exact mass measurement. Under electron impact (EI) conditions all the saturated compounds gave rise to complicated fragmentations, including several rearrangements. For the unsaturated compounds, a retro‐Diels‐Alder (RDA) process was the most favoured fragmentation pathway, which took place with hydrogen rearrangement to yield RDA + H fragments. The EI mass spectra did not permit isomeric differentiation. Under chemical ionization conditions, stereochemical effects were more perceptible, but isomeric differentiation was still difficult.
Competition in the formation of ion–neutral complexes. Expulsion of methane from the molecular ion of acetamide
Authors: Morton Thomas Hellman 
Published: May 2005

AbstractAn ion–neutral complex is a non‐covalently bonded aggregate of an ion with one or more neutral molecules in which at least one of the partners rotates freely (or nearly so) in all directions. A density‐of‐states model is described, which calculates the proportion of ion–neutral complex formation that ought to accompany simple bond cleavages of molecular ions. Application of this model to the published mass spectrum of acetamide predicts the occurrence of ions that have not hitherto been reported. Relative intensities on the order of 0.1 (where the abundance of the most intense fragment ion = 1) ere predicted for [M – HO]+ and [M – CH4]+˙ ions, which have the same nominal masses as the prominent [M – NH3]+˙ and [M – NH2]+ fragments. High‐resolution mass spectrometric experiments confirm the presence of the predicted fragment ions. The [M – HO]+ and [M – CH4]+˙ fragments were observed with relative abundances of 0.02 and 0.04, respectively. Differences between theory and experiment may be ascribed to effects of competing distonic ion pathways.
Electron impact and methane chemical ionization mass spectrometry of trisilanes and trisiloxanes
Authors: Lin Zis‐En , Wu Shi‐Hui , Yao Zhong‐Ping 
Published: May 2005

AbstractThe electron impact and methane chemical ionization mass Spectrometry of fifteen trisilanes and trisiloxanes containing various substituents was studied with the aid of exact mass measurements and metastable ion analyses. Migration reactions of the two kinds of compounds are discussed.
Characteristic ortho‐methoxycarboxylate fragmentation of yerrinquinone and its derivatives on electron impact
Authors: Vairamani M. , Rao B. Nageswara , Pardhasaradhi M. 
Published: May 2005

AbstractMass Spectrometry of a natural product, yerrinquinone, isolated from fungal‐infested Diospyros montana, and isomeric 1‐tetralonecarboxylates has revealed fragmentation pathways characteristic of a methoxy group flanked by a carboalkoxy and a carbonyl group.
[C7H7]+ and [C6H5]+ fragment ions produced from methylphenol isomers by electron impact
Authors: Selim Ezzat T. M. , Fahmey M. A. , Ghonime Hoda S. 
Published: May 2005

AbstractAppearance energies for [C7H7]+ and [C6H5]+ fragment ions obtained from methylphenol isomers were measured at the threshold using the electron impact technique. Different processes for the formation of the ions are suggested and discussed. Metastable peaks were detected and the kinetic energies released were determined. The results indicate that [C7H7]+ ions are formed from metbylpbenois with both benzyl and tropylium structures, whereas [C6H5]+ ions are formed with the phenyl structure at the detected thresholds. Kinetic energies released on fragmentation of reactive [ C7H7]+ and [C6H5]+ ions were used as a probe for the structure of the ions at 70 eV.
252Cf plasma desorption mass spectrometry of some group 8 metal‐containing coordination compounds
Authors: van Veelen Peter A. , Tjaden Ubbo R. , Greef Jan Van Der , Hage Ronald 
Published: May 2005

Abstract252Cf plasma desorption mass Spectrometry was applied to some series of ionic coordination compounds and was demonstrated to yield better results than fast atom bombardment mass Spectrometry. Intra‐ligand fragmentadon was observed regularly, and evidence was also obtained for a fission fragment‐induced methylene transfer reaction.
Mass spectra of some diazadiamides
Authors: Shu Kelun , Liou Yuh‐Liang , Chung Chung‐Sun 
Published: May 2005

AbstractElectron impact mass spectra at nominally low electron energies are reported for a series of diazadiamides. Diazadiamides are of interest because of their use as ligands in transition metal complexes.
Electron impact mass spectra of some nickel(II) and palladium(II) complexes of diphenylphosphinoacetone and 3‐diphenylphosphinobutan‐2‐one
Authors: Hadjieva P. , Petrov G. , Georgiev E. M. 
Published: May 2005

AbstractThe electron impact mass spectral fragmentation of five newly synthesized Ni(II) and Pd(II) complexes of diphenylphosphinoacetone (HL), i.e. trans‐[ NiCl2(HL)2] and trans‐[PdCl2(HL)2] and their enolates cis‐[NiL2] and cis‐[PdL2] and the bis‐enolate of 3‐diphenylphosphinobutan‐2‐one (HLMe), trans‐[Ni(LMe)2], is discussed. The proposed fragmentation mechanisms and the ion structures were confirmed by high‐resolution data for three of the compounds and by Ni and Pd isotope abundances. The results obtained reveal that a mass spectral differentiation is useful in the identification of these types of complexes. Especially with phosphinoenolate bis‐chelates molecular ion peaks are observed.
Electron impact mass spectra of novel tetrahydroimidazo [4, 5, l‐jk] [1, 4]benzodiazepin‐2(1H)‐one derivatives
Authors: Caldwell Gary W. , Kukla Michael J. , Masucci John A. , Breslin Henry J. , Jones William J. , Gauthier Diane A. , Fedde Cynthia L. 
Published: May 2005

AbstractMass spectral fragmentations of nine benzodiazepin derivatives were examined by exact mass measurement and by metastable ion analysis. Under electron impact conditions, all compounds give rise to a molecular ion and ions of m/z 160, 159, 147, 131, 104, 77, 56, 41, and 39. Key fragmentation pathways are discussed for these ions.
Electron impact mass spectra of new 5‐substituted‐2‐amino‐2‐oxazolines
Authors: Bourgeois G. , Jarry C. , Bose J. J. , Deleris G. , Pays E. 
Published: May 2005

AbstractThe electron impact mass spectra of fifteen 5‐substituted‐2‐amino‐2‐oxazolines classified in two series according to the nature of the substituent are discussed. For the 5‐(l‐aryl‐4‐piperazino)methyl compounds the main fragments are derived from the arylpiperazine moiety, whereas for the phenoxymethyl compounds the main ions are derived from the heterocyclic oxazoline ring.
Assignment of isomeric hydroxyhydantoins: Linked‐scan, tandem and high‐resolution studies
Authors: Onisko Bruce , Chang Lydia , Lewis Sydell 
Published: May 2005

AbstractThe mass spectral fragmentation of hydroxyhydantoins was studied by a combination of high‐resolution, linked‐scan and collisionally activated decomposition (CAD) experiments. This endeavor resulted in the structural assignment of four pairs of synthetic hydroxyhydantoin isomers. A key feature in differentiating l‐methyl‐3‐ aryl‐5‐hydroxy‐2,4‐imidazolidinediones from 1‐aryl‐3‐methyl‐5‐hydroxy‐2,4‐imidazolidinediones is that under electron ionizarion (EI) conditions only the 1‐methyl‐3‐aryl‐5‐hydroxy‐2,4‐imidazolidinediones yield the [MeNHCHO]+˙ ion. The analogous [ArNHCHO]+˙ ion (where Ar is the aryl group) was present in the EI spectra of both isomers and its origins are explained by the linked‐scan and CAD experiments performed.
Fragmentations of peptide derivatives depending on the positions of proline in negative‐ion fast atom bombardment mass spectrometry
Authors: Tsunematsu Hideaki , Nakashinia Shizuko , Yoshida Shiro , Yamamoto Magobei , Isobe Ryuichi 
Published: May 2005

AbstractFragmentations of N‐benzyloxycarbonyl‐protected tripeptide ethyl esters, in which changes in the numbers and positions of prolyl residues were observed, were examined by negative‐ion fast atom bombardment mass spectrometry. A significant difference was found among the intensities of the fragment ions formed by cleavage of the benzyloxycarbonyl group, depending on the numbers and positions of prolyl residues in the derivatives. These results suggest that the fragmentations of the peptide derivatives in negative‐ion fast atom bombardment mass spectrometry depend on the conformational differences in the peptide derivatives due to the existence of proline, and permit the prediction of the positions of proline in the peptides.
Ammonia/desorption chemical ionization mass spectrometry of some cyclopentane iridoid glucosides
Authors: Demirev Plamen A. , Handjieva Nedjalka , Saadi Houcine , Popov Simeon S. , Reshetova Olga S. , Rozynov Boris V. 
Published: May 2005

AbstractThe ammonia/desorption chemical ionization (DCI) mass spectra of nine cyclopentane iridoid glucosides were measured. The dependences cf the intensities of different peaks on the structures and stereochemistries of the compounds investigated is discussed.
Reduction processes in fast atom bombardment mass spectrometry: Methylene blue in glycerol‐thioglycerol and glycerol‐nitrobenzyl alcohol matrices
Authors: Kazakoff Clement W. , Rye Robin T. B. 
Published: May 2005

AbstractReduction of the methylene blue cation during fast atom bombardment was studied in glycerol–thioglycerol and glycerol–nitrobenzyl alcohol matrices. The relative abundances of reduced species are significantly lower in a matrix containing 0.2 m thioglycerol in glycerol than they are in pure thioglycerol. Pure 3‐nitrobenzyl alcohol or a glycerol–nitrobenzyl alcohol mixture is a less effective matrix material. These results are discussed in terms of a postulated mechanism for the formation of the reduced dye cation species.
Mass spectra of trimethylsilyl derivatives of naturally occurring flavonoid aglycones and chalcones
Authors: Creaser Colin S. , Koupai‐Abyazani Mohammed R. , Stephenson G. Richard 
Published: May 2005

AbstractElectron impact mass spectra of the trimethylsilyl derivatives of a series of flavonoid aglycones and chalcones are reported. The spectra show prominent ions arising from fragmentation of the trimethylsilyl (TMS) groups. Inter‐actions between adjacent TMS groups, and between TMS groups in the 3‐ or 5‐position (6′‐position for the chalcones) and the C‐ring carbonyl, yield structurally significant ions. Few fragments associated with the retro‐Diels‐Alder cleavage of the C‐ring characteristic of the underivatized compounds, are observed. The TMS derivatives thus provide complementary information for the identification of flavonoid aglycones and chalcones in biological systems.
Accurate mass measurements of organic compounds by an internal standard method for laser desorption/electron impact fourier transform mass spectrometry
Authors: Jiang Chun‐Gang , Sheng Long‐Sheng , An Deng‐Kui 
Published: May 2005

AbstractA method for determining accurate relative molecular masses and elemental compositions of several non‐volatile and thermally labile organic compounds in the source cell was established. The experimental sequence included laser desorption/electron impact Fourier transform mass spectrometry and direct‐mode observation over a narrow mass range. Perfluorotributylamine was used as internal calibrant. Errors were about 1 ppm.
A laser desorption fourier transform mass spectrometric study of dimethyl 8‐acetyl‐3,7,12,17‐tetramethylporphyrin‐2,18‐dipropanoate
Authors: Nguyen T. Hiep , Clezy Peter S. , Willett Gary D. , Paul George L. , Tann John , Derrick Peter J. 
Published: May 2005

AbstractLaser desorption Fourier transform ion cyclotron resonance positive‐ and negative‐ion mass spectra are presented for dimethyl 8‐acetyl‐3,7,12,17‐tetramethylporphyrin‐2,18‐dipropanoate. The 248‐nm laser ionization thresholds for both positive and negative ions are observed to be about 2.5 MW cm−2. The M+˙ molecular ion is assigned to the base peak in the low‐power spectra whereas it is the M−˙ ion for the corresponding anion spectra. Increased intensities of [M + H]+ and [M − H]− are observed with increased laser fluences of up to 38 MW cm−2. At high laser powers the negative‐ion results reveal that a series of carbon‐nitrogen cumulene and polyacetylene cluster ions are formed. Laser evaporation/multiphoton ionization/ and thermal evaporation/electron impact ionization/collision‐induced dissociation experiments carried out on the porphyrin M+˙ and [M + H]+ ions over a range of translational kinetic energies and delay times after acceleration are compared and used to obtain mechanistic and structural information. In contrast to the electron impact experiments, which show only side‐chain cleavage, the laser‐based collision‐induced dissociation experiments reveal that, in addition to side‐chain cleavage, it is possible to cleave the porphyrin ring to various extents depending on the ion translational energy selected.
Study of the rate of methyl loss and the structure of the product ion as a function of the lifetime of the molecular ion of pent‐3‐en‐2‐ol
Authors: Zappey Herman W. , Ingemann Steen , Nibbering Nico M. M. 
Published: May 2005

AbstractThe normalized unimolecular rate constant for loss of a methyl radical from pent‐3‐en‐2‐ol molecular ions with lifetimes ranging from 10−11 to 10−9 s was studied by field ionization kinetics (FIK). The normalized rate curve shows maxima at molecular ion lifetimes of 10−10.5 and 10−10.1 s. Based on results for deuterium and 13C‐labelled pent‐3‐en‐2‐ol, the maximum at 10−10.5 s is ascribed to loss of the methyl group at the 1‐position by a direct cleavage reaction. The maximum at 10−10.1 s is attributed to a 1,2‐H shift‐initiated rearrangement of the molecular ion, which leads to loss of the methyl group at the 5‐ and 1‐positions. The time dependence of the processes in the form of the maxima on the normalized rate curve is discussed qualitatively in terms of a lower critical energy and a tighter transition state of the 1,2‐H shift than those of the direct cleavage reaction. Collision‐induced dissociation of the [C4H7O]+ product ions in combination with FIK provides evidence that at molecular ion lifetimes corresponding to the first maximum on the rate curve protonated crotonaldehyde is formed, whereas protonated methyl vinyl ketone and the butyryl cation are formed at times corresponding to the second maximum.
Unusual neutral and radical losses in 2′‐substituted N‐phenylanthranilic acids on electron impact
Authors: Ramana D. V. , Srinivas R. , Mahalakshmi P. 
Published: May 2005

AbstractUnusual expulsions of [H2O + CO2] from the M+˙ of N‐(o‐carboxyphenyl)anthranilic acid, [H2O + CH2O] from the M+˙ of N‐(o‐methoxyphenyl)anthranilic acid and [H2O + ˙NO2] from the M+˙ of N‐(o‐nitrophenyl) anthranilic acid were observed under electron impact conditions. These processes are stepwise in the corresponding para‐substituted N‐phenylanthranilic acids. The proposed fragmentation pathways and their mechanisms are supported by B/E linked‐scan spectra, collision‐activated decomposition (CAD)–mass‐analysed ion kinetic energy (MIKE) spectra, high‐resolution data, deuterium labelling and chemical substitution.
Analysis of regioisomers of α‐O‐ and α‐N‐substituted oxazolidines using tandem mass spectrometry with electron impact and ammonia chemical ionization
Authors: Lange C. , Cherton J.‐C. , Ladjama D. , Paris C. 
Published: May 2005

AbstractFragmentations induced by collision‐activated dissociation of α‐O‐ and α‐N‐substituted oxazolidines are demonstrated under ammonia chemical ionization (CI) and electron impact (El) conditions. Discrimination of these regioisomers is achieved using either conventional EI mass spectra or daughter ion mass spectra of the protonated molecules under ammonia CI conditions.
Combined gas chromatography/tandem mass spectrometry using laser photodissociation
Authors: Creaser C. S. , McCoustra M. R. S. , O'Neill K. E. 
Published: May 2005

AbstractTwo fibre‐optic interfaces were constructed for laser photodissociation/tandem mass spectrometry using an ion trap spectrometer. These interfaces allow sample introduction from a liquid reservoir, solids probe and gas chromatograph. The laser/ion trap configuration was applied to the analysis of a mixture of alkylbenenes separated by gas chromatography using 573 nm photons.
Dissociation of the tertiary butanol radical cation
Authors: Beveridge William , Garioch Iain W. , Hunter John A. , Johnson Chris A. F. , Parker John E. 
Published: May 2005

AbstractThe ionzation and lowest energy unimolecular dissociation of tert‐butanol were modelled by ab initio molecular orbital methods. The ion is formed on a repulsive surface and gives a methyl radical and protonated acetone as products with the liberation of 0.54 eV of energy. The calculations predict the formation of an electrostatically bound ion‐neutral complex which is also subject to steric constraints.
Synthesis and characterization by fast atom bombardment mass spectrometry of peptides related to the B‐domain of staphylococcal protein A
Authors: Wait R. , James B. , Calder M. R. 
Published: May 2005

AbstractSolid‐phase synthesis was used to prepare several peptides related to Staphylococcal protein A, including a 58‐residue sequence corresponding to the entire B‐domain of the protein. These materials were characterized by a combination of fast atom bombardment mass spectrometry and microchemical methods, including Edman degradation and tryptic digestion. The errors identified included incomplete removal of blocking groups, premature chain termination and the dehydration of an aspartic add residue in the sequence. All of these problems would have been extremely difficult to elucidate by conventional techniques of protein chemistry, and demonstrate that mass spectrometry is the method of choice for verifying the structural integrity of the products of solid‐phase synthesis.
A novel quadrupole, quistor, quadrupole tandem mass spectrometer
Authors: Kofel P. , Reinhard H. , Schlunegger U. P. 
Published: May 2005

AbstractA quadrupole, quistor, quadrupole tandem mass spectrometer allowing selected ion/selected molecule reactions was built. The quistor will be used as a reaction chamber for the study of organic ion‐molecule reactions. Ions are generated in a differentially pumped ion source, quadrupole mass selected and injected into the quistor. The ions are trapped in the quistor by the combined action of a deceleration lens, the presence of helium buffer gas and the quistor RF field. As a first test of the performance of the instrument, the reaction rate constant of the reaction of O2+˙ with methane was measured to be 5 × 10−12 cm3s−1. This is in good agreement with literature values, indicating that the ions are near thermal equilibrium after a few milliseconds of trapping time.
Neutralization‐reionization mass spectrometry: Efficiency of the charge‐exchange process
Authors: Hop C. E. C. A. , Holmes J. L. 
Published: May 2005

AbstractThe efficiency of the neutralization step in neutralization‐reionization mass spectrometry was examined in detail. Coilisional charge exchange between a large number of common organic and inorganic cations and He, N2, H2, SF6, CH4, Xe, O2, cyclo‐C3H6 and NO revealed that the energy defect for the charge‐exchange reaction and the vertical Franck‐Condon overlaps of the projectile ion and its neutral counterpart and those of the target species determine the efficiency.
Mechanisms of repeller‐induced effects in thermospray liquid chromatography/mass spectrometry
Authors: Heeremans C. E. M. , van der Hoeven R. A. M. , Niessen W. M. A. , van der Greef J. , Nibbering N. M. M. 
Published: May 2005

AbstractThe application of a high potential at the repeller electrode, positioned opposite to the sampling cone in order to increase the sampling efficiency, can induce fragmentation in thermospray mass Spectrometry. Until now, this fragmentation has been attributed to collision‐induced dissociation. As a result of studies on the changes in the reagent gas composition in the thermospray buffer ionization mode as a function of the repeller potential in the positive‐ion mode, it appears that three different processes are occurring. At low repeller potentials, the thermospray mass spectra of the eluent are determined by the proton affinities and the concentrations of the various solvent constituents, and the stabilities of the formed cluster ions under the ion source conditions. With an increase in the repeller potential, collision‐induced dissociation of the background ions starts to occur. When the kinetic energy of the ions and cluster ions becomes high enough, endothermic proton transfer and solvent‐switching reaction pathways are opened. For the relatively volatile analytes studied, e.g. aniline, acetophenone, benzaldehyde and benzoic acid, similar effects are observed.