bluuebunny/crossref_metadata_2025 huggingface dataset:
Determination of the fragmentation mechanisms of organophosphorus ions by H2O and D2O atmospheric‐pressure ionization tandem mass spectrometry II—dialkyl alkylphosphonate ions
Authors: Snyder A. Peter , Harden Charles S.
Published: May 2005

Diethyl methylphosphonate (DEMP), diisopropyl methylpbosphonate (DIMP), diethyl isopropylphosphonate (DEIP) and diethyl ethylphosphonate (DEEP) were characterized by H2O and D2O atmospheric pressure ionization tandem mass Spectrometry (API‐MS/MS). Collision‐induced dissociation (CID)/fragmentation pathways included alkyl ions by direct cleavage, alkyl radical and water loss processes and McLafferty and McLafferty‐type rearrangements by six‐ and five‐membered ring transition states, respectively. D2O API proved particularly useful in that certain decomposition pathways (i.e. water and methanol neutral losses) had a statistical distribution as to the loss of an acid deuteron and proton(s). This phenomenon was manifested by two pairs of ions in the D2O API daughter‐ion mass spectrum for each phosphonate compound (e.g. both m/z 79/80 and 65/66 for DEMP and DIMP). The observed ion intensity ratios for these pairs of ions served as guides in the determination of their predicted ion relative abundance ratios and CID decomposition pathways.

Water neutral losses as opposed to ether and alcohol neutral losses were favored for most of the protonated organophosphonate molecular ion decomposition schemes.
Isomerization and fragmentation of aliphatic ether radical cations: Interconversion of distonic ions and cyclopropane intermediates
Authors: Audier Henri Edouard , Sozzi Georges , Milliet Arielle , Hammerum Steen
Published: May 2005

The reactions of propyl ether radical cations close to threshold are initiated by (reversible) formation of γ‐disitonic isomers, R\documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\rm O}\limits^ + $\end{document} (H)CH2CH2CH2·. The three methylene groups in these ions lose their positional identity by ring closure/ring opening via [cyclopropane + alcohol]+· intermediates. Extensive hydrogen exchange occurs within the C3‐chain. When R is not methyl the γ‐distonic isomer undergoes further intramolecular hydrogen atom transfer reactions that lead to formation of α‐ and β‐distonic ions. The α‐distonic isomers expel ethyl and propyl radicals by CO bond cleavage.
Single and double hydrogen migration in the fragmentation of 3‐methyl‐2‐butyl trifluoroacetate
Authors: Fǎrcaşiu Dan , Miller Glen , Hsu Chang S.
Published: May 2005

Three of the main oxygen‐containing fragments resulting from 3‐methyl‐2‐butyl trifluoroacetate (11) had been identified previously as the 1‐triflnoroacetoxyethyl cation (m/z 141, 12, product of simple cleavage), and the products of single (m/z 142) and double hydrogen transfer (m/z 143, protonated ethyl trifluoroacetate). Collisionally activated dissociation of m/z 142 and the isotopomers resulting from 11‐2‐d, 11‐1‐d3, 11‐5,6‐d6, and 11‐18O2 has established that m/z 142 is the oxygen protonated 1‐trifluoroacetoxyethyl free radical (17) formed by hydrogen shift irom a γ‐methyl group to oxygen in the molecular ion, rather than in a complex (18) between 12 and the 2‐propyl free radical, as expected based on a mechanistic model existing in the literature. The second hydrogen transferred originates in the other γ‐methyl group; its migration may occur, but does not have to, in the complex between 17 and a molecule of propene, prior to dissociation of the two fragments. Collision‐activated dissociation has now shown that the m/z 140 ion observed in the spectrum is the molecular ion of vinyl trifluoroacetate, possibly formed by a hydrogen transfer from 12 to the 2‐propyl radical in the complex 18. The hydrogen migration to oxygen exhibits no isotope effect, whereas the transfers to carbon atoms exhibit small primary and α secondary kinetic isotope effects. Exclusive migration of the tertiary hydrogen from C(3) occurs in the formation of 2‐methylbutene cation radical (m/z 70) from the molecular ion. The hydrocarbon ion fragments and the heteroatom‐containing fragments are formed from 11 by disjoint pathways.
Ring opening reaction of protonated polyfluorinated benzenes in the gas phase. A theoretical MNDO study
Authors: Hrušák Jan
Published: May 2005

The MNDO calculations of protonated polyfluorobenzenes [Ph‐Fn]H+ indicate the possibility of a relatively free migration of the hydrogen proton with energy barriers of 125–145 kJ mol−1. At a higher degree of substitution (n) the protonation of the ipso carbon atom occupied by fluorine becomes energetically feasible, along with analogous migrations of fluorine, which, however, are energetically the most advantageous (ΔEa ∼ 230 kJ mol−1). In addition to bridged fluoronium ions, relatively stable cyclic intermediates were also found, which make possible a rearrangement to the difluoromethylenecyclopentadienyl cation and thus the elimination of CF2 observed in collision‐induced dissociation mass spectra.
Anomalies in the molecular ion region in the electron impact mass spectra of α‐ and β‐hydroxyesters
Authors: Konopski Leszek
Published: May 2005

In 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

The 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

A 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

Mass 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

An 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

The 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

Mass 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

Appearance 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

252Cf 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

Electron 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

The 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

Mass 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

The 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

The 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

Fragmentations 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

The 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

Reduction 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

Electron 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

A 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

Laser 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

The 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

Unusual 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

Fragmentations 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

Two 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

The 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

Solid‐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

A 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

The 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.
Electron impact mass spectrometry of praziquantel derivatives
Authors: Martinez Roberto , Rubio Manuel F. , Rosado A. Raul Cetina , Ibarra Monica B. Perez
Published: May 2005

The electron impact mass spectra of a series of compounds related to the anthelmintic substance praziquantel are described in sufficient detail to permit their assay in biological samples by selected ion monitoring.
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

The 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.
Ionization energies of homologous organic compounds and correlation with molecular size
Authors: Holmes J. L. , Lossing F. P.
Published: May 2005

The empirical relationship IE ∝︁ 1/n, between the ionization energy (IE) and molecular size (as represented by the number of atoms, n) in homologous series of organic compounds has been confirmed for n‐alkanes, alkyl halides, cyclic ethers and alkyl‐subsiituted cycloalkanes. For each series, the plot of IE vs. 1/n produces a line of characteristic slope. The only exception is the cycloalkanes themselves, whose IE values (from C3 to C8) are closely similar. The possible relationship between the IE, the polarizability of the molecules and the energy of the highest occupied molecular orbital is briefly discussed.
Formation of charged clusters during electrospray ionization of organic solute species
Authors: Meng Chin Kai , Fenn John B.
Published: May 2005

Electrospray dispersion of solutions into a bath gas can produce solute ions with many charges per molecule. In contrast to such multiple charging, it can also result in ‘fractional charging’ by which cluster ions are formed with more than one solute molecule per charge. Examples of such fractional charging or clustering are presented and discussed. In the case of arginine solutions, which are reported in some detail, ion masses corresponding to clusters containing as many as 24 solute molecules and up to four charges were identified. The number and size of these cluster ions increased markedly with increase in the initial solute concentration. When co‐solutes consisting of acids, salts or bases were present, at up to millimolar concentrations in the initial solution, clustering was often strongly suppressed, especially by strong acids and their salts. This clustering phenomenon not only provides insight into the chemistry of solute precipitation in solution, but also offers a means of producing new kinds of clusters for experimental studies.
Mass spectra of 2‐ and/or 6‐alkyl‐3‐hydroxypyridines
Authors: Lin Shaw‐Tao , Tien Ling‐Ling , Kuo Yueh‐Hsiung , Shih Kae‐Shyang
Published: May 2005

The mass spectra of 2‐ and/or 6‐aIkyI‐3‐hydroxypyridines were measured. The fragmentation processes include the loss of 1, 28 and 29 u and RCN from the molecular ions. Among the characteristic ions, the [M – 1]+ ions are the base peak for all of the ethyl‐containing pyridines. According to a labelling study, the hydrogen on the β‐caroon is the major contributor to the formation of [M – 1]+.
Electron impact ionization mass spectrometry and tandem mass spectrometry of phenylalkylpyridazines
Authors: Pittenauer Ernst , Allmaier Günter , Schmid Erich R. , Stanek Wolfgang , Heinisch Gottfried
Published: May 2005

The mass spectrometric fragmentation behaviour of pyridazine and four monosubstituted derivatives containing a pbenylalkyl side‐chain (3‐ and 4‐benizylpyridazine, 3‐ and 4‐(2‐pbenylethyl)pyridazine) was investigated. In the electron impact ionization mess spectra of the 3‐substituted compounds abundant [M – H]+ peaks are observed. This allows a clear distinction between 3‐ and 4‐substituted pyridazines, as the spectra of the latter isomers show only very weak [M – H]+ signals. The stability of [M – H]+ ions derived from 3‐alkylpyridazines (deduced from only the very low abundance of further fragment ions) gives strong evidence for a cyclic structure of these ions. One fragmentation pathway typical of the parent pyridazine, the [M ‐ N2] fragmentation, was not detectable with any of the phenylalkylpyridazines investigated. Instead, loss of HCN, H3CN+ and N2H+ was observed. An interesting fragmentation, observed with 3‐(2‐phenylethyl)pyridazine, is the loss of +CH3 from the molecular ion and also from the [M – H]+ ion.
Stereochemical effects in mass spectrometry. Part 10‐reaction mass spectrometry of cyclic glycols and monosaccharides with methylene chloride as reagent gas
Authors: Tu Ya‐Ping , Yang Guan‐Yu , Liu Yu‐Hua , Chen Shao‐Nong , Chen Yao‐Zu
Published: May 2005

The reaction mass spectrometry of cyclic glycols and monosaccharides with methylene chloride as reagent was studied. In the presence of ammonia, it was found that methylene chloride reacted stereoselectively with the quasi‐molecular ions of cyclic glycols and monosaccharides to form characteristic ions, by comparison of the relative abundances of which the stereoisomers of cyclopentane‐l,2‐diols and cyclohexane‐l,2‐diols and some monosaccharides could be definitely distinguished.
Electron impact mass spectra of 5,5‐bis(carboethoxy)‐1,3‐dioxanes
Authors: Horn Mihai , Mager Sorin , Palibroda Nicolae , Culea Monica
Published: May 2005

Electron impact‐induced fragmentations of 2‐substituted 5,5‐bis(carboethoxy)‐l,3‐dioxanes were studied by exact mass measurements and metastable ion analysis. The substituent R on C(2) of the heterocyclic ring has little influence on the principal cleavage reactions. Elimination of CH2O/CO and C2H4O/C2H4/C2H5OH are common fragmentations for ions containing the 1,3‐dioxane moiety or the OC2H5 group, respectively. The abundant ions at m/z 173 and 127 serve as structural probes for the class of compounds studied. Primary fragmentations implying the ester function are of little importance.
Dithia[3.3 ]phanes. 4—mass spectrometry of some dithia[3.3]‐naphthalenophanes1
Authors: Kus̀ Piotr
Published: May 2005

The mass spectral fragmentation of 23 dithia [3.3]naphthalenophanes is discussed. The most characteristic species for these compounds are the M+ ion and ions at m/z 115, 135 (or 136), 141, 155 (or 154) and 185.
Reactions of ions of iron and cobalt acetylacetonates with macrocyclic thioiurea derivatives in the gas phase
Authors: Zagorevskii D. V. , Nekrasov Yu. S. , Timofeev O. S. , Gren' A. I.
Published: May 2005

Ion‐molecule reactions of (acac)2M+ ions (M = Fe, Co) with macrocyclic thiourea derivatives (L) were studied. The formation of acacML+ and acacM(L – H)+ were observed. AcacM(L – H)+ ions arise from loss of the hydrogen atom of the NH group. The ion peak intensity ratios, Z = [acacML+]/[acacM(L – H)+], for M = Co are higher than those for M = Fe, in accordance with the easier reduction of Co(III) to Co(II) than that of Fe(III) to Fe(II). It is proposed that the metal‐containing ions preferentially attack the thiourea fragment of the macro‐cycles studied.
Mass spectrometry of π‐complexes of transition metals 38—keto‐enol tautomerization of molecular ions of acetyl‐ and propionyl‐ferrocenes in the gas phase
Authors: Zagorevskii Dmitrii V. , Volkova Tatyana V. , Yakushin Sergey O. , Antipov Boris G. , Nekrasov Yurii S.
Published: May 2005

Fragmentation of the acetyl‐ and propionyl‐ferrocenes under electron impact together with the rupture of CCO bonds, characteristic of ketones, also includes elimination of water and migration of the OH group to the central metal atom, which is due to keto‐enol tautomerization of the acyl group in molecular or fragment ions.
On‐target deuteration technique in time‐of‐flight 252Cf plasma desorption mass spectrometry
Authors: Bondarenko P. V. , Zubarev R. A. , Knysh A. N. , Rozynov B. V.
Published: May 2005

A new on‐target deuteration technique in plasma desorption mass Spectrometry (PDMS) is proposed, involving replacing labile hydrogen atoms in a molecule with deuterium atoms. This technique is very simple and allows direct comparison of spectra before and after deuteration for the same probe. The utility of the deuteration procedure in PDMS has been demonstrated in obtaining additional information on the structure of a molecule and its fragments and on the mechanism of quasi‐molecular ion formation.
Mass spectral study of substituted methyl (E)‐and (Z)‐cinnamates under 1,2‐dibromoethane chemical ionization
Authors: Vairamani M. , Saraswathi M. , Rao G. K. Viswanadha
Published: May 2005

Dibromoethane chemical ionization mass spectra of ten pairs of methyl (E)‐ and (Z)‐cinnamates were studied. C2H4Br+ ion forms stable adducts with E‐isomers and the adducts of Z‐isomers show preferential loss of methanol. The observed results suggest that the probability of ring alkylation is greater than with the carbonyl group.
Behaviour of isomeric methyl ethyl and ethyl methyl halosuccinates under electron impact. Elimination of a halogen atom by a multi‐step mechanism
Authors: Bornstein D. , Mandelbaum A. , Vidavsky I. , Domon B. , Mueller D. , Richter W. J.
Published: May 2005

The electron impact mass spectra of isomeric methyl ethyl and ethyl methyl halosuccinates (X = Cl and Br) are surprisingly different. Only the isomers with the ethyl group remote from the halogen give rise to [M ‐ X]+ ions. A low‐energy collision‐induced dissociation study of deuterium‐labelled analogues of the former isomers indicates that the [M ‐ X]+ ions are mixtures of protonated methyl ethyl maleate (major component, > 85%) and fumarate, and the loss of the halogen atom is a multi‐step process including at least two specific hydrogen transfers. Migration of a β‐hydrogen atom to the carbonyl oxygen within the ethoxycarbouyl group produces a primary radical site in a distonic intermediate which, by subsequent abstraction of a hydrogen atom from C(3), triggers the ejection of X from C(2) with concomitant double bond formation. Whereas in the other isomer an [M ‐ X]+ ion is absent or negligible, a characteristic double loss of C2H4 and CO2 is observed.
Field desorption mass spectrometry, fast atom bombardment mass spectrometry and fast atom bombardment tandem mass spectrometry of echinacoside, the main caffeoyl‐glycoside from Echinacea angustifolia roots (Asteraceae)
Authors: Facino Roberto Maffei , Sparatore Anna , Carini Marina , Gioia Bruno , Arlandini Emanuele , Franzoi Luigi
Published: May 2005

The mass spectral fragmentation of echinacoside, a pharmacologically active caffeoyl‐glycoside isolated from Echinacea angustifolia roots, has been investigated using different soft‐ionization techniques, field desorption and fast atom bombardment (positive and negative ions) mass Spectrometry. Both ionization modes are successful in molecular mass determination and furnish approximately equivalent structural information. A fast atom bombardment tandem mass spectrometry approach (negative ions) was developed for the study of the fragmentation pathways and for the detection of echinacoside in crude plant extracts. The results demonstrate the usefulness of this technique for the rapid search of this important caffeoyl‐glucoside directly in natural complex matrices.
Gas chromatographic/mass spectrometric identification of some organic compounds and odours in poultry wastes
Authors: Sturaro Alberto , Parvoli Giorgio , Doretti Lucio , Daolio Sergio
Published: May 2005

Air and waste samples coming from poultry breeding farms have been analysed by means of thermal desorption coupled to the gas chromatographic/mass spectrometric technique. The solid samples not only showed the presence of organic compounds such as acids, sulphides, benzopyrroles and phenols originated by anaerobic biotransfor‐mation of the natural products, but also the occurrence of anti‐oxidant substances: 2,6‐di‐tert‐butylcresol, 2,6‐di‐tert‐butylphenol and two of their oxidation derivatives. In the air, four artificial benzoquinones were detected, two of which had already been identified in the solid waste. In this work, the mechanism by which oxidized compounds are formed, is suggested.
Fragment‐molecule adduct ion formation in the mass spectra of cyclic N‐acetylamines and related nitramines
Authors: Burrows Elizabeth P.
Published: May 2005

Mass spectra of seven related N‐heterocyclics, introduced by direct exposure probe, were determined in electron impact (EI) and positive‐ and negative‐ion chemical ionization (PCI and NCI) modes. Proton adducts were the predominant molecular ion species in the EI and PCI modes. In addition, a variety of fragment–molecule adduct ions were observed for each compound in one or more of the modes. The propensity of 1,3,5‐trinitrohexahydro‐1,3,5‐triazine for fragment–molecule adduct formation was high in all three ionization modes. Fragmentation processes were documented by collision‐induced dissociation experiments.
Improved metal vapor neutralization and resolution in neutralization‐reionization mass spectrometry
Authors: Drinkwater Donald E. , Fura Aberra , Zhang Mei‐Yi , McLafferty Fred W.
Published: May 2005

Increased differential pumping improves the simultaneous sequential operation of ion‐beam neutralization, neutral dissociation, neutral product ionization, and ion product dissociation for neutralization‐reionization (NR) mass spectrometry. Following Porter's developments for neutralized ion‐beam spectroscopy, instrument modifications allow a wider variety of metals (vaporization up to 800 °C) to be used for neutralization and eliminate multiplier instabilities seen previously using neutralization metals such as sodium. Irreproducibility of recovered precursor ion signals using metal vapors of low ionization potential has been traced to mercury background. Double focusing of the ionized neutral beam yields NR mass spectra of the highest resolution yet reported.
Comparative electron impact mass spectra of new 5‐benzylidene‐4,5‐dihydro‐(2H)‐pyridazin‐3‐ones and 4‐benzylidene‐4,5‐dihydrooxazin‐6‐ones
Authors: Chabard Jean‐Louis , Taoufik Jamal , Couquelet Jacques , Tronche Pierre
Published: May 2005

Electron impact mass spectra are reported for a series of 5‐benzylidene‐4,5‐dihydro‐(2H)‐pyridazin‐3‐ones and 4‐benzylidene‐4,5‐dihydrooxazin‐6‐ones.
Study of selected ions in the ammonia desorption chemical ionization mass spectra of peracetylated gentiobiose and two isotopically labelled peracetylated gentiobioses
Authors: Peltier John M. , Smith Richard W. , Maclean David B. , Szarek Walter A.
Published: May 2005

The ammonia desorption chemical ionization (NH3‐DCI) mass spectra of peracetylated gentiobiose (1) and two isotopically labelled gentiobioses (2 and 3) were examined. Compound 2 is labelled with trideuteroacetyl groups in the non‐reducing moiety and 3 with trideuteroacetyl groups in the reducing moiety. It is shown that the [M + NH4 – 42]+ ion is not formed direct from [M + NH4]+ by loss of ketene but appears to be formed by way of a nucleophilic acyl substitution reaction resulting in a neutral species which complexes with NH4+. The disaccharides undergo cleavage at either side of the glycosidic oxygen joining the two sugar residues, a process which is accompanied by addition of H or CH3CO to afford neutral species which complex with NH4+. The structures of the ions resulting from H transfer have been inferred by comparison of their mass‐analysed ion kinetic energy (MIKE) spectra with MIKE spectra of the [M + NH4]+ ions of compounds of established structure. A ring fragmentation reaction of 1, 2 and 3 is reported.
Methylene chloride chemical ionization of fumaric and maleic acids and their esters
Authors: Tu Ya‐Ping , Liu Ya‐Qin , Yang Guan‐Yu
Published: May 2005

The chemical ionization (CI) mass spectrometry of fumaric and maleic acids and their esters with methylene chloride as reagent gas is described. The introduction of methylene chloride to the CI(CH4) plasma led to the formation of new characteristic ions in addition to the protonation and the subsequent fragmentation, revealing diagnostic information on the configuration of geometrical isomers. The new characteristic ions have been found to arise from the addition of the reactant ion of methylene chloride, [CH2Cl]+, to the substrates and, for higher dialkyl esters, from the further McLafferty rearrangement of the adduct ion [M + CH2Cl]+.
Study of the reactions and reaction mechanisms of phosphine (Ph3P) and of phosphite ((PhO)3P) with sulphur (S8)
Authors: Zhang Haiying , Peng Jiarou , Peng Shiqi , Wu Guowang , Dai Duenhua , Zhu Guozheng
Published: May 2005

The reactions of sulphur with phosphine and phosphite were investigated by low‐energy electron impact mass spectrometry and fast atom bombardment mass spectrometry. A previously reported mechanism of the Ph3P–S8 reaction was supported and a possible mechanism for the (PhO)3P–S8 reaction is proposed.
Mass spectral study of derivatives of 2‐aryloxy‐2‐methylpropanoicacids
Authors: Vairamani M. , Kumar K. V. Siva , Rao G. K. Viswanadha
Published: May 2005

Electron impact mass spectra are reported for series of 2‐aryloxy‐2‐methylpropanoic acids, 2‐aryloxy‐2‐methylpropanamides and N‐phenyl‐2‐aryloxy‐2‐methylpropanamides. Fragmentation mechanisms are discussed on the basis of deuterium labelling, meastable ions and accurate mass measurements.
Gas‐phase chemistry of the methyl carbamate radical cation, H2NCOOCH. II—A test case for ion structure assignment
Authors: McGibbon Graham A. , Kingsmill Carol A. , Terlouw Johan K. , Burgers Peter C.
Published: May 2005

The unimolecular chemistry of the methyl carbamate radical cation, H2NCOOCH, 1, has been further investigated by a combination of mass spectrometry‐based experiments (metastable ion (MI), collisional activation (CA), collision‐induced dissociative ionization (CIDI), neutralization‐reionization (NR) Spectrometry and 2H labelling) and ab initio molecular orbital calculations, executed at the MP3/6–31G*//4–31G level of theory and corrected for zero‐point vibrational energies. Apart from the previously located maxima, i.e. H2NCOOCH3+·, 1, the distonic ion H2NC(OH)OCH3+·, 2, hydrogen‐bridged ions [H2NCO…︁ H…︁OCH2]+·, 5, and [H2NCHO…︁…︁H…︁OCH]+·, 7, there exist at least two other equilibrium structures, viz. the iminol ion HNC(OH)OCH, la, and the hydrogen‐bridged species [H2CO…︁H…︁N(H)COH], 6a, which is closely related to ion 5. Although the iminol ion la lies only 30 kJ mol−1 above 1, our calculations indicate that the barriers for its formation either directly from ionized methyl carbamate 1 via a 1,3‐hydrogen shift or indirectly via 1,4‐hydrogen shifts from the distonic ion 2 are too high to allow the iminol ion to be involved in the unimolecular chemistry of ionized methyl carbamate. This explains the earlier observation that there are no H‐D exchange reactions prior to decomposition of ionized labelled methyl carbamate, in contrast to the related ion methyl acetate. However, attempts to generate the iminol ion by loss of CH3CN from CH3CHNNHCOOCH3 produced the more stable distonic ion 2 instead, but it proved very difficult to assign its structure unequivocally because 2 can rapidly interconvert with 1 and so virtually identical dissociation characteristics ensue. Only by integration of results obtained from many experiments and from ab initio calculations could structure 2 be assigned. The distonic ion 2 can undergo two transformations: after stretching of the COCH2 bond the incipient formaldehyde can migrate within the electrostatic field of ionized hydroxyaminocarbene to the OH end to generate 5, but it can also migrate to the NH end to generate 6a. This explains the previous puzzling observation that H2NCOOCD forms both CD2OD· and CD2OH· in CA and NR experiments. The calculations and experiments indicate that, although the ion is exceedingly difficult to characterize, the distonic ion 2 is the key intermediate for all the observed dissociations of methyl carbamate.