bluuebunny/crossref_metadata_2025 huggingface dataset:
Suppression of matrix ions in ultraviolet laser desorption: Scanning electron microscopy and raman spectroscopy of the solid samples
Authors: Chan T‐W. Dominic , Colburn A. W. , Derrick Peter J. , Gardiner Derek J. , Bowden Michael
Published: May 2005

Suppression of low‐mass ion peaks in matrix‐assisted ultraviolet laser desorption has been found to occur at low matrix‐to‐analyte molar ratios when using nicotinic acid as matrix, independent of the angle of illumination. Microscopic Raman scattering spectroscopy has been employed to investigate the matrix–analyte solid‐state composition. The matrix‐to‐analyte molar ratios employed in preparing the solutions are reliable guides to the relative amounts of matrix and analyte molecules in the solid crystals, given the method of sample preparation employed involving drying under a stream of nitrogen. A qualitative model based on the proton supply‐and‐demand argument is tentatively proposed to explain the suppression phenomenon.
Advantages of high‐resolution and high‐mass range magnetic‐sector mass spectrometry for electrospray ionization
Authors: Chapman John R. , Gallagher Richard T. , Barton E. C. , Curtis Jonathan M. , Derrick Peter J.
Published: May 2005

Electrospray ionization (ESI) mass spectra have been measured on a magnetic‐sector double‐focusing mass spectrometer for a number of proteins and peptides. It is pointed out how in theory raising the mass resolution of a mass spectrometer from 800–1000 to 2400–3000 significantly increases the precision with which the envelope of isotopic peaks of a protein ion (or other organic ion) can be defined, particularly at higher masses. Better definition of the isotopic envelope ought to lead to higher precision in the experimental determination of molecular mass, which has been demonstrated. It is shown how ESI mass spectra of high‐mass molecules are significantly less congested at higher m/z values, so that for these molecules (RMM > 40 000) there is an advantage in being able to record peaks at higher m/z values (m/z > 2000) representing ions with fewer charges. Fragmentation of a small peptide in the ESI source has been found to provide sequence information.
Identification of aminophospholipid stereomers by positive‐ion fast atom bombardment combined with collisional activation mass‐analysed ion kinetic energy analysis and high‐performance liquid chromatography
Authors: Chen Su , Menon Giampaolo , Traldi Pietro
Published: May 2005

Two methods for the identification of aminophospholipid stereomers are described. After a chemical derivatization, 9‐fluorenylmethoxycarbonyl derivatives of diacyl‐sn‐2‐ and diacyl‐sn‐3‐phosphoserine and diacyl‐sn‐2‐ and diacyl‐sn‐3‐phosphoethanolamine can be characterized by positive‐ion fast atom bombardment combined with collisional activation mass‐analysed ion kinetic energy analysis based on the differentiation of relative abundances [M + H + diethanolamine − 89]+ and [M + H]+ fragments derived from [M + H + diethanolamine]+ ions, the protonated solvated molecules, and normal phase high‐performance liquid chromatography on the basis of different elution times of the derivatives of the aminophospholipid stereomers on an aminopropyl‐bonded column.
Contribution of mass spectrometric techniques to the structure elucidation of antibiotic GE2270A, a novel inhibitor of bacterial protein synthesis
Authors: Colombo L. , Tavecchia P. , Selva E. , Gallo G. G. , Zerilli L. F.
Published: May 2005

GE2270A is a novel antibiotic active against Gram‐positive bacteria and anaerobes. Its structure originates from a peptidic backbone, the amino acids of which have been modified to produce a macrocycle and a side‐chain. It contains a heterocyclic chrornophonc system, a number of thiazoleamino acids and three unmodified natural amino acids. The structure [relative molecular mass (RMM) 1289] was determined using various spectroscopic techniques, of which fast atom bombardment mess spectrometry, gas chromatography/mass spectrometry, desorption chemical ionization mass spectrometry and fast atom bombardment tandem mass spectrometry played an important role. The mass spectrometric approach was applied to the intact molecule and to the various hydrolysis products, including the chromophoric part (RMM 634).
Mass spectrometric investigation of some macrocyclic and macroacyclic compartmental schiff bases
Authors: Guerriero P. , Tamburini S. , Vigato P. A. , Seraglia R. , Traldi P.
Published: May 2005

The mass spectrometric behaviour of four macroacyclic and five macrocyclic Schiff bases using two ionization methods (electron impact and fast atom bombardment) was studied in detail with the aid of mass‐analysed ion kinetic energy (MIKE) spectrometry. It was possible to propose a common electron impact‐induced decomposition pattern for the acyclic compounds, whereas for the cyclic compounds, analysed by fast atom bombardment, peculiar fragmentation routes occurred, which were strongly dependent on the macrocyclic structure and on the different side‐chains.
Ion–molecule reactions in the gas phase. XVIII.—nucleophilic substitution of diastereomeric norborneols, norbornyl acetates and benzoates under ammonia chemical ionization
Authors: Despeyroux Dominique , Cole Richard B. , Tabet Jean‐Claude
Published: May 2005

The comparative behaviour of the endo‐ and exo‐norborneols and diastereomeric derivatives (acetates and benzoates) towards the NH3/NH4+ system was investigated. It appears that the proton affinity (PA) of the substrate relative to Pa(NH3) strongly influences competition between the protonation and nucleophilic substitution processes yielding the MH+ and [M + NH4 − H2O]+ ions, respectively. Tandem mass spectrometry was used to compare collision‐activated dissociation spectra of [M + NH4 − H2O]+ with those of analogous endo‐ and exo‐norbornylamines protonated in the source. This demonstrates that an SNimechanism occurs specifically for the isomeric norborneols; in contrast, for acetates and benzoates, stereospecific SNi and SN2 pathways take place for exo and endo derivatives, respectively. This particular behaviour is explained by considering the steric effect induced by the endo‐H at C(6). In addition, the competitive decompositions of [M + NH4 – H2O]+ into NH4+ and [C7H11]+ daughter ions are consistent with the formation of a proton‐bound complex intermediate. The observed stereochemical effects for these dauther ions are rationalized by means of arguments based on the estimated heats of formation of the transition states, which is lower for the exo‐norbonyl protonated amine, consistent with anchimeric assistance, rather than a stepwise pathway which is proposed for the endoisomer.
Radical‐induced aromatic substitution between benzoyl peroxide and benzenediols in the gas phase characterized by mass spectrometry
Authors: Tu Ya‐Ping , Liu Ya‐Qin
Published: May 2005

A radical‐induced aromatic substitution mechanism for the reaction between benzoyl peroxide and benzenediols in the gas phase was characterized by mass spectrometry. The benzoyloxy radical produced from the homolysis of benzoyl peroxide associates at its carbonyl group with the phenolic hydroxyl group. The pairing tendency of the unpaired electron on the oxygen of the radical induces electron transfer along the hydrogen bond, which results in the rupture of the OH bond of the phenol and aromatic substitution at the ortho position of the benzoyloxy radical. Supporting evidence for the mechanism was obtained by isotope labelling.
Skeletal rearrangement of metastable molecular ions of monosubstituted benzyl cyanides prior to elimination of [H, C, N], [H2, C2, N]˙ and [H, C, N, O]
Authors: Molenaar‐Langeveld Tineke A. , Fokkens Roel H. , Ingemann Steen , Nibbering Nico M. M.
Published: May 2005

The mechanism of [H, C, N) loss from metastable molecular ions of benzyl cyanides containing an F, Cl, CF3, CH3, HO or CH3O substituent was investigated by deuterium and 13C labelling. The elimination of [H, C, N] from the metastable molecular ions of benzyl cyanides substituted with F, CI or CF3 is preceded by randomization of the hydrogen atoms and tc some extent by a skeletal rearrangement of the CH2CN function, which leads to incorporation of the benzylic carbon atom in 20–30% of the expelled [H, C, N] molecules. By contrast, the metastable molecular ions of benzyl cyanides with a CH3, HO or CH3O substituent eliminate [H, C, N] molecules containing the intact cyano function and predominantly a hydrogen atom from fhe substituent. This preference for a hydrogen atom from the substituent irrespective of its position with respect to the CH2CN function is proposed to be the result of a rearrangement of the meta and para isomers to the ortho isomer possibly involving norcaradiene/cycloheptatriene radical cations. In addition to (H, C, N] loss, the metastable ions of o‐, m‐ and p‐methoxybenzyl cyanide eliminate a [H2, C2, N]˙ radical consisting of the cyano function and the carbon atom and mainly two of the hydrogen atoms from the methoxy substituent. The occurrence of this reaction from the metastable ions of m‐ and p‐methoxybenzyl cyanide supports the indicated isomerization to the ortho configuration prior to dissociation. This skeletal rearrangement is manifested also in the loss of [H, C, N, O] from the metastable ions of m‐andp‐hydroxybenzyl cyanide.
Proton and hydrogen atom transfers between ionized enols and neutral aldehydes
Authors: Audier Henri‐Edouard , Bouchoux Guy , Mourgues Philippe , Penaud‐Berruyer Florence
Published: May 2005

The rates of proton transfer and hydrogen atom abstraction between ionized enols [CH2CHOH]+˙ and [CH2C(CH3)OH]+˙ were measured by Fourier transform ion cyclotron resonance Spectrometry. It was observed that proton transfer is favoured by its high rate even when it does not reach the limiting collision rate. When a competition is in principle possible between H+, H˙ and H− transfers, only the former process is observed. This phenomenon and the low efficiency of hydrogen atom abstraction are discussed in terms of the potential energy profile, where the stability of the intermediate complexes plays a critical role.
Single‐photon and multi‐photon ionization of infrared laser‐desorbed biomolecules
Authors: Köster Claus , Grotemeyer Jürgen
Published: May 2005

Results from investigations of the 10.5 eV photoionization of infrared laser‐desorbed, jet‐entrained peptides are presented. The instrumental set‐up for vacuum ultraviolet generation and the coupling to a reflectron‐time‐of‐flight mass spectrometer is described. Single‐photon ionization makes possible the investigation of molecules without any chromophoric group. Examples of the application of this ionization method to di‐ and tripeptides containing glycine, alanine, leucine and proline are shown. A comparison between single‐ and multi‐photon ionization of tryptophan and tryptophar‐containing peptides up to four amino acids is made and discussed in terms of soft ionization and generation of fragment ions.
Evaluation of methane negative ion chemical ionization mass spectra of polycyclic aromatic hydrocarbons and related compounds
Authors: Daishima Shigeki , Lida Yoshio , Shibata Akihiro , Kanda Fujihiro
Published: May 2005

Negative ion chemical ionization (NICI) mass spectra with methane as reagent gas and the ion abundance ratios of the negative to the positive base peak for 51 polycyclic aromatic hydrocarbons and related compounds were measured and evaluated for highly sensitive detection and isomer differentiation. Either [M  H]−, M−˙ or MH− was the base peak, except for one compound with [M  H2]−˙ as its base peak. The numbers of compounds with [M  H]−, M−˙ or MH− as their base peaks were 17, 26 and 7, respectively. Many of the compounds with [M H]− as the base peak had an aliphatic part in their structure. The average value of N/P (negative/positive ion abundance ratio at the base peaks) was < 1. Many of the compounds with M−˙ as the base peak had a relatively high electron affinity. A correlation between electron affinities and ion abundances was found. In most cases, the N/P ratios were > 1, and even reached 400 in benzo [a] pyrene. Many of the compounds with MH− as their base peaks had a phenyl group, in which cases the N/P ratios were < 1. In the case of compounds with 18 or fewer carbon atoms, in particular, it was easy to distinguish isomers by comparing their NICI mass spectra. The N/P values served as a guideline in sensitive detection. Nine compounds achieved an N/P of ≥50.
Two competing fragmentation processes in dimethoxybenzenes depending on their positional isomers: Elimination of CH3 and CHnO (n = 1–3) and formation of methoxycyclopentadienyl and protonated phenol ions
Authors: Mori Yoshihiro , Ogawa Yoshikazu , Shinoda Hiroyuki , Kitagawa Taiji
Published: May 2005

All the metastable transitions observed above m/z 39 in the first field‐free region were compared for the three positional isomers of dimethoxybenzene. The observed isomer‐dependent fragmentation processes, in particular the formation and decomposition of the m/z 95 (C6H7O)+ ion, are discussed in terms of two competing fragmentations [elimination of CH3 and CHnO (n = 1–3) and formation of methoxycyclopentadienyl and protonated phenol ions] and the relative energies of several isomers of the C6H7O+ ion calculated with molecular orbital theory.
Identification of esters by collisional charge inversion of their enolate ions
Authors: Tkaczyk Martin , Harrison Alex G.
Published: May 2005

The collisional charge inversion and neutralization‐reionization (−NR) mass spectra of the enolate ions of m/z 115 derived from the four butyl acetates, the two propyl propionates, ethyl butyrate, ethyl isobutyrate, methyl valerate, methyl 2‐methylbutyrate and methyl 3‐methylbutyrate were recorded. The major primary fragmentation reactions of the unstable carbenium ion formed by charge inversion involve elimination of an alkoxy radical to form a ketene or alkylketene molecular ion and formation of an alkyl ion consisting of the R1 group of RCOOR1. A minor fragmentation reaction involves elimination of an alkyl radical by cleavage of a CC bond α to the ether oxygen. The alkylketene ions fragment by β‐cleavage eliminating an alkyl radical to form an olefinic acylium ion. In most cases the charge inversion mass spectra of the enolate ions allow identification of the ester.
Mass spectrometry of some 2‐styryl‐ and 2,5‐distyrylfuran and ‐thiophene derivatives
Authors: Karminski‐Zamola Grace , Bajić Miroslav , Blažević Nikola
Published: May 2005

Mass spectra of fourteen 2‐styryl‐ and 2,5‐distyrylfuran and ‐thiophene derivatives are reported. Each styryl substituent has an α‐carboxylic acid or methyl carboxylate substituent. Although the parent ion is the base peak for the styryl and distyryl derivatives, the distyryl species showed less fragmentation than the styryl species. In addition to simple bond cleavages, loss of formic acid or methyl formate was important in many of the species, presumably forming acetylenic fragments.
Negative ion mass spectra of some unsaturated C‐glycosides following keV ion bombardment
Authors: Brakta Mohamed , Sinou Denis , Becchi Michel , Banoub Joseph
Published: May 2005

A series of anomeric unsaturated C‐glycosides were studied by negative ion mass spectrometry following keV ion bombardment The compounds bearing an acidic hydrogen show a prominent [M  H]− peak; in the other cases, the [M  H]− peak is of very low intensity. A retro‐Diels–Alder fragmentation and the abstraction of a hydrogen atom from the aglycon residue are observed in all cases.
New interpretation algorithm for molecular negative ion resonance states
Authors: Khvostenko Victor I. , Pogulay Andrei V.
Published: May 2005

A new interpretation algorithm for molecular negative ion resonance states is proposed. This algorithm may be used when there exists a set of resonance states where the energetic distance between the resonances coincides with the corresponding distance between ionization energies. This set arises by a mechanism of electron‐excited Feschbach resonance. In this mechanism, during the collision of electrons with a molecule, one electron from an occupied molecular orbital (MO) is promoted to an unoccupied MO and the striking electron is captured to the same MO. An assumed MO, excited in the set of resonances, is determined by quantum chemical calculations. This assumption is checked by the construction of correlation diagrams for electron states. The algorithm was applied to the monothiocarbonates and perfluoroalkenes and gave satisfactory results.
Collision‐induced dissociation study of cyclization of α‐diazo‐ω‐arylsulphonylaminoalkan‐2‐ones
Authors: Lebedev Albert T. , Samguina Tatyana Yu. , Petrosyan Valery S. , Blumenthal Tomas , Sipyaguin Aleksey M. , Kartsev Victor G.
Published: May 2005

The collision‐induced dissociation mass‐analysed ion kinetic energy (CID MIKE) spectra (electron impact and chemical ionization) of five α‐diazo‐ω‐arylsulphonylaminoalkan‐2‐ones and corresponding N‐arylsulphonylazetidin‐3‐ones and N‐arylsulphonylpyrrolidin‐3‐ones were studied. The [M  N2]+˙ and [MH  N2]+ ions of two types of the diazo ketones provide CID MIKE spectra similar to those of the corresponding M+˙ and MH+ of the heterocyclic compounds, i.e. a cyclization analogous to that in solution takes place. For the other three types of diazo compounds the Wolff rearrangement prevails in both the gas and liquid phases. The effect of the substituents on the cyclization process was studied. The data obtained permit the results of acid‐catalysed cyclization of similar diazo ketones to be predicted on the basis of their CID MIKE spectra. Chemical ionization provides a closer similarity with reactions in solution than electron impact ionization, which can be rationalized by the protonation of the diazo ketone molecule being the driving force of the cyclization reaction either in solution or in the ion source of a mass spectrometer.
Effective Coupling of an Nd: YAG Q‐switched laser with fibre optics for mass spectrometric experiments
Authors: Cecchetti Walter , Polloni Riccardo , Traldi Pietro , Seraglia Roberta
Published: May 2005

A simple method, based on the use of a vacuum cell, is described for the coupling of an Nd: YAG Q‐switched laser with 600 μm fibre optics. By such a device the usually observed damage of the fibre optical surface is completely avoided.
Formation and decay of doubly charged ions in n‐alkanes from methane to triacontane
Authors: Hagan D. A. , Eland J. H. D.
Published: May 2005

Coincidence techniques were used to study dissociative double ionization of selected n‐alkanes from methane to triacontane (C30H62) and of the hexane isomers. Following photoionization at 40.8 eV, both covalent and coulombic dissociations of the molecular dications take place. The main decay route of doubly charged alkanes larger than butane is fast charge separation followed by secondary dissociation of energetic singly charged primary ions. A simulation based on quasi‐equilibrium theory and the spectra of the isomers confirm this breakdown mechanism for hexane.
Structure‐specific fragmentations of 2,2,4‐trisubstituted 1,2‐dihydroquinazolines
Authors: Ann Qinghong , Ou Mark , Madigan Raymond , Adams Jeanette
Published: May 2005

Fragmentations of a series of 2,2,4‐trisubstituted 1,2‐dihydroquinazolines were studied by electron impact (EI) ionization and positive‐ and negative‐ion fast atom bombardment (FAB) coupled with collision‐induced decomposition (CID). The EI mass spectra give information that directly indicates the specific location of each substituent. The FAB–CID spectra provide data regarding the masses of each substituent, but no definitive information regarding location.
Structural identification of alkene isomers by photodissociation–photoionization mass spectrometry
Authors: Van Bramer Scott E. , Johnston Murray V.
Published: May 2005

Photodissociation‐photoionization, mass spectrometry (PDPI/MS) is used to probe the neutral dissociation chemistry of branched alkenes and dienes. Molecules are photodissociated with an ultraviolet laser and the resulting neutral fragments are subsequently photoionized with coherent vacuum ultraviolet radiation. The neutral fragmen tation observed is useful for characterizing compounds which isomerize prior to ionic fragmentation. Unimolecular photodissociation of dienes and branched alkenes is dominated by cleavage of the β CC bond. In a few cases, α‐cleavage is also observed. When two isomers produce isomass primary products, secondary fragmentation can be used to distinguish the structures. The primary and secondary product distributions are predictable and usually occur without iomerization. As a result, PDPI/MS can be used to determine the sites of branching and unsaturation in small (C5–C8) aliphatic compounds.
Ionspray mass spectrometric and tandem mass spectrometric investigations of N‐aliyl‐N′‐arylsulphonylthioureas, ‐isothioureas and ‐guanidines
Authors: Hans Martin , Schöffinann Thomas , Waidelich Dietmar , Bayer Ernst
Published: May 2005

Mass and tandem mass Spectrometric results for N‐allyl‐N′‐arylsulphonylthioureas,‐isothioureas and ‐guanidines using the pneumatically assisted electrospray (ionspray) technique are presented. The mass Spectrometric experiments show dominant quasi‐molecular peaks of the monomers and signals of dimers and, more weakly, fragments. Full mass spectra are available from amounts below 500 fmol, indicating a high sensitivity. By tandem mass spectrometry of the protonated molecular ions and their fragments (sequential dau ghter‐ion scanning) and using the chlorine and bromine isotope patterns, the fragmentation pathways were elucidated.
Evidence for the entrapment of C60, C70 and odd‐numbered high‐mass carbon clusters
Authors: Hopwood F. G. , Dance I. G. , Fisher K. J. , Willett G. D. , Wilson M. A. , Pang L. S. K. , Hanna J. V.
Published: May 2005

The carbon are soot from a fullerene generator was exhaustively extracted with toluene, pyridine, toluene then pyridine, benzene and carbon disulphide. Complete extraction of C60 and C70 was not fully achieved with any solvent since the residue was shown to contain occluded C60 and C70. Fourier transform infrared, solid‐state nuclear magnetic resonance and threshold laser desorption Fourier transform ion cyclotron resonance mass spectrometric experiments were used to show the presence of C60 and C70 in the exhaustively extracted residues. Low‐power laser irradiation also indicated the presence of higher fullerenes in the extracted are soot. Laser ablation of the extracted arc soot gave FT ion cyclotron resonance mass spectra which showed regions with odd‐numbered carbon clusters. It is suggested that the smaller fullerenes and possibly the odd‐numbered clusters may be trapped in hyperfullerenes such as the ‘Russian egg’ or in ‘buckytubes’.
Hydrogen–carbon, carbon–carbon double rearrangement induced by proximity effects. Part 3: Essential structural requirements in methoxydiphenylmethanes
Authors: Ceraulo Leopoldo , Agozzino Pasquale , Ferrugia Mirella , Lamartina Liliana , Natoli Maria Concetta
Published: May 2005

The hydrogen–carbon, carbon–carbon double rearrangement, responsible for the formation of benzyl or tropylium ions previously observed in the electron ionization mass spectra of several substituted 1,1‐bis(dimethoxydiphenyl)methanes bearing an ortho methoxy group, also occurs for 2‐methoxydiphenylmethane (1) itself, the simplest compound of the series. It was shown using deuterium and 13C labelled 2‐methoxydipnenylmethanes (2, 3) that in this instance benzyl or tropilium ions are also formed through two alternative fragmentation routes.
Electrospray analysis of proteins: A comparison of positive‐ion and negative‐ion mass spectra at high and low pH
Authors: Kelly Michele A. , Vestling Martha M. , Fenselau Catherine C. , Smith Philip B.
Published: May 2005

Cationic and anionic electrospray mass spectra were measured for equine myoglobin, lactalbumin and hen egg white lysozyme from acidic and basic solutions. Both positive and negative ions were detected from all solutions in which the proteins were soluble. This was observed in both nebulization‐assisted and thermally assisted electrospray. As in other studies, the distribution of the charge states reflected functional groups in the proteins, and also folding or extension of the protein.
Electron impact and fast atom bombardment mass spectrometry in the characterization of some new macrocycles containing a 1,3,5‐triazine moiety
Authors: Corda L. , Bullitta M. P. , Maccioni E. , Podda G. , Favretto D. , Traldi P.
Published: May 2005

The mass spectrometric behaviour of four new macrocyclic compounds, all containing the 1,3,5‐triazine moiety, was studied with the aid of different ionization methods and mass‐analysed ion kinetic energy Spectrometry. Extensive fragmentation of the oligoethylene glycol side‐chains is observed, with the usual loss of C2H4O units. The favoured cleavage of the ethereal bond nearest to the etherocyclic ring gives rise to both complementary ions.
Investigation of some 2,3‐didehydro amino acids by fast ion bombardment, chemical ionization and mass‐selected collision‐induced dissociation mass spectrometry
Authors: Hamdan M. , Tarzia G. , Balsamini C. , Bedim A.
Published: May 2005

Four 2,3‐didehydro amino acids were investigated by fast ion bombardment (FIB) and ammonia chemical ionization (NH3‐CI) mass Spectrometry. The protonated molecules formed by the two techniques were mass selected and their respective collision‐induced dissociations (CIDs) in the translational energy range 5–200 eV (in the laboratory frame of reference) were investigated. No obvious quantitative differences between the FIB and NH3‐CI mass spectra of the (E)‐ and (Z)‐isomers were observed. Different internal excitation of the protonated molecules formed by the two techniques and the role of CID data in clarifying this particular observation are discussed.
Analysis of conjugated bile acids by on‐line supercritical fluid chromatography/thermospra mass spectrometry
Authors: Scalia Santo , Games David E.
Published: May 2005

A rapid method was developed for the analysis or polar conjugated bile acids by combined packed column super‐critical fluid chromatography/mass spectrometry. Direct coupling of the column to the mass spectrometer was effected with a modified thermospray interface operated in the filament‐on mode. Maximum sensitivity for the bile acid conjugates was achieved by recording the negative ions generated in the ionization process. The effects of vaporizer and source temperatures, repeller voltage and discharge conditions on the bile acid response were investigated. The mass spectra obtained for the common glycine and taurine conjugates yielded only the [M – H]− pseudo‐molecular ions. In contrast with the taurine derivatives, the glycine forms produced a weak ion current and exhibited broad hands. The applicability of the technique is illustrated with a sample of human bile.
Fast atom bombardment mass spectra of keto acid and keto ester phosphoranes
Authors: Abell Andrew D. , Clark Bruce M. , Morris Kathryn B. , Taylor Jane M.
Published: May 2005

Positive‐ion fast atom bombardment mass spectra of 13 keto acid and keto ester phosphoranes were examined. All compounds gave a protonated molecular ion and characteristic peaks at m/z 303, 279, 262 and 201.
Secondary ion mass spectrometry of sugar nucleotides
Authors: Ii Tadashi , Okuda Satoshi , Hirano Takashi , Tsujimoto Kazuo , Ohashi Mamoru
Published: May 2005

Secondary ion mass spectra of fifteen sugar nucleotide sodium salts were investigated. In the negative‐ion mode. deprotonated free acid molecules, desodiated sodium salts and some structurally significant fragment ion swere obtained. The linked scan at constant B/E gave information on the characteristics of the sugar, nucleosides and base moieties in the sugar nucleotides.
Gas chromatographic/mass spectrometric analysis of cembrenoid diterpenes in kerogen from a lacustrine sediment
Authors: Barakat Assem O. , Rullkötter Jürgen
Published: May 2005

Alkaline hydrolysis of kerogen from a Miocene lacustrine sediment (Nördlinger Ries, southern Germany) afforded a series of cembrenoid diterpenes characterized by a 14‐membered ring system together with a second, probably related, series of yet unidentified structure. This is the first report of the occurrence of these compounds in fossil organic matter. The interpretation of cembrenoids as molecular markers of arid or semiarid climate is consistent with other information about the depositional environment of the former Nördlinger Ries crater lake.
Chemical reactions at interfaces: Hydrogen–deuterium exchange using a solid ND4Cl matrix in molecular secondary ion mass spectrometry
Authors: Hand Owen W. , Ranasinghe Asoka , Cooks R. Graham
Published: May 2005

Organic compounds containing active hydrogens (e.g. imino, amino, carboxylic acid and hydroxy functional groups) undergo hydrogen–deuterium (H–D) exchange reactions in the course of argon ion bombardment in molecular secondary in mass spectrometry (SIMS) when examined as solids in solid ND4Cl matrix. The positive‐ion SIMS spectra of non‐ionic compounds (M) display ions resulting from exchange of active hydrogens in both the deuterated ((M + D)+) and cationized ((Ag + M)+ and (C+ + M)+) forms, while ionic compounds display exchange products in the intact cation (C+, where C = cation). Analogous H–D exchange is observed in the negative SIMS spectra of compounds bearing active hydrogen atoms. The fact that the exchange reactions are dependent on the primary ion dose demonstrates that they occur in the energized sample and not prior to ion bombardment. Information on the mechanisms of interfacial reactions, insights into the SIMS mechanism and confirmation of the number of acidic hydrogens in non‐volatile organic ompounds are revealed by this experiment.
Comparative study of Møller–Plesset perturbation theory and configuration interaction theory for the structure of the N4+ cation
Authors: Kemister Gary , Peel J. Barrie
Published: May 2005

A theoretical study of the ground electronic state of N4+, the dimer ion of N2, has shown, in agreement with other studies, that the Møller–Plesset perturbation expansion for open‐shell molecular species is unstable and divergent when used with certain spin‐contaminated UHF reference wavefunctions. This failure is more serious than in the earlier studies, which noted that the breakdown occurred for the extended bond lengths descriptive of potential energy curves of diatomic systems. In this study the breakdown occurs for the potential energy surface of N4+ close to the global minimum structure, which is incorrectly determined as corresponding to a trans‐planar geometry. In comparison variational configuration interaction procedures represented by the CISD and QCISD methods are clearly superior in the case of N4+, with both yielding the correct linear geometry. The QCISD calculation provides a calculated antisymmetric vibration frequency which is in good agreement with, and hence confirms, the assignment of the neon‐matrix infra‐red spectrum attributed to the N4+ species. The search for a bound excited electronic state of N4+ was partly successful in that a configuration of rectangular geometry shows properties in fair agreement with experimental results.
Negative‐ion mass spectrometric study of ion‐pair formation in the vacuum ultraviolet. VII—SO2 → O− + SO+, O− + S+ + O
Authors: Mitsuke Koichiro , Suzuki Shinzo , Imamura Takashi , Koyano Inosuke
Published: May 2005

Ion‐pair formation from photoexcitation of SO2 was studied by negative‐ion mass spectrometry using synchrotron radiation in the 15–35 eV photon energy range. Negative ions O− from SO2 were observed. The appearance energy in the photodissociation efficiency curve for O− is in good agreement with the thermochemical threshold of 14.49 eV for the formation of O−(2Pu) + SO+(X̃2Π). Three vibrational progressions in the efficiency curves are assigned as resulting from predissociation of the s‐type Rydberg states converging to SO2+(D̃2A1). The O− efficiency rises markedly at wavelengths of 622 and 570 Å. These onsets are attributed to formation of triplets of fragments: O−(2Pu) + S+(4Su) + O(3Pg) and O−(2Pu) + S+(2Du) + O(3Pg).
A kinetic approach to the proton affinities of amine bases
Authors: Li Xiaoping , Harrison Alex. G.
Published: May 2005

The fragmentation of proton‐bound clusters [B1—H—B2]+ of amine bases B1 and B2 were studied at collision energies of 10–50 eV in the quadrupole collision cell of a hybrid tandem mass spectrometer. The relative abundances of the fragment ions B1H+ and B2H+ were correlated with the proton affinities of the amines. The proton affinities of 21 amines are reported based on the expanded proton affinity scale of Meot‐Ner and Sieck [J. Am. Chem. Soc. 113, 4448 (1991)]. It is found that the fragmentation of mixed proton‐bound clusters of α‐amino acids and amines can be used to establish the proton affinities of simple amino acids such as glycine, alanine, valine, leucine and phenylalanine. However, low values are obtained by this method for the proton affinities of amino acids containing a functional group (additional to the carboxyl group) capable of stabilizing the protonated species by intramolecular hydrogen bonding.
Collision‐induced decomposition of large organic ions and inorganic cluster ions. Effects of pressure on energy losses
Authors: Bradley Caroline D. , Derrick Peter J.
Published: May 2005

Translational energy losses ΔE in keV‐collisions have been determined for peptide ions and for caesium iodide cluster ions subsequently decomposing to specific fragment ions, and the dependences of these energies upon transmission have been investigated. Parent ions decomposing to certain fragment ions exhibit energy losses which are independent of transmission, while parent ions associated with other fragment ions show strong dependence of energy loss upon transmission. These findings are interpreted in terms of energy redistributions of tens of eV taking place in single collisions via direct momentum‐transfer.
Stereochemically controlled decomposition of silver‐cationized methyl glycosides
Authors: Berjeaud Jean‐Marc , Couderc François , Prome Jean‐Claude
Published: May 2005

Silver ion adducts of several methyl glycopyranosides were generated by fast atom bombardment of 1:1 mixtures of the glycosides with silver nitrate. The unimolecular decompositions of [M + Ag]+ ions showed dramatic differences related to the relative positions of both the hydroxyl group on C(2) and the anomeric methoxyl group. When these groups were in the cis position, methanol was exclusively expelled. When they were in the trans position, silver hydride was preferentially lost. The stereoselective elimination reaction is proposed to proceed through a five‐membered silver‐containing intermediate complex, from the oxygen on C(2) to the anomeric substituent (methoxyl group or hydrogen atom).
Behaviour of salts of very strong proton‐sponge bases in the gas phase: Extended proximity effects and maintenance of the hydrogen bridge under soft ionization. An electron impact and liquid secondary ion mass spectrometric/collision‐induced dissociation tandem mass spectrometric study
Authors: Rentzea Marina , Kühn Fredy , Staab Heinz A.
Published: May 2005

The liquid secondary ion mass spectrometry and electron impact ionization fragmentation pathways of 1,9‐bis(dimethylamino)‐2,8‐dimethoxy‐dibenzofuran (1), a new proton‐sponge base with increased steric compression (buttressing) and much higher basicity (pKa = 14.3), and of its monoprotonated (2) and monodeuterated (3) salts were invetigated in a collision‐induced dissociation (CID) tandem mass spectrometric study supported by unimolecular linked scans at constant B/E, CID mass‐analysed ion kinetic energy spectra and accurate mass measurements. They show an ‘extended’ proximity effect, involving the stepwise participation of all the four functional groups, in addition to the ‘normal’ proximity effect involving loss of Me2NH and H˙. The behaviour of 1 appears to differ in some ways from that of its protonated (2) or deuterated (3) salts. The unprecedented observation of the maintenance of the hydrogen (or deuterium) bridge under soft ionization in the salts of very strong proton‐sponge bases, which show buttressing effects in solution, is strong experimental support for the conservation of these buttressing effects in the gas phase, where the protonated (or deuterated) cations of salts such as 2 (or 3) are very stable, H+ (or D+) being completely ‘sequestered.’
Reaction dynamics of the dichlorocarbene anion using tandem mass spectrometry
Authors: Leyh Bernard , Mélon Pierre
Published: May 2005

The dissociation dynamics of CCl2− anions were studied under various internal energy conditions. This study involved the measurement of daughter‐ion spectra and branching ratios and of the amount of kinetic energy released (KER) on the fragments. The competition between C and Cl loss for CCl2− ions created by any of the following sequence of processes:
equation image
was particularly investigated. For process (1), the amount of fragmenting CCl2− ions is 8–10 times larger with Kr than with Xe or C6H6. The KER for Cl loss is smaller than 0.20 eV with the three target gases used. For the loss of C, the KER is much larger (0.7 eV). This KER is, however, equal to 0.21 eV for the collisionally activated C loss in process (2). For this latter process, the C loss vs. Cl loss branching ratio decreases with increasing internal energy. The KERs measured for process (3) are very similar to those obtained for process (1). It is suggested that repulsive or slightly bound excited states which correlate directly to the Cl2− (X2Σu+) + C asymptote and which are vibronically coupled to the ground state play an important role in these dissociation processes.
Hybrid tandem mass spectrometry of electrospray‐produced peptide ions
Authors: Tomer Kenneth B. , McGown Steven R. , Deterding Leesa J.
Published: May 2005

The collision‐induced decomposition spectra of electrospray‐produced molecule ions were investigated on a hybrid tandem mass spectrometer. The molecular mass of the peptides investigated ranged from m/z 409 (as the singly protonated molcule ion) to 1758 (as the singly, doubly and triply protonated molecules). The effect of changing the center‐of‐mass collision energy by changing either the laboratory collision energy or the mass of the target gas was investigated. The spectra of all ions investigated showed a large number of sequence ions representative of the peptides' structures.
Is droplet evaporation crucial in the mechanism of electrospray mass spectrometry?
Authors: Siu K. W. M. , Guevremont R. , Le Blanc J. C. Y. , O'Brien R. T. , Berman S. S.
Published: May 2005

Evaporation of solvent from charged droplets was found not to be a prerequisite to ion desorption in electrospray mass spectrometry. Evidence of evaporation was absent in an examination of the electrospray mass spectral profiles of cytochrome c and myoglobin in 0.2% acetic and propionic acid solutions; the pHs of these two acid solutions are expected to change in opposite directions with evaporation. The results strongly suggest that ions, as observed in electrospray mass spectrometry, are desorbed from solutions that have undergone minimal evaporation, in other words, at the beginning rather than later parts of the electrospray process. It is speculated that ions are desorbed directly from the solution‐air interface at the needle tip.
Determination of collision‐induced dissociation mechanisms and cross‐sections in organophosphorus compounds by atmospheric pressure ionization tandem mass spectrometry
Authors: Harden Charles S. , Snyder A. Peter , Eiceman Gary A.
Published: May 2005

Nineteen organophosphorus compounds (OPCs) of the generic classes (dialkyl alkyl′‐phosphonates (twelve compounds) and tri‐alkyl phosphates (seven compounds) were investigated by atmospheric pressure ionization (API) tandem mass spectrometry (MS/MS). All OPCs showed consistent and comparable collision‐induced dissociation (CID) pathways allowing for a generalized scheme for dissociation. When the alkyl groups are equal to or larger than ethyl, CID mechanisms are dominated by McLafferty rearrangements and neutral losses are stable molecules in all cases except cleavage of PC or OC bonds to form alkyl fragment ions. CID cross‐sections for the OPCs were determined with excellent reproducibility and a good correlation was found with a simple model. Inferences with respect to ionic structures were made from observed trends in the cross‐section measurements. Limitations in API‐MS/MS instruments of this design are found in the energy distribution of the ionization and ion sampling events.
Structural characterization of reactive dyes using liquid secondary ion mass spectrometry/tandem mass spectrometry
Authors: Richardson Susan D. , Thruston Alfred D. , McGuire John M. , Weber Eric J.
Published: May 2005

Reactive Blue 19 (RB 19), its reactive form (RB 19‐VS) and its hydrolyzed form (RB 19‐OH) were examined using liquid secondary ion mass spectrometry/tandem mass spectrometry (LSIMS/MS/MS) in the negative‐ion mode under low‐energy collision conditions (240–300 eV). Structurally characteristic fragment ions were obtained, none of which has been previously reported for these reactive dyes. Among the ions obtained were SO3− ions, ions due to central amino cleavage and reactive group cleavage, and ions due to loss of SO3 and SO2. Possible pathways for the formation of product ions are proposed. The structural information obtained should help to characterize and identify reactive dyes better.
Electron impact mass spectra of synthetically modified milbemycins
Authors: Jones M. T. , Millen W. G. , Thomson M. L.
Published: May 2005

The potent endectocide 23‐(O‐methyloximino)‐F28249α and related compounds were identified and characterized by mass spectrometry. The fragmentation pathway of 23‐(O‐methyloximino)‐F28249α was identified by its high‐resolution mass spectrum and the electron impact unit mass spectra of its homologs. This fragmentation pathway is presented and discussed.
Gas‐phase oxirane addition to acylium ions on reaction with 1,3‐dioxolanes elucidated by tandem and triple stage mass spectrometric experiments
Authors: Eberlin Marcos N. , Cooks R. G.
Published: May 2005

Acylium ions containing a variety of substituents all undergo an unprecedented reaction with 1,3‐dioxolanes which gives rise to a cyclic, resonance‐stabilized oxonium ion, formally the product of oxirane (C2H4O) addition to the reagent ion. The structure for the ion–molecule product is supported by multiple‐stage mass spectrometric experiments, performed in a pentaquadrupole mass spectrometer, which show the expected fragmentation by C2H4O loss to yield the original reactant acylium ions. The oxonium ions are formed in relatively high abundance in many cases and are observed even when proton‐transfer reactions would be expected to occur competitively owing to the acidity of some of the acylium ions studied. This ion–molecule reaction is proposed to serve as a general method for identification and/or trapping of ions of the whole acylium ion class and also for the gas‐phase generation of the oxonium ions. The reaction with 1,3‐dioxolane is also useful in distinguishing the most stable C2H3O+ ion, the acetyl cation, from its two stable isomers, O‐protonated ketene and the oxiranyl cation. The thioacetyl cation, the only sulfur analog investigated, also reacts with dioxolane to form the corresponding oxirane addition product, indicating that the C2H4O addition reaction occurs and that it may be useful for identification of the thioacylium class and for the gas‐phase generation of sulfur analogs of oxonium ions.
Identification of Diels–Alder regioisomers by mass spectrometry coupled with theoretical calculations
Authors: Cativiela C. , García J. I. , Garín J. , Mayoral J. A. , Orduna J. , Salvatella L.
Published: May 2005

Differences in the mass spectra of Diels–Alder cyclohexene regioisomers are explained with the aid of a simple model based on the relative stability differences of the open‐chain structures resulting from the alternative cleavage of the C(1)–C(2) and the C(5)–C(6) bonds of the 1‐substituted cyclohexene ring. Theoretical SCF‐MO calculations at a semi‐empirical level proved to be useful tools for determining the relative stabilities of these open‐chain radical cation structures and hence in the interpretation of mass spectra and the correct assignment of regioisomer structures from these spectra.
A fast atom bombardment mass spectrometric study of room‐temperature 1‐ethyl‐3‐methylimidazolium chloroaluminate(III) ionic liquids. Evidence for the existence of the decachlorotrialuminate(III) anion
Authors: Abdul‐Sada Ala'a K. , Greenway Anthony M. , Seddon Kenneth R. , Welton Thomas
Published: May 2005

Previous studies of 1‐ethyl‐3‐methylimidazolium chloride–aluminium(III) chloride ([emim]Cl–AlCl3) ionic liquids have been hampered by significant contamination of these liquids by oxide impurities. Treatment of these liquids with phosgene removes the oxide impurities, and the use of a specially constructed sample inlet system for air‐sensitive materials permitted them to be studied by fast atom bombardment mass spectrometry. The ions Cl−, [Cl2]−, [AlCl4]−, [Al2Cl7]−, [emim]+ and [(emim)2X]+ (X = Cl or AlCl4) were observed for the basic ionic liquid. In addition, the anion [Al3Cl10]− was observed for the acidic composition. Within the mass spectrometer, the hydrolyses of [Al3Cl10]− to produce [Al3Cl8O]− and of [Al2Cl7]− to produce [Al2Cl5O]− were observed. Comparison of these results with published 17O NMR data suggests that the primary hydrolysis products in acidic ionic liquids are [Al3Cl8O]− and [Al2Cl5O]− and that the principal secondary hydrolysis product is [Al2Cl6(OH)]−.
Characterization of positional and anomeric isomers of methyl 2‐O‐ and 3‐O‐sulfo‐D‐glucopyranosiduronic acids and methyl 2‐O‐ and 3‐O‐sulfo‐D‐glucopyranosides by secondary ion mass spectrometry
Authors: Ii Tadashi , Okuda Satoshi , Hirano Takashi , Tsujimoto Kazuo , Ohashi Mamoru
Published: May 2005

Secondary ion mass spectrometry (SIMS) of anomeric pairs of methyl 2‐O‐ and 3‐O‐sulfo‐D‐glucopyranosiduronic acids and methyl 2‐O‐ and 3‐O‐sulfo‐D‐glucopyranosides show the deprotonated molecule in the negative‐ion mode and ammoniated and sodiated molecules in the positive‐ion mode. The four isomers were distinguished from each other by linked scanning at constant B/E in negative‐ and positive‐ion SIMS, which gave information characteristic of the position of the sulfate group and even the configuration of the anomeric methoxy group. The main fragmentation processes correspond to the loss of methanol and the elimination of SO3.
Electron impact‐induced fragmentation of 2,1‐benzisothiazoline 2,2‐dioxide
Authors: Danikiewicz Witold , Wojciechowski Krzysztof , Fokkens Roel H. , Nibbering Nico M. M.
Published: May 2005

The electron impact‐induced fragmentation patterns of 2,1‐benzisothiazoline 2,2‐dioxide nitro derivatives were studied. The rationalizations proposed for the fragmentations are supported by accurate mass measurements, daughter ion (mass analysed ion kinetic energy and B/E linked‐scan), parent ion, and constant neutral loss spectra in metastable and collision‐induced dissociation modes and deuterium labelling.