bluuebunny/crossref_metadata_2025_split huggingface dataset:
Vibrational excitation of N2 by C+ ions
Authors: Lee A. R. , Enos C. S. , Brenton A. G. 
Published: May 2005

AbstractHigh‐resolution translational energy spectroscopy (0.1 eV full width at half maximum) has been performed on 3 keV C+ ions scattered off N2 molecules. The intriguing energy loss spectrum with well‐resolved vibrational structure is explained on the basis of simultaneous transitions involving changes of states in the C+ ion and the N2 molecule.
Endothermic ion/molecule reactions III. High energy collisional activation at low kinetic energies
Authors: Orlando Ron , Fenselau Catherine , Cotter Robert J. 
Published: May 2005

AbstractEndothermic reactions between leucine enkephalin and ammonia have been carried out at very low beam energies, and compared with activation obtained by conventional collision‐induced dissociation at both low and high energies. The similarity between the high‐energy and the reactive‐collisions spectra suggest that comparable energies are imparted by these two methods. The upper limit of the collision energy deposited by reactive collisions is only 0.30 eV. In addition, a substantial increase in the collection efficiency is observed with endothermic reactions, with the sum of the fragment ions exceeding the intensity of the surviving parent ions.
A study of relevant parameters in collisional‐activation of ions in the ion‐trap mass spectrometer
Authors: Gronowska Janina , Paradisi Christina , Traldi Pietro , Vettori Umberto 
Published: May 2005

AbstractVariously substituted aryl ketones served as models to gain insight into the collisional‐activation process in an ion‐trap mass spectrometer. The effects of different targets (helium, argon) at different pressures were examined. The investigation also involved the comparison of the results of tandem mass spectrometry experiments in the ion trap with those obtained in high‐energy collision and mass‐analysed ion kinetic energy experiments in a sector instrument. Use of argon and low helium pressures in the ion trap results in both an increase of the average internal energy of the activated ion and, presumably, a less broad energy deposition profile. The results indicate that the maximum value of internal energy achieved by an ion through multiple collisions in the ion‐trap mass spectrometer is limited by the presence of low‐energy reaction channels.
High‐temperature gas chromatography/mass spectrometry of triacylglycerols with ammonia negative‐ion chemical ionization
Authors: Evershed R. P. , Prescott M. C. , Goad L. J. 
Published: May 2005

AbstractAmmonia negative‐ion chemical ionization of intact triacylglycerols at an ion‐source‐block temperature of 300°C produces simple mass spectra from which the nature of the component acyl moieties can be readily deduced. The technique is compatible with combined high‐temperature gas chromatography/mass spectrometry and it has a potentially wide application.
Deconvolution of kinetic‐energy release signals from singly, doubly, and triply charged metastable ions
Authors: Koyanagi Gregory K. , Wang Jianyao , March Raymond E. 
Published: May 2005

AbstractA new geometric model has been developed and applied to the deconvolution of ion kinetic‐energy release signals observed from fragmentation of metastable ions in the second field‐free region of a reversed geometry mass spectrometer. The model takes account of: (i), fragmentations occurring throughout the entire length of the field‐free region; (ii), the difference in ion beam intensity before and after the intermediate slit; (iii), the slight difference in angular acceptance between backward‐ and forward‐scattered product ions; (iv), fragmentations of singly and multiply charged ions; and (v), ion kinetic‐energy releases of any magnitude. Several examples of metastable peaks are given together with the associated kinetic‐energy release distribution and the theoretical metastable peak generated from the kinetic‐energy release distribution.
A fourier transform‐ion cyclotron resonance study of the reactivity of ionized vinylalcohol with selected unsaturated compounds
Authors: Berruyer Florence , Bouchoux Guy 
Published: May 2005

AbstractReactions between CX2CXOX+· (X  H or D) and alkenes, an alkyne, benzene, aldehydes and ketones have been studied by Fourier transform mass spectrometry. Most of the neutral species undergo charge exchange or proton transfer reactions with high rates; l‐alkenes lead to slower cycloaddition reactions. The thermochemistry and considerations on the reaction specificities are discussed.
High‐ and low‐energy tandem mass spectrometry of oxonium ions formed by fast‐atom bombardment ionization of a series of diastereoisomeric 1,2‐trans‐2‐deoxy‐2‐iodoglycosyl azides
Authors: Banoub Joseph , Becchi Michel , Lafont Dominique , Fraisse Daniel , Descotes Gerard 
Published: May 2005

AbstractPositive‐ion fast‐atom bombardment mass spectrometry has aided the structural characterization of a novel series of diastereomeric 1,2‐trans‐2‐deoxy‐2‐iodoglycosyl azides. Daughter‐ion tandem mass spectrometry (MS/MS) analyses (high‐energy mass‐analysed ion kinetic energy spectrometry and low‐energy MS/MS with collisionally‐activated dissociation), of the precursor oxonium ions for this series of diastereoisomers provided distinct and reproducible fingerprint patterns which permit discrimination amongst the individual configurations.
Unimolecular decomposition of M+˙ and [M + H]+ species of some fluorosubstituted acyclic nucleoside analogs
Authors: Favretto Donata , Traldi Pietro , Bravo Pierfrancesco , Viani Fiorenza 
Published: May 2005

AbstractElectron ionization and fast‐atom bombardment mass spectrometry are shown to provide a valid analytical tool for the structural characterization of the title compounds. In fact, diagnostic fragmentation pathways were observed depending on the presence of different substituents (benzyloxy, p‐tolylthio, p‐tolylsulphinyl) as swell as of different bases. Regioisomeric compounds could be differentiated by kinetic energy release measurements.
Direct determination of the sequence of destruxins (cyclodepsipeptides) using negative‐ion fast‐atom bombardment mass spectrometry
Authors: Lange C. , Mulheim C. , Vey A. , Pais M. , Aubagnac J.‐L. 
Published: May 2005

AbstractFast‐atom bombardment negative‐ion mass spectra of various natural destruxins (cyclodepsipeptides) using a glycerol matrix are investigated to clarify their regular pattern of fragmentation. Deprotonated molecules allow characterization of the molecular weight. Also, at lower masses, anion Y of significant intensities permit the determination of their amino acid sequences.
Metastable decay of peptides and proteins in matrix‐assisted laser‐desorption mass spectrometry
Authors: Spengler Bernhard , Kirsch Dieter , Kaufmann Raimund , Cotter R. J. 
Published: May 2005

AbstractFragmentation of protein and peptide ions generated by matrix‐assisted laser desorption has been investigated using a modified LAMMA 1000 reflecting time‐of‐flight (TOF) mass spectrometer. Whereas fragmentation of covalent bonds prior to ion acceleration (i.e., within several ns after the laser pulse) in general is not observed using the matrix technique, extensive fragmentation on a longer time scale can be studied in our instrument. The high mass resolution (M/ΔM≈1200–1800 for insulin and peptides) permits the investigation of even small mass losses from parent molecular ions (occuring in the first section of the field‐free drift region) by measuring flight time differences of daughter ions acquired during passage through a two‐stage reflection. The kind and extent of this metastable decay has been found to depend strongly on the substance under investigation. Typical fragmentations are loss of ammonia and parts of the amino acid side‐chains. The large abundances of peaks due to such metastable fragmentation, observed for most of the peptides and proteins investigated, may, at least in part, explain peak broadening (and, hence, poor mass resolution) typical in matrix‐assisted laser‐desorption TOF mass spectra.
Factors affecting the ionization efficiency of quaternary ammonium compounds in electrospray/ionspray mass spectrometry
Authors: Raffaelli Andrea , Bruins Andries P. 
Published: May 2005

AbstractA series of quaternary ammonium salts was analysed by the ionspray technique under different conditions in order to study the influence of some important factors on the ionization efficiency, The factors taken into account were droplet charging, sample ion, counter ion, solovent composition, and concentration. Measurement of the spray current leaving the nebulizer has shown that the spray current increases linearly with sample concentration up to at least 50 pmol/μL. The measured spray current is approximately 30% of the calcualated current corresponding to a given concentration of quaternary ammonium ions in solution leaving the nebulizer at a given flow rate. The results obtained show that tetraakylammonium salt give the best sensitivitly with no influence of sample‐ion shape or counter ion. The dynamic range for full‐scan mass spectra of the compounds studied appears to the linear for concentrations from 0.1 pmol/μL (10−7M) up to 10 pmol/μL (10−5M).
An A priori relationship between the average and monoisotopic masses of peptides and oligonucleotides
Authors: Zubarev R. A. , Bonddarenko P. V. 
Published: May 2005

AbstractA straightforward relationship between the average and the monoisotopic masses of peptides (proteins) and oligonucleotides is proposed which allows one to calculate the monoisotopic mass from aknown average mass with a 0.1 u order of precision. The approach offered here can be applied to any type of biopolymer.
Molecular weight determination of recombinant interleukin 2 and interferon gamma by electrospray ionization mass spectroscopy
Authors: Maquin Francis , Schoot Bernard M. , Devaux Philippe G. , Green Brian N. 
Published: May 2005

AbstractThe molecular weights of the recombinant proteins interleukin 2 and interferon gamma were determined by electrospray ionization (ESI) mass spectroscopy on the whole molecules. For interleukin 2 an average experimental mass of 15 549.4 u, was observed in excellent agreement with the theoretical average mass of 15 547.2 u. The mass observed for interferon gamma (16 908.4 u) agreed with the theoretical molecular weight of the monomeric species (16 907.3 u). By ESI mass spectrometry it was possible to determine the presence of proteins lacking one or two amino acids.
Electrospray ionization for analysis of platelet‐activating factor
Authors: Weintraub Susan T. , Pinckard R. Neal , Hail Mark , Gaskell S. J. 
Published: May 2005

AbstractPlatelet‐activating factor (PAF) was analyzed by electrospray‐ionization spectrometry (ESI‐MS) using a single quadrupole mass spectrometer. The positive‐ion spectrum was dominated by an ion corresponding to a sodiated molecule when a low potential difference between the capillary exit (nozzle) and the skimmer was employed, but when the capillary exit voltage was increased, fragmentation of PAF was observed. Initial fragmentation involved the loss of the elements of trimethylamine from the sodiated molecule to yield [M+Na−59]+. An intense ion at m/z 147, generated by the loss of trimethylamine from the sodiated phosphocholine portion of the molecule was also detected, along with a lower intensity ion at m/z 184 which is representative of a protonated phosphocholine moiety. With negative‐ion detection the major molecular species was [M + Cl]−. Interpretation of the mass spectral fragments was verified by ESI tandem mass spectrometry on a triple‐quadrupole tandem mass spectrometer.
Gas‐phase chemistry of metal oxide anions. The reactions of dioxomanganate(III), MnO and trioxomanganate(V), MnO ions with aliphatic alcohols
Authors: Fokkens R. H. , Gregor I. K. , Nibbering N. M. M. 
Published: May 2005

AbstractResults of gas‐phase reactions of MnO and MnO ions with a series of aliphatic C1C4 alcohols show that C2C4 primary alcohols are oxidized by MnO in reaction channels which involve proton abstraction and hydride‐ion transfer, along with the appearance of [H.Mn.O.OH]− ions. Secondary alcohols are oxidized in slower processes while menthanol and t‐butanol are unreactive. MnO/alcohol reactions are more complex and involve the formation of [H.MnO3]−, [H.Mn.O2.OH]−, [RO.Mn.O.OH]−, [(RO)2 Mn.O]− and the terminal solvated ion [(RO)3.Mn.OH]−.
Matrix‐assisted laser desorption ionization with a magnetic mass spectrometer
Authors: Hill James A. , Annan Roland S. , Biemann Klaus 
Published: May 2005

AbstractMatrix‐assisted laser desorption ionization has been carried out with a high mass double‐focusing magnetic mass spectrometer. The pulsed ion signal, generated by irradiation of the sample (substance P, ubiquitin, and cytochrome c) embedded in 2,5‐dihydroxybezoic acid with a XeF excimer laser (353 nm, 12 ns pulse, 10–160 Hz), was recorded with an integrating array detector. Good resolution of 2600 (full width at half maximum) and high sensitivity (a few pmol) were obtained. The loss of small neutral fragments was observed, supporting the notion that the peak broadening observed in the time‐of flight mass spectrometers commonly used for this ionization mode is due to such metastable decomposition.
Isomerization reaction of [C6H6 C4H] π complexes
Authors: Berthomieu Dorothée , Audier Henri‐Edouard , Monteiro Candida , Denhez Jean‐Pierre , Maquestiau A. 
Published: May 2005

AbstractMetastable protonated butylbenzenes have been studied by extensive labelling and kinetic energy release measurements. Protonated s‐butylbenzene isomerizes by 1–2 hydrogen shift to the π complex [C6H6 SC4H], and the SC4H cation rearranges to t‐C4H. The interconversion between [C6H6 SC4H] and [C6H C4H8] ion/neutral complexes is demonstrated. Protonated t‐butylbenzene reacts without hydrogen exchange to give t‐C4H, while protonated n‐butylbenzene isomerizes to s‐butylbenzene prior to dissociation. Protonated iso‐butylbenzene isomerizes to protonated t‐butylbenzene and to protonated s‐butylbenzene. In the 2nd field‐free region, the dissociation of this last form predominates.
Mass spectrometry of nuphar alkaloids
Authors: Bortolini Olga , Curcuruto Orenella , Traldi Pietro , Wróbel Jerzy T. , Vékey Kàroly 
Published: May 2005

AbstractThis paper summarizes the data obtained during the last 20 years on the mass spectrometric behaviour of C15 and thio−C30 nuphar alkaloids. The usefulness of this technique in the solution of stereochemical problems is confirmed.
Structure determination of the antibiotic desertomycin B by fast‐atom bombardment mass spectrometric techniques
Authors: Dinya Zoltán , Sztaricskai Ferenc , Horváth Géza , Vékey Kàroly 
Published: May 2005

AbstractBy means of different fast‐atom bombardment (FAB) mass spectrometric techniques (i.e., positive‐ and negative‐ion FAB ionizations and high resolution measurements) we have determined the chemical structure of desertomycin B which is a novel representative of the family of macrolide antibiotics carrying a guanidino function in its side‐chain.
Laser‐pulse ejection of organic molecules from a matrix: Lessons from fast‐ion‐induced ejection
Authors: Johnson R. E. , Sundqvist B. U. R. , Ens W. 
Published: May 2005

AbstractLessons learned from electronic sputtering by incident ions of condensed‐gas solids and solids composed of biomolecules are applied to laser‐pulse‐induced ejection of biomolecules inbedded in a matrix of small molecules. In electronic sputtering by fast ions, single excitation desorption, thermally activated sputtering, and pressure‐pulse sputtering have been observed. In addition, yields for ejected ions have been shown to exhibit trends different from yields for ejected neutrals. The parallel processes are considered for laser‐pulse ejection of a martix with imbedded molecules and expressions are given to examine the yield data.
Thermally induced dissociation of ions from electrospray mass spectrometry
Authors: Rockwood Alan L. , Busman Mark , Udseth Harold R. , Smith Richard D. 
Published: May 2005

AbstractThe thermally induced dissociation (TID) of inos at near atmospheric pressure, followed by their mass spectraometric analysis, is demonstrated. The TID occurs in a heated metal capillary interface, and should be broadly applicable to any system capable of producing ions at high pressure. The heated capillary provides a reaction vessel, potentially very useful for kinetic and mechanistic studies of ions. The technique has been applied to the fragmentation of large multiply charged ions from an electrospray ionization source. Preliminary results show that stability for multiply protonated petide or protein molecules in inversely related to its charge.
Ion counting and ion intensity measurements in time‐of‐flight mass spectrometry. Application to matrix‐assisted laser desorption
Authors: Baptista G. B. , Brunelle A. , Chaurand P. , Della‐negra S. , Depauw J. , Le Bayec Y. , Chait B. T. 
Published: May 2005

AbstractA time‐to‐digital converter coupled to a charge‐to‐digitalconverter has been used to record mass spectra in matrix‐assisted laser desorption(MALD) time‐of‐flight mass spectrometry. Masses above 100 000 Da have been detected by ion counting. Utilizing an electrostatic mirror, good mass resolution has been achieved in MALD. When the number of detedted secondary ions is small the sensitivity of mass measurements is improved by using a charge‐to‐digital converter rather than a transient recorder.
Mass spectrometric analysis of a transition‐metal‐binding peptide using matrix‐assisted leaser‐desorption time‐of‐flight mass spectrometry. A demonstration of probe tip chemistry
Authors: Nelson Randall W. , Hutchens T. William 
Published: May 2005

AbstractMatrix‐assisted laser desorption time‐of flight mass spectrometry has been used to investigate the affinity of aqueous copper ions for a 26‐residue synthetic peptide predicted to have metal‐binding properties. A specific reaction occurred upon the dirct application of aqueous CuSO4 to the matrix/peptide sample remaining on the probe tip ater initial mass spectrometric investigation. Results indicated the binding of up to one copper ion per histidine residue and the loss of one proton for each bound copper. Bound copper was not returned to solution upon subsequent cold water washings of the probe tip. These results suggest that covalent interations, between the copper and the peptide, occurred during the probe‐tip application of the metal ion to the sample.
Negative‐ion fragmentations of deprotonated heterocycles. The pyrazole and imidazole ring systems
Authors: Adams Gregory W. , Bowie John H. , Hayes Roger N. 
Published: May 2005

AbstractImidazole and pyrazole deprotonate preferentially at the 1‐position, and a number of fragmentations are best rationalized as occurring through common ring‐opened intermediate −NHCHCHCN. C‐Methylomidazoles and pyrazoles fragment similarly.
Development of a condensation technique for thin‐layer chromatography/fast‐atom bombardment mass spectrometry of non‐visible compounds
Authors: Oka Hisao , Ikai Yoshitomo , Kondo Fumio , Kawamura Norihisa , Hayakawa Junko , Masuda Katsuyoshi , Harada Ken‐Ichi , Suzuki Makoto 
Published: May 2005

AbstractIn Order to prevent the diffusion of sample when a matrix is deposited on the sample spot on a thin‐layer chromatography (TLC) plate and to obtain constructively high sensitivity in mass spectrometry, we developed a conedensation technique including ‘trapezoid technique’ for TLC/fast‐atom bombardment mass spectrometry (FABMS) on both silica gel and C18 plates. For colored samples and colorless samples having a chromophore, the condensation technique previously in use, that condenses the sample towards the center of the spot in a line, using methoanol, was effective. The trapezoid condensation technique has been newly developed for colorless compounds having no chromophore. The mass spectra obtained using this technique clerly showed molecular ion species at relatively lower concentrations of samples, and the technoique can improve the detection limits of molecular ion species in TLC/FABMS by 3‐100 times with good reproducibility.
Secondary‐ion generation from large keV molecular primary ions incident on a stainless‐steel dynode
Authors: Kaufmann Raimund , Kirsch Dieter , Rood Hans‐Achim , Spengler Bernhard 
Published: May 2005

AbstractPositive and negative secondary ions from large (up to 40 KDa) peptide and protein primary ions incident at 5–40 keV collisional energies on a stainless‐steel (mesh) conversion dynode have been investigated in a tandem (reflectron) time‐of‐flight arrangement. Negative secondary‐ion spectra consisted mainly of H− and C2H−, C2H ions; positive secondary‐ion spectra were more complex and contained prominent signals due to H+, Na+ and K+, and further signals at m/z. 28, 41, 43, 45, 73 up to m/z 326. The secondary mass spectra were qualitatively very similar amongst the various peptide primaries and not different from those of other organic projectiles such as, for example, coronene or cyclodextrin. With increasing mass of the primary ion, ratios of the secondary‐ion abundances changed drastically in the negative secondary‐ion spectra (increase of higher m/z signals, decrease of H−). Since most of the positive secondary ions could be attributed to a silicon‐organic surface contamination of the dynode (vacuum grease), it is concluded that the formation of such secondary ions is due to sputtering rather than surface‐induced dissociation.
Triphosphorus disulfide: The elusive P3S radical generated and identified by neutralization/reionization mass spectrometry
Authors: Keck Helmut , Kuchen Wilhelm , Tommes Peter , Wong Thomas , Terlouw Johan K. 
Published: May 2005

AbstractThe dissociative ionization by electron impact (70 eV) of terraphosphorus trisulfide, P4S3, yields P3S ions whose neutralization/reionization mass spectrum shows that the elusive P3S radical is a viable species in the rarefied gas phase. Ab initio molecular orbital calculations indicate that the structure of this radical is that of a planar five‐membered PPSPS ring of C2v symmetry.
Negative‐ion fast‐atom bombardment mass spectra of fluorosilicates. Reactivity of matrices
Authors: Aubagnac Jean‐Louis , Poirier Monique 
Published: May 2005

AbstractNegative‐ion fast‐atom bombardment mass spectra of fluorosilicates allow their identification. Both a glycerol matrix and a m‐nitrobenzyl alcohol matrix show specific reactivities towards the anions.
Gas‐phase chemistry of first transition series carbonyl metallate ions, [Metal(CO)x]−: Reactions with 13C‐ and 18O‐Labelled carbon dioxide. A Fourier‐transform ion cyclotron resonance study
Authors: Gregor I. K. , Gregor R. C. 
Published: May 2005

AbstractGas‐phase reactions between 13CO2 and C18O2 and a series of carbonyl metallate ions [Metal(CO)x]− with x=3, 4 for the metals chromium, manganese, iron and also x=2 for iron, have ben examined at low pressures by Fourier‐transform ion cyclotron resonance mass spectrometry. while the 16‐and 17‐electron ions [Mn(CO)4]− and [Fe(CO)4]− were unreactive, both ligand displacement and oxidative reactions have been identified for the other 13‐, 14‐ and 15‐electron metal‐ion systems as a consequences of Metal‐C, O13 and 18OC cleavages in [(CO)x. Metal. η2‐OCO]− intermidiates.
Electron impact and chemical ionization mass spectrometry of heterocumulenes produced by flash vacuum pyrolysis
Authors: Brown Jeff , Flammang Robert , Govaert Yasmine , Plisniedr Michel , Wentrup Curt , Van Haverbeke Yves 
Published: May 2005

AbstractHeterocumulenes such as ketenes, propadienones and comulogs of isocyanates are produced by flash vacuum pyrolysis of Meldrum's acid. Real‐time monitoring of the pyrolysis products is performed by methods of tandem mass spectrometry. In particular, chemical ionization is show, for the first time, to generate protonated moleculular ions of these kinetically unstable neutral molecules which can be identified by collisional activation experiments.