bluuebunny/crossref_metadata_2025_split huggingface dataset:
Collision‐induced dissociations of peptide ions 2. Remote charge‐site fragmentations in a tandem, hybrid mass spectrometer
Authors: Alexander A. J. , Thibault P. , Boyd R. K. 
Published: May 2005

AbstractCollision‐induced dissociation of peptide ions yields „sequence”︁ ions arising from dissociations of the peptide backbone. Recently, Biemann and his collaborators have elucidated fragment ions involving cleavage of all or part of the side‐chains, and have characterized them as remote‐site fragmentations of the type investigated for other molecular species by Gross et al. The present work reports results of experiments conducted using a tandem, hybrid mass spectrometer, and devoted to investigating whether remote‐site fragmentations (including side‐chain cleavages for peptide ions) can be observed for collision energies substantially lower than the keV range used previously. It was found that (laboratory‐frame) collision energies of at least 200 eV, and preferably greater, are required for the formation of such fragments. At collision energies in this range the transmission efficiency of the qQ assembly is much lower than for the more usual range of a few tens of eV; this drop in transmission efficiency becomes increasingly severe with increasing mass of the precursor.
Mass range extension in a quadrupole ion‐trap mass spectrometer
Authors: Kaiser Raymond E. , Cooks R. Graham , Moss James , Hemberger Phillip H. 
Published: May 2005

AbstractA quadrupole ion‐trap mass spectrometer having half the dimensions of the commercial ion‐trap instrument has been built. When operated in the mass‐selective instability mode using the commercial electronics and data system and the standard vacuum system, it yields a mass range of > 2500 Da. This represents achievement of the expected fourfold increase in mass range upon halving the trap radius (to 0.5 cm). The sensitivity of the miniature trap is comparable to that of the commercial ion‐trap; however, resolution is inferior, partly due to the high mass‐scan rate. The effects of using relatively high pressures of helium as a buffer gas are discussed in relation to improving sensitivity and resolution. The use of the high‐mass ion‐trap as a device for studying biomolecules is discussed and methods of extending the mass range even further are suggested.
Fast‐atom bombardment and thermospray mass spectrometry for the characterization of two glucuronide metabolites of methapyrilene
Authors: Lay J. O. , Getek T. A. , Kelly D. W. , Slikker W. , Korfmacher W. A. 
Published: May 2005

AbstractTwo conjugated metabolites of methapyrilene hydrochloride isolated from mouse‐hepatocytes were examined by mass spectrometry using fast‐atom bombardment (FAB) and thermospray ionization. The major metabolite, methapyrilene glucuronide, was identified based on a prominent peak due to the protonated molecule as well as the loss of the dimethylamine and sugar moieties. Identification of the second metabolite was complicated by large signals associated with the biological sample matrix. The complementary nature of the fragmentation observed in the mass spectra using FAB and thermospray ionization allowed this metabolite to be identified as the desmethylmethapyrilene glucuronide. The fragmentation observed using FAB ionization was not greatly affected by the presence of the glucuronide moiety. While loss of the sugar moiety indicated a glucuronide, additional fragmentation confirmed the presence of the underlying ethylenediamine substructure which is characteristic of this class of antihistamines.
Mass spectrometric indication of double‐bond position in dodecenyl acetates based on a fuzzy classification
Authors: Horiike Michio , Gu Yuan , Hirano Chisato 
Published: May 2005

AbstractTen positional isomers of dodecenyl acetate were analyzed by conventional combined gas chromatography/electron ionization mass spectrometry. The relative intensities of some predominant fragments in the isomers examined varied with the double‐bond position in the chain. The mass spectra were interpreted in terms of the standard parameters, similarity coefficients, clustering weight and clustering coefficients. The original double‐bond position in the acetates was located unambiguously.
Ion‐spray mass spectrometry of marine neurotoxins
Authors: Quilliam Michael A. , Thomson Bruce A. , Scott George J. , Siu K. W. Michael 
Published: May 2005

AbstractIon‐spray mass spectrometry was investigated for the analysis of three marine neurotoxins: domoic acid, saxitoxin and tetrodotoxin. All three compounds gave positive‐ion spectra with abundant ions of protonated molecules and no significant fragmentation. Domoic acid gave a negative‐ion spectrum with a strong [M–H]−ion. Tandem mass spectrometry provided useful fragment‐ion spectra for all compounds. Detection limits for flow injection analyses with selected‐ion monitoring were determined to be 30 pg for saxitoxin, 100 pg for domoic acid and 200 pg for tetrodotoxin. Combining liquid chromatography with ion‐spray mass spectrometry allowed the determination of domoic acid and some of its isomers in toxic shellfish tissue extracts.
The oxyisocyanate [ONCO]− and amidoisocyanate [HNNCO]− negative ions
Authors: Waugh Russell J. , Eichinger Peter C. H. , O'Hair Richard A. J. , Sheldon John C. , Bowie John H. , Hayes Roger N. 
Published: May 2005

AbstractAb initio calculations indicate that the ion [ONCO]− is linear, whereas [HNNCO]− is effectively coplanar. The ions may be formed by collisional activation of deprotonated hydroxy and aminocarbamates. The characteristic fragmentations of [ONCO]− and [HNNOO]− are losses of O and NH respectively.
Influence of metal ions on the acquisition and quality of 252Cf plasma‐desorption mass spectra
Authors: Deprun Claude , Szabó Ladislas 
Published: May 2005

AbstractThe presence of a few mol per cent of Ca2+ ions considerably modified the 252Cf plasma‐desorption mass spectrum of a phosphorylated glycolipid. In the negative‐ion mode, increasing amounts of Ca2+ caused gradual disappearance of the spectrum; it was quenched at the molar ratio 3 Ca2+/4 glycolipid. Clusters as big as 5500 were observed at certain ratios of Ca2+/glycolipid. Similar, but less pronounced effects were seen in the positive‐ion mode.
Charge separation of triply charged ions
Authors: Hagan D. A. , Eland J. H. D. 
Published: May 2005

AbstractFormation of multiply charged ions is shown to contribute a significant fraction of the total ionization by high energy electrons, and multiple ionization is almost always followed by charge‐separation reactions. Triple ionization and subsequent dissociations can be well characterized by the electron‐three ion coincidence technique. Results obtained using this new technique are compared with computer simulations of the dissociations of OCS3+ and SO3+2, and the initial momenta and relátive angles of all three fragments are thereby determined. Triply charged benzene ions are shown to undergo many competing charge‐separation reactions.
Determination of appearance energy for ions formed in the gaseous phase over alkali iodide and rare earth iodide systems
Authors: Popovič A. , Muhič S. , Marsel J. , Ajtony Zs. , Bencze L. , Kaposi O. , Zmbov K. F. 
Published: May 2005

AbstractKnudsen cell mass spectrometric measurements are reported on the composition of vapour over solid and fused NaI, CsI, HoI3, DyI3, (NaI + HoI3), (NaI + DyI3, (CsI + HoI3) and (CsI + DyI3 systems. For the determination of evaporation thermodynamics, the assignment of the essential ions to their neutral precursors was carried out by determining ionization efficiency curves. Due to the spread in electron energy, the linear extrapolation and vanishing current methods, which are generally used in high temperature mass spectrometry for evaluation of efficiency curves, could be used with limitations only. The analytical energy‐distribution difference method was used to determine the fine structure of the ionization efficiency curves. The method uncovered relationships between the detected ions and neutral vapour‐phase species, and served to determine thermodynamic data with improved precision.
Mass spectrometry of some carbamoyl‐ and thiocarbamoylcyclohexanones
Authors: Srzić D. 
Published: May 2005

AbstractThe fragmentation of some carbamoyl‐ and thiocarbamoylcyclohexanones under electron ionization has been investigated by means of high‐ and low‐resolution mass spectrometry and deuterium labelling. Some characteristic fragmentation processes observed in the mass spectra of thiocarbamoylcyclohexanones indicate that both keto and enol forms of their molecular ions exist in the gas phase. The fragmentation data for carbamoylcyclohexanone show that the keto form is largely predominant in the keto‐enol tautomeric equilibrium.
Kinetic energy release in metastable‐ion fragmentations
Authors: Burgers Peter C. , Holmes John L. 
Published: May 2005

AbstractThe average kinetic energy, (〈T〉), released in a number of well known metastable‐ion decompositions (reaction‐time 10−5‐10−6s−1) has been related to the excess energy in the fragmenting ion (E). It was observed that for small values of E (< 1 eV) the fraction of energy released, 〈T〉/E, increases rapidly as E decreases, as predicted by statistical theory.
Philanthotoxins. A mass spectrometric investigation
Authors: Kenny Peter T. M. , Goodnow Jr Robert A , Konno Katsuhiro , Nakanishi Koji 
Published: May 2005

AbstractA method employing liquid secondary‐ion mass spectrometry (SIMS) in conjunction with metastable‐ion measurements (linked scanning at constant B/E) to obtain sequence‐specific information for three synthetic polyamine isomers was developed. The normal liquid SIMS spectra gave molecular weight information, but important sequence ions were of low intensity or obscured by the background. The metastable‐ion spectra contained important fragment ions in particular due to cleavage along the polyamine chain. One of the three synthetic isomers was identical with a toxin present in the venom of the digger wasp. In conjunction with nuclear magnetic resonance spectroscopic studies, this should be a powerful method for the structural characterization of other closely related toxins present in the venom of this wasp.
Fourier transform ion cyclotron resonance study of the gas‐phase reaction of the yttrium ion with silane
Authors: Decouzon M. , Gal J‐F. , Géribaldi S. , Rouillard M. , Sturla J‐M. , Bouchoux G. 
Published: May 2005

AbstractPreliminary results obtained with a home‐made Fourier transform ion cyclotron resonance mass spectrometer on the sequential clustering reactions of silane using yttrium cation activation are reported. [YSinH2n]+ and [YSinH2n − 2]+ ions are formed. So far, we have observed these ions up to n = 7, and a sequential clustering mechanism is proposed. The ion structures are characterized by collision‐induced dissociation, and kinetic measurements to determine the formation and decay rates of each ion are performed.
The formation of cyclopentadienone ions. An internal oxidation process
Authors: Maquestiau A. , Flammang R. , Govaert Y. , Chen L. Z. , Longevialle P. 
Published: May 2005

Abstract1‐(2‐nitrophenyl)benzotriazole loses nitrogen upon electron ionization. This reaction is followed by a Wolff‐type ring contraction to give cyclopentadienylidene methanimine ions which undergo an internal oxidation process producing ionized cyclopentadienone.
Plasma‐desorption mass spectrometry of intact enzymes and proenzymes
Authors: Lacey M. P. , Keough T. , Chait B. T. 
Published: May 2005

AbstractThe plasma desorption (PD) mass spectra of several enzymes and proenzymes are reported. Chymotrypsin and chymotrypsinogen both yield usable PD mass spectra; however, the single‐chain chymotrypsinogen exhibits better sensitivity and less fragmentation than the multi‐chain chymotrypsin. Porcine pepsinogen contains 11 more basic residues (lysine and arginine) than porcine pepsin, but this does not lead to an increase in positive ion response. In fact, the additional basic residues may hinder response by increasing the strength of the interaction between the protein and the nitrocellulose surface. A series of subtilisins showed comparable PD mass spectrometric, response despite the fact that they differ considerably in primary sequence. Finally, PD mass spectrometry was used to correct the previously reported mass of a heat‐stable protease, a value that we found to be in error by almost 5000 Da.
Translational energy release and stereochemistry of steroids. 14. Epimeric dihydroxy steroids of the androstane series
Authors: Zaretskii Z. V. I. , Ghosh D. , Brenton A. G. , Beynon J. H. 
Published: May 2005

AbstractThe stereochemistry of dihydroxy steroids, both the mode of the A/B ring junctions and the configuration of OH groups, may be determined from translational energy (T50%) measurements for the loss of a CH3 radical, from the ratios of metastable‐ion peak heights to those of the main beam (determined for the dehydration reactions), and by comparing unimolecular and collision‐induced, mass‐analysed ion kinetic energy spectra of the new main beam of [M H2O]+˙ ions (i.e. those formed via dehydration of metastable molecular ions of epimeric hydroxy steroids in the first field‐free region of a double‐focusing mass spectrometer).
Gas chromatography/negative‐ion chemical ionization mass spectrometry of tertiary amines following Hofmann degradation. Application to the characterization of Loperamide
Authors: Leis Hans Jörg 
Published: May 2005

AbstractA method for negative‐ion chemical ionization mass spectrometry of tertiary amines with special reference to the antidiarrhoeal Loperamide is presented. The method involves quaternization by reaction with pentafluorobenzyl bromide, conversion to the hydroxide base with silver oxide; subsequent Hofmann degradation occurs in the hot injector of the gas chromatograph. The method shows greater sensitivity than more orthodox Hofmann degradation reactions.
Three stable (PhenylC7H) isomers
Authors: Stone David J. M. , Eichinger Peter C. H. , Bowie John H. 
Published: May 2005

AbstractStable PhC7H isomers may be formed by deprotonation of diphenylmethane, phenylcycloheptatriene and 7‐phenylnorbornadiene. Each species has a characteristic fragmentation pattern—the elucidation of which is aided by deuterium‐labelling studies. There is no evidence of interconversion of the three species.
Metastable ions arising from pseudomolecular [M  H]− ions produced by fast‐atom bombardment negative‐ion mass spectrometry of ecdysteroids
Authors: Evershed Richard P. , Prescott Mark C. , Kabbouh Mohamed , Rees Huw H. 
Published: May 2005

AbstractMetastable ions arising from pseudomolecular [M  H]− ions produced by fast‐atom bombardment negative‐ion mass spectrometry of a range of free ecdysteroids, ecdysteroid conjugates and polar metabolites were investigated by means of linked scanning at constant B/E. Free ecdysteroids displayed daughter‐ion spectra which allow 20‐hydroxyecdysteroids and ecdysteroids lacking C‐20 hydroxylation to be readily distinguished. The ejection of acetic acid from acetylated ecdysteroids was also readily detectable. Characteristic metastable‐ion decomposition of ecdysteroid acids was not observed, presumably as a result of charge localization. High‐mass daughter ions were also lacking in the case of phosphate conjugates.
Laser desorption/fourier transform mass spectrometry of organometallic complexes
Authors: Bjarnason Asgeir 
Published: May 2005

AbstractA study of the analytical potential of laser desorption Fourier transform mass spectrometry for the mass spectral analysis of complexes is reported. Two platinum complexes, which are also organometallic, were successfully analyzed using this technique. Previous attempts using fast‐atom bombardment mass spectrometry had not yielded any useful information for these compounds. Two complexes of a different nature, 1,3‐bis(diphenylphosphino)propanenickel(II) chloride and N,N′ ‐bis(salicylidene)dianilinocobalt(II) were also analyzed to further evaluate this technique.
Measurement of unimolecular decay in peptides of masses greater than 1200 units by a reflecting time‐of‐flight mass spectrometer
Authors: Tang X. , Ens W. , Mayer F. , Standing K. G. , Westmore J. B. , Boyd R. K. 
Published: May 2005

AbstractDaughter ions from decomposition of [M + H]+ parent ions have been observed in a time‐of‐flight mass spectrometer fitted with an ion mirror. Unit mass resolution is obtained for parent ions of masses up to several thousand u when the mirror voltage is set at a value determined by the usual velocity‐focusing criterion for parent ions. Under this condition the daughter‐ion resolution in the low‐mass range suffers. Considerable improvement is obtained when the daughter‐ion spectrum is examined in several segments, with the mirror voltage optimized for each segment. The daughter‐ion spectrum from decay of metastable [M + H]+ parent ions in Substance P is measured using this technique. Reasons are suggested for differences between the spectrum obtained and a spectrum for the same compound recently obtained using a tandem double‐focusing instrument.
The intramolecular migration of a trimethylsilyl group located α to a sulfone in substituted cyclohexyl systems
Authors: Wood K. V. , Rothwell A. P. , Anderson M. B. , Fuchs P. L. 
Published: May 2005

AbstractThe intramolecular migration of a trimethylsilyl moiety α to a sulfone group of some modified cylcohexyl ring systems is investigated. The large difference in the relative abundance of this rearrangement ion for similar compounds is related to the stability of the protonated species.
Capillary‐zone electrophoresis with fraction collection for desorption mass spectrometry
Authors: Takigiku Ray , Keough T. , Lacey M. P. , Schneider R. E. 
Published: May 2005

AbstractA simple method for off‐line coupling of desorption mass spectrometry and capillary‐zone electrophoresis (CZE) is described. Use of a “porous glass joint”, near the cathodic end of the CZE column, facilitates fraction collection in a manner similar to that used with liquid chromatography. This method allows independent optimization of both the CZE and mass spectrometry parts of the experiment. It is directly applicable to a number of desorption mass spectrometry methods (including plasma desorption (PD) and UV laser desorption (LD)). In the present study, PD mass spectrometry was used for eluant characterization. The fraction collection procedure is described, as is mass transfer through the porous glass joint. Detection limits are discussed and the approach is illustrated by analysis of a simple mixture of bradykinin derivatives. Finally, a brief comparison to current on‐line CZE/mass spectrometric methods is presented.
Influence of sequence on the fragmentation of serine‐ and threonine‐containing peptides in 252Cf‐plasma desorption mass spectrometry
Authors: Lam‐Thanh Hung , Deprun Claude , Le Beyec Yvon 
Published: May 2005

AbstractThe molecular weights of four linear synthetic peptides, fragments of a snake α‐neurotoxin, were measured by 252Cf‐plasma desorption mass spectrometry. The fragmentation phenomenon observed at the level of serine and/or threonine residue with a concomitant ion/fragment association is reported for a group of two peptides (B and D) in contrast with the group (A and C) in spite of the high ratio of serine and threonine, namely peptide A. The propensity for specific fragmentation of peptide D seems to be correlated to the repetitive sequence, (Gly‐Ser)2. Finally, based on the m/z of the daughter‐ions measured, we propose an overall mechanism as an N→O acyl shift analogous to that observed for serine‐ and threonine‐ containing peptides in solution chemistry.
Translational energy release and stereochemistry of steroids 15. Reaction conformations of metastable molecular ions in stereoisomers of 3‐hydroxy steroids
Authors: Zaretskii Z V I , Ghosh D , Brenton A G , Beynon J H 
Published: May 2005

AbstractThe reaction conformations of the metastable molecular ions of the 3‐hydroxy steroids were characterized using translational energy (T50%) release values and the ratios of metastable‐ion peak heights to those of the main beams determined for the M+· → [M‐H2O]+· reactions.
Types of quasimolecular ions in thermospray ionization
Authors: Maeder H. 
Published: May 2005

AbstractThermospray mass spectra are usually dominated by [M + H]+ and [M + NH4]+ quasimolecular ions. Several years' work with various classes of compounds using the technique of liquid chromatography/thermospray ionization mass spectrometry has given us the opportunity of observing further adduct ions of lower intensity. Knowledge about these ions facilitates interpretation of thermospray spectra, enables the analysis of peak purity and gives additional confirmation of correct molecular weight assignment.
Mass spectral fragmentations of ionized alkylperhydro‐1,3‐oxazines
Authors: Vainiotalo Pirjo , Romppanen Tuula , Mälkönen Pentti J. 
Published: May 2005

AbstractThe mass spectral fragmentations of perhydro‐1,3‐oxazine and twelve of its alkyl derivatives were studied by metastable‐ion analysis and exact mass measurement. The role of the nitrogen atom was dominant in these fragmentations. Almost all the primary decompositions of the molecular ions started as α‐cleavage reactions with respect to the nitrogen atom, leading to the loss of a substituent from an adjacent carbon or to a ring‐cleavage reaction. Preference for the ring‐cleavage reaction was increased by a substituent at position 2. Some rearrangement reactions were observed as well. The expulsion of C2H3O˙ from the molecular ion was particularly favoured for the 3‐methyl substituted compounds. In this elimination, ring carbons 5 and 6 were lost simultaneously with a hydrogen atom transfer to the nitrogen atom.
Fragment pathway analysis using automated tandem mass spectrometry on an ion‐trap mass spectrometer
Authors: Pannell L. K. , Quan‐long Pu , Mason R. T. , Fales H. M. 
Published: May 2005

AbstractA “key‐sequence” procedure is presented for the automated tandem mass spectrometric analysis of compounds on a Finnigan ion‐trap mass spectrometer. This allows fragmentation pathways of a range of masses or even a complete spectrum to be prepared automatically, obviating the tiresome preparation and optimization of individual scan‐editor files. The procedure is limited by the speed of the driving computer; an “IBM‐AT”, for example, permits more than 10 mass units to be scanned per minute. It is calibrated with perfluorotributylamine and methyl stearate is used to demonstrate its results. The Finnigan ion‐trap “programming option” is necessary for implementation of the procedure.
Peptide sequencing with electrospray ionization on a magnetic sector mass spectrometer
Authors: Meng C. K. , McEwen C. N. , Larsen B. S. 
Published: May 2005

AbstractSequence information is obtained by in‐source fragmentation of electrospray‐generated peptide ions. The complete sequences of leucine enkephalin, angiotensin I, and renin substrate are determined from their fragment ions and consume only low picomole amounts of material. The method involves collision‐induced fragmentation of singly and multiply charged molecular ions in the electrospray ion source and does not involve tandem mass spectrometric instrumentation. The charge on the fragment ions is determined by the spacing of the isotope peaks.
Mass spectrometric investigation of the thermal decomposition of lithium fluoroborate
Authors: Veljković Miomir , Ya. Borshcevskii Adrey , Nešković Olivera , Miletić Miodrag , Golobočanin Dušan , Vaisberg Victorya E. , Zmbov Kiro F. 
Published: May 2005

AbstractEvaporation of crystalline LiBF4 was studied by Knudsen‐cell mass spectrometry in the temperature range 70–140°C. Only BF3 molecules were identified in the saturated vapour. The temperature dependence of BF3 pressure was measured and ΔrH°374 = 105.4 ± 9.6 kJ mol−1 for the reaction LiBF4(c) = LiF(c) + BF3(g) was obtained from the second‐law analysis. The corresponding heat of formation ΔfH° (LiBF4, c, 374) = −1856.4 ± 10.5 kJ mol−1 was evaluated and compared with Literature data.