bluuebunny/crossref_metadata_2025_split huggingface dataset:
Surface effects in fast atom bombardment mass spectrometry of ethylene glycol‐glycerol mixtures
Authors: Dube Gunther , Vollhardt Dieter 
Published: May 2005

AbstractBinary mixtures of ethylene glycols HO(CH2CH2O)xH (x = 3–5) with glycerol were investigated by fast atom bombardment mass Spectrometry. The relative intensities in the ethylene glycol partial mass spectra as a function of concentration exhibit a steep slope in the low concentration range. With increasing concentration the curves asymptotically approach the 100% line. This effect increases from triethylene to pentaethylene glycol. Comparison of these results with those of surface tension measurements leads to the conclusion that the high sensitivity of fast atom bombardment mass Spectrometry for ethylene glycols is caused by the surface‐active properties of these compounds, which lead to an enrichment of the surface investigated with the substance molecules.
Mass spectra of 1‐aryl‐2, 2‐dibromocyclopropanes
Authors: Lin Shaw‐Tao , Lin Mei‐Ling , Lin Wen‐Chung 
Published: May 2005

AbstractThe electron impact (EI) mass spectra of sixteen 1‐aryl‐2,2‐dibromocyclopropanes give an ion at m/z 115, the structure of which is proposed to be the indenium ion based on a collision‐activated decomposition experiment.
Collision‐activated decomposition of peptides by Fourier transform ion cyclotron resonance spectrometry
Authors: Sheil Margaret M. , Guilhaus Michael , Derrick Peter J. 
Published: May 2005

AbstractThe dynamics of the collision‐activated decomposition (CAD) of large peptide ions by Fourier transform ion cyclotron resonance (FT‐ICR) spectrometry have been investigated in detail. The results presented concern [ M + H]+ ions of the cyclic depsipeptides beauvericin (M = 783.4 u) and valinomycin (M = 1110.6 u) and demonstrate that these peptide ions with less than 100 eV translational energy can undergo collisions with netrual gas atoms and decompose to yield abundant fragment ions. The effects of varying two parameters, the duration of the radiofrequency pulse used to accelerate the precursor ions and the time allowed for collisions, are illustrated. Increasing the former is shown to increase the extent and nature of CAD fragmentation; however, the same effect was not observed on increasing the collision time, and hence the number of collisions, at the pressures used in these experiments.
Fast atom bombardment mass spectrometry of some alkoxv‐ and chloro‐silanes
Authors: Kallury Krishna M. R. , Krull Ulrich J. , Thompson Micliael 
Published: May 2005

AbstractThe positive and negative FAB mass spectra of a series of alkoxy‐ and chloro‐silanes Xm(CH3)3‐mSi(CH2)nR [m = 1 or 3, n = 3, 10 or 17, X = Cl or OMe or OEt, R = Me, NH2, glycidoxy, COOMe, NHCO(CH2)7COOMe or NHCO(CH2)10CH2OAc] were recorded in NBA and NPOE matrices. The chlorosilanes underwent rapid hydrolysis into silanols which condense to form siloxanes, the process being complete in NBA and partial in NPOE, yielding siloxane‐based fragment ions in the positive spectra and silyloxyanions in the negative spectra. The alkoxysilanes were more resistant to hydrolysis, affording abundant [MH – HX]+ ions (X = OMe or OEt) in their positive FAB spectra and moderate to high intensity [M – H]− ions in the negative mode, the latter undergoing characteristic sequential loss of C2H4, EtOH and C2H4. Significant variations were observed in the positive spectra of all the silanes with change of matrix.
Electron impact and chemical ionization mass spectra of some unsaturated anomeric C‐glycosides
Authors: Brakta Mohamed , Lhoste Paul , Sinou Denis , Banoub Joseph 
Published: May 2005

AbstractElectron impact mass spectra at 70 eV electron energy and chemical ionization mass spectra with ammonia as the reagent gas are reported for certain unsaturated C‐glycosides. Comparisons are made between the mass spectra of anomeric pairs of these glycosides.
Electron impact‐induced fragmentation of some aminonitropyridines
Authors: Gawinecki Ryszard , Rasała Danuta 
Published: May 2005

AbstractThe fragmentation behaviour of 18 vicinally substituted aminonitropyridines was studied under electron impact conditions. Tbe decomposition patterns were found to be strongly dependent on the position of substituents. The formation of the aza analogue of carbazole seems to affect considerably the fragmentation of 3‐nitro‐2‐phenylaminopyridine.
Mass spectral fragmentation pathways of N‐acetylnitramines: 1‐acetylhexahydro‐3,5‐dinitro‐1,3,5‐triazine and 1‐acetyloctahydro‐3,5,7‐trinitro‐1,3,5,7‐tetrazocine
Authors: Burrows Elizabeth P. 
Published: May 2005

AbstractMass spectra of the N‐acetylnitramines l‐acetylhexahydro‐3,5‐dinitro‐l,3,5‐triazine (TAX) and 1‐acetyloctahydro‐3,5,7‐trinitro‐l,3,5,7‐tetrazocine (SEX) were recorded in electron impact (EI) and positive and negative chemical ionization (PCI and NCI) modes, and the fragmentation pathways were compared with those of other nitramines which have been well documented and characterized. Unexpectedly, for both acetylnitramines in the EI mode (and in the PCI mode) proton adducts were the only molecular ion species observed; in neither mode was there evidence for higher adducts. In contrast, for TAX in the NCI mode the [M + NO2]− adduct was the second most abundant ion (70%); relatively small amounts of the [M + NO]− adduct (2%) and the hydrogen adduct [MH]− (3%) were observed. Under identical NCI conditions no molecular ion species or adduct ions were detected for SEX; the ion of highest m/z corresponded to loss of NO2 or HNO2 from a molecular ion species. The findings of collision‐induced dissociation experiments are also discussed.
Electron impact mass spectrometry of some 3‐substituted 1,2,3,4‐tetrahydroisoquinolines
Authors: Ibañez Adriana F. , Iglesias Graciela Y. Moltrasio 
Published: May 2005

AbstractThe electron impact mass spectral fragmentation of a series of 3‐substituted‐l,2,3,4‐tetrahydroisoquinolines are reported. The principal fragmentation modes of these compounds comply with the main generalizations reached earlier with simpler systems. Complete aromatizations to form the isoquinolinium ion are observed only for compounds 5 and 7 and no retro‐Diels‐Alder cleavage is observed when R1 is a benzyl group.
Determination of the proton affinity of carbon dioxide by photoionization mass spectrometry
Authors: Traeger John C. , Kompe Barbara M. 
Published: May 2005

AbstractThe adiabatic ionization energies and COOH+ appearance energies for a series of carboxylic acids have been measured by dissociative photoionization mass Spectrometry. Using the stationary electron convention, a heat of formation of 143.5 ± 0.7 kcal mol−1 (1 kcal = 4.184 kJ) at 298 K is derived for the carboxyl cation in the gas phase, which corresponds to an absolute proton affinity for carbon dioxide of 128.1 ± 0.7 kcal mol−1.
Low‐Energy, low‐temperature mass spectra. 14—A simple model for the rate coefficient
Authors: Maccoll A. 
Published: May 2005

AbstractThe Kassel quantum model for the unimolecular rate coefficient is applied to mass spectral fragmentation. The inadequacy of the classical model is emphasized. The kinetic effect, the competitive effect and the thermal effect are discussed. Finally, the mass spectrum is presented as a function of energy. The quantum model, involving summation over states rather than integration over an energy range of the classical model, is ideally suited to simple computation.
[C6H6, C3H7+]and [C6H7+, C3H6] ion‐neutral complexes intermediate in the reactions of protonated propylbenzenes
Authors: Berthomieu Dorothée , Audier Henri , Denhez Jean‐Pierre , Monteiro Candida , Mourgues Philippe 
Published: May 2005

AbstractFrom the mass‐analysed ion kinetic energy spectra of labelled ions, kinetic energy releases and thermodynamic data, it is proved that protonated n‐propylbenzene (1) isomerizes into protonated isopropyl benzene (2). It is also shown that the dissociation of the less energetic metastable ions of (2), leading to [iso‐C3H7]+ and [C6H7]+ product ions, is preceded by H exchange. This H exchange involves two interconverting ion‐neutral complexes [C6H6, iso‐C3H7+] (2π) and [C6H7+, C3H6] (2α).
Highly specific fragmentation processes of isomeric mixed esters of phenylsuccinic acid under electron impact
Authors: Vidavsky I. , Mandelbaum A. , Tamiri T. , Zitrin S. 
Published: May 2005

AbstractIsomeric mixed dialkyl phenylsuccinates, PhCH(COOR)CH2COOR′, undergo a highly specific elimination of ROH under electron impact. A deuterium‐labelling study showed that the hydrogen atom from the benzylic position 2 is abstracted in this process. These results suggest the occurrence of a ‘hidden’ hydrogen migration of the benzylic hydrogen atom to the carbonylic oxygen of the remote ester group, followed by the elimination of ROH from the adjacent ester group with the involvement of that hydrogen. Alkoxyl group migrations resulting in the formation of [PhCHOR]+ and [PhCHOR′]+ ions are less specific, although the migration of the remote R′O˙ is significantly preferred in all the pairs of isomers examined. Mechanisms are suggested for the formation of the two ions.
Metastable ion decomposition and collisional activation mass spectra of 1,2,3‐triarylpropen‐1‐ones
Authors: Madhusudanan K. P. , Durani S. , Reddy D. M. , Kapil R. S. , Itagaki Y. , Nojima K. 
Published: May 2005

AbstractSubstituents have been found to have a marked influence on the metastable ion decompositions and collisionally activated (CA) fragmentations of the M+˙ ion of a number of 1,2,3‐triarylpropen‐1‐ones. An attempt has been made to confirm the structures of the rearrangement ions, [C14H10]+˙, [C13H11]+˙, [C13H9]+ and [C12H8]+˙ by comparison of their CA spectra with those of the corresponding ions produced from reference compounds. The results imply that [C14H10]+˙ and the M+˙ ions of phenanthrene and diphenylacetylene have a common structure, [C13H9]+ and the fluorenyl cation have a common structure and [C12H8]+˙ and biphenylene molecular ion have a common structure. The available data indicate that the ion at m/z 167 consists of a mixture of structures, likely possibilities being diphenylmethyl, phenyltropylium and dihydrofluorenyl cations.
Energy studies of atomic atmospheric ions in collisions with molecular nitrogen and oxygen
Authors: Enos C. S. , Lee A. R. , Brenton A. G. 
Published: May 2005

AbstractStudies of internal energy changes between the partners in ion‐molecule collisions can be facilitated by high‐resolution translational energy spectroscopy. Collisions of keV H+, N+ and O+ on molecular nitrogen and oxygen have shown that for 30 reaction channels all are consistent with spin conservation, which has not been generally acknowledged in previous studies. Estimations of the fractional metastable composition in each ion beam have also been made.
Collision‐Induced decomposition of peptides. An investigation into the effect of collision gas pressure on translational energy losses
Authors: Bradley Caroline D. , Derrick Peter J. 
Published: May 2005

AbstractThe dependence on the gas pressure of translational energy losses, ΔE, suffered by incident ions in collision with helium target gas atoms was investigated for the [M + Na]+ ion of valinomycin. ΔE was measured from the fragment ion peak positions in the mass‐analysed ion kinetic energy (MIKE) spectra. The variation of ΔE with target gas pressure was found to be different for different fragment ions. The implications of the results for the number of collisions which may occur under normal collision‐induced decomposition conditions (30–40% transmission) are discussed.
Mass spectra of alkenyl methyl ethers
Authors: Bowen Richard D. , Wright Andrew D. , Thomas Steven R. , Jennings Keith R. , Maccoll Allan 
Published: May 2005

AbstractElectron impact ionization mass spectra of numerous alkenyl methyl ethers CnH2n‐1OCH3 (n = 3–6) recorded under normal (4 kV, 70 eV, 175°C) and low‐energy, low‐temperature (8 kV, 12 eV, 75 °C) conditions are reported. The influence of the position and stereochemistry of the double bond on the dissociation of ionized alkenyl methyl ethers is discussed. The mechanisms by which these ethers fragment after ionization have been further investigated using extensive 2H‐labelling experiments and by studying the energy dependence of the reactions. Ethers of allylic alcohols show spectra that are distinct from those of the isomeric species in which the double bond is separated by one or more sp3 carbon atoms from the carbon atom carrying the methoxy group. Three principal primary fragmentations are observed. The most common process, especially for ionized ethers of allylic alcohols, is loss of an alkyl group. This reaction often occurs by simple α‐cleavage of radical‐cations of the appropriate structure; however, alkyl groups attached to either end of the double bond are also readily lost. These formal β‐ and γ‐cleavages are explained in terms of rearrangements via distonic ions and, at least in the case of γ‐cleavages, ionized methoxycyclopropanes. Ionized homoallyl methyl ethers tend to eliminate an allylic radical, particularly at high internal energies, with formation of an oxonium ion (CH3 +OCH2 or CH3 +OCHCH3). The ethers of linear pentenols and hexenols show abundant [M ‐ CH3OH]+⋅ ions in their spectra, especially when a terminal methoxy group is present Methanol loss also takes place from ionized ethers of allylic alcohols in which there is a Δ‐hydrogen atom; this process is significantly favoured by cis, rather than trans, stereochemistry of the double bond.
Searching for the ionized alkene/aikanol complexes [C2H4+⋅/HOCH3] and [C2H4+⋅/HOCH2CH3]
Authors: Cao J. R. , George M. , Holmes John L. 
Published: May 2005

AbstractExperiments on a variety of isomeric [C3H8O]+⋅ and [C4H10O]+⋅ ions have failed to produce direct evidence for the involvement of the complex ions [C2H4+⋅/HOCH3] and [C2H4+⋅/HOC2H5]. For the isomers studied, the rearrangements prior to their dissociation of lowest energy requirement (loss of H2O and C2H5⋅, respectively) are proposed to involve distonic and ylid ions.
The ‘infinity cell’: A new trapped‐ion cell with radiofrequency covered trapping electrodes for fourier transform ion cyclotron resonance mass spectrometry
Authors: Caravatti P. , Allemann M. 
Published: May 2005

AbstractThe excitation event in Fourier transform ion cyclotron resonance mass spectrometry is optimized in order to obtain more reliable relative signal intensities and enhance the ion‐selection performance in multi‐tandem mass spectrometric experiments. Standard trapped‐ion cells suffer from the undesirable ejection of ions along the symmetry axis (z‐axis) of the cell, which is oriented parallel to the magnetic field lines. This z‐eiection effect is difficult to predict, and thus difficult to avoid, especially when complicated broad‐band excitation schemes are applied to the ions. An improved trapped‐ion cell design, referred to as the ‘Infinity Cell’, is discussed which eliminates z‐ejection. The Infinity Cell concept is based on the finding that it is possible to model the electric excitation field of an infinitely long cell with a cell of finite dimensions. The virtual elimination of z‐ejection effects is demonstrated in several suitable experiments by comparing the operation of the standard cell and the Infinity Cell.
Association reactions of trimethylsilyl ions
Authors: Lin Yi , Ridge D. P. , Munson Burnaby 
Published: May 2005

AbstractAdduct ions, [M + (CH3)3Si]+, were produced by bimolecular association reactions of trimethylsilyl ions, (CH3)3Si+, with acetone, cydohexaoone, anisole, dimethyl ether, 2,5‐dimethylfuran, 2‐methylfuran and furan in ion cyclotron resonance experiments at 300 K and at pressures of ∼10−7 Torr (1 Torr = 133.3 Pa). The rate constants, ka, for the association reactions varied from 100% to 2% of the collision rate constants, kc. The rate constants were independent of pressure, except for furan. Measurements were also made of bond dissociation energies for these adduct ions, D[(CH3)3Si+–X], from equilibrium measurements. The association efficiency, ka/kc, increased with increasing bond dissociation energy and with increasing numbers of degrees of freedom, in qualitative agreement with theoretical predictions. Observations pertinent to the dependence of ka on reactant temperature and relative kinetic energy are discussed. The possibility of determining ion‐neutral complex binding energies from radiative association rate constants is considered.
Unimolecular gas‐phase reactions of the methyl acetoacetate radical cation. Oxygen atom permutation via ion‐molecule complexes
Authors: Berthomieu Dorothée , Tortajada Jeanine , Morizur Jean‐Pierre , Audier Henri‐Edouard 
Published: May 2005

AbstractThe reactions of metastable decomposing methyl acetoacetate (a mixture of keto a ad enol tautomers) are reported and discussed. The unimolecular fragmentations of the tautomers are different. The metastable decomposing radical cation of the keto form displays four specific ions: [M –CO]+˙, [M – CH2O]+˙, [M – CH2CO]+˙ and m/z 43. The results derived from D‐, 13C‐ and 18O‐labelled precursors together with thermochemical data have been used to study the mechanisms. Experimental results indicate that an unexpected isomerization occurs before dissociation. It formally corresponds to oxygen atom permutation of the two carbonyl groups without participation of the carbon atoms. This remarkable process is interpreted in terms of a mechanism involving ion‐molecule complexes.
Identification of caffeine and its metabolites in human urine extracts by electron impact ionization tandem mass spectrometry
Authors: Liguori A. , Mascaro P. , Porcelli B. , Sindona G. , Uccella N. 
Published: May 2005

AbstractElectron impact ionized purine bases such as caffeine and its metabolites (theopbylline, theobromine, paraxanthine, 1‐methylxanthine, 3‐metnybumthine and 7‐methyIxanthine) were characterized by tandem mass spectrometry. The direct analysts of human urinary extracts by tandem mass spectrometry allows the unambiguous identification of caffeine and its metabolites present simultaneously in the urine.
Gas chromatographic/mass spectrometric measurement of deuterium‐labelled valine, leucine, isoleucine and phenylalanine in the human body
Authors: Zhu Peifen , Yu Zhonghua , Wan Guangmei , Sha Huixin , Su Keman , Yu Bingyao , Zhao Guangsheng 
Published: May 2005

AbstractN‐Trifluoroacetyl‐n‐butyl ester derivatives of deuterium‐labelled valine, leucine, isoleucine and phenylulanine were analysed by the isotope dilution technique and gas chromatography/mass spectrometry (GC/MS). Selected ion retrieval and peak‐area integration were applied. The conditions adopted gave good separations with a short experimental time and high intensity. Ratios of the total isotopic abundance and metabolic kinetic curves were obtained. The regression coefficient of the standard dilution curve was 0.99 and the relative standard deviation was 0.3%. The stabilities of the amino acid derivatives were also tested.
Electron impact ionized benzoylnitroanilines and their N‐alkyl and N‐acyl derivatives
Authors: Ayyangar N. R. , Sudalai A. , Daniel Thomas 
Published: May 2005

AbstractThe behaviour of some benzoylnitroanilines and their derivatives under electron impact ionization was invest gated by means of low‐resolution mass spectrometry. Some characteristic rearrangement processes are discussed.
Isomeric [C,H3,N,O]+˙ ions and their neutral counterparts
Authors: Hop Cornelis E. C. A. , Chen Hongwen , Ruttink P. J. A. , Holmes John L. 
Published: May 2005

AbstractThe isomeric ions [H2NC(H)O]+˙, [H2NCOH]+˙, [H3CNO]+˙ and [H2CNOH]+˙ were examined in the gas phase by mass spectrometry. Ab initio molecular orbital theory was used to calculate the relative stabilities of [H2NC(H)O]+˙, [H2NCOH]+˙, [H3NCO]+˙ and their neutral counterparts. Theory predicted [H2NC(H)O]+˙ to be the most stable ion. [H2NCOH]+˙ ions were generated via a 1,4‐hydrogen transfer in [H2NC(O)OCH3]+˙, [H2NC(O)C(O)OH]+˙ and [H2NC(O)CH2CH3]+˙. Its metastable dissociation takes place via [H3NCO]+˙ with the isomerization as the rate‐determining step. [H2CNOH]+˙ undergoes a rate‐determining isomerization into [H3CNO]+˙ prior to metastable fragmentation. Neutralization‐reionization mass spectrometry was used to identify the neutral counterparts of these [H3,C,N,O]+˙ ions as stable species in the gas phase. The ion [H3NCO]+˙ was not independently generated in these experiments; its neutral counterpart was predicted by theory to be only weakly bound.
Unique thermospray mass spectrometry of 1,4‐benzoquinone and analogs in ammonium acetate solutions
Authors: Gctek T. A. , Vestal M. L. , Vestal C. H. , Korfmacher W. A. , Miller D. W. , Freeman J. P. 
Published: May 2005

AbstractIn general, ions corresponding to [M + H]+ and/or [M + NH4]+ are observed in thermospray mass spectrometry (TSMS) when using ammonium acetate in the liquid carrier. For several quinones investigated, unique thermospray mass spectra were detected with a mass spectral peak corresponding to an [M + 16]+ ion being observed in aqueous ammonium acetate solutions. Investigation of l,4‐benzoquinone (BQU) and structurally analogous quinones indicated that amine conjugate formation with BQU and similar quinones was the origin of the unique [M + 16]+ ion in TSMS. When methanol was added to the liquid carrier, ions corresponding to methoxy conjugation were detected. High‐performance liquid chromatography followed by TSMS or electrochemical detection gave evidence that this amine and methoxy conjugate formation was occurring in the thermospray source area.
Isomer differentiation and structural characterization of penem β‐lactam antibiotics by mass‐analyzed ion kinetic energy spectrometry
Authors: Das Pradip R. , Pramanik B. N. , Girijavallabhan V. M. , Ganguly A. K. 
Published: May 2005

AbstractA number of clinically significant penem β‐lactams, both free acids and sodium salts, were investigated by mass‐analyzed ion kinetic energy spectrometry (MIKES) following fast atom bombardment (FAB) ionization. The collisionally activated dissociation (CAD) products of [M + H] + and [M + Na]+ ions are described. Carbon dioxide loss was observed for some of the free acids, whereas a daughter ion generated by β‐lactam ring cleavage was characteristic of the sodiated species. Other fragments included successive cleavages and rearrangements of the substituent side‐chain, permitting complete characterization of these chains. The fragmentation pattern for both protonated and sodiated species were more clearly established by CAD MIKES than by normal FAB mass spectral analyses. A notable feature of this technique was its ability to differentiate between pairs of regioisomeric penems on the basis of their fragmentation patterns. These compounds could not be differentiated in the usual mass spectra.
Laser photolysis of chlorodiaminotriazines and detection of their fragmentation and clusterization products
Authors: Giardini‐Guidoni Anna , Mele Aldo , Pizzella Giulia , Teghil Roberto 
Published: May 2005

AbstractThe laser photolysis of three 2‐chloro‐4‐6‐diamino‐1,3,5‐triazines, namely simazine, atrazine and propazine, was investigated. The products formed were detected by time‐of‐flight mass spectromety. The results illustrate that the main process is fragmentation competing with cluster formation. The hydrogen bonding proposed for the crystal structure of diaminotriazines should be responsible for the gas‐phase clusterization occurring by laser ablation.