bluuebunny/crossref_metadata_2025_split huggingface dataset:
Use of bond orders and valences for the description and prediction of primary fragmentation processes
Authors: Somogyi Árpád , Gömöry Ágnes , Vékey Károly , Tamás József 
Published: May 2005

AbstractSome approaches and examples are shown to demonstrate the usefulness of inherently ‘classical’ parameters, such as bond orders and valences derivable from quantum mechanical wavefunctions, in the description and prediction of mass spectral primary fragmentation processes.
Fast atom bombardment mass spectrometry of ionic gold(I) and gold(III) carbene derivatives: An investigation of the formation of [M – H]+ species
Authors: Banditelli G. , Bandini A. L. , Pacchioni G. , Minghetti G. , Seraglia R. , Traldi P. 
Published: May 2005

AbstractFast atom bombardment (FAB) mass spectrometry of the gold(I) and gold(III) derivatives, {Au[C(Y)–NHAr]2}+X− and {Au[C(Y)–NHAr]2I2} + X− (Y =OC2H5 or NHAr; X− = CIO4− or BF4−; Ar = p‐CH3C6H4) has led to the detection, for the alkoxyamino derivatives only, of [M–H]+˙ molecular species. The mechanism of the formation of these unusual species has been studied with respect to the oxidation state of gold, nature of the matrix, matrix acidity and ligand structure. The energetics of two possible alternative mechanisms has been studied by means of ab initio theoretical calculations. Both experimental and theoretical data indicate that [M–H]+˙ formation is due to the reaction of M+ with H+‐philic and/or H˙‐philic species produced from the matrix by FAB. Whatever the operative mechanism, the [M–H]+˙ formation is to be considered a FAB‐induced oxidative process.
Stereochemical studies by mass spectrometry: C15Nuphar alkaloids
Authors: Bortolini O. , Fantin G. , Curcuruto O. , Traldi P. , Iwanow A. , Wróbel J. T. 
Published: May 2005

AbstractRepresentative C15 Nuphar alkaloids, containing the quinolizidine system, were studied by high‐resolution mass spectrometry and metastable‐ion decomposition analysis. The appearance with N‐oxide species of ions at m/z 168, useful in ascertaining the stereochemistry of the quinolizidinic ring junction, are also discussed.
Electron impact mass spectrometric investigation of pyrrole mono‐, di‐ and tri‐carboxylic acids
Authors: Costa Carlo , Bertazzo Antonella , Allegri Graziella , Catinella Silvia , Traldi Pietro 
Published: May 2005

AbstractThe electron impact‐induced fragmentation processes of pyrrole‐2‐, ‐3‐, ‐2,3‐, ‐3,4‐, ‐2,5‐ and ‐2,3,4‐carboxylic acids were investigated with the aid of metastable ion, collisional and deuterium labelling experiments. The general behaviour of these compounds is discussed in detail, together with the reasonable structures of the more relevant fragment ions.
Mass spectrometry in stereochemical problems. 6 — The case of mono and di‐substituted norbornanes
Authors: Curcuruto O. , Favrctto D. , Traldi P. , Ajo D. , Cativiela C. , Mayoral J. A. , Lorez M. P. , Fraile J. M. , Garcia J. I. 
Published: May 2005

AbstractThe mass spectrometric behaviour of pairs of stereoisomeric mono‐ and di‐substituted norbornanes, namely bicyclo[2.2.1]heptane‐2‐endo‐ and ‐exo‐carboxylic acid, methyl bicyclo[2.2.1]heptane‐2‐endo‐ and ‐exo‐carboxylate, 2‐exo‐acetamidobicyclo[2.2.1]heptane‐2‐endo‐ and 2‐endo‐acetamidobicyclo[2.2.1]heptane‐2‐exo‐carboxylic acid and methyl 2‐exo‐acetamidobicyclo[2.2.1]heptane‐2‐endo‐ and 2‐endo‐acetamido‐bicyclo[2.2.1]heptane‐2‐exo‐carboxylate was studied in detail with particular emphasis on characterization of the stereoisomers. The fragmentation patterns, studied with the aid of mass‐analysed ion kinetic energy spectrometry, were supported by semi‐empirical MO–SFC calculations, performed using the AM1 method included in the AMPAC program.
Dissociative charge exchange of C3F6
Authors: Habibi‐Goudarzi Sohrab , Kotiaho Tapio , Cooks R. G. , Ast T. 
Published: May 2005

AbstractCharge exchange of neutral C3F6 by a variety of atomic and molecular ions in the 1 to 25 eV range of collision energies is used to characterize the energies associated with formation of [C3F6]+˙. The internal energy of the nascent [C3F6]+˙ ion, assessed by observing the degree to which it fragments, increases with the recombination energy of the charge‐exchange reagent. The existence of excited states of the reagent ions is identified from the fragmentation behaviour of [C3F6]+˙ in the cases of [CS2]+˙, NO+, O2+˙, [NH3]+˙ and possibly [CH4]+˙. In addition, the data confirm that the [C3F6]+˙ parent ion fragments from both the ground state and a long‐lived isolated electronic state. The latter is populated by near‐resonant charge transfer. Translational excitation contributes relatively little to internal excitation of the charge‐exchanged product ion and even less in the case of the isolated state.
Aryl cations: Searching for and assigning structures to [C7H5]+ isomers
Authors: Bissonnette Martine C. , George M. , Holmes John L. 
Published: May 2005

AbstractThe energetics and mass spectral characteristics of a number of [C7H5]+ ions have been examined. No compelling evidence could be found to show that the 2‐cyclopropaphenyl cation was produced by loss of bromine from the ionized 2‐bromo derivative. It was proposed that the ethynylcyclopentadienyl cation may be the global minimum on the [C7H5]+ hypersurface.
Interannular proton exchange and fragmentation of carbonyl‐protonated benzophenones
Authors: Sun Jing , Grützmacher Hans‐Friedrich 
Published: May 2005

AbstractBenzopbenones a initially protonated at the carbonyl group were prepared by electron‐impact induced dissocation of 1,1‐diphenylpropanols (compounds 1‐5). These protonated ketones decompose in the ion source and the second field‐free region of a reversed geometry mass spectrometer by proton migration to one of the phenyl groups and subsequent elimination of benzene. In the case of derivatives substituted by methoxy groups and trifluoromethyl groups respectively, the proton migrates predominantly to the more bask benzene ring, resulting in the elimination of anisole in the former case and of benzene in die latter case. A study of protonated benzopbenones labelled at the phenyl ring and at the carbonyl group shows that only a few interannular H/D exchange steps precede the fragmentation. This is observed not only for metastable ions in the magnetic sector instilment but also for ions of long lifetimes investigated by Fourier‐transform‐ion cyclotron resonance (FT‐ICR) Spectrometry. This is in contrast to the arene elimination from protonated 1,ω‐dipbenylalkanes and related polyphenylalkanes which fragment by complete positional exchange of all hydrogen atoms at the aromatic rings. The special behaviour of protonated benzophenones is attributed to a low barrier for the decomposition of a chemically activated arenium ion b, which arises from the initial proton transfer. Once b is formed, it decomposes quickly without much interannular proton exchange.
Investigation of aliphatic dienes by chemical ionization with nitric oxide
Authors: Budzikiewicz H. , Blech St. , Schneider B. 
Published: May 2005

AbstractIt is shown that the position of the double bond close to the hydrocarbon end of an aliphatic diene functionalized at C(1) can readily be determined by chemical ionization with NO+. Owing to the low abundance of the ions characteristic for the position of the other double bond, its localization may be difficult. Measurement of the chemical ionization (nitric oxide as reagent gas) spectra of the corresponding epoxides or collision activation studies can help.
Characterization of synthetic N‐acetylcysteine conjugates by positive‐ and negative‐ion 252Cf plasma desorption mass spectrometry
Authors: Pittenauer Ernst , Pachinger Anton , Allmaier Günter , Schmid Erich R. 
Published: May 2005

AbstractN‐Acetylcysteine and nine N‐acetylcysteine conjugates of synthetic origin were characterized by positive‐ and negative‐ion plasma desorption mass Spectrometry. For sample preparation the electrospray technique and the nitrocellulose spin deposition technique were applied. The fragmentation of these compounds, which are best seen as S‐substituted desaminoglycylcysteine dipeptides, shows a similar behaviour to that of linear peptides. In the positive‐ion mass spectra intense protonated molecular ion peaks are observed. In addition, several sequence‐specific fragment ions (A+, B+, [Y + 2H]+, Z+), immonium ions (I+) and a diagnostic fragment ion for mercap‐turic acids (RM+) are detected. The negative‐ion mass spectra exhibit deprotonated molecular ions and in contrast only one fragment ion corresponding to side‐chain specific cleavage ([RXS]−) representing the xenobiotic moiety. In the case of a low alkali metal concentration on the target, cluster molecular ions of the [nM + H]+ or [nM ‐ H]− ion type (n = 1‐3) are observed. The analysis of an equimolar mixture of eight N‐acetylcysteine conjugates shows different quasi‐molecular ion yields for the positive‐ and negative‐ion spectra.
Temperature effects in mass spectrometry. Estimation of thermal energies of organic molecules
Authors: Turecek Frantisek 
Published: May 2005

AbstractThermal energies of gaseous organic molecules, relevant to unimolecular dissociations of odd‐ and even‐electron ions, are estimated by ab initio/RRHO and empirical calculations. Thermal energies can be estimated with good accuracy by integration of molar heat capacities obtained from quadratic least‐squares fits. Thermal energies in gaseous n‐alkanes, alkanols, cholesterol, polyethylene glycols and oligopeptides are calculated and compared with estimates based on the equipartition principle.
Mass spectra of some 2‐(o‐R1‐phenyl)‐indole‐3‐carboxaldehyde derivatives. II
Authors: Cortés C. Eduardo , Martínez Roberto , Ramírez José I. 
Published: May 2005

AbstractThe electron impact mass spectra of thirteen new substituted 2‐(o‐R1‐phenyl)‐indole‐3‐carboxaldehydes which have potentially useful pharmacological properties, ate presented.
Measurement of initial translational energies of peptide ions in laser desorption/ionization mass spectrometry
Authors: Pan Ying , Cotter Robert J. 
Published: May 2005

AbstractThe initial kinetic energy distribution of [Arg]‐vasopressin molecular ions generated by matrix‐assisted UV laser desorption/ionization was measured using a delayed ion extraction, linear time‐of‐flight mass spectrometer. Energy distributions of the nicotinic acid matrix ions, with or without the presence of peptide, were also measured. These were compared with the kinetic energy distribution of gramicidin‐S ions using IR laser desorption. The measured molecular ion kinetic energy distribution from vasopressin is much broader than that from gramicidin‐S, and is characterized by a high‐energy tail that most likely results from entrainment of anlayte ions in the higher velocity matrix ions and fragments as they leave the surface.
Examination of Ortho effects in the collisionally activated dissociation of closed‐shell aromatic ions
Authors: Donovan Tracy , Brodbelt Jennifer 
Published: May 2005

AbstractThe collisionally activated dissociation of a variety of isomeric disubstituted aromatic ions formed by ion–molecule reactions were examined in order to characterize ortho effects in closed‐shell systems. Closed‐shell ions of methoxyacetophenone, hydroxyacetophenone, methoxyphenol, anisaldehyde and hydroxybenzaldehyde were formed by proton transfer, methyl addition or methyne addition by using dimethyl ether or ethylene oxide as chemical ionization reagents, and then the structures of these adducts were studied by deuterium‐labelling methods and by collisionally activated dissociation techniques in a triple quadrupole mass spectrometer or a quadrupole ion trap. Typically, the meta and para isomers have qualitatively similar dissociation spectra which reflect the types of dissociation reactions observed for the corresponding monosubstituted aromatic ions. The predominant dissociation pathways of the [M + H]+ and [M + 15]+ ions are directed by the electron‐withdrawing substituents, whereas the major dissociation pathways of the [M + 13]+ ions are related to the electron‐releasing substituent. In contrast, the dissociation routes of the corresponding ortho isomers are dramatically different. This is attributed to the opportunity for functional group interactions of the ortho isomers which facilitate alternative pathways.
Electron impact mass spectra of 1‐methyl‐3‐(2‐benzothiazolylhydrazono)‐2‐indolinones
Authors: Varma R. S. , Singh A. P. , Singh S. P. 
Published: May 2005

AbstractA study of the fragmentation of l‐methyl‐3‐(2‐benzothiazolylhydrazono)‐2‐indolinones on electron impact reveals that the major processes involve NN bond fission and the competing loss of CO from the molecular ion.
Studies in organic mass spectrometry. 12–Electron impact ionization mass spectra of some 3‐nitropyrroles
Authors: Ceraulo Leopoldo , Ferrugia Mirella , Sprio Vincenzo 
Published: May 2005

AbstractThe positive‐ion electron impact ionization mass spectra of eight substituted 3‐nitropyrroles were examined. The major fragment ions arise by ortho interactions between the 3‐nitro group and the 2‐methyl or 2‐aryl group.
Electron impact mass spectrometry of diethyl 2‐oxysubstituted alkylphosphonates—a remarkably regiospecific α‐cleavage
Authors: Modro T. A. , Mphahlele M. J. 
Published: May 2005

AbstractThe major electron impact induced fragmentation of 2‐hydroxyphosphonic esters, XCH2CH(OH)CH2PO3Et2 (and their O‐derivatives) involves the C(2)–C(3) α‐cleavage, yielding the XCH2· radical and the oxocarbonium ion, +HO = CHCH2PO3Et2. No evidence for a competitive C(1)–C(2) α‐cleavage was obtained, and the results suggest a stabilizing effect of the phosphonyl group on the α‐oxocarbonium system.
Mass spectrometric differentiation of huperzinine, N,N‐dimethylhuperzine A and N‐methylhuperzine B
Authors: Hu Peifeng , Cross Michael L. , Yuan S. Q. , Wei T. T. , Lu Y. Q. 
Published: May 2005

AbstractThe newly isolated Lycopodium alkaloids huperzinine, N,N‐dimethylhuperzine A and N‐methylhuperzine B were studied by high‐resolution and tandem mass Spectrometry. Differentiation of these subtly different isomers from each other and from the general class of Lycopodium alkaloids can be achieved by taking advantage of the structure‐specific fragment ions formed upon electron ionization (El) or collisional activation of these alkaloids. β‐Obscurine was identified as an impurity component in the N‐methylhuperzine B sample and contributed to the El mass spectrum. The previously published El mass spectrum of N‐methylhuperzine B is likely to be that of a mixture of N‐methylhuperzine B and β‐obscurine. The presence of the impurity can now be readily recognized on the basis of two characteristic fragment ions of m/z 215 and 187.
Gas‐phase reactions of mono‐ and dichlorophenols
Authors: Mattina M. J. Incorvia , Sears L. J. 
Published: May 2005

AbstractReactions occurring within the high‐pressure mass spectrometer source during argon‐enhanced negative‐ion mass Spectrometry (NIMS) of mono‐ and dichlorophenols result in the formation of adduct ions. The reactants for the formation of the adduct ions are derived solely from the chlorophenol. High‐resolution accurate mass ‐measurements of the adducts and comparison of the argon NIMS of the phenols with the argon‐enhanced NIMS of authentic chlorinated phenoxyphenol and dichlorodioxin suggest that gas‐phase intermolecular and intramolecular nucleophilic substitutions are occurring. The products of the source reactions reflect the stability of the gas‐phase species involved and may be compared with the photolysis and pyrolysis reaction products of chlorophenols, chlorinated phenoxyphenols and chlorophenates reported in the literature.
Mass spectrometric studies of phosphodiesters linked to oxysterols and nucleosides, a family of biologically potent oxygenated sterols
Authors: Pannecoucke Xavier , Dorsselaer Alain Van , Luu Bang 
Published: May 2005

AbstractNegative‐ion fast atom bombardment mass spectra of five compounds resulting from combinations between oxysterols and nucleoside analogues linked by phosphodiester bonds are presented and interpreted. This method seems to be the most appropriate for elucidating the structure of these complex, labile and non‐volatile phosphate‐containing molecules which exhibit important antitumour and/or immunosuppressive activities.
Ion‐trap detector electron impact mass spectrometry: Practical considerations
Authors: Vella Alfred J. 
Published: May 2005

AbstractAn investigation of the quality of mass spectra obtainable by the Finnigan ion‐trap detector (ITD) and on how this quality may depend on sample size is described. For compounds which are not very thermolabile or too prone to fragmentation, near‐normal spectra can be expected if the sample sizes do not exceed amounts of the order of 100 ng. Analyte loads which generate acceptable total ion current chromatograms with narrow‐bore capillary columns (about 500 ng) could still produce ITD mass spectra having enhanced quasi‐molecular ions, [M + 1]+, abnormal distributions of peak intensities and unusual fragments. Even under optimum conditions, certain analytes, e.g. acyclic alkanes, n‐alkanols and pyridines, will manifest spectral characteristics which are strictly typical of the ITD. In favourable cases, the formation of quasi‐molecular ions can be exploited for relative molecular mass determination. Even under conditions of self‐chemical ionization, the ITD spectra of most analytes generally retain enough electron impact mass spectral character to be readily recognizable by inspection or by library algorithms.
Characterization of phospho‐proteins in bovine and buffalo caseins using atmospheric pressure ionization mass spectrometry
Authors: Casetta Bruno , Bonner Ron , Shushan Bori , Fior Gianni 
Published: May 2005

AbstractThe specific bovine and buffalo caseins have been characterized with the aim of using atmospheric pressure ionization mass spectrometry as an alternative to electrophoretic and immunological methods in the detection of the fraudulent addition of bovine milk to buffalo milk used in the production of speciality cheeses.
Experimental investigation of double ionization to ground and electronically excited states of chlorobenzene, 1,2‐, 1,3‐ and 1,4‐dichlorobenzene, 1,2,3‐, 1,2,4‐ and 1,3,5‐trichlorobenzene, 1,2,3,4‐and 1,2,4,5‐tetrachlorobenzene and pentachlorobenzene dications
Authors: Harris F. M. , Jackson P. J. , Rontree J. A. , Griffiths W. J. 
Published: May 2005

AbstractDouble‐charge‐transfer spectrometry was used to measure double‐ionization energies to ground and electronically excited states of various chlorobenzenes. Since OH+ was the projectile ion used in these experiments, it is probable that triplet states of the dications were populated because of spin conservation in the double‐electron‐capture reactions which are the basis of this type of spectrometry. The lowest double‐ionization energies for all the molecules studied are within ±0.3 eV of 25.9 eV, except that for 1,3‐dichlorobenzene, which is at 26.6 eV. In general, double‐ionization energies to three higher lying states (or groups of states) were measured for each molecule. The energies of these states are the same, within experimental uncertainties, for the three trichlorobenzenes, two tetrachlorobenzenes and pentachlorobenzene dications, suggesting that they have the same or very similar distributions of triplet‐state energies.
Time‐dependent mass spectra and breakdown graphs: 15—toluene‐d8
Authors: Ohmichi N. , Gotkis I. , Steens L. , Lifshitz C. 
Published: May 2005

AbstractThe ion storage time in the cylindrical trap of a pbotoionization mass spectrometer has been extended to ∼500 ms. Time‐resolved photoionization efficiency (PIE) curves were meaured for [C7D8]+ and [C7D7]+ for toluene‐d8 and for the ion‐molecule reaction product [C8D9]+. PIE curves were modeled by k(E) dependences via RRKM/ QET calculations based on a model by Huang and Dunbar, with critical energy E0 = 2.13 eV and a 1000 K activation entropy ΔS≠ = −14.6 e.u. No energy range was found, even under long storage times, for which [C7D7]+ is pure tropylium, Tr+. The results are interpreted via the case C behaviour in isomerizing ions, due to Baer and co‐workers, according to which Tr+ and [benzyl]+, Bz+, are formed at equal rates for energies in excess of both of their dissociation limits. Dissociation is suppressed at internal energies lower than ∼2.S eV due to radiative decay in the infrared region. Dissociations observed at photon energies lower than ∼11.3 eV (8.8 eV ionization energy +2.5 eV internal energy) are ascribed to the offsetting effects of an intrinsic kinetic shift of ∼0.4 eV and the thermal energy distribution in the molecular ions.
Unusual fragmentation of 1,1,2,2,3,3‐hexamethylindan. Methyl group equilibration and multi‐step skeletal rearrangements in the [M  CH3]+ ions prior to the formation of t‐C4H9+ and other fragment ions
Authors: Kuck Dietmar , Mehdizadeh Ahmad 
Published: May 2005

AbstractBased on the surprising observation of an intense C4H9+ (m/z 57) peak in the electron impact mass spectrum, the fragmentation of 1,1,2,2,3,3‐hexamethylindan (2) was studied by mass‐analysed ion kinetic energy Spectrometry of its deuterium‐labelled analogues. While methyl loss from ions [2]+˙ occurs with high selectivity (92%) from the positions 1 and 3 without any rearrangement, ions [2  CH3]+ undergo complete equilibration of the five methyl groups as intact entities. Subsequent multi‐step skeletal rearrangement of the [2 ‐ CH3]+ ions leads to formation of ferf‐butyl ions and to the loss of isobutene and propene, again without concomitant hydrogen exchange. Several kinetic isotope effects and also probably a thermodynamic isotope effect associated with each of these fragmentation processes have been found and their origin is discussed. The possibility of the formation of ion‐neutral complexes [t‐C4H9+ C10H10] aud [s‐C3H7+ C11H12] is considered on the basis of the labelling and reactivity pattern.
Some aspects of isobutane and ammonia chemical ionization for the analysis of volatile esters and phenylpropanoids occurring in essential oils
Authors: Lange G. , Schultze W. 
Published: May 2005

AbstractThe fragmentation reactions of some terpenoid esters and pbenylpropanoids under the conditions of isobutane and ammonia chemical ionization (CI) arc discussed. The esters show different behaviour with these two gases with respect to determination of the relative molecular mass and information about the structure of the molecules. The structural isomers of the phenylpropanoids can unequivocally be distinguished with both isobutane and ammonia CI. Cis/trans isomers of the phenylpropanoids show virtually identical CI spectra.
Fragmentation behaviour of alkylated thiophene‐1,1‐dioxides,
Authors: Budzikiewicz H. , Lange D. 
Published: May 2005

AbstractIt is shown that thiophene‐1,1‐dioxides carrying an alkyl chain in the 2‐ and 3‐positions can be readily distinguished by the characteristic fragmentation mode of the latter, viz. benzylic cleavage of the side‐chain with back‐transfer of two hydrogen atoms ([M  ˙CnH2n−1]+). By deuterium labelling it is shown that the migrating hydrogens come very specifically from the γ‐ and δ‐positions. Since alkylated thiophenes are important geological markers, a ready differentiation of the two types by gas chromatography/mass spectrometry is possible in this way.
Characterization of Z‐blocked isomeric dipeptides by fast atom bombardment tandem mass spectrometry and kinetic energy release measurements
Authors: Mammoliti Ezio , Sindona Giovanni , Uccella Nicola 
Published: May 2005

AbstractFast‐ and slow‐reacting, protonated, Z‐blocked (Z = benzyloxycarbonyl) phenylalanylphenylalanine and alanylpbenylalanyl diasteromeric dipeptides undergo decarboxylation through two competing pathways assisted by the migration of the urethane benzyl group either to the terminal or to the amidic nitrogens. The reaction mechanism has been proved by tandem mass spectrometric experiments. The different kinetic energy released associated with CO2 elimination allows the distinction of the S,S from the R,S isomers by moss‐analysed ion kinetic‐energy experiments.