bluuebunny/crossref_metadata_2025_split huggingface dataset:
Mass spectrometric investigation of some macrocyclic and macroacyclic compartmental schiff bases
Authors: Guerriero P. , Tamburini S. , Vigato P. A. , Seraglia R. , Traldi P. 
Published: May 2005

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

AbstractSecondary ion mass spectra of fifteen sugar nucleotide sodium salts were investigated. In the negative‐ion mode. deprotonated free acid molecules, desodiated sodium salts and some structurally significant fragment ion swere obtained. The linked scan at constant B/E gave information on the characteristics of the sugar, nucleosides and base moieties in the sugar nucleotides.