bluuebunny/crossref_metadata_2025_split huggingface dataset:
Metastable fragmentation of somatostatin‐14 (SS‐14) and a series of SS‐14 analogs formed with liquid secondary ion mass spectrometry: Observation of fragment ions which involve unsymmetric disulfide bridge cleavage concomitant with peptide chain cleavage
Authors: Craig A. Grey , Rivier Jean E. 
Published: May 2005

AbstractSomatostatin‐14 (SS‐14) and several SS‐14 analogs were analyzed using liquid secondary ion mass spectrometry (LSIMS). The observed isotope distributions showed low levels of [H2‐SS‐14] (reduced SS‐14). The daughter‐ion spectra of the protonated molecule ions of SS‐14 and several SS‐14 analogs contained a number of metastable fragment ions. Two fragments in these spectra were assigned to cleavage of the peptide chain concomitant with unsymmetric cleavage of the disulfide bridge. Single alanine‐substituted analogs of SS‐14 were used to confirm these assignments, while single D isomer‐substituted analogs of SS‐14 were used to investigate the dependence of the cleavages on conformation.
Fast atom bombardment mass spectra of iodonium salts
Authors: Schurz Helen H. , Busch Kenneth L. 
Published: May 2005

AbstractPositive‐ion fast atom bombardment mass spectra and linked‐scan tandem mass spectra were measured for aromatic iodonium salts. The mass spectra usually contain the intact cation of the iodonium salt as the base peak, fragment ions of lower abundance resulting from simple cleavages or rearrangements, and a characteristic loss of atomic iodine. High‐level semi‐empirical calculations suggest that an obtuse ringI+ring angle facilitates loss of atomic iodine through concomitant ringtoring bond formation.
Electron impact mass spectrometry of isomeric [(5‐N‐methyl) and (12‐N‐methyl)]‐11‐(o‐ and p‐R‐aniline)‐5H‐dibenzo [b, e] [1,4]diazepines
Authors: Cortés C. Eduardo , Cortés R. Eduardo , Rojas Raymundo 
Published: May 2005

AbstractThe mass spectra of twelve isomeric [(5‐N‐methyl) and (12‐N‐methyl)]‐11‐(o‐ and p‐R‐aniline)‐5H‐dibenzo [b, e] [l,4]diazepines which have potentially useful pharmacological properties are presented.
Fast atom bombardment positive‐ion mass spectra of 1,2,2‐tris(sulfonyl)hydrazines
Authors: Giordano Giuseppe , Shyam Krishnamurthy , Sartorelli Alan C. , McMurray Walter J. 
Published: May 2005

AbstractSeveral 1,2,2‐tris(sulfonyl)hydrazines, conceived as prodrugs of 1,2‐bis(sulfonyl)hydrazines and synthesized as potential antineoplastic and trypanocidal drugs, were analyzed by mass Spectrometry as part of the confirmation of the structure of these compounds. Since these compounds showed activity against several transplanted animal tumors, an understanding of the mass spectral behavior of these agents is important to gain information should clinical trials and metabolic studies be undertaken. In all spectra, protonated molecular ions were observed. Collision activation resulted in considerable fragmentation in the fast atom bombardment spectra. Rearrangement ions formed by elimination of substituted diimides from the middle of the molecule were observed. Other rearrangements involving the alkyl substituent and sulfonyl oxygen also occurred.
Fragmentation behavior of disaccharides during desorption–ionization
Authors: Carroll James A. , Lebrilla Carlito B. 
Published: May 2005

AbstractThe fragmentation behavior of native and singly derivatized protonated disaccharides were examined by fast ion bombardment Fourier transform mass spectrometry to determine the origin of various fragment ions produced during desorption–ionization. The lack of interfering matrix ions in this technique allowed the investigation of model disaccharides. Three major product ions were observed, corresponding in mass to a loss of H2O, a loss of a monosaccharide unit and a combination of both losses. The oxygen of the lost H2O molecule originates from an oxygen attached to the anomeric carbon. The other two product ions come from two different monosaccharide units and are due to competing processes. The relative ion intensities of these two fragment ions are governed by the basicities of the fragments. The basicity of the reducing end increases when the hemiacetal is converted into the methyl glycoside. This increase in basicity is due to the increased size of the alkyl group and the ability of the alkyl group to prevent the opening of the reducing glycosidic ring.
Protonation susceptibility of functional groups: A new parameter for interpreting chemical ionization mass spectra of bifunctional organic compounds
Authors: Nakata Hisao 
Published: May 2005

AbstractA new parameter, the protonation susceptibility (PS), of functional groups in the chemical ionization mass spectrometry of bifunctional organic compounds is presented. In terms of quasi‐equilibrium theory of unimolecular decomposition of the molecular protonated ion of [MH]+, the relative PS corresponds to the relative area under P(E) curves of [MH]+ ions that have a proton at different functional groups. Numerical evaluation of the PS values of pertinent functional groups was made by using particularly selected compounds. The results clearly indicate that PS is independent of proton affinity (PA).
Fast atom bombardment mass spectra of telluronium salts
Authors: Fu Gui‐Xiang , Zhou Zhang‐Lin , Yu Lu , Huang Yao‐Zeng 
Published: May 2005

AbstractThe fast atom bombardment (FAB) mass spectra of telluronium salts were studied. The spectra exhibit the intact cation (C+) and cluster ions ([M + C]+). The principal fragment ions in the FAB mass spectra of telluronium salts are [RTe]+, [R2Te]+˙, [R2Te − H]+, [RTeR′]+˙, and [RTeR′ + H]+. When the anion was [BPh4]−, interesting cluster ions such as [M + C − BPh3]+ appeared.
Metastable ion study of organosilicon compounds. Part V—tetramethoxysilane and trimethoxymethylsilane
Authors: Tabei Eiichi , Mori Shigeru , Okada Fumio , Tajima Susumu , Ogino Kazuo , Okawara Yuzuru , Tobita Seiji 
Published: May 2005

AbstractThe fragmentations of tetramethoxysilane ((CH3O)4Si (1)) and trimethoxymethylsilane ((CH3O)3SiCH3 (3)) induced by electron impact were investigated by mass‐analysed ion kinetic energy (MIKE) spectrometry and a deuterium‐labelling study. These molecular ions begin to fragment by the loss of CH3 or CH3O. These fragmentations are followed by the loss of an aldehyde molecule (H2CO), as commonly observed in the mass spectra of alkoxysilanes. Almost complete scrambling of the methoxy hydrogens takes place in the metastable molecular ion, [1]+˙, prior to the decomposition. On the other hand, a moderate extent of scrambling of the hydrogens takes place in [3]+˙. The fragmentations of [1]+˙ and [3]+˙ were compared with those of the corresponding carbon analogues, tetramethoxymethane ((CH3O)4C (2)) and 1,1,1‐trimethoxyethane ((CH3O)3CCH3 (4)), respectively.
Investigation of some pentasubstituted 1,4‐dihydropyridines by means of fast ion bombardment, chemical ionization and electron impact mass spectrometry
Authors: Hamdan M. , Scandola M. , Tarzia G. 
Published: May 2005

AbstractPositive fast ion bombardment, positive chemical ionization (CI+) and positive electron impact (EI) ionization mass spectrometry were used to investigate a number of relatively large and structurally related organic molecules. Some of the major dissociation pathways observed in the CH4‐CI+ mass spectra are not present under NH3‐CI+ conditions, but are obtained in the collision‐induced dissociation (CID) spectrum of the 50 eV MH+ molecular ion, formed in the latter reaction. The resemblance between the EI mass spectra and their fast ion bombardment counterparts, the effect of changing the energy of the bombarding Cs+ ion beam over the range 2–16 keV and the different degrees of internal excitation of ions formed in different CI reagent gases are discussed.
Stereochemical effects in mass spectrometry XIII—Determination of absolute configuration by fast atom bombardment mass spectrometry
Authors: Yang Hou‐Jun , Chen Yao‐Zu 
Published: May 2005

AbstractIt was found that in the fast atom bombardment mass spectra of some asymmetric secondary alcohols and amines, when a pair of enantiomers, such as (2R,3R)‐ and (2S,2S)‐2,3‐diacetoxysuccinic anhydride and (2R,3R)‐ and (2S,3S)‐2,3‐dibenzoyloxysuccinic anhydride, were used as reagents, the relative abundances of characteristic ions formed by the stereoselective reaction between a sample and a reagent of different configurations were much higher than those of ions formed by a sample and a reagent of the same configuration. The absolute configurations of the sample molecule may be predicted by examination of the mass spectra of the sample measured with reagents of R and S configurations. This approach proved to be a convenient way to determine the absolute configuration of organic molecules at the micromole level by fast atom bombardment mass Spectrometry, and it has advantages over the chemical ionization method reported previously for the analysis of polar and involatile compounds.
Characterization of cytokinins from plant pathogenic Pseudomonades by fast atom bombardment tandem mass spectrometry
Authors: Greco Francesco , Sindona Giovanni , Uccella Nicola , Evidente Antonio 
Published: May 2005

AbstractNaturally occurring cytokinins produced from two phytopathogenic Pseudomonas bacteria, and some of their derivatives and analogues, were characterized by fast atom bombardment tandem mass spectrometry. The proto‐nated molecular ions of the examined cytokinins can be fingerprinted from breakdown pattern of their gaseous unimolecular dissociations, thus providing means for their identification by desorption ionization methods.
Characterization of glucosamine and N‐acetylglucosamine oligomers by fast atom bombardment mass spectrometry
Authors: Bosso C. , Domard A. 
Published: May 2005

AbstractThe oligomers of N‐acetylglucosamine [degree of polymerization (d.p.) 2–6] and of glucosamine (d.p. 3–9) were systematically studied by the fast atom bombardment technique. Positive‐ and negative‐ion detection were used successively in each case. The latter provided more information in respect of the number of fragmentation pathways. In addition to the classical fragmentations usually obtained with other oligosaccharidic chains, new species specific to these two series were observed. They depend mainly on the nature of the substituents located on the C(2) positions of the glucosidic units constituting the chain.
Participation of halogen atoms in hydrogen transfer between remote positions in gas‐phase ionized isomeric haloresorcinols
Authors: Weisz Adrian , Andrzejewski Denis , Mandelbaum Asher 
Published: May 2005

AbstractMono, di‐ and trihaloresorcinols substituted by a halogen atom at position 2 exhibit a highly specific elimination of H2O on electron impact ionization and under conditions of collisionally induced dissociation (CID). The high isomer specificity suggests the intermediacy of a hydrogen transfer from one of the hydroxy groups to the adjacent halogen atom. A subsequent hydrogen migration to the other hydroxy group readily explains the facile elimination of H2O from the M+· ions of these particular isomers. An analogous three‐step hydrogen transfer has not been observed in 2,3‐dihalo‐l,4‐hydroquinones. 4‐Bromo‐ and 4‐icdoresorcinol undergo elimination of the halogen atom followed by a very fast loss of CO under CID conditions, affording [M − Hal]+ ions of low abundance and highly abundant[M − Hal − CO]+ ions. The elimination of CO is suppressed in the isomeric 5‐haloresorcinols, resulting in very highly abundant [M − Hal]+ ions. This behavior suggests that a ‘hidden hydrogen transfer’ accompanies the elimination of the halogen atom from the molecular ions of 4‐haloresorcinols.
The [M − 1 ]+ quasi‐molecular ion in chemical ionization mass spectrometry. Fragmentation of bis(benzyloxy)silanes by intramolecular reactions
Authors: Bild Norbert , Chapeaurouge Alexander , Gfeller Stefan , Bienz Stefan 
Published: May 2005

AbstractThe unusual chemical ionization mass spectrometric behavior of bis(benzyloxy)silanes showing heavy fragmentation and an [M − 1]+ fragment, instead of the expected [M + 1]+ ion with isobutane as the reactant gas, was investigated by means of (chloromethyl)bis(benzyloxy)methylsilane and model compounds. It could be shown that probably an intramolecular hydride transfer to an adjacent proton via a six‐membered transition state gives rise to the uncommon [M − 1]+ quasi‐molecular ion. Similar intramolecular reactions transferring a hydride, a chloro‐methyl, a phenyl or a benzyl group via cyclic transition states to a neighboring electrophile are held responsible for five of the six additional major fragments. The results demonstrate that fragmentation reactions become important in chemical ionization mass spectrometry if a molecule or an initially formed cluster ion possesses reactive groups which are in close proximity to each other.
Pyrolysis–desorption chemical ionization and high‐energy tandem mass spectrometry of the O‐specific antigen of Yersinia ruckeri
Authors: Helleur Robert J. , Thibault Pierre , Banoub Joseph H. , Shaw Derek H. 
Published: May 2005

AbstractApplication of pyrolysis‐desorption chemical ionization mass spectrometry (Py‐DCI‐MS) is demonstrated for the structural characterization of the native O‐specific antigen of Yersinia ruckeri. Under proper pyrolytic and chemical ionization conditions this antigenic polysaccharide yields anhydrohexosamine fragments which facilitate identification of the trimeric repeating unit sequence. Tandem mass spectrometric analyses of the trimeric repeating unit fragments provided additional evidence for the proposed structure and permitted rationalization of the observed fragment ions. Furthermore, Py‐DCI‐MS of smaller hexosamine subunits isolated during off‐line pyrolysis experiments showed fragmentation characteristics almost identical with those observed in the mass spectra of the whole antigen, hence confirming the stability of the pyrolysis fragments.
Gas‐phase chemistry of metal oxide anions: Reactions of dioxomanganate(III), MnO2−, and trioxomanganate(V), MnO3−, ions with monofluoro‐ and pentafluoro‐aromatic compounds
Authors: Fokkens R. H. , Gregor I. K. , Nibbering N. M. M. 
Published: May 2005

AbstractGas‐phase reactions of MnO2− and MnO3− ions with a series of monofluoro‐ and pentafluoro‐aromatic compounds, i.e. C6H4FX with X = o‐, m‐ and p‐CHO and o‐, m‐ and p‐OH and C6F5Y with Y = OH, OCH3, CHO, CN, NO2, COCH3 and F, were studied at low pressures by Fourier transform ion cyclotron resonance mass spectrometry. The principal reaction channels identified involve electron transfer from the MnO2− and MnO3− ions to the fluorinated aromatic substrates and proton abstraction and nucleophilic displacement of fluorine by these oxometallate ions. The results obtained indicate that in the gas phase MnO2− is less basic than MnO3− and that neutral MnO2 has a lower electron affinity than MnO3, both values lying between 0.52 and 0.94 eV.
Laser desorption fourier transform mass spectrometric study of porphyrins attached to hydrocarbon spacers
Authors: Antolovich Michael , Nguyen T. Hiep , Paddon‐Row Michael N. , Willett Gary D. 
Published: May 2005

AbstractThe 248 nm laser desorption Fourier transform ion cyclotron resonance positive‐ and negative‐ion mass spectra are presented for two novel porphyrin‐spacer‐quinone bichromophoric systems in which the spacer consists of a polynorbornyl‐type hydrocarbon and also for a model tetraphenylporphyrin compound. The compounds are 1,2,3,4‐tetrahydro‐1.4‐methano‐7,10,13,16‐tetraphenylbenzo [g] quinoxalino [2,3‐b] porphyrin, 5,20‐dihydro‐5,20‐methano‐l,4‐dimethoxy‐8,11,14,17‐tetrapherylnaphtho [2,3‐g]quinoxalino[2,3‐b] porphyrin and 5,10,15,20‐tetraphenyl‐porphyrin. The two‐step laser desorption multiphoton ionization mass spectra recorded at laser powers < 2 MW cm−2 produce only the parent ions M+˙ and M−˙. At increased laser powers of up to 5 MW cm−2 the [M + H]+ and [M  H]− ions are observed to increase significantly in relative abundance. At laser powers >8 MW cm−2 the porphyrins show extensive photodissociation and rearrangement and, in one case, the production of an extensive distribution of carbon cluster fragment ions including the fullerene [C60]+˙.
A tandem time‐of‐flight mass spectrometer
Authors: Jardine Daniel R. , Morgan John , Alderdice David S. , Derrick Peter J. 
Published: May 2005

AbstractA tandem time‐of‐flight mass spectrometer Incorporating a fast atom bombardment source has been designed and constructed for the purpose of studying collision‐induced decomposition spectra. A deflection of the secondary ion beam is used to form the ion packets for time‐of‐flight analysis. A floating collision cell that represents a potential barrier to ions transversing the time‐of‐fiight tube enables ionic and neutral fragments from collision‐induced decomposition reactions to be separated in time from the parent ion. The instrument operating in the tandem mode is capable of performing charge exchange and collision‐induced decomposition studies of both positive and negative incident ions.
Intermolecular dehydration reactions of protonated alkenol adducts
Authors: Liou C.‐C. , Eichmann E. S. , Brodbelt J. S. 
Published: May 2005

AbstractCollisionally activated intermolecular dehydration reactions of proton‐bound alkenol dimers and proton‐bound alkenol‐dimethyl ether adducts were examined in both a triple quadrupole mass spectrometer and a quadrupole ion trap mass spectrometer. Ion‐molecule reactions of profonated dimethyl ether (DME) with allyl alcohol, 3‐buten‐1‐ol and 4‐penten‐l‐ol (M) produced the ions [M + H]+, [2M + H]+, [M + H + DME]+ and [M + H + DME − H2O]+. Collisionally activated dissociation was used to characterize the structures of the product ions, and energy‐minimized structures and heats of formation of ions were calculated by molecular mechanics and semiempirical computational methods. The loosely bound [M + H + DME]+ ions rearrange and dissociate by an intermolecular dehydration reaction to form [M + H + DME ‐ H2O]+ ions, with methylated ether stuctures. These [M + H + DME − H2O]+ ions dissociate predominantly via direct cleavage of the ether linkage. Comparisons of the bimolecular and dissociation reactions of the alkenols were made with those of simple alcohols, diols and alkenes to demonstrate that the presence of the carbon‐carbon double bond specifically assists in many of the observed processes.
Claisen rearrangement in phenyl allenyl ethers on electron impact
Authors: Ramana D. V. , Sudha M. S. 
Published: May 2005

AbstractPhenyl allenyl ethers undergo Claisen rearrangement under electron impact conditions producing intense [M  CO] ions. Another competing fragmentation pathway in these compounds is an intramolecular aromatic substitution followed by the loss of H˙ or the substituent to give rise to fragments corresponding to benzopyrilium cations. Electron‐withdrawing substituents on the phenyl ring favour the cyclization reaction. An interesting ortho interaction of the nitro group with the allenic moiety leads to the expulsion of CO2 from the molecular ion. The proposed fragmentation pathways and the ion structures are established with the help of linked‐scan spectra (B/E, B2/E), collision activation decomposition spectra and high‐resolution data.
A secondary ion mass spectrometric study of thallium oxide thin films grown via metal organic chemical vapour deposition
Authors: Daolio Sergio , Ajò David , Rossetto Gilberto , Aschieri Carla , Armelao Lidia 
Published: May 2005

AbstractWithin a comprehensive programme including synthesis via metal organic chemical vapour deposition (MOCVD) and characterization of inorganic compounds and materials of possible interest in technologies based on thin films, results concerning the deposition of metal oxides by means of volatile organometal precursors are reported. In particular, thallium oxide films obtained by the MOCVD technique and commercial powders of Tl2O3 and Tl2O adsorbed on several metal substrates (stainless steel, Si, Cu, Mo, Pt) were studied by secondary ion mass Spectrometry (SIMS) under ion beam bombardment at different ion energies. The positive‐ and negative‐ion mass spectra exhibit typical isotopic patterns of several ionic species produced by interesting interfacial reactions, and the analysis of their relative abundances provides a measure of oxide reactivity towards different substrates. SIMS measurements of metal substrates were also performed. The ability and limits of SIMS in the reactivity study of thallium oxide powders and films and, in addition, in the identification of reaction products evidencing impurity species that, in turn, can be ascribed to the substrates or to the precursors used for the oxide synthesis is pointed out.
Fast atom bombardment mass spectrometry of cyclic hydrido dithio‐ and dioxycarbene complexes of platinum(II)
Authors: Bertani R. , Mozzon M. , Michelin R. A. , Seraglia R. , Traidi P. 
Published: May 2005

AbstractFast atom bombardment (FAB) mass Spectrometry of the two hydrido carbene compounds trans‐[(PPh3)2HPt(carbene)]BF4 (carbene = and was studied. Some retrosynthetic processes are involved in the fragmentation pathways. The reactions with NaCI were also studied under FAB conditions and the results were compared with those obtained in solution.
Fast atom bombardment in the structural identification of intermediates in the hydrolytic degradation of polyphosphazenes
Authors: Caliceti P. , Veronese F. M. , Marsilio F. , Lora S. , Seraglia R. , Traldi P. 
Published: May 2005

AbstractFast atom bombardment mass Spectrometry was employed in a study related to the hydrolytic degradation of alanine ethyl ester‐ and imidazole‐substituted polyphosphazenes, to be used as matrices for drug release. Some intermediates were identified and their structural assignment was accomplished by means of mass‐analysed ion kinetic energy data. All the detected species show the same phosphazene skeleton, consisting of a P4N3 chain, with an increasing number of alanine ethyl ester substituents, and no evidence was found for the presence of imidazole bound to the polymer backbone.
Comparison of collisional activation by the ‘boundary effect’ vs. ‘tickle’ excitation in an ion trap mass spectrometer
Authors: Paradisi Cristina , Todd John F. J. , Vettori Umberto 
Published: May 2005

AbstractIt has been shown previously that collisional activation in an ion trap mass spectrometer can be achieved by storing parent ions within a narrow zone extending close to the theoretical boundaries βr = 0 or βz = 0 of the stability diagram. This procedure can be used for obtaining collision‐induced dissociation of selected parent ions without the need to apply a precisely tuned resonant ‘tickle’ potential between the end‐cap electrodes. In this investigation a comparison was made between the two methods (‘tickle’ and ‘boundary’) of activation based on the efficiency of parent‐to‐daughter conversion and on the relative abundance of daughter ions for a model system (the m/z 91/92 ratio for n‐butylbenzene). The data show that, under conditions of maximum efficiency, a comparable amount of internal energy is present in the ions after activation with the two methods. However, with the ‘tickle’ technique it is possible to increase the internal energy of the parent ions even further, although at the expense of the efficiency, whereas in the case of the “boundary” activation, the conditions for optimum efficiency almost coincide with those for maximum activation and a drastic loss of ions follows any attempt to overcome these limits. It is also found that at any given qz value used for storing and activating parent ions the permitted mass difference between parent and fragment ions is greater with ‘boundary’ than with ‘tickle’ excitation.