bluuebunny/crossref_metadata_2025_split huggingface dataset:
Proferrioxamine siderophores of Erwinia amylovora. A capillary liquid chromatographic/electrospray tandem mass spectrometric study
Authors: Feistner Gottfried J. , Stahl Douglas C. , Gabrik Ann H. 
Published: May 2005

AbstractOn‐line capillary liquid chromatography–electrospray mass spectrometry and tandem mass spectrometry, in combination with precursor feeding and acetylation studies, were used to identify and characterize the siderophores of the fire blight pathogen Erwinia amylovora. Proferrioxamines D2, E, G1, G2, X1, and X2 were found, with D2 and E being the major siderophores for all strains of E. amylovora studied. These proferrioxamines have previously been observed with other microbial species. In addition, eleven additional hydroxamate compounds were found, nine of which occur naturally and two which were induced by directed fermentation. The novel natural proferrioxamines included three cyclic tetrahydroxamates, designated T1–3. The most abundant of these, T1, consists of four 5‐succinylamino‐1‐hydroxyaminopentane residues. In T2 and T3, one of these residues is substituted by 4‐succinylamino‐1‐hydroxyaminobutane and 3‐succinylamino‐1‐hydroxyaminopropane, respectively. E. amylovora also incorporated 3‐succinylamino‐1‐hydroxyaminopropane into a novel trihydroxamate, which has been designated X7. The novel finding that proferrioxamines may partly be comprised of 1,3‐diaminopropane residues is noteworthy because previous feeding studies with Streptomyces olivaceus Tü 2718 suggested that 1,3‐diaminopropane is biosynthetically not tolerated. A truncated proferrioxamine G1 was also identified, which is referred to as G1t, and, on feeding of diaminobutane, tetrahydroxamates T7 and T8, which are derived from T1 by substitution of two and three diaminopentane with diaminobutane residues. The structures of five other hydroxamates, with molecular masses of 530 (X8), 544 (X9), 622 (T4), 719 (T5) and 733 (T6), are not yet known. The results prove that the biosynthetic capabilities of E. amylovora for proferrioxamine production are flexible. E. amylovora may therefore be a good organism for the fermentative production of novel proferrioxamines that may be useful for reversing or avoiding aluminum and iron intoxications in man, for tumor diagnosis and therapy with radiolabeled antibodies and for use as DNA‐cleaving reagents. On the other hand, the production of all the different proferrioxamines involves common biosynthetic steps, some of which are not used in higher plants or vertebrates. Interference with the biosynthesis of proferrioxamines may therefore provide an opportunity for the development of alternative fire blight control agents.
Computer‐aided interpretation of mass spectra using databases with spectra and structures. I. Structure searches
Authors: Henneberg D. , Weimann B. , Zalfen U. 
Published: May 2005

AbstractFor databases containing spectra and structures of the reference compounds, structural descriptors (‘fragments’) have been derived that are used for structure searches in the databases. The 190 fragments have been defined according to the contents of the Wiley/NBS Mass Spectral Database and to fragmentation behaviour. A search for structures with defined fragments (absence or presence of certain fragments) retrieves certain classes of compounds. An application for checking a reference spectrum is discussed. A search for structures similar to a target structure has been developed to be used in cases where a structure can be proposed for the unknown compound. The most closely related structures existing in the database will be selected, the respective spectra often being the key for interpretation or structure elucidation, as illustrated by an example.
Spectroscopy and fragmentation of alkylamines investigated by photoionization,
Authors: Moritz F. , Grotemeyer J. 
Published: May 2005

AbstractThe fragmentation of some alkylamines and their deuterated analogues were investigated by single‐ and multiphoton ionization. The internal energies of the molecular ions were varied prior to ionization through different expansions in a supersonic beam. Further, it is demonstrated that the difference between nano‐ and femtosecond pulses used for multi‐photon ionization has an influence on the fragmentation pattern of the amines due to a change in the activation scheme. Spetroscopy and the fragmentation reactions were investigated with respect to the internal energy of the ions. It is shown that large differences are observed in the mass spectra depending of the ionization method used. Photoionization yields intense molecular ions whereas electron impact ionization leads to strong fragmentation.
Formation of isomeric ethylenehalonium and α‐haloethyl cations and the role of ion–neutral complexes in the decomposition of protonated β‐haloethanols
Authors: Heck Albert J. R. , de Koning Leo J. , Nibbering Nico M. M. 
Published: May 2005

AbstractDecomposition of protonated β‐haloethanols was found to proceed predominantly via the loss of water. The mechanism was studied in the decomposition of metastable and collisionally activated isotopically labelled protonated β‐haloethanols. The study involved the characterization of the resulting fragment ions by collisionally activated decomposition and by low‐pressure ion/molecule probe reactions. The results indicate that loss of water from protonated β‐haloethanols proceeds via two competing mechanisms. The competition between these mechanisms appears to be governed by the nature of the halogen and by the internal energy of the decomposing protonated β‐haloethanol. In the first mechanism, loss of water is considered to be initiated by a concerted 1,2‐elimination of H3O+ resulting in an ion–molecule complex between H3O+ and haloethene. Rapid and reversible proton transfers between the two species in the complex is followed by a relatively slow dissociation ofthe intermediate complex resulting in the formation of an water molecule and an α‐haloethyl cation. In competition with this mechanism, loss of water can be initiated by carbon–oxygen bond cleavage, which is assisted by halogen–carbon bond formation resulting in the formation of a water molecule and cyclic ethylenehalonium ion.
Mass spectrometry with extraction of dissolved ions at atmospheric pressure for prostaglandin identification in biological materials
Authors: Isay S. V. , Kafanova T. V. , Matveeva E. R. , Mirgorodskaya O. A. 
Published: May 2005

AbstractProstaglandins (PGA2, PGE1, PGE2, PGF2α) and their methyl esters served as standards to show the possibility of application of mass spectrometry with extraction of dissolved ions at atmospheric pressure (EDIAP) for prostaglandin identification. Applying EDIAP mass spectrometry to the soft coral Plexaura homomalla, all the prostaglandins and their derivatives described in the literature were identified.
Comparison of keV and eV collision‐induced dissociation of some protonated isomeric cyclopropane derivatives
Authors: Hamdan M. , Curcuruto O. , Tarzia G. , Balsamini C. 
Published: May 2005

AbstractA number of protonated isomeric cyclopropane derivatives formed by isobutane chemical ionization (CI) were mass selected and their respective collision‐induced dissociation (CID) spectra were investigated at ion kinetic energies of 30 and 150 eV and 6 keV. Qualitative differences which may stem from different molecular structures and/or different internal excitation which may accompany the ionization process were observed in some CI mass spectra and in the low‐energy CID spectra but not in their keV counterparts. This experimental observation and the dissociation of polyatomic ions in two different energy ranges are discussed.
Photodissociation studies of small peptide ions by Fourier transform mass spectrometry
Authors: Gorman Greg S. , Amster I. Jonathan 
Published: May 2005

AbstractFourier transform mass spectrometry was used to study the 193 nm photodissociation of laser‐desorbed peptide ions. The output of an excimer laser was split and the two beams were directed sequentially at a sample probe to form ions, and through an aperture in the analyzer cell, to cause photodissociation of trapped ions. A solenoid‐driven shutter that is capable of rapid switching (30 ms) between the open and closed states allowed a single laser to be used for both desorption/ionization and photodissociation. Multiple laser pulses were required to fragment a significant fraction of the precursor ions (five pulses yielded 40% dissociation). Collisionally activated dissociation (CAD) mass spectra of the peptides were recorded and compared with the photodissociation mass spectra. Photo‐activation of peptide ions produced lower yields of fragment ions formed by loss of small molecules (H2O, NH3, CO, CO2) than did CAD, and produced higher yields of structurally informative sequence ions. For most peptides, the efficiency of ion fragmentaton by photodissociation paralleled the condensed‐phase molar absorptivity of the peptide at 193 nm. A comparison of these data with those of previous studies suggested that both the ionization method and the observation time (dictated by the type of mass spectrometer) influence the appearance of the photodissociation mass spectrum.
Formation and collision‐induced dissociation behaviour of doubly charged gas‐phase fullerene anions C, C and higher homologues. Collision‐induced electron‐stripping process
Authors: Mandelbaum A. , Etinger A. 
Published: May 2005

AbstractDoubly charged molecular anions M2− of fullerenes are formed in the gas phase under chemical ionization conditions with isobutane as the reagent gas. The efficiency of double electron attachment increases with increasing size of the fullerenes: the C ion is the most abundant doubly charged anion in the negative‐ion CI mass spectrum, although the concentration of C70 was about 12% in the fullerene mixture examined. Under low‐energy collision‐induced dissociation conditions an electron is ejected from the doubly charged C ion resulting in the singly charged molecular anion C˙. This process appears to be the first report of the ejection of an electron (electron stripping) from a doubly charged anion in the gas phase:

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In situ enzymatic digestion of oligopeptides on a direct insertion probe tip combined with fast atom bombardment and tandem mass spectrometry
Authors: Mák Marianna , Tamás József 
Published: May 2005

AbstractThe applicability of an approach to establish the sequence of oligopeptides involving on‐probe‐tip enzymatic fragmentation and subsequent direct fast atom bombardment (FAB) mass spectrometry (MS) and FAB‐MS/MS of the subpeptide mixture was tested using two model peptides consisting of 19 and 25 amino acid residues. The method was found to be both time and sample sparing and flexible enough to use even subsequent digests, if necessary, with enzymes of different specificity. It provided in both cases complete information, not only for the sequence of enzymic fragments but also for their order in the original oligopeptide. Consequently, this approach to the sequence analysis of oligopeptides can be a method of choice when the FAB‐MS/MS technique itself is unsuitable for obtaining detailed structural information. The method seems to be applicable to enzymically digestible peptides with an upper mass limit of about 3500.
Electron impact mass spectra of phosphine sulphides and selenides
Authors: Miranda René , Salas Ismael , Salceda Catalina , Velasco Luis , Cabrera Armando , Salmón Manuel 
Published: May 2005

AbstractAn electron impact mass spectral study of phosphine sulphides and selenides established the effect of the heteroatom and the role of the ortho substituent in the fragmentation pattern.
Mass displacements in quadrupolar field analysers
Authors: Traldi Pietro , Favretto Donata , Catinella Silvia , Bortolini Olga 
Published: May 2005

AbstractThe influence of different instrumental parameters on the mass displacements observed in an ion trap and a quadrupole mass filter was investigated. In ion trap measurements it was observed that isolated ions (obtained by both ‘apex’ and ‘two‐step’ isolation methods) show the same mass displacements determined in the usual mass spectra; isobaric ions of different structure irradiated with supplementary a.c. fields are ejected at different a.c. voltages, and different cooling times do not affect the mass value. In the quadrupole mass filter, differences in mass were found among isobaric ions of different structure, although to a smaller extent than those observed in the ion trap. All the data obtained are in agreement with the hypothesis of ion–r.f. field interactions originating from the polarizability of the ion.
Fullerenes from kerogen by laser ablation fourier transform ion cyclotron resonance mass spectrometry
Authors: Rose Harry R. , Smith Derek R. , Fisher Keith J. , Dance Ian G. , Willett Gary D. , Wilson Michael A. 
Published: May 2005

AbstractRaw oil shale, kerogen (demineralized shale) and carbonaceous residues from kerogen pyrolysis in the range 350–700°C (at 50°C intervals) were studied by laser ablation Fourier transform ion cyclotron resonance mass spectrometry using the fundamental frequency of Nd: YAG laser (1064 nm). Normally, pyrolysis of the raw materials produces oil and the resulting residues have decreased hydrogen to carbon ratios and exhibit relative increases in aromatic carbons. Raw shale and kerogen give positive‐ion spectra with mainly protonated species of m/z 100–400. Laser ablation positive‐ion mass spectra of the pyrolysis products of the kerogen show the presence of C60, C70 and other fullerene ions with a distribution of higher mass fullerene ions up to m/z 4000. Using high laser powers (100–3000 MW cm−2), the residue from pyrolysis at 350°C initially did not produce any fullerene ions (apart from traces of C60 and C70), but after continued ablation a cavity was formed in the target and a wide distribution of fullerene ions was obtained with subsequent laser pulses. Residues obtained from the pyrolysis of kerogen at 400–500°C produced fullerene ions at both low (4–200 kW cm−2) and high laser powers. The 550°C pyrolysis residue gave only small amounts of C60 and C70 positive ions at low laser power whereas residues from the pyrolysis of kerogen above 550°C did not give fullerene ions over a wide range of laser powers. It is proposed from the above results that the changes in the aromatic nature of the kerogen residues with increasing pyrolysis temperature are directly related to the ease of fullerene formation. This is possibly due to the formation of large polycyclic aromatic systems at pyrolysis temperatures above 400°C, formed in the residues. It should be noted that the shale samples (raw or pyrolysed) did not generate fullerene ions under any of the conditions employed in these experiments.
Metastable fractions in fullerenes
Authors: Lifshitz Chava , Laskin Julia , Peres Tikva 
Published: May 2005

AbstractMetastable fractions were determined for the series of reaction Cn+ → C + C2 in fulleren samples. A reverse‐geometry double‐focusing instrument was employed with electron impact ionization and high energy resolution. Reactions were studied in the second field‐free region and corrections were made for artifact peaks due to decompositions in the first field‐free region. The metastable fractions D were converted into apparent decay constant k̄ and the results were compared with previous data from sector and time‐of‐flight instruments, respectively. The differences in the behaviour of evaporative ensembles from laser ablation of graphite and of ionized fullerenes are discussed.
The search for the gas‐phase negative‐ion pinacol rearrangement. 2—aryl rearrangements
Authors: Dua Suresh , Alexander Margaret J. , Bowie John H. 
Published: May 2005

AbstractDeprotonated phenyl ethylene glycols, on collisional activation, lose water by a negative ion pinacol rearrangement involving phenyl migration. For example, deprotonated benzpinacol undergoes the following reactions: Ph2C(OH)C(O−)Ph2 → [PhCOCPh3 – H]− + H2O. It is proposed that this rearrangement proceeds from an eclipsed (or near eclipsed) conformer which is stabilized by the HO and O− groups forming a strong intramolecular hydrogen bond.
Unimolecular reactions of isolated organic ions: The chemistry of the oxonium ions CH3CH2CH2CH2+O = CH2 and CH3CH2CH2CH = O+CH3
Authors: Bowen Richard D. , Derrick Peter J. 
Published: May 2005

AbstractThe reactions of the metastable oxonium ions CH3CH2CH2CH2+O = CH2 and CH3CH2CH2 = O+ CH3 are reported and discussed. Both these isomers of C5H11O+ expel predominantly CH2O (75–90% of the metastable ion current), a moderate amount of C3H6 (5–15%), a minor amount of CH3OH (2–8%) and a very small proportion of H2O (0.5–3%). All these processes give rise to Gaussian metastable peaks. The kinetic energy releases associated with fragmentation of these oxonium ions are similar, but slightly larger for dissociation of CH3CH2CH2CH = O+CH3. The behaviour of labelled analogues confirm that the reactions of CH3CH2CH2CH = O+CH3 are closely related, but subtly different. Elimination of CH2O and C3H6 is intelligible by means of mechanisms involving CH3CH+CH2CH2OCH3. This open‐chain cation is accessible to CH3CH2CH2 +O = CH2 by a 1,5‐H shift and to CH3CH2CH2‐CH = O+CH3 by two consecutive 1,2‐H shifts (or, possibly, a direct 1,3‐H shift). The rates of these 1,2‐, 1,3‐ and 1,5‐H shifts are compared with one another and also with the rates of CH2O and C3H6 loss from each of the two oxonium ions. The 1,5‐H shift that converts CH3CH+CH2CH2OCH3 formed from CH3CH2CH2CH = O+ CH3 into CH3CH2CH2+O = CH2 prior to CH2O elimination is essentially unidirectional. In contrast, the corresponding step converting C5H11O+ ions generated as CH3CH2CH2CH2+O = CH2 into CH3CH+ CH2CH2OCH3 competes effectively with expulsion of CH2O and C3H6. The implications of the latter finding for the degree of concert in the hydrogen transfer and carbon‐carbon bond fission steps in alkene losses from oxonium ions via routes that are formally isoelectronic with the retro ‘ene’ pericyclic process are emphasized.
Dissociation mechanisms of energy‐selected chlorobutane ions: Experiment and theory
Authors: Ferreira M. A. Almoster , Cabral B. J. Costa , Oliveira M. C. , Baer T. 
Published: May 2005

AbstractThe breakdown diagrams and photoionization efficiency curves of isomeric chlorobutane ions were obtained by energy‐selected molecular ions with the photoelectron–photoion coincidence (PEPICO) technique. The loss of HCl from 1‐ and 2‐chlorobutane molecular ions was found to be fast, and accurate dissociation onsets were determined from the crossover energy in the breakdown diagrams and appropriately corrected for the precursor thermal energy. In spit of the low activation energy, the isochlorobutane molecular ion was found to dissociate slowly near the dissociation limit, the time‐of‐flight distribution having been analyzed in terms of two exponential decay rates. The dissociation reaction involved a large kinetic energy release that pointed to a 1,2‐elimination leading to a stable C4H ion. AB initio calculations indicated that the reaction path involved an H‐atom transfer through a barrier, which is a favorable case for a tunneling model to explain the slow decomposition rate. The kinetic energy release of chlorine radical loss from tert‐chlorobutane was determined as a function of the ion internal energy. At low energies the kinetic energy release was nearly statistical but the dissociation from the excited electronic states resulted in a large and non‐statistical kinetic energy release.
Mechanism, energetics, kinetics and dynamics of the reaction C2H6+˙ → C2H4+˙ + H2
Authors: Bråten Svein Magne , Helgaker Trygve , Uggerud Einar , Vulpius Tore 
Published: May 2005

AbstractThe distributiosn of relative translational energy released during (i) loss of H2 from metastable CH3CH3+˙ ions, (ii) loss of HD from metastable CH3CD3+˙ ions and (iii) loss of D2 from metastable CD3CD3+˙ ions were measured. The relevant parts of the potential energy surface of the reaction C2H6+˙ → C2H4+˙ + H2 (including isotopic variants) were investigated using various theoretical methods (high‐level ab initio quantum chemistry, RRKM calculations, dynamic reaction trajectory calculations). A consistent reaction model is presented which reproduces available experimental data. Quantum mechanical barrier tunnelling is found to be important, leading to an activation energy (on the microsecond time‐scale) which is approximately 0.1 eV below the critical energy.
Oxirane as a chemical ionization gas: Reactivity towards different classes of compounds
Authors: Lange C. 
Published: May 2005

AbstractOxirane chemical ionization (CI) gives numerous ions, including C2H3O+ and C2H5O+. These ions react with organic molecules through various specific ion–molecule reactions such as hydride abstraction, protonation, additions or cycloadditions. Oxirane CI allows discrimination between unsaturated compounds with [M + 43]+ and [M + 57]+ adduct ions and heteroatom functions with [M + 45]+ adduct ion. All are diagnostic ions. Oxirane CI permits selectivity during the ionization process of a mixture and discrimination of isomers.
The role of ion–neutral complexes in the reactions of onium ions and related species
Authors: Bowen Richard D. 
Published: May 2005

AbstractAn account is given of the development of the proposal that ion–neutral complexes are involved in the unimolecular reactions of onium ions (R1R2CZ+R3; Z = O, S, NR4; R1, R2, R3, R4 = H, CnH2n + 1), with particular emphasis on the informative C4H9O+ oxonium ion system (Z = O; R1, R2 = H; R3 = C3H7). Current ideas on the role of ion‐neutral complexes in cation rearrangements, hydrogen transfer processes and more complex isomerizations are illustrated by considering the behaviour of isomeric CH3CH2CH2X+ and (CH3)2CHX+ species [X = CH2O, CH3CHO, H2O, CH3OH, NH3, NH2CH3, NH(CH3)2, CH2NH, CH2NCH3, CO, CH3˙, Br˙ and I˙]. Attention is focused on the importance of four energetic factors (the stabilization energy of the ion–neutral complex, the energy released by rearrangement of the cationic component, the enthalpy change for proton transfer between the partners of the ion neutral complex and the ergicity of recombination of the components) which influence the reactivity of the complexes. The nature and extent of the chemistry involving ion‐neutral complexes depend on the relative magnitudes of these parameters. Thus, when the magnitude of the stabilization energy exceeds the energy released by cation rearrangement, the ergicity of proton transfer is small, and recombination of the components in a new way is energetically favourable, extensive complex‐mediated isomerizations tend to occur. Loss of H2O from metastable CH2O+C3H7 ions is an example of such a reaction. Conversely, if the stabilization energy is small compared with the magnitude of the energy released by eation rearrangement, the opportunities for complex‐mediated processes to become manifest are decreased, especially if proton transfer is endoergic. Thus, CH3CH2CH2CO+ expels CO, with an increased kinetic energy release, after rate‐limiting isomerization of CH3CH2CH2+CO to (CH3)2CH+CO has taken place. When proton transfer between the components of the complex is strongly exoergic, fragmentation corresponding to single hydrogen transfer occurs readily. The proton‐transfer step is often preceded by cation rearrangement for CH3CH2CH2X+ species. In such circumstances, the involvement of ion–neutral complexes can be detected by the observation of unusual site selectivity in the hydrogen‐transfer step. Thus, C3H6 loss from CH2N+(R1)CH2CH2CH3 (R1 = H, CH3, C3H7) immonium ions is found by 2H‐labelling experiments to proceed via preferential α‐and γ‐hydrogen transfer; this finding is explained if the incipient +CH2CH2CH3 ion isomerizes to CH3CH+CH3 prior to proton abstraction. In contrast, the isomeric CH2N+(R1)CH(CH3)2 species undergo specific β‐hydrogen transfer because the developing CH3CH+CH3 cation is stable with respect to rearrangements involving a 1,2‐H shift.