bluuebunny/crossref_metadata_2025_split huggingface dataset:
Generation of large radical ions from oligometallocenes by matrix‐assisted laser desorption ionization
Authors: Juhasz Peter , Costello Catherine E. 
Published: May 2005

AbstractNon‐polar polymers containing ferrocene, ferrocenylnaphthalene, and ruthenocenylnaphthalene groups in their repeating units were studied by matrix‐assisted laser desorption ionization (MALDI) time‐of‐flight mass spectrometry. Sample preparation for these polymers utilized tetrahydrofuran as solvent and several new matrices such as dithranol, 9‐nitroanthracene, and quinizarin (all of these are anthracene derivatives). By comparing the mass spectra of oligometallocenes recorded with different matrices at different wavelengths (337 nm and 2.94 μm) and laser desorption ionization mass spectra recorded without matrix, it could be verified that the major analyte‐related peaks in the MALDI mass spectra corresponded to the radical molecular ions. Radical ions have not been seen in the MALDI mass spectra of biopolymers such as proteins, peptides, and carbohydrates. Radical formation was demonstrated for samples in the mass range (1 kDa–13 kDa). Even in the presence of potential cationization sites such as methyl ester groups in the repeating units of some polyferrocene samples, MALDI mass spectra were dominated by radical ions of the analyte. Two possible mechanisms for radical formation in MALDI are discussed. Comparison of results with different matrices suggested that the distribution of masses observed in the mass spectra and characterized by the polydispersity index was independent of the matrix, but significant differences (5%) in the average molecular weights of the mass distributions were found.
Carbon clusters from coal‐derived materials
Authors: Herod A. A. , Kandiyoti R. , Parker J. E. , Johnson C. A. F. , John P. , Smith G. P. , Li C.‐Z. 
Published: May 2005

AbstractThe production of carbon clusters (but not fullerenes) from coal‐derived material by the use of laser desorption mass spectrometry is described. Benzo(e)pyrene, a standard polynuclear hydrocarbon found in coal tars, also gave carbon clusters despite using low laser power to avoid pyrolysis of target molecules. Positive‐ and negative‐ion spectra of the standard included carbon clusters. These clusters are formed by the laser energy and can be confused with aromatic hydrocarbons of the same nominal masses. They have no relevance for studies of coal structure.
High‐performance liquid chromatography/mass spectrometry with thermospray lonization of free ecdysteroids
Authors: Evershed Richard P. , Prescott Mark C. , Kabbouh Mohamed , Rees Huw H. 
Published: May 2005

AbstractHigh‐performance liquid chromatography/mass spectrometry (HPLC/MS) with thermospray ionization has been applied to the analysis of free ecdysteroids (polyhydroxylated steroids that serve as arthropod moulting hormones). Of a range of analytical conditions that were tested, optimum results were obtained by the use of re versed‐phase HPLC using a methanol + water mixture containing 0.1 M ammonium acetate. The positive‐ion spectra of ecdysteroids showed pseudo‐molecular ions, [M + H]+, and fragment ions corresponding to the sequential losses of hydroxyl groups. The [M + H − H2O]+ and [M + H − H2O]+ ions were the most abundant for all the compounds tested. Ecdysteroids bearing a C‐20 hydroxyl group (e.g. 20‐hydroxyecdysone) showed ions characteristic of cleavage of the side‐chain from the steroid nucleus. This mode of fragmentation was much less obvious in the case of ecdysteroids lacking C‐20 hydroxylation (e.g. ecdysone). Full‐scan mass spectra were readily obtained from 1 μg of free ecdysteroids, while a limit of detection of 5 ng (signal‐to‐noise ratio 3) was attained in the selected‐ion monitoring mode. The application of HPLC/MS to the study of ecdysteroids in biological materials is demonstrated by the analysis of extracts of newly laid eggs of the desert locust (Schistocerca gregaria) and pupae of the cotton leafworm (Spodoptera litoralis).
Gas chromatography/isotope ratio mass spectrometry of leaf wax n‐alkalines from plants of differing carbon dioxide metabolisms
Authors: Rieley Gareth , Collister James W. , Stern Benjamin , Eglinton Geoffrey 
Published: May 2005

AbstractIndividual n‐alkalines isolated from the leaf‐surface waxes of plants utilizings differing photosynthetic pathways were analysed using gas chromatography/isotope mass spectrometry (GC/IRMS), in order to obtain the ratios of 13C to 12 (δ13). Marked differences in the average 13C‐depletion of the n‐alkalines relative to whole leaf tissues were observed (C3 = −7.7‰; C4 = −9.9‰; CAM = −11‰). Additionally, all three metabolic types exhibited considerable differences of 13C‐depletion between n‐alkaline homologues isolated from the same plant.
Resonance ionization mass spectroscopy of atomic products formed by photodissociation of sodium iodide molecules
Authors: Collier J. L. , Telle H. H. 
Published: May 2005

AbstractThe products produced by photofragmentation in a molecular beam of sodium iodide, NaI, are investigated utilizing the technique of resonance ionization spectroscopy for the metal fragment, Na. Time‐of‐flight mass spectra are recorded, as a function of the wavelength of the resonant excitation step, and in dependence of the laser pulse energy. In particular, the appearance of non‐resonantly generated atomic and molecular ions is discussed, highlighting the importance of mass‐selective analysis of the ions formed in the interaction volume of the laser and molecular beams.
A comparative study of theoretical methods for the analysis of high‐resolution double‐charge‐transfer spectra, applied to the ethene molecule
Authors: Andrews S. R. , Parry D. E. 
Published: May 2005

AbstractThe low‐energy electronic states of the ethene dication are investigated theoretically, a comparison being made between the predictions of the ab initio ADC(2) Green's function method and of the recently developed semi‐empirical MSXα method. Both methods provide a consistent unambiguous analysis of the closely‐spaced peak structure recently observed in a high‐resolution double‐charge‐transfer spectrum for the ethene molecule.
Fast‐atom bombardment/mass‐analysed ion kinetic energy spectrometry of inositol phosphates
Authors: Walton Terence J. , Hughes Soraya Y. 
Published: May 2005

AbstractThe application of fast‐atom bombardment mass Spectrometry and collisiorutlly induced dissociation with mass‐analysed ion kinetic energy (CID/MIKE) Spectrometry of representative inositol mono‐, bis‐ and trisphos‐phates is described. Based on their CID/MIKE spectra, inositol polyphosphates containing vicinal phosphate groups could be distinguished from isomers in which adjacent phosphate groups were absent. The potential value of this procedure in studies of the biochemistry of intracellular second messengers is discussed.
New desorption strategies for the mass spectrometric analysis of macromolecules
Authors: Hutchens T. William , Yip Tai‐Tung 
Published: May 2005

AbstractWe present two new desorption strategies for the mass spectrometric analysis of macromolecules. These desorption strategies are based on the molecular design and construction of two general classes of sample ‘probe’ surfaces. The first class of surfaces is designed to enhance the desorption of intact macromolecules presented alone (neat) to the surface; we call this surface‐enhanced neat desorption (SEND). The availability of probe surfaces derivatized with, or composed of, multiple types and defined numbers of energy‐absorbing molecules will facilitate investigations of energy transfer and desorption/ionization mechanisms. The second class of probe surfaces is designed to enhance the desorption of specific macromolecules captured directly from unfractionated biological fluids and extracts; we call this surface‐enhanced affinity capture (SEAC). Use of these new probe surfaces as chemically defined solid‐phase reaction centers will facilitate protein discovery through molecular recognition in situ, and also macromolecular structure analysis through the sequential chemical and/or enzymatic modification of the adsorbed analyte in situ. Specific examples of laser‐assisted SEND and SEAC time‐of‐flight mass spectrometry are presented to illustrate the potential for increased selectivity, analyte detection sensitivity, and mass measurement accuracy.
Comparative study of kinetic energy release distribution in unimolecular and collision‐induced dissociations of molecular ions
Authors: Cho Seung Il , Choe Joong Chul , Kim Myung Soo 
Published: May 2005

AbstractEven though the kinetic energy release distribution in metastable ion decomposition is known to be useful for the study of ion structure and dissociation mechanism, the same information available from collisionally activated decomposition has not been used widely. One of the main obstacles preventing such a general use is related to the uncertainty in the internal energy content of the parent ion in the latter process. In the present work, a method based on a scaling relation has been developed to circumvent such a difficulty. Validity of the method is tested by applying it to a few well‐known reactions.
Superbases in the gas phase: Amidine and guanidine derivatives with proton affinities larger than 1000 kj mol−1
Authors: Decouzon M. , Gal J.‐F. , Maria P.‐C. , Raczyńska E. D. 
Published: May 2005

AbstractBy building a relative basicity ladder, the current basicity scale (Lias et al., J. Phys. Chem. Ref. Data, 17 Suppl. No. 1 (1988)) has been reexamined in its upper part, and extended for organic compounds (amenable to proton transfer measurements) up to proton affinity, PA = 1050 kJ mol−1. Structural effects involved in superbasicities are briefly discussed and routes to further extension of the gas‐phase basicity scale for organic compounds are proposed.
Investigation of the metabolism of felodipine using on‐line liquid chromatography/UV diode array detection/atmospheric pressure chemical ionization mass spectrometry as a diagnostic tool
Authors: Macrae P. V. , Jones B. C. , Todd J. F. J. 
Published: May 2005

AbstractThe utility of on‐line liquid chromatogaphy coupled to UV diode array detection and atmospheric pressure chemical ionization mass spectrometry for the analysis of microsomal metabolites of felodipine has been investigated. A previously unreported metabolite of felodipine, extracted from male rat microsomes, has been detected using this technique. UV diode array detection has been used to characterize this metabolite as a dihydropyridine metabolite and tandem mass spectrometry data used to assign a structure.
Ionization of C60 (buckminsterfullerene) by electron impact
Authors: Srivastava S. K. , Jong G. , Leifer S. , Saunders W. 
Published: May 2005

AbstractUtilizing a crosses electron‐beam/molecular‐beam collision geometry, mass spectra of C60 and C70 ions have been obtained for an electron impact energy range of 20 eV to 600 eV. These spectra are dominated by singly and doubly ionized species. The intensity of fragment ions is very weak, which is in agreement with previous observations. Ionization efficiency curves for the formation of C and C have also been obtained near their threshold regions. From these curves, appearance energies (AE) of these ions have been derived. The AE for C is found to be 7.8±0.3 eV, which agrees well with previous measurements. However, our value of 16.4±0.3 eV for the formation of C is much lower than the value of 19.0±0.3 eV obtained by photo‐ionization techniques.
Collision‐induced dissociations of deprotonated peptides. Dipeptides containing methionine or cysteine
Authors: Waugh Russell J. , Bowie J. H. , Gross Michael L. 
Published: May 2005

AbstractThe collisional activation mass spectra of the [M – H]− ions of dipeptides containing Met or Cys show the usual backbone fragmentation allowing the sequence of the peptide to be determined. A methionine residue may be identified by the presence of a pronounced peak resulting from loss of MeSH, while a cysteine residue may be identified by the presence of a peak corresponding to loss of either H2S or (H2S + CO2).
Electron ionization mass spectrometry of spiroepoxides generated from E‐3‐arylideneflavanones
Authors: Lipták Miklós , Dinya Zoltán , Nemes Csaba , Lévai Albert , Patonay Tamás , Vékey Karoly 
Published: May 2005

AbstractThe electron‐impact induced decomposition of some spiroepoxides prepared from E‐3‐arylideneflavanones has been examined by means of low‐ and high‐resolution mass spectrometry, mass‐analysed ion kinetic energy (MIKE) spectrometry and collision‐induced dissociation (CID) experiments. The compounds studied were found to undergo a rearrangement reaction resulting in a very intense odd‐electron ion. The MIKE and CID‐MIKE spectra of this type of ion generated from the unsubstituted epoxide proved to be identical to those of the molecular ion of trans‐stilbene. The isomerization of epoxides to the corresponding carbonyl compounds prior to fragmentation was not observed.
A comparison of the fragmentation patterns of 5‐fluoromethyl‐3,4‐disubstituted isoxazoles and 5‐methyl analogs
Authors: Favretto Donata , Traldi Pietro , Bravo Pierfrancesco , Diliddo Dario , Resnati Giuseppe 
Published: May 2005

AbstractThe influence of fluorine substitution on the fragmentation processes of some substituted isoxazoles has been studied by comparing the electron‐impact‐induced mass spectrometric behaviour of some 5‐monofluoromethyl‐3,4‐disubstituted isoxazoles with that of the corresponding 5‐methyl analogs. Some interesting and unusual cleavages have been detected and a rationale has been developed for them on the basis of metastable ion studies and accurate mass measurements. Evidence has been found of the influence of fluorine in the stabilization of molecular and fragment ions.
Investigation of some thiosulfonate derivatives by means of chemical ionization and tandem mass spectrometry
Authors: Curcuruto O. , Winders J. , Franchi D. , Hamdan M. 
Published: May 2005

AbstractA number of thiosulfonate derivatives have been investigated by means of ammonia chemical ionization (NH3‐CI), electron impact ionization (El) and mass‐selected collision induced dissociation (CID). For most of the compounds investigated, the NH3‐CI positive‐ion mass spectra exhibit the addition ion, [M + NH4]+, as the dominant species, which implies that the proton affinities of the compounds investigated are less than the proton affinity of NH3. Deviation from true chemical ionization conditions resulted in efficient dissociation of the addition ion to yield substantial amounts of the protomated molecule, [M + H]+. The major fragment ions observed in the EI mass spectra and in the CID spectra indicate the cleavage of the sulfur‐sulfur bond to be more efficient than other competing cleavages. This and other experimental observations are discussed.
Collisions of C and C at fluorinated and non‐fluorinated self‐assembled monolayer films
Authors: Callahan J. H. , Somogyi Á. , Wysocki V. H. 
Published: May 2005

AbstractWe report here the spectra that result when singly and doubly charged buckminsterfullerene ions, C· and C, collide with self‐assembled monolayer films at collison energies ranging from 125 to 320 eV. The surfaces were prepared by the spontaneous assembly of octadecanethiol (CH3(CH2)17SH), perdeuteroeicosanethiol (CD3(CD2)19SH), and 2‐(perfluorooctyl)‐ethanethiol (CF3(CF2)7CH17CH2SH) on vapor‐deposited gold. The fluorinated surface causes the greatest conversion of kinetic energy into internal energy, more extensive fragmentation of doubly charged buckminsterfullerene C is detected in collisions with this surface than in collisions with the alkanethiolate surfaces.
Short time‐scale observation of an electrospray current
Authors: Charbonnier Florence , Rolando Christian , Saru Florence , Hapiot Philippe , Pinson Jean 
Published: May 2005

AbstractThe design and use of an experimental device for investigating the time‐dependent structure of an electrospray current is described. Various electrolytes, including aqueous solutions, were submitted to electrospray and the instantaneous current intensities were monitored by means of a fast current measurer. The intensity proved discontinuous and roughly periodic in almost every case. By recording the intensity pattern on a fast oscilloscope, an estimate of the ‘period’ was obtained. A typical structure (obtained from a 10 mM NaBr methanolic solution, ‘reduction mode’) consists of series of groups of peaks. The charge per peak is approximately 10−10C and does not change much with the experimental parameters (electrolyte concentration, nature of the solvent, value of the high voltage). The current variation seems to be mainly related to the number of peaks rather than to the heights of the peaks. These results are consistent with commonly observed averaged spray intensities (0.1 to 1 μA) and suggest a pulsed droplet emission frequency of the order of 300 kHz.
On the kinetic energy released upon collision‐induced dissociation of oriented diatomic ions
Authors: Kumar G. Ravindra , Krishnamurthi Vidhya , Mathur D. 
Published: May 2005

AbstractThe kinetmatics of collision‐induced dissociation of oriented singly and doubly charged diatomic molecular ions have been investigated using computer simulation techniques. Asymmetries are predicted in the translational‐energy spectra of forward‐scattered and backward‐scattered fragment ions when dissociation occurs, in those cases where the internuclear axis of the diatomic molecules is oriented along the direction of the incident ion beam. Simulated translational energy spectra are compared with experimental data obtained for dissociation of oriented CO2+ ions in collision with helium atoms.
Oxidation of peptides during electrospray ionization
Authors: Morand Kenneth , Talbo Gert , Mann Matthias 
Published: May 2005

Abstract[M+H+16]+ ions were observed in the electrospray ionization mass spectra of several synthetic and maturally occurring peptides. Initial results have shown that the appearance of the modification is dependent on the field strength at the electrospray needle and the flow rate of the solution passing through the capillary. Mass spectrometric experiments on peptides showing the +16 Da modification attributed the change to the selective oxidation of either a methionyl, tryptophanyl, or tyrosyl residue present in the peptide. These results were further confirmed by tandem mass spectrometry experiments on prptides with a methionyl residue at either the N‐ or C‐tgerminus, or within the peptide chain. This effect can occur under normal operating conditions and therefore care must be taken in the analysis of samples containing these oxidizable residues. Conversely, the selectivity of the oxidative process may be used to enhance the information obtained from the mass spectrometric analysis. For example, we show results for the analysis of a tryptic digest of the protein myoglobin where the occurrence of the [M+H+16]+ ion is used, along with the molecular weight data, to correctly identify the tryptic fragment.
Use of an on‐line liquid chromatography trapping column for the purification of protein samples prior to electrospray mass spectrometric analysis
Authors: Kay I. , Mallet A. I. 
Published: May 2005

AbstractA number of reagents, commonly used in protein chemistry and purification, suppress the electrospray ionization signal response of proteins in a concentration‐dependent manner. An on‐line trapping column device has been developed which enables the purification of protein samples containing these reagents, prior to their introduction into the mass spectrometer ion source.
On the mechanisms of electron‐impact‐induced sulfur dioxide elimination from the molecular ions of 4‐nitro‐ and 6‐nitro‐2,1‐benzisothiazoline 2,2‐dioxide derivatives
Authors: Danikiewicz Witold , Wojciechowski Krzysztof , Fokkens Roel H. , Bibbering Nico M. M. 
Published: May 2005

AbstractIt is shown that metastably decomposing molecular ions of the title compounds eliminate sulfur dioxide via two reaction pathways provided that an α‐hydrogen atom adjacent to the heterocyclic ring nitrogen atom is present. One of the channels leads to the initial formation of an o‐azaxylylene ionic species and is associated with the narrow component of the accompanying composite metastable peak. The other channel involvel a multistep pathway which eventually leads to the formation of an aldimine ionic species and which is associated with the broad component of the accompanying composite metastable peak. Collision‐induced dissociation and deuterium‐labelling experiments have provided evidence that the initially generated o‐azaxylylene ionic species, both as long‐lived and as decomposing ions, have rearranged to the aldimine ionic species via a 1,5‐shift of the α‐hydrogen atom adjacent to the heterocyclic ring nitrogen atom.
Identification of molecular masses up to 270 000 u in coal and coal‐derived products by matrix‐assisted laser desorption mass spectrometry
Authors: John P. , Johnson C. A. F. , Parker J. E. , Smith G. P. , Herod A. A. , Li C.‐Z. , Kandiyoti R. 
Published: May 2005

AbstractMolecular masses up to 270 000 u have been observed during matrix‐assisted laser desorption mass spectroscopy on a sample of bituminous coal; the major fraction of desorbed ions appeared between m/z values of 800 and 5000. Similar mass distributions have been found in a coal‐liquefaction extract and a pyrolysis tar. The highest molecular masses identified in this work far exceed previously reported high molecular masses found in coal‐derived products (12 000 u), which were also detected by laser‐desorption mass spectrometry.
A new type of graphite emitter for field ionization/field desorption mass spectrometry
Authors: Kosevich Marina V. , Shelkovsky Vadim S. 
Published: May 2005

AbstractA new type of field ionization/field desorption (FI/FD) emitter made of graphite is proposed. The method of emitter preparation is based on the observation that, on the fracture‐surface of graphite, fine microcrystallites are exposed, the sharpness of which is sufficient to provide, under conditions of field mass spectrometry, field strength values sufficient for the ionization of molecules by a tunnelling mechanism. The ease of preparation and handling of such graphite emitters is noteworthy. The efficiency of the graphite emitters is illustrated by examples of FI/FD measurements of a number of substances with different physical and chemical parameters, producing M+·, MH+, MCat+, Cat+, MnH+ types of ions. The main advantage of graphite emitters is seen as the possibility of precise control and direct measurement of the emitter temperature, which facilitates the obtaining of mass‐thermograms of thermodegradation and the study of various temperature‐dependent processes. Some specific potentialities of graphite emitters are outlined, namely the feasibility of direct analysis of organic inclusions in emitter material and switching to the surface‐ionization mode.
Electron ionization mass spectra and metastable‐ion studies on some ethylenedithiotetrathiafulvalene derivatives
Authors: Andreu R. , Garín J. , Orduna J. , Savirón M. , Uriel S. 
Published: May 2005

AbstractElectron ionization mass spectra of ethylenedithiotetrathiafulvalene and some derivatives were studied by accurate mass measurements, metasable analysis and collisional activation. A retro Diels‐Alder reaction involving ethylene extrusion is the most characteristic fragmentation process for these compounds.