bluuebunny/crossref_metadata_2025_split huggingface dataset:
A theoretical and experimental study of the structures and stabilities of the [C5H3]+ cation
Authors: Kompe Barbara M. , Peel J. Barrie , Traeger John C. 
Published: May 2005

AbstractThe structures and energies for 16 different [C5H3]+ isomers were geometry optimized from ab initio molecular orbital calculations. The global minimum on the [C5H3]+ surface at the MP3/6–31G* level was found to be the ethynyl cyclopropenylium cation (a), with a penta‐1,3‐diynylium structure (b) and a penta‐1,4‐diynylium structure (c) being 90 and 100 kJ mol−1 higher in energy, respectively. An isodesmic reaction was used to calculate a value of 1339 kJ mol−1 for the enthylpy of formation of b. Photoinization appearance energies were measured for the [C5H3]+ ions from penta‐1,3‐diyne, hexa‐2,4‐diyne and hexa‐1,5‐diyne as 11.66, 12.25 and 11.8 eV respectively The penta‐1,3‐diyne fragmentation was used to estimate an experimental enthalpy of formation for b of 1315 ± 2 kJ mol−1. There is some theoretical evidence that the penta‐1,3‐diyne fragmentation occurs without any significant reverse activation energy whereas both the hexa‐2,4‐diyne and hexa‐1,5‐diyne fragmentations involve excess energy.
Analysis of xanthates by negative‐ion fast atom bombardment mass spectrometry
Authors: Fourie L. , Kruger H. G. 
Published: May 2005

AbstractA new technique using negative‐ion fast atom bombardment mass spectrometry for the analysis of xanthates and related compounds is described. Electron impact and positive‐ion fast atom bombardment mass spectrometry produced no structurally related fragment ions or observable molecular ions at the expected m/z values. It was demonstrated that negative‐ion fast atom bombardment ionization was the most suitable method of ionization for structure elucidation studies for the compounds described.
Electrospray mass spectrometry: Ethylene glycol as a solvent and its effects on ion desorption
Authors: Guevremont R. , Le Blanc J. C. Y. , Siu K. W. M. 
Published: May 2005

AbstractEthylene glycol solutions of gramicidin S, myoglobin and tetrabutylammonium bromide were analysed by means of electrospray mass spectrometry and their spectra were compared with those of aqueous solutions. The evaporation of water and ethylene glycol droplets, initially at room or elevated temperature, in air at room temperature was modelled. It was found that under conditions where a water droplet's radius would shrink by ∼30%, an ethylene glycol droplet shrinks negligibly. Further, droplets that are initially hot (such as those that are ejected from a heated electrospray needle) cool very rapidly owing to evaporation and heat loss to ambient air, and subsequently evaporate much like droplets that are initially at room temperature. For gramicidin S, the ion abundances in ethylene glycol as solvent were ∼200 times lower than those in water under room temperature operating conditions. In experiments where the spray probe was heated to ∼100°C to reduce the viscosity of ethylene glycol, the gramicidin response difference between the solvents decreased to about a factor of 40. Similar trends were observed for myoglobin and the tetrabutylammonium ion. The gramicidin abundances in ethylene glycol, relative to those in water, are orders of magnitude too large to be accounted for using the conventional solvent evaporation model. It is speculated that decreasing the viscosity increases the velocity of ions drifting in ethylene glycol towards the solution/air interface and increases the total number of analyte ions desorbed at the Taylor cone during electrospray.
Effect of electrospray ionization conditions on low‐energy tandem mass spectra of peptides
Authors: Kilby Greg W. , Sheil Margaret M. 
Published: May 2005

AbstractThe effect of electrospray ionization (ESI) conditions on low‐energy tandem mass spectra of peptides in the relative molecular mass range 400–1200 was examined. For singly charged peptide ions the source skimmer potential (which determines the degree of acceleration of the ions through the intermediate pressure region in the source) can strongly influence the extent of fragmentation observed in tandem mass spectra, especially at low collision energies. For each peptide there is an optimum skimmer potential which represents a balance between generating ions with sufficient internal energy for subsequent tandem mass spectrometric experiments and inducing the onset of other processes such as source fragmentation. The fragmentation which can be achieved in tandem mass spectra with high skimmer potentials differs from ESI source fragmentation for the same peptides. We have found that fragmentation in ESI mass spectra depends both on skimmer potential and on solvent pH, presumably because the latter determines the proportion of doubly charged species generated from a given peptide. Low‐energy tandem mass spectra of peptides following ESI are equally as sensitive to peptide structure and the type of adduct studied (e.g. [M + H]+ vs. [M + NH4]+) as tandem mass spectra obtained following older ionization methods such as fast atom bombardment.
Suppression of metastable interference in matrix‐assisted laser desorption/ionization (MALDI) spectra in a reflecting time‐of‐flight mass spectrometer
Authors: Ens Werner , Spicer Victor , Standing Kenneth G. , Zhou Jie 
Published: May 2005

AbstractMetastable interference in matrix‐assisted laser desorption/ionization (MALDI) spectra is reduced by modulating the accelerating potential (by <∼100 V) on alternate laser shots. Both parent and daughter ions are reflected on every second shot but only daughter ions are reflected on the next shot. The parent‐ion spectrum is then obtained by subtraction. In order to ensure the necessary well defined energy distributions, signals with similar intensity (preferably small) are selected by transferring each transient to a computer for examination. This procedure decreases the complexity in reflected spectra (especially spectra of mixtures) in the lower mass range and improves the mass resolution in the intermediate mass range around 10 000 u. Continuous background in reflected spectra is also suppressed by the technique.
On‐target deuteration for peptide sequencing by laser mass spectrometry
Authors: Spengler Bernhard , Lützenkirchen Frank , Kaufmann Raimund 
Published: May 2005

AbstractHydrogen–deuterium exchange was evaluated as a tool for sequence analysis of peptides by matrix‐assisted laser desorption–ionization utilizing post‐source decay (PSD‐MALDI). The number of exchangeable hydrogens (EH) of precursor ions and product ions can be determined from the mass difference between ion signals originating from the deuterated and the non‐deuterated form of a peptide, resulting in a second dimension of structural information. The reliability of sequence determination by combinatorial algorithms or pattern recognition techniques is considerably increased by employng this ‘EH spectroscopy.’ On‐target deuteration is a simple preparatory step which can be performed reversibly with the already mass‐analysed sample within a few minutes and without consumption of additional sample material. The efficiency of hydrogen–deuterium exchange with this technique is about 98.5%. In addition to supporting sequence analysis, deuteration can be used to investigate fundamental fragmentation mechanisms of peptides in PSD‐MALDI. Inconsistencies with expected fragmentation pathways have been found for fragments a1–a3 of substance P.
Gas‐phase protonation of simple inorganic molecules: A stimulating interplay between theory and experiment
Authors: Grandinetti Felice 
Published: May 2005

AbstractA brief account of some of the results obtained recently during the investigation of the gas‐phase protonation of some simple inorganic molecules. The combined use of structurally diagnostic mass spectrometric techniques, such as mass‐analyzed ion kinetic energy (MIKE) and collisionally activated dissociation (CAD) spectrometry and ab initio calculations allows the successful probe of the corresponding potential energy surfaces. Information is obtained on the structure and the stability of the various protonated intermediates, as well as on the details of the mechanisms of their interconversion and unimolecular decomposition processes.
Cross‐chiral examinations of molecular enantioselective recognition by fast atom bombardment mass spectrometry: Host–guest complexations between chiral crown ethers and chiral organic ammonium ions
Authors: Sawada Masami , Okumura Yasuo , Yamada Hitoshi , Takai Yoshio , Takahashi Shigetoshi , Kaneda Takahiro , Hirose Keiji , Misumi Soichi 
Published: May 2005

AbstractUsing fast atom bombardment (FAB) mass spectrometry (MS), cross‐chiral relationships were confirmed for the first time for the diasteromeric host‐guest complexations between the chiral crown ether host (1) and the chiral organic ammonium ion guest (2) on the basis of the relative peak intensities (RPI). Both host–guest combinations (R, R, R, R) – 1, (R) – 2 and (S, S, S, S) – 1, (S) – 2 obviously provided larger RPI values than the combination of both (R, R, R, R) – 1, (S) – 2 and (S, S, S, S) – 1, (R) – 2 by a factor of 1.6 as an averaged value: 1.87 (n = 4)/1.16 (n = 4) = 1.6. These results are consistent with the expected stabilities of the host‐guest complexations by CPK model examinations. Successfully observed cross‐chiral examinations strongly suggest a potentially useful FABMS/RPI methodology for rapidly searching newly designed and synthesized crown ether‐like host compounds with a higher degree of enantioselectivity.
Competitive formation of M+˙ and [M + H]+ ions under fast atom bombardment conditions
Authors: Takayama Mitsuo , Tanaka Yoshiaki , Nomura Taro 
Published: May 2005

AbstractThe competitive formation of molecular ions M+˙ and protonated molecules [M + H]+ under fast atom bombardment (FAB) conditions was examined using various kinds of organic compounds. The use of protic/hydrophilic matrices such as thioglycerol and glycerol resulted in relatively large values of the peak intensity ratio I([M + H]+)/I(M+˙) compared with the use of relatively aprotic/hydrophobic matrices such as m‐nitrobenzyl alcohol and o‐nitrophenyl octyl ether. The change of matrix from thiol‐containing such as thioglycerol and dithiothreitol to alcoholic such as glycerol and pentamethylene glycol increased the I([M + H]+)/I(M+˙) ratio. Furthermore, the change of matrix increased the peak intensity ratio of the doubly charged ion [M + 2H]2+ to [M + H]+ in the FAB mass spectra of angiotensin I and gramicidin S. The addition of acids to the matrix solution increased the I([M + H]+)/I(M+˙) ratio, although such an effect did not always occur. The acetylation of simple aniline compounds markedly increased the I([M + H]+)/I(M+˙) ratio. It was concluded from these results that the hydrogen bonding interaction between hydroxyl groups(s) of the matrix and basic site(s) of analyte molecules in solution acts advantageously as a quasi‐preformed state for [M + H]+ formation, and that the presence of significant proton acceptor(s) such as carbonyl group in analytes hinder the M+˙ formation which may generally occur under FAB conditions. The formation of M+˙ and [M + H]+ ions seemed to occur competitively, reflecting or according to the interaction or solvation states between the analyte and matrix molecules in solution and the structural characteristics of the analytes.
Computer processing and interpretation of mass spectral information. Part IX—generalized characteristics of mass spectra
Authors: Sukharev Yu. N. , Nekrasov Yu. S. , Molgachova N. S. , Tepfer E. E. 
Published: May 2005

AbstractThe formation of numerical generalized characteristics (indices) of mass spectra by using one or two experimental parameters (mass numbers and/or ion peak amplitudes) is suggested. The influence of the measuring error of peak amplitudes on the statistical characteristics of indices was studied. It was ascertained by four classes of organometallic compounds that within an isolated class the value of each index is distributed by a normal law. The possibility of using mass spectral indices for the identification of unknown compounds is demonstrated.
Radical‐type reactivity of the methylenedimethylsulfonium ion, (CH3)2S+CH2˙
Authors: Smith Rebecca L. , Chyall Leonard J. , Stirk Krista M. , Kenttämaa Hilkka I. 
Published: May 2005

AbstractAb initio molecular orbital calculations at the MP2/6–31G*//6–31G* + ZPVE level of theory suggest that the ion (CH3)2S+CH2˙ is 75 kJ mol−1 higher in energy than ionized ethyl methyl sulfide. However, this distonic ion is stable toward isomerization to the conventional structure: the two ions show distinctly different reactivity in a dual‐cell Fourier transform ion cyclotron resonance mass spectrometer. Molecular orbital calculations further indicate that the charge site of the ion is on the sulfur atom whereas the odd‐spin density is localized on the CH2 group. The chemical properties of the ion reflect this description. The coordinatively saturated sulfonium charge site is chemically inert. This radical cation possesses unique chemical reactivity in that its reactions are associated with the radical site. Most of these reactions involve a homolytic bond cleavage in the neutral molecule, resulting in abstraction of an atom or a radical by the ion. The reaction efficiency correlates with the homolytic bond dissociation energy of the bond being broken in the neutral molecule, suggesting a simple radical abstraction mechanism for these reactions. Hence, the methylenedimethylsulfonium ion is best described as on electrophilic radical with an inert charge site.
Reactive ion–surface collisions: Application of ionized acetone‐d6, DMSO‐d6 and pyridine‐d5 as probes for the characterization of self‐assembled monolayer films on gold
Authors: Kane Thomas E. , Somogyi Árpád , Wysocki Vicki H. 
Published: May 2005

AbstractLow‐energy collisions of ionized acetone‐d6, DMSO‐d6 and pyridine‐d5 with alkanethiolate self‐assembled monolayer (SAM) surfaces prepared on gold were investigated. These experiments can be used to monitor routinely the condition of the surfaces and to determine whether a surface is acceptable for a given application. In addition to the surface‐induced dissociation of the molecular ions, intense peaks corresponding to the addition of H (or D) to the ionized molecules are observed in the ion–surface collision spectra. The relative abundance of the [M + H(D)]+ reaction products was found to be dependent on several variables, including (i) the chemical composition of the monolayers (alkanethiolate, perdeuteroalkanethiolate, fluorinated alkanethiolate), (ii) the chain length of the alkanethiolate monolayers, (iii) the time for which the vapor‐deposited Au surfaces are exposed to the thiol solution during surface preparation and (iv) the degree of deliberate damage of the SAM film (70 eV Ar+˙ beam bombardment). The variation in [M + H(D)]+ abundance with induced surface changes illustrates the utility of these adduct ions for the characterization of the quality of the monolayers. The general trend observed is an increase in the [M + H]+ peak with the increased presence of hydrocarbon adsorbates, which in turn is believed to be directly related to increased disorder (inherent or induced) of the monolayer film. The increase in [M + H]+ is seen with a decrease in chain length, with shorter monolayer preparation times, and with an increase in surface damage. In general, a fluorinated surface that has been intentionally damaged by an Ar+˙ beam retains its highenergy deposition characteristics and is appropriate for use as a collision target for many types of projectiles.
Collision‐induced dissociation studies of protonated alcohol and alcohol—water clusters by atmospheric pressure ionization tandem mass spectrometry. 1Methanol
Authors: Karpas Z. , Eiceman G. A. , Harden C. S. , Ewing R. G. , Smith P. B. W. 
Published: May 2005

AbstractCluster size distribution and collision‐induced dissociation (CID) studies of protonated methanol and protonated methanol—water clusters yield information on the structure and energetics of such ions. Ions were formed at atmospheric pressure in a corona discharge source, and were subjected to CID in the center quadrupole of a triple quadrupole mass spectrometer. Cluster ions containing up to 13 molecules of methanol and/or water were observed and examined using CID experiments. The CID of all (CH3OH)n · H2O · H+ clusters, where n ⩽ 8, showed that water loss was statistically favored over methanol loss and that the preferred dissociation channel involved loss of water with methanol molecules. These results support a model employing a chain of hydrogen‐bonded solvent molecules rather than one in which fused rings of ligands surround a central hydronium ion. However, CID of larger clusters, where n ⩾ 9, showed that loss of one methanol was equal to or less than loss of water, reflecting a change in structure.
A new window on fullerene chemistry: An electrospray mass spectrometric study of the amination of C60
Authors: Wilson Stephen R. , Wu Yunhui 
Published: May 2005

AbstractPolyamines derived from C60 were characterized by electrospray ionization mass spectrometry in 1:1 methanoltoluene containing 2.5% trifluoroacetic acid. Peak assignments are consistent with the formula C60On(RNH2)m for the protonated products. The preferential formation of the hexaaminated product C60O6(RNH2)6 was also observed.
Significant differences in site of protonation and extent of fragmentations in chemical ionization and fast atom bombardment mass spectrometry of simple bifunctional compounds. A mechanistic implication for formation of protonated molecules
Authors: Nakata Hisao , Arakawa Naofumi , Mizuno Rika 
Published: May 2005

AbstractChemical ionization (CI) and fast atom bombardment (FAB) mass spectra of simple bifunctional aromatic compounds were compared. Some significant differences were revealed with respect to the site of protonation and extent of fragmentations. Unlike conventional CI ionization, the protonated molecule formation by FAB could not be accounted for by ordinary proton transfer reactions in the gas phase. The observed ions under FAB conditions appear to be regulated by proton exchange reactions through frequent collisions in some particular region between the matrix and the gas phase.
Multiply charged ions of ruthenium(II), rhodium(III) and cobalt(III) complexes in electrospray ionization mass spectrometry
Authors: Arakawa Ryuichi , Matsuo Takekiyo , Ito Hiroyuki , Katakuse Itsuo , Nozaki Koichi , Ohno Takeshi , Haga Masa‐Aki 
Published: May 2005

AbstractMultiply charged ions from electrospray ionization (ESI) were observed for ruthenium‐bidentate ligand complexes, such as [RuL2B]X2 and [(RuL2)2B]X4, where L is 2,2′‐bipyridine, B are tetradentate ligands of 2,2′‐bis(2′‐pyridyl)bibenzimidazole and 2,6‐bis(2′‐pyridyl)benzodiimidazole, bidentate ligand of 2‐(2′‐pyridyl)benzimidazole and related compounds and X is CIO4‐ or CI‐. ESI mass spectra showed a simple mass pattern for easy structural assignment and detecting impurities. The mass spectra for binuclear complexes provide a charge state distribution ranging from 4+ to 2+ for Ru(II)—Ru(II) compounds and 5+ to 2+ for Ru(II)—Rh(III) compounds. It was found that different multiply charged ions are generated by loss of counterions and by protonation/deprotonation at the proton site of ligands B. The abundances of these ions are qualitatively explained in terms of the acidity of metal complexes depending on the bridging ligand structures and the charge of the metal ions. Ions produced by removal of ligands were hardly observed.
Dimethyl ether and dimethyl‐d6 ether chemical ionization mass spectrometry of nitramines, nitroaromatics and related compounds
Authors: Burrows Elizabeth P. 
Published: May 2005

AbstractDimethyl ether (DME) chemical ionization mass spectrometry with introduction by direct exposure desorption was utilized for the characterization of a variety of nitramines, nitroaromatics and related compounds. For the nitramines and for many of the nitroaromatics the most abundant ions were fragment‐molecule adduct ions resulting from ion‐molecule reactions with the reagent gas. Nitroaromatic positional isomers were readily distinguished by large differences in the abundances of the various adduct ions. For the nitramines, collision‐induced dissociations of the prominent methoxymethylene adduct ions were studied and contrasted with those of the corresponding adducts derived from DME‐d6 as reagent gas.
Structural analysis of rapamycin and related compounds using [M + Li]+ ions generated by liquid secondary ion mass spectrometry
Authors: Kiplinger J. P. , Guadliana M. A. 
Published: May 2005

AbstractCationization of the macrocyclic immunosuppressant rapamycin with lithium ion upon liquid secondary ion mass spectrometric ionization yields a number of fragment ions, which are observable in the full‐scan spectrum. These are clearly assigned using B/E linked scanning (fragment ion scanning), B2/E linked scanning (precursor ion scanning) and peak matching for accurate mass measurement. Many of the fragments are produced by processes that open the macrocyclic ring, and it is possible to observe several different pieces of the molecule as fragment ions. The diversity of fragments produced facilitates the elucidation of new rapamycin‐like structures through mass spectrometry. Three structurally modified rapamycin analogues have been examined by this technique, and the modifications to the molecule may be located based on the nominal masses of their fragments.
The potential of pyrolysis/gas chromatography/mass spectrometry for determining the progress of lignification: An investigation of maturing asparagus sclerenchyma tissue
Authors: Mellon Fred. A. , Waldron Keith W. , Selvendran Robbie R. , Galletti Guido C. 
Published: May 2005

AbstractSclerenchyma tissues from semi‐mature and mature asparagus spears were analysed by pyrolysis/gas chromatography/mass spectrometry and by conventional chemical methods in order to determine the degree of lignification and compare analytical techniques. The pyrolysis data are similar to those obtained by a chemical method involving alkaline extraction at 70°C followed by spectrophotometric determination of phenolic content. The pyrolysis method was more rapid, sensitive and informative than the chemical technique and shows considerable potential for studying the chemical basis of the textural development of plant foods.
Pyrolysis/gas chromatography/mass spectrometry of asphaltene fractions
Authors: Nali M. , Calemma V. , Montanari L. 
Published: May 2005

AbstractTwo n‐heptane‐precipitated asphaltene samples, characterized by elemental analysis and nuclear magnetic resonance spectrometry, were fractionated according to relative molecular size by gel permeation chromatography (GPC). Both the whole asphaltene samples and their fractions were analysed by pyrolysis/gas chromatography/mass spectrometry. The data obtained from the pyrograms (average side‐chain length, aromaticity index, sulphur compounds vs. aliphatic compounds, presence of SO2 and CO2) demonstrated that, in the case of asphaltenes, GPC fractionation results in the separation of different chemical structures ranging from lower molecular mass, highly aromatic and polar compounds to higher molecular mass, less polar and aromatic compounds.
Fast atom bombardment mass spectrometry of reaction products between C3O2 and stabilized phosphorus ylides
Authors: Seraglia Roberta , Traldi Pietro , Bertani Roberta , Facchin Giacomo , Pandolfo Luciano 
Published: May 2005

AbstractA fast atom bombardment (FAB) mass spectrometric study on the open‐chain compound 1,3‐bis(cyanomethylenetriphenylphosphorane)propane‐1,3‐dione and on the cyclic zwitterionic compounds 4‐oxy‐5‐triphenylphosphonium‐6‐methyl‐2‐pyrone and 4‐oxy‐5‐triphenylphosphonium‐6‐phenyl‐2‐pyrone, obtained by reaction of carbon suboxide, C3O2, with stabilized phosphorus ylides, Ph3PCHX (XCN, COMe, COPh), is described. The FAB mass spectrometric behaviour of these compounds is compared with that shown by tri‐phenylphosphoranilideneketene, Ph3P  C  C  O, and by 4‐hydroxy‐6‐methyl‐2‐pyrone, with the aid of metastable ion data and collision spectroscopy.