bluuebunny/crossref_metadata_2025_split huggingface dataset:
Acetone chemical ionization studies VI: Hexenyl acetates
Authors: Vairamani M. , Kumar K. V. Siva 
Published: May 2005

AbstractAcetone chemical ionization mass mass spectra of four isomeric hexenyl acetates were investigated. The characteristic decomposition of [M + CH3CO]+ adducts in the field‐free region reveals site‐specific adduct formation of acetyl ion with the double bond and the acetoxy group.
Fast atom bombardment and tandem mass spectrometry of quaternary pyridinium salt‐type tryptophan derivatives
Authors: Prokai Laszlo , Prokai‐Tatrai Katalin , Pop Emil , Bodor Nicholas , Lango Jozsef , Roboz John 
Published: May 2005

AbstractFast atom bombardment and collision‐induced dissociation tandem mass spectrometry were used to study the fragmentation of quaternary pyridinium salt‐type amides of tryptophan (α‐amino‐3‐indolepropionic acid) esters and their analogs which incorporate the α‐nitrogen into the quaternary pyridinium structure. By cleavage directly at the pyridine nitrogen, the 1‐alkyl‐substituted nicotinamides decompose exclusively to a carbocation, which then becomes the intermediate to further fragments. Rearrangement of the 3‐indolepropionate‐2‐yl carbocations may involve a five‐ to seven‐membered ring expansion, which generates alternative fragmentation pathways; the formation of an even‐electron and a radical cation, respectively. In trigonellyl amide‐type tryptophan derivatives, fragmentation of the pyridinium ion proceeds on multiple pathways induced by the positive charge which may not be localized on the quaternary nitrogen, and isomerization to a dihydropyridinyl structure is probably involved. Besides the formation of protonated nicotinamide and alkene from tryptophan amides that contain methylene or ethylene units between the amino and the quaternary pyridinium nitrogens, a fragmentation route leading to the carbocation identical with that of the 1‐alkyl‐substituted nicotinamides has also been revealed.
Mass spectra of oxazolidines derived from sugars
Authors: Vega‐Pérez José M. , Espartero José L. , Ruiz Francisco J. , Alcudia F. 
Published: May 2005

AbstractThe electron impact mass spectra of 29 oxazolidines derived from sugars were examined. Four general pathways of fragmentation were encountered, the importance of which depends on the nature of the different substitutents.
Rearrangement of aromatic sulfonate anions in the gas phase
Authors: Binkley Roger W. , Flechtner Thomas W. , Tevesz Michael J. S. , Winnik Witold , Zhong Boyu 
Published: May 2005

AbstractCollisionally activated dissociation of deprotonated aromatic sulfonic acids in the gas phase causes rearrangement and fragmentation to produce the corresponding phenoxide ions. The mechanism for this reaction has been investigated and the results of this study favor initial intramolecular nucleophilic addition of a sulfonate oxygen atom to the aromatic ring, a process which is followed by heterolytic cleavage of the carbon–sulfur bond to rearomatize the ring. The product from this addition–elimination sequence is the anion of a sulfurous acid half‐ester, which loses SO2 to generate the corresponding phenoxide ion.
Mixed silicon carbide clusters studied by laser ablation Fourier transform ICR mass spectrometry
Authors: Greenwood Paul F. , Willett Gary D. , Wilson Michael A. 
Published: May 2005

AbstractIons produced by the 1064 nm Nd:YAG laser ablation of various Si–C samples include mixed silicon carbon (SixCy) cluster ions of low molecular mass. Unique SixCy cluster ion distributions are observed. A charge state effect for SixCy clusters is evident from differences between the respectively charged distributions. This may be accounted for by either differing energetics and/or differing formation mechanisms for positive and negative SixCy cluster ions. Several specific SixCy clusters of probable high stability consistently dominate the mass spectra. The chemistry of the more abundant SixCy ions was probed by collision‐induced dissociation and ion–molecule reactivity experiments. Similar SixCy+˙ dissociation results in the common loss of an Si ion. Parent SixCy ion and small neutral reagent reactants give rise to oxidation, addition and exchange reactions.
Effect of alkali metal cationization on the collision‐induced decomposition of alkyl per‐O‐acetyl‐2‐deoxy‐2‐halo‐α‐O‐mannopyranosides
Authors: Madhusudanan K. P. , Rani A. , Kumar B. , Suryawanshi S. N. 
Published: May 2005

AbstractThe effect of alkali metal cationization on the collision‐induced decomposition of alkyl per‐O‐acetyl‐2‐deoxy‐2‐bromo‐and‐iodo‐α‐O‐mannopyranosides was studied. The bromo sugars gave fairly abundant MH+, whereas for the iodo sugars the MH+ ions were insignificant. However, both the bromo and the iodo derivatives gave abundant M + alkali metal ion complexes. In contrast to the behaviour of the MH+ ion, the [M + Li]+, [M + Na]+ and [M + K]+ ions of these compounds do not decompose by loss of the C(1) substituent. Elimination of AcOH is the preferred fragmentation pathway of [M + Cat]+. Elimination of HX occurs only after loss of AcOH and CH2CO from MH+, whereas [M + Cat]+ directly loses HX. The elimination of HX is more pronounced from [M + Na]+ and [M + K]+ than from [M + Li]+. Loss of AcOLi is an additional fragmentation route observed in the case of the decomposition of [M + Li]+ ion.
Collision‐induced ionization of neutral peptides
Authors: Wu Zhuchun , Fenselau Catherine 
Published: May 2005

AbstractA four‐sector mass spectrometer was employed to study fragments formed by the high‐energy collision of neutral peptides with molecular oxygen. Neutral peptides were generated in the gas phase from proton‐bound dimers by the method of Wesdemiotis and co‐workers [Anal Chem. 65, 1594 (1993)]. B/E scanning was used in MS‐2 to collected the fragment ions from neutral precursors. Molecular ions (radical ions) were not obtained in most of the spectra, but a variety of fragment ions were recorded. High resolution and mass accuracy allowed most fragment ions to be assigned. Most fragment ions are of the same types as those produced from protonated peptides by collisional activation. Formation of y‐type ions is significantly reduced in the processes induced by collisional ionization, compared with high‐ and low‐energy collisional activation of protonated peptide precursors.
Rearrangement of ethane‐1,2‐diol radical cations: Processes involving dipole‐catalyzed proton shifts and charge transfer
Authors: Ruttink Paul J. A. , Burgers Peter C. 
Published: May 2005

AbstractRearrangement and dissociation processes of solitary ethane‐1,2‐diol radical cations were investigated by ab initio MO calculations, executed at the SDCI/RHF/DZP level of theory, including Pople‐type size‐consistency corrections. In order to obtain an accurate description of the chemistry involved, part of the potential energy surface was investigated by using the multi‐reference CI method and also by using the valence bond (VB) method followed by SDCI calculations using the natural orbitals of the VB wavefunction. The ethane‐1,2‐diol radical cation is metastable with respect to CH3OH2+ + HCO˙; it has been shown recently that the isotopologue DOCH2CH2OD loses (exclusively) HCO˙ to produce CH2DOHD+, not the isotopomer CH3OD2+ expected from earlier mechanistic proposals. We have traced a low‐energy pathway which explains the observed label distribution and which takes place at the experimentally derived energy level. First, ionized ethane‐1,2‐diol collapses to the one‐electron bond species [HOCH2‥ + ˙‥CH2OH]+˙ which subsequently rearranges to the hydrogen‐bonded species CH2O…︁HO(H)CH. Next, transformation to the transient CH2O…︁HCH2OH+˙ takes effect and this rearrangement can be viewed as the 1,2‐hydrogen shift, CH2OH → CH3OH+˙, catalyzed by formaldehyde. Following this, charge transfer takes place from the methanol cation to the formaldehyde molecule which thus becomes charged; because it is now charged, the formaldehyde unit can rotate and donate a proton to the methanol molecule, after which dissociation follows. Our calculations and experimental results can be interpreted in terms of proton shifts rather than hydrogen shifts taking place in ion–molecule (proton‐bound) complexes.
Methyl group effect on the proton affinity of methylated acetophenones studied by two mass spectrometric techniques
Authors: Kukol A. , Strehle F. , Thielking G. , Grützmacher H.‐Fr. 
Published: May 2005

AbstractThe proton affinities (PA) of all isomeric dimethylacetophenones were determined using the ‘kinetic method’ with a tandem mass spectrometer and by measurements of the proton transfer equilibrium in the gas phase by Fourier transform ion cyclotron resonance mass spectrometry. For both methods acetophenone and p‐methylacetophenone, with well known PA values, were used as reference bases. Both methods yielded identical PA values for all dimethylacetophenones. The PA of the dimethylacetophenones were in a narrow range between 872 and 880 kJ mol−1 except for 2,6‐dimethylacetophenone, for which a PA of 856 kJ mol−1 was found. The results are discussed in terms of possible mesomeric structures stabilizing the positive charge with regard to the substitution pattern in the phenyl ring. Obviously, the significant smaller PA of 2,6‐dimethylacetophenone compared with the other isomers is due to the distortion of the conjugation of the CO double bond with the aromatic π system.
Sequencing of cyclosporins by fast atom bombardment and linked‐scan mass spectrometry
Authors: Havlíček Vladimír , Jegorov Alexandr , Sedmera Petr , Ryska Miroslav 
Published: May 2005

AbstractThe mass spectrometric sequence determination of amino acid residues in cyclosporins using fast atom bombardment, collisionally activated dissociations in the first field‐free region and linked B/E scan is described. The general fragmentation scheme was derived from the spectra of cyclosporins A, B, C, D, F, G, L and [DH‐MeBmt1]CS. The main fragmentation pathways start by primary splitting between amino acids 2–3, 1–11 and 5–6. The corresponding N‐terminal b‐type ions are common fragment types in the mass spectra. The 1–11 splitting can be enhanced by the introduction of a lactone group into the peptide ring by conversion of cyclosporins into isocyclosporins. The fragmentation scheme was used for amino acid sequence determination in four new natural cyclosporins, [MeLeu1]CS, [Leu4]CS, [Ile4]CS and [Leu5]CS.
Laser‐induced electron impact ionization in a reflectron time‐of‐flight mass spectrometer
Authors: Moritz F. , Dey M. , Zipperer K. , Prinke S. , Grotemeyer J. 
Published: May 2005

AbstractSome details of the generation of electrons by impinging a laser beam on a metal surface are described. It is shown that highly efficient electron generation is observed only during the laser pulse. Therefore, this technique delivers intense pulses of electrons. The process is investigated and different ion source set‐ups are discussed. In conjunction with a time‐of‐flight mass spectrometer this technique can be used to produce mass spectra of different samples ranging from simple organic molecules to peptides.
Ion–molecule reactions between organometallic ions and crown ethers in the gas phase
Authors: Zagorevskii Dmitri V. , Nekrasov Yurii S. 
Published: May 2005

AbstractIon–molecule reactions of the metal‐containing ions LM+ (L = (acac)2, acac, C6H6, C5H5; M = In, Ga, Co, Fe, Ni, Cr, Mn, Pd, Rh, Tl, La, Pr, Yb, Nd) with crown ethers in the gas phase were studied. Two major reactions were observed: adduct formation and substitution of a metal atom ligand by a crown ether. The relative abundances of the two reactions depends on the ease with which the metal atom may be reduced. Ligand substitution can involve hydrogen rearrangements with loss of acetylacetone or cyclopentadiene for crown ethers having mobile H atom(s). The use of ion–molecule reactions in the structural characterization of crown ethers and transition metalcontaining ions is discussed.
Mass spectrometric investigation of the equilibrium gas‐phase composition over InI3 at elevated temperatures
Authors: Bencze L. , Marsel J. , Popovič A. , Lesar A. 
Published: May 2005

AbstractMass spectra of the saturated vapour and partial pressures of different species over solid InI3 were measured between 350 and 450 K with a mass spectrometric Knudsen effusion technique. By measuring appearance energies (AE) for different ions in the mass spectra, it was proved that InI3 evaporates congruently from the solid phase as InI3(g) and In2I6(g). Values of AE for In2In+ ions (n = 0–5) increase as n decreases, showing an interesting periodicity with InI bond strengths. For these measurements an improved deconvolution of the ionization efficiency curves by fast Fourier transformation, using a combined Maxwellian and Gaussian electron energy distribution, was performed. By measuring ion abundances as a function of temperature, the Clausius–Clapeyron plots for all ions appearing in the mass spectra were drawn.
Application of site‐selective ion–molecule reactions to the analysis of the cinchona alkaloids
Authors: Eichmann Erika S. , Brodbelt Jennifer S. 
Published: May 2005

AbstractFunctional group interactions within biologically relevant molecules are among the most influential yet least understood factors in determining their reactive behaviors. Reactions of dimethyl ether ions, which have previously been shown to be site‐selective, with four cinchona alkaloids, cinchonine, cinchonidine, quinine and quinidine, have been examined. These reactions are each shown to produce qualitatively similar spectra for the stereoisomeric pairs cinchonidine–cinchonine and quinidine–quinine, but small variations in the relative abundances of the products indicate that some stereoselectivity can be observed. The site selectivity of each of the reagents was investigated by observing the reactions occurring with model subunits of the alkaloids.
Site specificity in the H–D exchange reactions of gas‐phase protonated amino acids with CH3OD
Authors: Gard Eric , Willard Dale , Bregar Jennifer , Green M. Kirk , Lebrilla Carlito B. 
Published: May 2005

AbstractH–D exchange reactions of methanol‐d1 with protonated amino acids were performed in an external‐source Fourier transform mass spectrometer. Absolute rate constants were determined for the group which included glycine, alanine, valine, leucine, isoleucine and proline. By comparing reactivities with selected methyl esters, it was found that exchange on the carboxylic acid occurs 3–10 times faster than exchange on the amino group. No simple correlation is observed between the rates of H–D exchange on the acid group and the size of the alkyl group. However, the rates of exchange on the amine decrease with increasing gas‐phase basicity. Glycine, the least basic amino acid, exchanges its amine hydrogens the fastest. These results are useful for determining the interaction of methanol with protonated amino acids and can provide insight into the H–D exchange reactions observed with polyprotonated proteins produced by electrospray ionization.
Primary to quaternary protein structure determination with electrospray ionization and magnetic sector mass spectrometry
Authors: Loo Joseph A. , Loo Rachel R. Ogorzalek , Andrews Philip C. 
Published: May 2005

AbstractElectrospray ionization with a forward‐geometry magnetic sector mass spectrometer was used for collisionally activated dissociation studies of multiply charged polypeptides and for studying non‐covalently bound protein systems. The high‐resolution capabilities of a high‐performance instrument allow the resolution of isotopic contributions for product ions and molecular ion species. Determination of product ion charge states by this method reduces difficulties in the interpretation of product ion mass spectra from multiply charged precursors, which are generated either in the atmospheric pressure/vacuum electrospray interface or in the collision chamber of the mass spectrometer. Extended tandem mass spectrometric experiments have the potential for sequencing larger polypeptides. However, evidence for isomerization of gas‐phase product ions from substance P and substance P analogues was observed, complicating the interpretation of product ion spectra. Non‐covalent complexes can also be studied by electrospray ionization magnetic sector MS. The higher m/z range of such an instrument is a major advantage for studying weakly bound systems, such as heme–protein systems (myoglobin, hemoglobin) and protein aggregates (concanavalin A), because of their tendency to form complex ions with relatively low charge states.
Mass spectrometry of some 10β‐Fluoro‐1,4‐estradien‐3‐oxo steroids
Authors: Desmarteau D. D. , Resnati G. , Seraglia R. , Traldi P. 
Published: May 2005

AbstractThe mass spectrometric behavior of some 10β‐fluoro‐1,4‐estradiene‐3‐oxo steroids under two different ionization conditions (electron inpact and fast atom bombardment) was studied with the aid of mass‐analyzed ion kinetic energy spectroscopy. The influence of fluorine in the fragmentation pattern was investigated by comparison with the behavior of 10‐methyl analogs. In particular, the presence of fluorine at position 10 seems to reflect the weakening of C(9)C(10) bond. Further, when an acyloxy moiety is present at position 17, the primary ring cleavages typical of steroids become disfavored and fragment ions related to the acyloxy substituents are detected.
Mass spectrometric study of 2‐acyloxy‐4,6‐dimethoxy‐1,3,5‐triazines
Authors: Sochacki Marek , Kami Zbigniew J. 
Published: May 2005

AbstractElectron impact ionization mass spectra of 2‐acyloxy‐4,6‐dimethoxy‐1,3,5‐triazines were examined. Two general pathways of fragmentation were found: (i) formation of an acylium ion typical for all the compounds studied, and (ii) rearrangement followed by loss of carbon monoxide, characteristic of derivatives of aromatic carboxylic acids.
Collision‐induced decompositions of metal‐cationized methyl‐6‐deoxy‐6‐bromo‐α‐D‐glucopyranoside derivatives
Authors: Madhusudanan K. P. , Dhami T. S. , Katiyar S. , Suryawanshi S. N. 
Published: May 2005

AbstractCollision‐induced decompositions (CIDs) of the [M + H]+, [M + Li]+, [M + Na]+, [M + K]+ and [M + Ag]+ ions of some methyl‐6‐deoxy‐6‐bromo‐α‐D‐glucopyranoside derivatives are discussed. Elimination of MeOH resulting in the glycosidyl cation is the predominant reaction of the [M + H]+ ion. This process is completely suppressed during CID of the metal‐cationized species, which, surprisingly, show elimination of the added metal in the form of RCOO‐metal and metal bromide in the case of the ester derivatives. These reactions appear to be assisted by neighbouring group participation. Because of the proximity of the C(3)‐oxygen with C(6), the benzyl ether derivative is characterized by the loss of PhCH2Br from the [M + metal]+ ion.
Li+‐ and Ag+‐cationized per‐O‐acetyl‐ and Per‐O‐benzyl‐α‐D‐thioglycosides: a collision‐induced decomposition study
Authors: Madhusudanan K. P. , Dhami T. S. , Katiyar S. , Suryawanshi S. N. 
Published: May 2005

AbstractThe collision‐induced decompositions of the [M + Li]+ and [M + Ag]+ ions of per‐O‐acetyl‐ and per‐O‐benzyl‐α‐D‐thioglycosides having phenyl sulphide, phenyl sulphoxide and phenyl sulphone as the aglycone moieties were studied. The [M + Li]+ ion of the acetyl derivative of the phenylthioglucoside shows loss of AcOLi, whereas its [M + Ag]+ ion shows elimination of PhSAg. Their sulphoxide and sulphone derivatives lose the C(1) and C(2) substituents to form the glucal under both Li+ and Ag+ cationization conditions. The corresponding benzyl derivatives do not show the loss of metal. The formation of glucal leads to ring fragmentation by retro‐Diels‐Alder reaction in the ring‐activated benzyl derivatives.
Reactivity of vinylamine radical cation with neutral dienes
Authors: Bouchoux Guy , Penaud‐Berruyer Florence 
Published: May 2005

AbstractThe gas‐phase ion—molecule reactions between ionized vinylamine ([CH2  CHNH2]+.) as a set of conjugated and unconjugated dienes were studied by Fourier transform is observed. Conjugated dienes lead to the elimination of NH3 or of an hydrocarbon radical from the adduct [M + CH2  CHNH2]+.. In the case of unconjugated dienes a regiospecific cyclobutanation‐cycloreversion process is observed. Reaction mechanisms are proposed to explain these experimental findings.
Rapid screening technique for tetrachlorodibenzo‐p‐dioxins in complex environmental matrices by gas chromatography/tandem mass spectrometry with an ion‐trap detector
Authors: Plomley Jeffry Blaise , Koester Carolyn Jean , March Raymond Evans 
Published: May 2005

AbstractA capillary column gas chromatographic/ion‐trap tandem mass spectrometric (GC/MS/MS) technique was applied to the determination of tetrachlorodibenzo‐p‐dioxins (TCDDs) in complex environmental matrices. A detection limit of 500 fg μl‐1 injected, with a signal‐to‐noise ratio of 6:1, was obtained when MS/MS was combined with broadband ion ejection of matrix ions and selected ion isolation. Calibration graphs were constructed from extracted fragment ion mass chromatograms and were found to be linear over the range 0.5‐200 pg. Concentrations of total TCDDs and of 2,3,7,8‐TCDD were determined for extracts from fish, air and soil; in most cases, the results found by GC/MS/MS were comparable to those obtained by high‐resolution MS and triple quadrupole MS.
Tandem mass spectrometry of peptides: Mechanistic aspects and structural information based on neutral losses. II—Tri‐ and larger peptides
Authors: Cordero Marcela M. , Wesdemiotis Chrys 
Published: May 2005

AbstractThe neutral products arising during the collisionally activated dissociation of protonated oligopeptides (MH+) are post‐ionized by collision and detected in neutral fragment‐reionization (+NfR+) mass spectra. For the isomeric tripeptides Ala‐Gly‐Gly, Gly‐Ala‐Gly and Gly‐Gly‐Ala, the amino acid and dipeptide losses from the C‐terminus and the diketopiperazine losses from the N‐terminus allow for differentiation. These neutral fragments are identified in the corresponding +NfR+ spectra by comparison to reference collision‐induced dissociative ionization (CIDI) mass spectra of individual amino acids, dipeptides and diketopiperazines. Peptides with distinct C‐termini but otherwise identical sequences are found to yield +NfR+ products that are characteristic of the respective C‐terminal amino acid. This is demonstrated for several peptide pairs, including leucine‐ and methionine‐enkephalin. In general, +NfR+ spectra are dominated by the heavier neutral losses; further, +NfR+ and CIDI cause extensive dissociation, indicating that the collisional ionization process imparts high average internal energies.
Side‐chain effects on the fragmentation behaviour of alkylthiophenes
Authors: Lange D. , Budzikiewicz H. 
Published: May 2005

AbstractThe processes leading to the fragment ions formed from alkylthiophene molecule ions by benzylic cleavage without and with transfer of one hydrogen from the side‐chain to the ring and the influence of additional methyl groups on the relative importance of these two fragmentation reactions were investigated.