bluuebunny/crossref_metadata_2025_split huggingface dataset:
Positive and negative methanol cluster ions using a direct fast atom bombardment technique
Authors: Xu Yaodong , Jarvis V. M. , Bostwick D. E. , Moran T. F. 
Published: May 2005

AbstractPositive and negative cluster ions in methanol have been examined using a direct fast atom bombardment (FAB) probe technique. Positive ion (CH3OH)IIH + clusters with n = 1‐28 have been observed and their clusters are the dominant ions in the low‐mass region. Cluster‐ion reaction products (CH3OH)II(H2O)H+ and (CH3OH)II(CH3OCH3)H+ are observed for a wide range of n and the abundances of these ions decrease with increasing n. The negative ion (CH3OH)II(CH3O)− clusters are also readily observed with n = 0‐24 and these form the most‐abundant negative ion series at low n. The (CH3OH)II(CH2O)−, (CH3OH)II(HIIO)(CH2O)− and (CH3OH)II(H2OXCH3O)− cluster ions are formed and the abundances of these ions approach those of the (CH3OH)II(CH3O)− ion series at high n. Cluster‐ion structures and energetics have been examined using semi‐empirical molecular orbital methods.
Triple mass spectrometry (MS/MS/MS) with a floated collision cell in a four‐sector tandem mass spectrometer
Authors: Wu Zhuchun , Bordas‐Nagy Joseph , Fenselau Catherine 
Published: May 2005

AbstractA method is described for carrying out triple mass spectrometry (MS/MS/MS) experiments with an electrically floated collision cell in the third field‐free region on a tandem double‐focusing mass spectrometer. The method described may use magnet calibration obtained at any accelerating voltage and is generally applicable at any value of the collision cell voltage. The utility of the method to acquire MS/MS/MS spectra of enhanced quality is demonstrated on a JEOL JMS‐HX110/HX110 four‐sector mass spectrometer.
Retrosynthetic fragmentation in the fast atom bombardment mass spectra of eserine and some related compounds
Authors: Rubino Federico M. , Zecca Luigi 
Published: May 2005

AbstractThe positive‐ion fast atom bombardment (FAB) mass spectra of eserine and some carbamate analogues were recorded and showed a partially different fragmentation process, with respect to that of the corresponding chemical ionization (Cl) fragmentation. This unexpected behaviour could be explained by taking into account the known solution chemical behaviour of the protonated species, and assigning to the molecular species observed under FAB a different–yet related–molecular connectivity. This may be considered as evidence that the sputtered species under FAB closely reflect the chemical behaviour of the analysed molecule in the solution environment.
Fourier transform ion cyclotron resonance study of ion‐molecule reactions of [M – OCH3]+ ions of methyl 2,3,4,6‐tetra‐O‐methyl‐d‐hexopyranosides with ammonia
Authors: Kovacik Vladimir , Hirsch Janos , Thölmann Detlef , Grützmacher Hans‐Friedrich 
Published: May 2005

AbstractGlycosidic oxocarbenium ions A1+ were formed by isobutane chemical ionization from methyl 2,3,4,6‐tetra‐O‐methyl‐β‐D‐mannopyranoside, methyl 2,3,4,6‐tetra‐0‐methyl‐β‐D‐galactopyranoside and methyl 2,3,4,6‐tetra‐O‐methyl‐β‐D‐glucopyranoside (the ring ‐ O‐being converted into  O  ), and then‐ reaction with ammonia was studied by Fourier transform ion cyclotron resonance Spectrometry. Very slow formation (reaction efficiency 0.6‐1.4%) of the adduct ion [A1 + NH3]4 was observed as the main process for carefully thermalized ions A1+. Interestingly, the efficiency of the adduct ion formation depends on the sterochemistry of ions A1+.
Mass spectrometry of N‐(Pyrimidin‐2‐yl)amino acids and their methyl esters
Authors: Plaziak Adam S. , Spychala Jaroslaw , Golankiewicz Krzysztof 
Published: May 2005

AbstractN(Pyrimidin‐2‐yl)‐glycine, ‐alanine and ‐phenylalanine (1‐3) and their methyl esters (4‐6) were investigated using electron impact (EI) mass Spectrometry. The results showed that EI‐induced decomposition occurs on the carboxylic group or involves the loss of R2OH. In contrast to earlier investigations on N‐(pyrimidin‐4‐yl)amino acids, elimination of water (in 1‐3) or methanol (in 4‐6) was found to be of EI‐induced nature. The loss of 'COOH from M+ of ester 4 suggests the occurrence of a skeletal rearrangement leading to the isomeric N‐methylamino acid.
Characterization of cyclotetramethylenetetranitramine (HMX) thermal degradation by isotope analyses with analytical pyrolysis‐atmospheric pressure ionization tandem mass spectrometry
Authors: Snyder A. Peter , Liebman Shirley A. , Bulusu Suryanarayana , Schroeder Michael A. , Fifer Robert A. 
Published: May 2005

AbstractAnalytical pyrolysis‐atmospberic pressure ionization (Py‐API) tandem mass Spectrometry was used in the structure elucidation of the oxidalive and non‐oxidative thermal decomposition products of cyclotetramethylenetetranitramine (HMX). The [15NO2]‐, [15N8]‐ and [2H8]‐HMX isotope preparations provided fundamental information in the determination of the identities of the various pyrolyzate species. All RDX pyrolysis product ions that were identified by Py‐API tandem mass Spectrometry, i.e. m/z 44, 60, 74, 75, 85 and 98, were present in the pyrolyzate of HMX. In both RDX and HMX investigations, these ions provided identical mass spectral daughter ion analyses. HMX, however, provided additional ions at m/z 30, 58, 69, 71, 83 and 141. Of all thirteen ions identified in the Py‐APJ mass spectrum of HMX, only that at m/z 75 contained a nitrogen atom that originated from the NO2 group. Standards analysis confirmed the identities of the ions at m/z 69, 71 and 141 as methyleneaminoacetonitrile, methylaminoacetonitrile and the caged compound hoxamethylenetetraamine, respectively. Isotopic analyses provided a high degree of confidence on the structural assignments of the ions at m/z 30 and 58 as methyleneimine and methyleneformamide; the ion at m/z 83, however, appeared to be a heterocyclic compound with daughter ion mass spectral elements similar to but not identical with that of 1‐methylimidazole and 3‐methylpyrazole.
Acetone chemical ionization studies III–displacement reactions in alkyl acetates
Authors: Vairamani M. , Saraswathi M. , Siva Kumar K. V. 
Published: May 2005

AbstractAcetone chemical ionization mass spectra of acyclic, cyclic and bicyclic alkyl acetates were studied. In addition to the formation of [M + H]+, [M + 43]+ and [M + 59]+ ions, ions corresponding to displacement by acetone were also observed. The results suggest that the displacement by acetone follows an SN1‐like mechanism in the source of the mass spectrometer. Similarity between solution‐phase solvolysis reactions and gas‐phase displacement reactions was observed with bicyclic alkyl acetates, 2‐phenylethyl acetate and cyclooctyl acetate.
Fragmentation of o‐nitrodiarylamines on electron impact: Formation of carbazole radical cations
Authors: Gawiuecki Ryszard , Rasaia Danuta , Bąk Tomasz 
Published: May 2005

AbstractThe HO· fragment eliminated on electron impact (EI) from the molecular ions of o‐nitrodiarylamines contains either the amine or the aryl hydrogen. Moreover, 2‐phenylamino‐3‐nitropyridine loses H· from the phenyl group. As confirmed by collision‐activated dissociation mass‐analysed ion kinetic energy spectra, the fragmentation of such compounds involves the formation of carbazole radical cations. Such a process was not observed for the corresponding o‐aminodiarylamines.
Proton and sodium ion affinities of glycine and its sodium salt in the gas phase. Ab initio calculations
Authors: Bouchonnet S. , Hoppilliard Y. 
Published: May 2005

AbstractThe energies of protonation and Na+ cationization of glycine (GLY) and its (GLY − H + Na) salt in the gas phase were calculated using ab inltio calculations. The proton affinity of GLY, valued at the MP2/6–31G*//3‐21G level, is 937 kJ mol−1. The amino function is confirmed to be the most favourable site of protonation: ‘proton affinities’ of the carbonyl and hydroxyl functions are calculated to be 75 and 180 kJ mol−1, respectively, lower than that of NH2 at the MP2/6‐31G*//3–21G level. Calculations performed up to the MP2/6–31G*//3–21G level give the Na+ affinity of GLY as 189 kJ mol−1 and the H+ and Na+ affinities of (GLY – H + Na) as 1079 and 298 kJ mol−1, respectively. The geometries of all neutral and protonated species optimized with the 3–21G basis set are described. Both H* and Na+ cations complex preferably between the nitrogen atom and the carbonyl oxygen atom, leading to pseudo‐five‐membered ring structures in which NaO and NaN bonds lengths are greater than 2 Å.
Fragmentation reactions of molecular dications of aromatic heterocyclic fused‐ring compounds containing more than one nitrogen atom
Authors: Perreault H. , Ramaley L. , Benoit F. M. , Sim P. G. , Boyd R. K. 
Published: May 2005

AbstractFragmentation reactions of both metastable and collisionally activated dications, formed by electron impact ionization of heterocyclic fused‐ring aromatic compounds containing more than one nitrogen atom, were investigated. This work is an extension of similar work on analogous compounds containing just one nitrogen atom and on the related polycyclic aromatic hydrocarbons. The results obtained are interpreted in terms of mechanistic proposals concerning the competition between charge‐separation and neutral‐expulsion reactions, based on variations in diradical character with increasing molecular size and nitrogen content of these molecular dications.
Electron impact mass spectrometry of 3‐(2‐hydroxyphenylcarbonyl)‐4‐(o‐ and p‐R‐phenyl)‐1,2,3,4‐tetrahydro‐2H‐benzo [f]quinolin‐2‐ones
Authors: Martínez Roberto , Cortés Eduardo , López L. Josué Alfaro 
Published: May 2005

AbstractThe major features of the mass spectra of eight substituted quinolones of potential pharmacological interest are reported.
Detection of fragment ions produced by collisional activation of multiply charged ions in a floated collision cell
Authors: Orlando Ron , Boyd R. K. 
Published: May 2005

AbstractA scan law is derived for the detection of fragment ions formed by collisional activation (CA) of a multiply charged precursor in a floated collision cell of a tandem mass spectrometer. Comparisons of the CA spectra of multiply charged ions obtained in either a floated or a grounded collision cell demonstrate the benefits associated with raising the collision cell above ground potential. In addition to the advantages observed for singly charged ions, floating the collision cell increases the transmission of multiply charged ions through the first mass spectrometer by permitting higher source potentials to be used. This technique also increases the detection efficiency for products of charge separation reactions, which may prove useful in the charge state assignment of the fragment ions.
Study of collision‐induced decomposition of phenothiazine by ion trap mass spectrometry
Authors: Constantin E. , Schnell A. , Guidugli F. , Traldi P. 
Published: May 2005

AbstractThe collision‐induced decomposition pathways of phenothiazine were studied in detail by ion trap mass spectrometry. With this approach, different amounts of energy can be deposited into the fragment ions, thus favouring particular structures. Different relative abundances in the fragmentation patterns of selected ions are observed, depending on whether they are produced by electron impact or multiple mass spectrometry [(MS)n] methods.
Comparison by mass spectrometry of ring cleavage in barbituric acid and 5‐fluorobarbituric acid derivatives
Authors: Desmarteau Darryl D. , Resnati Giuseppe , Favretto Donata , Traldi Pietro 
Published: May 2005

AbstractThe mass spectrometric behaviour of barbituric acid and 1,3‐dimethylbarbituric acid was compared with that of the corresponding 5,5‐difluoro derivatives and of some 5‐fluoro‐5‐alkyl derivatives in order to study the influence of fluorine in the fragmentation processes. This investigation, performed using both electron impact ionization and positive‐ and negative‐ion fast atom bombardment, evidences well the role of fluorine in barbiturate ring bond cleavages.
Investigation of lacidipine, a new 1,4‐dihydropyridine antihypertensive agent and three chemically related compounds by means of chemical ionization, mass spectrometry and collision‐induced dissociation
Authors: Harridan M. , Scandola M. , Franchi D. , Gaviraghi G. , Tarzia G. 
Published: May 2005

AbstractChemical ionization of two 1,4‐dihydropyridines, lacidipine and its Z‐isomer, and their corresponding pyridines in three different reagent gases and the collision‐induced dissociation (CID) of their respective mass‐selected protonated molecular ions in the collision energy range 10–200 eV were performed on a multiple quadrupole instrument. The weakness of the Breasted acid NH4+ as a protonating agent is clearly manifested in one of the ammonia positive‐ion chemical ionization (CI+) mass spectra which displays the addition ion, [M + NH4]+, as the favoured reaction channel. The stereochemistry of the precursor molecules, the exothermicity of the protonation process and the threshold of certain dissociation channels as a function of the collision energy are among the arguments invoked to explain some of the observed differences between the CI+ mass spectra and the CID data of the different isomers investigated. In an attempt to present a more comprehensive study, some high‐performance liquid chromatographic retention times and resolutions are also given.
Origin of adduct ions in the electron‐capture mass spectrum of tetracyanoethylene
Authors: Culbertson J. A. , Sears L. J. , Knighton W. B. , Grimsrud E. P. 
Published: May 2005

AbstractThe high‐pressure electron‐capture (HPEC) mass spectrum of tetracyanoethylene (TCNE) is dominated by unexpected hydrogen atom and hydrocarbon radical adduct ions when methane is used as the buffer gas. The origin of these unexpected ions was investigated by three separate mass spectrometric experiments: the electron‐capture (EC) rate constant of TCNE was determined and integrated into a previously developed kinetic model of HPEC ion source events; electron impact mass spectra of TCNE were obtained following exposure of the ion source surfaces to irradiated methane and irradiated carbon dioxide; and TCNE was determined by gas chromatographic introduction into the HPEC ion source with multiple ion monitoring. All of these experiments suggest that the reactions leading to the major adduct ions observed in the HPEC mass spectrum of TCNE are initiated by alteration of TCNE on the walls of the ion source rather than in the gas phase.
Quadrupole ion trap mass spectrometry of fullerenes
Authors: Morand Kenneth L. , Hoke Steven H. , Eberlin Marcos N. , Payne Greg , Cooks R. Graham 
Published: May 2005

AbstractThe fullerenes C60 and C70 can be ionized by desorption from a liquid matrix upon bombardment by Cs+ ions of 7 keV kinetic energy. The resulting radical cations, when activated in the ion trap by collisions with Xe target, in the presence of helium, undergo extensive dissociation by loss of multiple C2 units. Large internal energies are deposited into these molecular ions and the dissociation efficiency is in excess of 60%.
Electron impact‐induced fragmentation of 15N‐labelled 1,2,4‐triazoles
Authors: Carlsen Per H. J. , Gautun Odd Reidar , Olsrød Bjørn 
Published: May 2005

AbstractThe electron impact‐induced fragmentation patterns of 3,5‐diphenyl‐lH‐1,2,4‐[4‐15N]triazole, 4‐ethyl‐3,5‐diphenyl‐4H‐1,2,4‐[4‐15N]triazole, l‐ethyl‐3,5‐diphenyl‐lH‐1,2,4‐[4‐15N]triazole and the corresponding unlabelled compounds were established from exact mass measurements and from metastable ion evidence. Evidence for two fragmentation mechanisms was established for the formation of the m/z 104 peak in the spectrum of the 4‐ethyl compound. Only the 1‐alkylated triazole exhibited an intense peak at m/z 131. Major peaks at m/z 221 (222) and 118 are characteristic of the investigated triazoles.
Deacetylation of gaseous amidoalkylating reagents (N‐acyliminium ions) via iminium/ketene complexes: An unprecedented isotope effect
Authors: Burgers Peter C. , Kingsmill Carol A. , McGibbon Graham A. , Terlouw Johan K. 
Published: May 2005

AbstractThe prototype amidoalkylating reagent, the N‐acetylmethyliminium ion CH3C(O)N(H)CH2+ (a), was generated in the gas phase and its unimolecular chemistry was studied. Metastable ions a dissociate by deacetylation to CH2NH2 + with an exceedingly small translational energy release (0.03 kJ mol−1). A remarkable ‘all‐or‐nothing’ deuterium isotope effect is associated with this reaction. Hence although the deuterium‐labelled isotopomers CH3C(O)N(D)CH2 + (a‐d4) and CD3C(O)N(D)CH2 + (a‐d4) cleanly form CH2NHD+ + CH2CO and CH2ND2+ + CD2C‐O, respectively, the isotopomer CD3C(O)‐N(H)CH2+ (a‐d3) does not produce CH2NHD+ + CD2CO, but rather CH2ND2+ + CHDCO. By integration of results obtained from mass spectrometry‐based experiments (metustable ion (MI) and collisional activation (CA) Spectrometry and D‐labelling) and from ab initio molecular orbital calculations executed at the MP3/6–31G*//4–31G level of theory, a mechanism for deacetylation could be derived. The reaction commences with elongation of the C(O)N(H) bond in a and this is accompanied by a proton transfer to produce the hydrogen‐bridged complex OCCH2 …︁ H …︁ N(H)CH2+ (b) which then dissociates endothermically. The equilibration a ⇌ b leads to complete exchange of the NH and CH3 hydrogen atoms in a. The isotope effect observed for a‐d3 is interpreted in terms of differences in the zero‐point vibratioual energies (ZPVEs) of the sets of products CH2NHD+ + CD2CO versus CH2ND2+ + CHDCO. The NH bond in CH2NH2+ is shorter, stronger and has a higher harmonic frequency than the CH bond in ketene and thus the decrease in ZPVE is larger for CH2ND2+ + CHDCO than for CH2NHD+ + CD2CO (by 1.7 kJ mol−1). It is argued that such isotope effects can be expected for dissociations of ion‐molecule complexes and this provides a powerful indication for their intermediacy. The isomeric C3H6NO+ ions H2CCO …︁H…︁ N(H)CH2+ (c), magnified image CH2C(OH)N(H)CH2+ (e), H2NCH2CH2CO+ (f), CH3C(OH)NCH2+ (g) and protonated azetidin‐2‐one (h) were also briefly examined and characterized but with the possible exception of c and f they do not participate in the gas‐phase ion chemist of a.
Isomeric [C7H8]+˙ and [C7H7]+ ions
Authors: Zhao Guohong , Gäumann Tino 
Published: May 2005

AbstractThe photofragmentation of an equimolar mixture of cycloheptatriene and [1, Me‐13C2]toluene was studied with photons of wavelength 488 nm in order to obtain a direct comparison between the two isomers. The idea was to check the extent to which these photons could be used as a probe to study the fragmentation processes. Whenever feasible, the data were treated by a kinetic scheme and rate constants were obtained by a non‐linear regression. It could be shown that the decay of both isomers follows a time behaviour described by two exponential decays. Evidence is presented that the faster decay leads to the benzyl ion. The photofragmentation of the [C7H7]+ ions follows a complex behaviour that can be superimposed by selective ion–molecule reactions.
Four‐sector tandem mass spectrometry: A comparison of the molecular and quasi‐molecular ions of the cyclic depsipeptide valinomycin formed using electron impact, chemical ionization, fast atom bombardment, field desorption and electrospray lonizatfion
Authors: Curtis Jonathan M. , Bradley Caroline D. , Derrick Peter J. , Sheil Margaret M. 
Published: May 2005

AbstractFour‐sector tandem mass spectra of the molecular and quasi‐molecular ions of the cyclic depsipeptide valinomycin (RMM 1110.6) were compared. Electron impact (EI), chemical ionization (CI), fast atom bombardment (FAB), field desorption (FD) and electrospray ionization were used to create M+˙, [M + H]+, [M + Na]+ and [M + K]+ ions from valinomycin. Large differences were found between the FD and FAB tandem mass spectra of [M + Na]+ ions, and between the FD and EI tandem mass spectra of M+˙ ions. Differences between the spectra are ascribed to the formation of ions having the same mass but different structures. FAB tandem mass spectra of [M + Na]+ and [M + K]+ ions show greater degrees of fragmentation than do the FAB tandem mass spectra of [M +H]+ ions.
Chemical ionization mass spectra of the stereoisomeric 1,5‐anhydropentofuranoses, 1,6‐anhydrohexofuranoses and 1,6 : 3,5‐dianhydrohexofuranoses
Authors: Metzger J. O. , Schwarting W. , Köll P. , Winkler F. J. 
Published: May 2005

AbstractThe isobutane and methane direct chemical ionization (DCI) mass spectra of mono‐ and dianhydrosugars are substantially influenced by their stereochemistry at temperatures of 150–250°C. The best results are obtained under isobutane CI at 200 or 250°C. l,6:3,5‐Dianhydrogulofuranose gives proton‐bridge stabilized MH+ ions and fewer fragment ions compared with its ido epimer. The four diastereomeric 1,5‐anhydropentofuranoses show increased MH+ and M2H+ abundances for the lyxo and ribo isomers with cis‐1,2‐diol sites capable of proton bridging. The xylo isomer gives a dominant [M  OH]+ ion. All isomers, but especially xylo and ribo, give abundant [C3H5O2]+ skeleton cleavage ions. They are attributed to an RDA fragmentation of pyranoglycosyl‐type MH+ ions. The eight diastereomeric 1,6‐anhydrohexofuranoses with endo/exo configured triol structures show very characteristic MH+ abundances (4–41% Σ). They parallel the amount of proton solvation in cis‐diol sites of the isomers (gluco ⩽ ido ⩽ altro < gulo < galacto < talo < allo < manno). The [M  OH]+ ion abundances (15–47% Σ) are also very characteristic (galacto ⩽ talo < manno < altro ≪ atto < gluco ⩽ ido ≪ gulo). They reflect the possible H2O or C4H,OH loss from the MH+ and (M · C4H9]+ ions, respectively, with formation of protonated 1,6:3,5‐and 1,6: 23‐dianhydrehexofuranose species; the slightly flattened C(5) site of M might favour the departure of the 5‐OH group. In addition, there are especially high abundances of skeleton fragment ions, 15% Σ [MH  HCOOH]+, 10% Σ [M  OH  H3O  CH3O]+ and 42% Σ [M  OH  C2H4O2)+, for the ido, galacto and gluco isomers, respectively.
Unimolecular reactions of isolated organic ions: The chemistry of the unsaturated oxonium ion \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm CH}_{\rm 2} = {\rm CHCH =}\mathop {{\rm OCH}_{\rm 3}}\limits^{\rm +} $\end{document}
Authors: Bowen Richard D. , Colburn Alex W. , Derrick Peter J. 
Published: May 2005

AbstractThe reactions of metastable \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm CH}_{\rm 2} = {\rm CHCH =}\mathop {{\rm OCH}_{\rm 3}}\limits^{\rm +} $\end{document} oxonium ions generated by alkyl radical loss from ionized allylic alkenyl methyl ethers are reported and discussed. Three main reactions occur, corresponding to expulsion of H2O, C2H4/CO and CH2O. There is also a very minor amount of C3H6 elimination. The mechanisms of these processes have been probed by 2H‐ and 13C‐labelling experiments. Special attention is given to the influence of isotope effects on the kinetic energy release accompanying loss of formaldehyde from 2H‐labelled analogues of \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm CH}_{\rm 2} = {\rm CHCH =}\mathop {{\rm OCH}_{\rm 3}}\limits^{\rm + } $\end{document}. Suggestions for interpreting these reactions in terms of routes involving ion–neutral complexes are put forward.
Mass spectrometric study of novel estra derivatives of amino acids and peptides
Authors: He Meiyu , Ye Yunhua , He Xiaoran , Huang Yunsheng , Lin Xiao Yuan , Yu Zhenpei 
Published: May 2005

AbstractThe mass spectra of novel estra derivatives of amino acids and peptides were studied using electron impact and fast atom bombardment ionization, high‐resolution data and mass‐analysed ion kinetic energy spectrometry. The characteristic peaks of the basic nucleus of estrogenic steroids, the amino acid sequence of the peptide chain and partial skeletal rearrangement of some of these compounds were observed.