bluuebunny/crossref_metadata_2025 huggingface dataset:
Cold‐Cathode ion source for sputtered neutral mass spectrometry of metals
Authors: Swingler D. L.
Published: May 2005

A method involving cathodic sputtering and post‐ionization in the electronflux of a Penning discharge is described for the analysis of metals.
[C6H6, C3H7+]and [C6H7+, C3H6] ion‐neutral complexes intermediate in the reactions of protonated propylbenzenes
Authors: Berthomieu Dorothée , Audier Henri , Denhez Jean‐Pierre , Monteiro Candida , Mourgues Philippe
Published: May 2005

From the mass‐analysed ion kinetic energy spectra of labelled ions, kinetic energy releases and thermodynamic data, it is proved that protonated n‐propylbenzene (1) isomerizes into protonated isopropyl benzene (2). It is also shown that the dissociation of the less energetic metastable ions of (2), leading to [iso‐C3H7]+ and [C6H7]+ product ions, is preceded by H exchange. This H exchange involves two interconverting ion‐neutral complexes [C6H6, iso‐C3H7+] (2π) and [C6H7+, C3H6] (2α).
Highly specific fragmentation processes of isomeric mixed esters of phenylsuccinic acid under electron impact
Authors: Vidavsky I. , Mandelbaum A. , Tamiri T. , Zitrin S.
Published: May 2005

Isomeric mixed dialkyl phenylsuccinates, PhCH(COOR)CH2COOR′, undergo a highly specific elimination of ROH under electron impact. A deuterium‐labelling study showed that the hydrogen atom from the benzylic position 2 is abstracted in this process. These results suggest the occurrence of a ‘hidden’ hydrogen migration of the benzylic hydrogen atom to the carbonylic oxygen of the remote ester group, followed by the elimination of ROH from the adjacent ester group with the involvement of that hydrogen. Alkoxyl group migrations resulting in the formation of [PhCHOR]+ and [PhCHOR′]+ ions are less specific, although the migration of the remote R′O˙ is significantly preferred in all the pairs of isomers examined. Mechanisms are suggested for the formation of the two ions.
Metastable ion decomposition and collisional activation mass spectra of 1,2,3‐triarylpropen‐1‐ones
Authors: Madhusudanan K. P. , Durani S. , Reddy D. M. , Kapil R. S. , Itagaki Y. , Nojima K.
Published: May 2005

Substituents have been found to have a marked influence on the metastable ion decompositions and collisionally activated (CA) fragmentations of the M+˙ ion of a number of 1,2,3‐triarylpropen‐1‐ones. An attempt has been made to confirm the structures of the rearrangement ions, [C14H10]+˙, [C13H11]+˙, [C13H9]+ and [C12H8]+˙ by comparison of their CA spectra with those of the corresponding ions produced from reference compounds. The results imply that [C14H10]+˙ and the M+˙ ions of phenanthrene and diphenylacetylene have a common structure, [C13H9]+ and the fluorenyl cation have a common structure and [C12H8]+˙ and biphenylene molecular ion have a common structure. The available data indicate that the ion at m/z 167 consists of a mixture of structures, likely possibilities being diphenylmethyl, phenyltropylium and dihydrofluorenyl cations.
Energy studies of atomic atmospheric ions in collisions with molecular nitrogen and oxygen
Authors: Enos C. S. , Lee A. R. , Brenton A. G.
Published: May 2005

Studies of internal energy changes between the partners in ion‐molecule collisions can be facilitated by high‐resolution translational energy spectroscopy. Collisions of keV H+, N+ and O+ on molecular nitrogen and oxygen have shown that for 30 reaction channels all are consistent with spin conservation, which has not been generally acknowledged in previous studies. Estimations of the fractional metastable composition in each ion beam have also been made.
Collision‐Induced decomposition of peptides. An investigation into the effect of collision gas pressure on translational energy losses
Authors: Bradley Caroline D. , Derrick Peter J.
Published: May 2005

The dependence on the gas pressure of translational energy losses, ΔE, suffered by incident ions in collision with helium target gas atoms was investigated for the [M + Na]+ ion of valinomycin. ΔE was measured from the fragment ion peak positions in the mass‐analysed ion kinetic energy (MIKE) spectra. The variation of ΔE with target gas pressure was found to be different for different fragment ions. The implications of the results for the number of collisions which may occur under normal collision‐induced decomposition conditions (30–40% transmission) are discussed.
Mass spectra of alkenyl methyl ethers
Authors: Bowen Richard D. , Wright Andrew D. , Thomas Steven R. , Jennings Keith R. , Maccoll Allan
Published: May 2005

Electron impact ionization mass spectra of numerous alkenyl methyl ethers CnH2n‐1OCH3 (n = 3–6) recorded under normal (4 kV, 70 eV, 175°C) and low‐energy, low‐temperature (8 kV, 12 eV, 75 °C) conditions are reported. The influence of the position and stereochemistry of the double bond on the dissociation of ionized alkenyl methyl ethers is discussed. The mechanisms by which these ethers fragment after ionization have been further investigated using extensive 2H‐labelling experiments and by studying the energy dependence of the reactions. Ethers of allylic alcohols show spectra that are distinct from those of the isomeric species in which the double bond is separated by one or more sp3 carbon atoms from the carbon atom carrying the methoxy group. Three principal primary fragmentations are observed. The most common process, especially for ionized ethers of allylic alcohols, is loss of an alkyl group. This reaction often occurs by simple α‐cleavage of radical‐cations of the appropriate structure; however, alkyl groups attached to either end of the double bond are also readily lost. These formal β‐ and γ‐cleavages are explained in terms of rearrangements via distonic ions and, at least in the case of γ‐cleavages, ionized methoxycyclopropanes. Ionized homoallyl methyl ethers tend to eliminate an allylic radical, particularly at high internal energies, with formation of an oxonium ion (CH3 +OCH2 or CH3 +OCHCH3). The ethers of linear pentenols and hexenols show abundant [M ‐ CH3OH]+⋅ ions in their spectra, especially when a terminal methoxy group is present Methanol loss also takes place from ionized ethers of allylic alcohols in which there is a Δ‐hydrogen atom; this process is significantly favoured by cis, rather than trans, stereochemistry of the double bond.
Searching for the ionized alkene/aikanol complexes [C2H4+⋅/HOCH3] and [C2H4+⋅/HOCH2CH3]
Authors: Cao J. R. , George M. , Holmes John L.
Published: May 2005

Experiments on a variety of isomeric [C3H8O]+⋅ and [C4H10O]+⋅ ions have failed to produce direct evidence for the involvement of the complex ions [C2H4+⋅/HOCH3] and [C2H4+⋅/HOC2H5]. For the isomers studied, the rearrangements prior to their dissociation of lowest energy requirement (loss of H2O and C2H5⋅, respectively) are proposed to involve distonic and ylid ions.
Experiments on the formation of acylium ions from alkenic compounds following chemical ionization with no +
Authors: Schneider B. , Budzikiewicz H.
Published: May 2005

Alkenic compounds when subjected to chemical ionization with NO+ yield two acylium ions by oxidative cleavage of the double bond. Studies on the mechanism of formation of these ions are reported.
The ‘infinity cell’: A new trapped‐ion cell with radiofrequency covered trapping electrodes for fourier transform ion cyclotron resonance mass spectrometry
Authors: Caravatti P. , Allemann M.
Published: May 2005

The excitation event in Fourier transform ion cyclotron resonance mass spectrometry is optimized in order to obtain more reliable relative signal intensities and enhance the ion‐selection performance in multi‐tandem mass spectrometric experiments. Standard trapped‐ion cells suffer from the undesirable ejection of ions along the symmetry axis (z‐axis) of the cell, which is oriented parallel to the magnetic field lines. This z‐eiection effect is difficult to predict, and thus difficult to avoid, especially when complicated broad‐band excitation schemes are applied to the ions. An improved trapped‐ion cell design, referred to as the ‘Infinity Cell’, is discussed which eliminates z‐ejection. The Infinity Cell concept is based on the finding that it is possible to model the electric excitation field of an infinitely long cell with a cell of finite dimensions. The virtual elimination of z‐ejection effects is demonstrated in several suitable experiments by comparing the operation of the standard cell and the Infinity Cell.
Association reactions of trimethylsilyl ions
Authors: Lin Yi , Ridge D. P. , Munson Burnaby
Published: May 2005

Adduct ions, [M + (CH3)3Si]+, were produced by bimolecular association reactions of trimethylsilyl ions, (CH3)3Si+, with acetone, cydohexaoone, anisole, dimethyl ether, 2,5‐dimethylfuran, 2‐methylfuran and furan in ion cyclotron resonance experiments at 300 K and at pressures of ∼10−7 Torr (1 Torr = 133.3 Pa). The rate constants, ka, for the association reactions varied from 100% to 2% of the collision rate constants, kc. The rate constants were independent of pressure, except for furan. Measurements were also made of bond dissociation energies for these adduct ions, D[(CH3)3Si+–X], from equilibrium measurements. The association efficiency, ka/kc, increased with increasing bond dissociation energy and with increasing numbers of degrees of freedom, in qualitative agreement with theoretical predictions. Observations pertinent to the dependence of ka on reactant temperature and relative kinetic energy are discussed. The possibility of determining ion‐neutral complex binding energies from radiative association rate constants is considered.
Unimolecular gas‐phase reactions of the methyl acetoacetate radical cation. Oxygen atom permutation via ion‐molecule complexes
Authors: Berthomieu Dorothée , Tortajada Jeanine , Morizur Jean‐Pierre , Audier Henri‐Edouard
Published: May 2005

The reactions of metastable decomposing methyl acetoacetate (a mixture of keto a ad enol tautomers) are reported and discussed. The unimolecular fragmentations of the tautomers are different. The metastable decomposing radical cation of the keto form displays four specific ions: [M –CO]+˙, [M – CH2O]+˙, [M – CH2CO]+˙ and m/z 43. The results derived from D‐, 13C‐ and 18O‐labelled precursors together with thermochemical data have been used to study the mechanisms. Experimental results indicate that an unexpected isomerization occurs before dissociation. It formally corresponds to oxygen atom permutation of the two carbonyl groups without participation of the carbon atoms. This remarkable process is interpreted in terms of a mechanism involving ion‐molecule complexes.
Identification of caffeine and its metabolites in human urine extracts by electron impact ionization tandem mass spectrometry
Authors: Liguori A. , Mascaro P. , Porcelli B. , Sindona G. , Uccella N.
Published: May 2005

Electron impact ionized purine bases such as caffeine and its metabolites (theopbylline, theobromine, paraxanthine, 1‐methylxanthine, 3‐metnybumthine and 7‐methyIxanthine) were characterized by tandem mass spectrometry. The direct analysts of human urinary extracts by tandem mass spectrometry allows the unambiguous identification of caffeine and its metabolites present simultaneously in the urine.
Gas chromatographic/mass spectrometric measurement of deuterium‐labelled valine, leucine, isoleucine and phenylalanine in the human body
Authors: Zhu Peifen , Yu Zhonghua , Wan Guangmei , Sha Huixin , Su Keman , Yu Bingyao , Zhao Guangsheng
Published: May 2005

N‐Trifluoroacetyl‐n‐butyl ester derivatives of deuterium‐labelled valine, leucine, isoleucine and phenylulanine were analysed by the isotope dilution technique and gas chromatography/mass spectrometry (GC/MS). Selected ion retrieval and peak‐area integration were applied. The conditions adopted gave good separations with a short experimental time and high intensity. Ratios of the total isotopic abundance and metabolic kinetic curves were obtained. The regression coefficient of the standard dilution curve was 0.99 and the relative standard deviation was 0.3%. The stabilities of the amino acid derivatives were also tested.
Electron impact ionized benzoylnitroanilines and their N‐alkyl and N‐acyl derivatives
Authors: Ayyangar N. R. , Sudalai A. , Daniel Thomas
Published: May 2005

The behaviour of some benzoylnitroanilines and their derivatives under electron impact ionization was invest gated by means of low‐resolution mass spectrometry. Some characteristic rearrangement processes are discussed.
Isomeric [C,H3,N,O]+˙ ions and their neutral counterparts
Authors: Hop Cornelis E. C. A. , Chen Hongwen , Ruttink P. J. A. , Holmes John L.
Published: May 2005

The isomeric ions [H2NC(H)O]+˙, [H2NCOH]+˙, [H3CNO]+˙ and [H2CNOH]+˙ were examined in the gas phase by mass spectrometry. Ab initio molecular orbital theory was used to calculate the relative stabilities of [H2NC(H)O]+˙, [H2NCOH]+˙, [H3NCO]+˙ and their neutral counterparts. Theory predicted [H2NC(H)O]+˙ to be the most stable ion. [H2NCOH]+˙ ions were generated via a 1,4‐hydrogen transfer in [H2NC(O)OCH3]+˙, [H2NC(O)C(O)OH]+˙ and [H2NC(O)CH2CH3]+˙. Its metastable dissociation takes place via [H3NCO]+˙ with the isomerization as the rate‐determining step. [H2CNOH]+˙ undergoes a rate‐determining isomerization into [H3CNO]+˙ prior to metastable fragmentation. Neutralization‐reionization mass spectrometry was used to identify the neutral counterparts of these [H3,C,N,O]+˙ ions as stable species in the gas phase. The ion [H3NCO]+˙ was not independently generated in these experiments; its neutral counterpart was predicted by theory to be only weakly bound.
Unique thermospray mass spectrometry of 1,4‐benzoquinone and analogs in ammonium acetate solutions
Authors: Gctek T. A. , Vestal M. L. , Vestal C. H. , Korfmacher W. A. , Miller D. W. , Freeman J. P.
Published: May 2005

In general, ions corresponding to [M + H]+ and/or [M + NH4]+ are observed in thermospray mass spectrometry (TSMS) when using ammonium acetate in the liquid carrier. For several quinones investigated, unique thermospray mass spectra were detected with a mass spectral peak corresponding to an [M + 16]+ ion being observed in aqueous ammonium acetate solutions. Investigation of l,4‐benzoquinone (BQU) and structurally analogous quinones indicated that amine conjugate formation with BQU and similar quinones was the origin of the unique [M + 16]+ ion in TSMS. When methanol was added to the liquid carrier, ions corresponding to methoxy conjugation were detected. High‐performance liquid chromatography followed by TSMS or electrochemical detection gave evidence that this amine and methoxy conjugate formation was occurring in the thermospray source area.
Isomer differentiation and structural characterization of penem β‐lactam antibiotics by mass‐analyzed ion kinetic energy spectrometry
Authors: Das Pradip R. , Pramanik B. N. , Girijavallabhan V. M. , Ganguly A. K.
Published: May 2005

A number of clinically significant penem β‐lactams, both free acids and sodium salts, were investigated by mass‐analyzed ion kinetic energy spectrometry (MIKES) following fast atom bombardment (FAB) ionization. The collisionally activated dissociation (CAD) products of [M + H] + and [M + Na]+ ions are described. Carbon dioxide loss was observed for some of the free acids, whereas a daughter ion generated by β‐lactam ring cleavage was characteristic of the sodiated species. Other fragments included successive cleavages and rearrangements of the substituent side‐chain, permitting complete characterization of these chains. The fragmentation pattern for both protonated and sodiated species were more clearly established by CAD MIKES than by normal FAB mass spectral analyses. A notable feature of this technique was its ability to differentiate between pairs of regioisomeric penems on the basis of their fragmentation patterns. These compounds could not be differentiated in the usual mass spectra.
Laser photolysis of chlorodiaminotriazines and detection of their fragmentation and clusterization products
Authors: Giardini‐Guidoni Anna , Mele Aldo , Pizzella Giulia , Teghil Roberto
Published: May 2005

The laser photolysis of three 2‐chloro‐4‐6‐diamino‐1,3,5‐triazines, namely simazine, atrazine and propazine, was investigated. The products formed were detected by time‐of‐flight mass spectromety. The results illustrate that the main process is fragmentation competing with cluster formation. The hydrogen bonding proposed for the crystal structure of diaminotriazines should be responsible for the gas‐phase clusterization occurring by laser ablation.
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

Positive 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

A 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

The 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.
Increase in productivity by networking mass spectrometer data systems
Authors: Mellerio Giorgio G. , Vago Giorgio M.
Published: May 2005

Three personal computers (PCs) are linked in an ethernet network using D‐Link LenSmart protocol. Resource sharing and data transfer at very high speed between two different gas chromatography/mass spectrometry (GC/MS) data systems are obtained.
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

Glycosidic 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

N(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

Analytical 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

Acetone 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

The 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

The 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

Fragmentation 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

The 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

A 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

The 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

The 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

Chemical 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

The 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

The 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

The 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

The 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

The 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

Four‐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

The 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

The 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

The 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.
Internal energy deposition in doubly charged tungsten hexacarbonyl on low‐energy Charge exchange with organic targets
Authors: Dejarme Lindy E. , Cooks R. Graham , Ast Teodor
Published: May 2005

Estimates are reported for the internal energy distribution and the average internal energy deposited in the molecular ion of tungsten hexacarbonyl, W(CO)˙, when it is generated by charge exchange of the corresponding doubly charged ion. Charge exchange was performed in the collision energy range from nominal zero to 40 eV using a triple quadrupole mass spectrometer with a variety of polyatomic targets including alkanes, aromatics and tungsten hexacarbonyl itself. At all energies, dissociative charge exchange was accompanied by collision‐induced dissociation and this meant that the energetics of charge exchange had to be measured by extrapolation to zero collision energy and zero pressure. Under these conditions, the average internal energy deposited into the charge‐exchanged product W(CO)˙ was 1.0, 0.9, 1.3 and 2.3 eV for the targets isobutane, n‐pentane, n‐heptane and toluene, respectively. Data for the symmetrical charge exchange reaction
magnified image
demonstrated that partitioning of internal energy between the two products occurred equally. Hence, assuming equipartitioning over all degrees of freedom (at threshold) in the other cases also, the total internal energies deposited in the target molecules were determined to be 1.1, 1.1, 2.3 and 2.7 eV, respectively. Comparison of these values with the reaction exothermicities revealed that ∼2 eV (1.2–2.6 eV) of additional energy is liberated on charge exchange in each case. This is suggested to appear as translational energy of separation of the two charged products. Charge exchange in this system is suggested to occur by a Landau‐Zener curve‐crossing mechanism and the estimated values of the coulombic energies correspond to electron transfer at internuclear distances of the order of 7 ± 2 Å.
Simplification and accuracy test for the collision cross‐section‐based quantification of isomeric ion mixtures
Authors: Oh Hyeon Ju , Kim Myung Soo
Published: May 2005

A method was devised to determine the isomeric composition of an ionic mixture using collisionally activated decomposition mass spectrometry. Compared with the more rigorous approach based on collision cross‐sections reported previously, the main advantage of the proposed method is its experimental simplicity. Both the internal consistency and the accuracy of the method were tested for mixtures of isobaric ions, i.e. ions with the same nominal mass‐to‐charge ratios.
Mass spectral fragmentation pathways in some dinitroaromatic compounds studied by collision‐induced dissociation and tandem mass spectrometry
Authors: Yinon Jehuda
Published: May 2005

A collision‐induced dissociation study of a series of dinitroaromatic compounds was carried out using a tandem BB mass spectrometer. Fragmentation pathways were determined in the electron impact mode. Loss of NO2˙ from the molecular ion was observed In most of the investigated compounds. In some compounds loss of NO2˙ occurred only after loss of OH˙. In other compounds it was not observed at all because of competitive processes, such as loss of NO˙, CO2, CH2O, C2H4 or H2O. Loss of NO˙ was a major decomposition pathway, forming ‘dished peaks’ in some of the compounds having a nitro group ortho to a phenyl group, indicating a release of kinetic energy associated with the decomposition. Loss of OH˙ due to an ‘ortho effect’ occurred in compounds where a nitro group was ortho to a group containing a labile hydrogen, but was not observed when competitive processes such as loss of NO˙, NO2˙ or H2O occurred. ‘Nitro to nitrite’ isomerization was suggested to explain the decarboxylation process in 2,4‐ and 2,5‐dinitrobenzoic acid and the loss of COH2 in 2,4‐dinitroanisole.
Mass spectrometric studies on 17β‐estradiol‐17‐fatty acid esters: Evidence for the formation of anion‐dipole intermediates
Authors: Debrauwer Laurent , Paris Alain , Rao Dinesh , Fournier Françoise , Tabet Jean‐Claude
Published: May 2005

The behaviour towards low collision energy processes (eV range) of [M  H]− prepared under negative ion chemical ionization (NICI) ammonia conditions from 17β‐estradiol‐17‐fatty acid esters has been investigated. From such bifunctional compounds containing two acidic sites (i.e. phenol and ester groups), two isomeric forms (i.e. phenoxide and enolate forms) characterize the [M  H]− ion structures, whose distribution depends on the ion preparation mode. Here NICI (ammonia) provides both phenoxide and enolate forms as the [M  H]− species. This behaviour contrasts with the regioselectivity observed for proton abstraction from phenol under NICI (N2O) and fast atom bombardment conditions. Production of both phenoxide and enolate forms in NICI (ammonia) is demonstrated under NICI (ND3) conditions in which DO‐labelled [Md  H]− enolate ions are produced in a similar yield to unlabelled [Md  D]− phenoxide ions. Collisionally activated dissociation (CAD) spectra of both isomeric deprotonated molecules differ strongly by the presence of two different pairs of complementary daughter ions, suggesting that these ionic species are unconvertible. This is due to a steric hindrance effect on the long‐distance proton transfer. A mechanistic investigation on the formation of fragment ion pairs produced under CAD was performed with various deuterium‐labelled molecules. From these experiments, evidence is provided for molecular isomerizations into ion‐dipole complexes (prior to dissociation) which are structurally dependent on the initial charge location. Direct dissociation of these intermediates competes with the occurrence of exothermic proton transfer(s) yielding the formation of other isomeric intermediate forms. The orientation of these proton transfers is dictated by the relative acidities of both moieties of the complex.
Electron impact mass spectra of some tertiary aliphatic nitro compounds. Nitrocarbonyl compounds and some analogues
Authors: Konopski Leszek , Grela Karol
Published: May 2005

The mass spectra of some tertiary aliphatic nitroaldehydes, nitroketones, nitroesters, nitronitriles and related nitrocarbonyl compounds are discussed and compared with those of some analogous nitro compounds lacking the carbonyl function. The M+˙  NO2˙ and in several cases M+˙  HNO2 fragmentation seem to be the most characteristic features of all tertiary aliphatic nitro compounds. In the presence of the primary nitro group, the loss of NHO2 is always observed.
Electron impact‐induced decomposition of some substituted 7‐ethoxycarbonylpyridopyrrolidenequinolines
Authors: Plaziak Adam S. , Girek Tomasz , Śliwa Wanda
Published: May 2005

The electron impact ionization mass spectrometric behaviour of three cycloadducts of 4,6‐benzo[h]naphthyridinum ethoxycarbonylmethylide with acrylonitrile, ethyl acrylate and diethyl maleate was studied with the aid of exact mass measurements and metastable transitions. The study showed that the electron impact‐induced decomposition of substituted pyridopyrrolidenequinolines occurs exclusively on the aliphatic five‐membered ring.
Relative metal ion affinities of organic nitriles in the gas phase
Authors: Chen Lin‐Zhi , Miller Jack M.
Published: May 2005

The relative metal ion (Ni+ and Co+) affinities of 14 alkanenitriles, alkenenitriles and benzonitrile were estimated using Cooks' kinetic method in a fast atom bombardment mass spectrometer. The results are compared with proton affinities, affinities for other metal ions, two‐ligand dissociation enthalpies and the dipole moments of the nitriles. The RCNCo+ bond is found to be close to the RCNNi+ bond but weaker than the RCNAl+ bond. The effective temperature (T) of the metal‐bound dimer ions falls in the range 298 K < T < 400 K.