bluuebunny/crossref_metadata_2025 huggingface dataset:
Stereochemical effects in mass spectrometry XIII—Determination of absolute configuration by fast atom bombardment mass spectrometry
Authors: Yang Hou‐Jun , Chen Yao‐Zu
Published: May 2005

It was found that in the fast atom bombardment mass spectra of some asymmetric secondary alcohols and amines, when a pair of enantiomers, such as (2R,3R)‐ and (2S,2S)‐2,3‐diacetoxysuccinic anhydride and (2R,3R)‐ and (2S,3S)‐2,3‐dibenzoyloxysuccinic anhydride, were used as reagents, the relative abundances of characteristic ions formed by the stereoselective reaction between a sample and a reagent of different configurations were much higher than those of ions formed by a sample and a reagent of the same configuration. The absolute configurations of the sample molecule may be predicted by examination of the mass spectra of the sample measured with reagents of R and S configurations. This approach proved to be a convenient way to determine the absolute configuration of organic molecules at the micromole level by fast atom bombardment mass Spectrometry, and it has advantages over the chemical ionization method reported previously for the analysis of polar and involatile compounds.
Characterization of cytokinins from plant pathogenic Pseudomonades by fast atom bombardment tandem mass spectrometry
Authors: Greco Francesco , Sindona Giovanni , Uccella Nicola , Evidente Antonio
Published: May 2005

Naturally occurring cytokinins produced from two phytopathogenic Pseudomonas bacteria, and some of their derivatives and analogues, were characterized by fast atom bombardment tandem mass spectrometry. The proto‐nated molecular ions of the examined cytokinins can be fingerprinted from breakdown pattern of their gaseous unimolecular dissociations, thus providing means for their identification by desorption ionization methods.
Characterization of glucosamine and N‐acetylglucosamine oligomers by fast atom bombardment mass spectrometry
Authors: Bosso C. , Domard A.
Published: May 2005

The oligomers of N‐acetylglucosamine [degree of polymerization (d.p.) 2–6] and of glucosamine (d.p. 3–9) were systematically studied by the fast atom bombardment technique. Positive‐ and negative‐ion detection were used successively in each case. The latter provided more information in respect of the number of fragmentation pathways. In addition to the classical fragmentations usually obtained with other oligosaccharidic chains, new species specific to these two series were observed. They depend mainly on the nature of the substituents located on the C(2) positions of the glucosidic units constituting the chain.
Participation of halogen atoms in hydrogen transfer between remote positions in gas‐phase ionized isomeric haloresorcinols
Authors: Weisz Adrian , Andrzejewski Denis , Mandelbaum Asher
Published: May 2005

Mono, di‐ and trihaloresorcinols substituted by a halogen atom at position 2 exhibit a highly specific elimination of H2O on electron impact ionization and under conditions of collisionally induced dissociation (CID). The high isomer specificity suggests the intermediacy of a hydrogen transfer from one of the hydroxy groups to the adjacent halogen atom. A subsequent hydrogen migration to the other hydroxy group readily explains the facile elimination of H2O from the M+· ions of these particular isomers. An analogous three‐step hydrogen transfer has not been observed in 2,3‐dihalo‐l,4‐hydroquinones. 4‐Bromo‐ and 4‐icdoresorcinol undergo elimination of the halogen atom followed by a very fast loss of CO under CID conditions, affording [M − Hal]+ ions of low abundance and highly abundant[M − Hal − CO]+ ions. The elimination of CO is suppressed in the isomeric 5‐haloresorcinols, resulting in very highly abundant [M − Hal]+ ions. This behavior suggests that a ‘hidden hydrogen transfer’ accompanies the elimination of the halogen atom from the molecular ions of 4‐haloresorcinols.
The [M − 1 ]+ quasi‐molecular ion in chemical ionization mass spectrometry. Fragmentation of bis(benzyloxy)silanes by intramolecular reactions
Authors: Bild Norbert , Chapeaurouge Alexander , Gfeller Stefan , Bienz Stefan
Published: May 2005

The unusual chemical ionization mass spectrometric behavior of bis(benzyloxy)silanes showing heavy fragmentation and an [M − 1]+ fragment, instead of the expected [M + 1]+ ion with isobutane as the reactant gas, was investigated by means of (chloromethyl)bis(benzyloxy)methylsilane and model compounds. It could be shown that probably an intramolecular hydride transfer to an adjacent proton via a six‐membered transition state gives rise to the uncommon [M − 1]+ quasi‐molecular ion. Similar intramolecular reactions transferring a hydride, a chloro‐methyl, a phenyl or a benzyl group via cyclic transition states to a neighboring electrophile are held responsible for five of the six additional major fragments. The results demonstrate that fragmentation reactions become important in chemical ionization mass spectrometry if a molecule or an initially formed cluster ion possesses reactive groups which are in close proximity to each other.
Pyrolysis–desorption chemical ionization and high‐energy tandem mass spectrometry of the O‐specific antigen of Yersinia ruckeri
Authors: Helleur Robert J. , Thibault Pierre , Banoub Joseph H. , Shaw Derek H.
Published: May 2005

Application of pyrolysis‐desorption chemical ionization mass spectrometry (Py‐DCI‐MS) is demonstrated for the structural characterization of the native O‐specific antigen of Yersinia ruckeri. Under proper pyrolytic and chemical ionization conditions this antigenic polysaccharide yields anhydrohexosamine fragments which facilitate identification of the trimeric repeating unit sequence. Tandem mass spectrometric analyses of the trimeric repeating unit fragments provided additional evidence for the proposed structure and permitted rationalization of the observed fragment ions. Furthermore, Py‐DCI‐MS of smaller hexosamine subunits isolated during off‐line pyrolysis experiments showed fragmentation characteristics almost identical with those observed in the mass spectra of the whole antigen, hence confirming the stability of the pyrolysis fragments.
Gas‐phase chemistry of metal oxide anions: Reactions of dioxomanganate(III), MnO2−, and trioxomanganate(V), MnO3−, ions with monofluoro‐ and pentafluoro‐aromatic compounds
Authors: Fokkens R. H. , Gregor I. K. , Nibbering N. M. M.
Published: May 2005

Gas‐phase reactions of MnO2− and MnO3− ions with a series of monofluoro‐ and pentafluoro‐aromatic compounds, i.e. C6H4FX with X = o‐, m‐ and p‐CHO and o‐, m‐ and p‐OH and C6F5Y with Y = OH, OCH3, CHO, CN, NO2, COCH3 and F, were studied at low pressures by Fourier transform ion cyclotron resonance mass spectrometry. The principal reaction channels identified involve electron transfer from the MnO2− and MnO3− ions to the fluorinated aromatic substrates and proton abstraction and nucleophilic displacement of fluorine by these oxometallate ions. The results obtained indicate that in the gas phase MnO2− is less basic than MnO3− and that neutral MnO2 has a lower electron affinity than MnO3, both values lying between 0.52 and 0.94 eV.
Laser desorption fourier transform mass spectrometric study of porphyrins attached to hydrocarbon spacers
Authors: Antolovich Michael , Nguyen T. Hiep , Paddon‐Row Michael N. , Willett Gary D.
Published: May 2005

The 248 nm laser desorption Fourier transform ion cyclotron resonance positive‐ and negative‐ion mass spectra are presented for two novel porphyrin‐spacer‐quinone bichromophoric systems in which the spacer consists of a polynorbornyl‐type hydrocarbon and also for a model tetraphenylporphyrin compound. The compounds are 1,2,3,4‐tetrahydro‐1.4‐methano‐7,10,13,16‐tetraphenylbenzo [g] quinoxalino [2,3‐b] porphyrin, 5,20‐dihydro‐5,20‐methano‐l,4‐dimethoxy‐8,11,14,17‐tetrapherylnaphtho [2,3‐g]quinoxalino[2,3‐b] porphyrin and 5,10,15,20‐tetraphenyl‐porphyrin. The two‐step laser desorption multiphoton ionization mass spectra recorded at laser powers < 2 MW cm−2 produce only the parent ions M+˙ and M−˙. At increased laser powers of up to 5 MW cm−2 the [M + H]+ and [M  H]− ions are observed to increase significantly in relative abundance. At laser powers >8 MW cm−2 the porphyrins show extensive photodissociation and rearrangement and, in one case, the production of an extensive distribution of carbon cluster fragment ions including the fullerene [C60]+˙.
A tandem time‐of‐flight mass spectrometer
Authors: Jardine Daniel R. , Morgan John , Alderdice David S. , Derrick Peter J.
Published: May 2005

A tandem time‐of‐flight mass spectrometer Incorporating a fast atom bombardment source has been designed and constructed for the purpose of studying collision‐induced decomposition spectra. A deflection of the secondary ion beam is used to form the ion packets for time‐of‐flight analysis. A floating collision cell that represents a potential barrier to ions transversing the time‐of‐fiight tube enables ionic and neutral fragments from collision‐induced decomposition reactions to be separated in time from the parent ion. The instrument operating in the tandem mode is capable of performing charge exchange and collision‐induced decomposition studies of both positive and negative incident ions.
Intermolecular dehydration reactions of protonated alkenol adducts
Authors: Liou C.‐C. , Eichmann E. S. , Brodbelt J. S.
Published: May 2005

Collisionally activated intermolecular dehydration reactions of proton‐bound alkenol dimers and proton‐bound alkenol‐dimethyl ether adducts were examined in both a triple quadrupole mass spectrometer and a quadrupole ion trap mass spectrometer. Ion‐molecule reactions of profonated dimethyl ether (DME) with allyl alcohol, 3‐buten‐1‐ol and 4‐penten‐l‐ol (M) produced the ions [M + H]+, [2M + H]+, [M + H + DME]+ and [M + H + DME − H2O]+. Collisionally activated dissociation was used to characterize the structures of the product ions, and energy‐minimized structures and heats of formation of ions were calculated by molecular mechanics and semiempirical computational methods. The loosely bound [M + H + DME]+ ions rearrange and dissociate by an intermolecular dehydration reaction to form [M + H + DME ‐ H2O]+ ions, with methylated ether stuctures. These [M + H + DME − H2O]+ ions dissociate predominantly via direct cleavage of the ether linkage. Comparisons of the bimolecular and dissociation reactions of the alkenols were made with those of simple alcohols, diols and alkenes to demonstrate that the presence of the carbon‐carbon double bond specifically assists in many of the observed processes.
Claisen rearrangement in phenyl allenyl ethers on electron impact
Authors: Ramana D. V. , Sudha M. S.
Published: May 2005

Phenyl allenyl ethers undergo Claisen rearrangement under electron impact conditions producing intense [M  CO] ions. Another competing fragmentation pathway in these compounds is an intramolecular aromatic substitution followed by the loss of H˙ or the substituent to give rise to fragments corresponding to benzopyrilium cations. Electron‐withdrawing substituents on the phenyl ring favour the cyclization reaction. An interesting ortho interaction of the nitro group with the allenic moiety leads to the expulsion of CO2 from the molecular ion. The proposed fragmentation pathways and the ion structures are established with the help of linked‐scan spectra (B/E, B2/E), collision activation decomposition spectra and high‐resolution data.
A secondary ion mass spectrometric study of thallium oxide thin films grown via metal organic chemical vapour deposition
Authors: Daolio Sergio , Ajò David , Rossetto Gilberto , Aschieri Carla , Armelao Lidia
Published: May 2005

Within a comprehensive programme including synthesis via metal organic chemical vapour deposition (MOCVD) and characterization of inorganic compounds and materials of possible interest in technologies based on thin films, results concerning the deposition of metal oxides by means of volatile organometal precursors are reported. In particular, thallium oxide films obtained by the MOCVD technique and commercial powders of Tl2O3 and Tl2O adsorbed on several metal substrates (stainless steel, Si, Cu, Mo, Pt) were studied by secondary ion mass Spectrometry (SIMS) under ion beam bombardment at different ion energies. The positive‐ and negative‐ion mass spectra exhibit typical isotopic patterns of several ionic species produced by interesting interfacial reactions, and the analysis of their relative abundances provides a measure of oxide reactivity towards different substrates. SIMS measurements of metal substrates were also performed. The ability and limits of SIMS in the reactivity study of thallium oxide powders and films and, in addition, in the identification of reaction products evidencing impurity species that, in turn, can be ascribed to the substrates or to the precursors used for the oxide synthesis is pointed out.
Fast atom bombardment mass spectrometry of cyclic hydrido dithio‐ and dioxycarbene complexes of platinum(II)
Authors: Bertani R. , Mozzon M. , Michelin R. A. , Seraglia R. , Traidi P.
Published: May 2005

Fast atom bombardment (FAB) mass Spectrometry of the two hydrido carbene compounds trans‐[(PPh3)2HPt(carbene)]BF4 (carbene = and was studied. Some retrosynthetic processes are involved in the fragmentation pathways. The reactions with NaCI were also studied under FAB conditions and the results were compared with those obtained in solution.
Fast atom bombardment in the structural identification of intermediates in the hydrolytic degradation of polyphosphazenes
Authors: Caliceti P. , Veronese F. M. , Marsilio F. , Lora S. , Seraglia R. , Traldi P.
Published: May 2005

Fast atom bombardment mass Spectrometry was employed in a study related to the hydrolytic degradation of alanine ethyl ester‐ and imidazole‐substituted polyphosphazenes, to be used as matrices for drug release. Some intermediates were identified and their structural assignment was accomplished by means of mass‐analysed ion kinetic energy data. All the detected species show the same phosphazene skeleton, consisting of a P4N3 chain, with an increasing number of alanine ethyl ester substituents, and no evidence was found for the presence of imidazole bound to the polymer backbone.
Comparison of collisional activation by the ‘boundary effect’ vs. ‘tickle’ excitation in an ion trap mass spectrometer
Authors: Paradisi Cristina , Todd John F. J. , Vettori Umberto
Published: May 2005

It has been shown previously that collisional activation in an ion trap mass spectrometer can be achieved by storing parent ions within a narrow zone extending close to the theoretical boundaries βr = 0 or βz = 0 of the stability diagram. This procedure can be used for obtaining collision‐induced dissociation of selected parent ions without the need to apply a precisely tuned resonant ‘tickle’ potential between the end‐cap electrodes. In this investigation a comparison was made between the two methods (‘tickle’ and ‘boundary’) of activation based on the efficiency of parent‐to‐daughter conversion and on the relative abundance of daughter ions for a model system (the m/z 91/92 ratio for n‐butylbenzene). The data show that, under conditions of maximum efficiency, a comparable amount of internal energy is present in the ions after activation with the two methods. However, with the ‘tickle’ technique it is possible to increase the internal energy of the parent ions even further, although at the expense of the efficiency, whereas in the case of the “boundary” activation, the conditions for optimum efficiency almost coincide with those for maximum activation and a drastic loss of ions follows any attempt to overcome these limits. It is also found that at any given qz value used for storing and activating parent ions the permitted mass difference between parent and fragment ions is greater with ‘boundary’ than with ‘tickle’ excitation.
Triple quadrupole tandem mass spectrometric study of the 3‐picolinyl esters of fatty acids
Authors: Rubino Federico Maria , Zecca Luigi
Published: May 2005

Low‐energy collision‐induced dissociation of some representative 3‐picolinyl esters of fatty acids were investigated. The daughter‐ion spectra of the precursor ions showed similar features to the electron impact mass spectra, but the low intensity of the parent‐ion signal did not allow reliable deductions. The parent‐ion spectra of some fragments that retain the pyridine derivatizing group contain structurally useful information, and are suitable for analytical application. These spectra also contain fragment ions which may account for an alternative pathway to that currently proposed for the generation of certain fragment ions within the ion source. Both pathways were investigated in this tandem mass spectrometric study. Isomerization and decomposition of distonic fragment ions through loss of alkenes yield species with a shorter alkyl chain, which are particularly stable when they contain allylic radicals.
Tandem mass spectrometry in the structural analysis of an oviposition‐deterring pheromone
Authors: Domon B. , Müller D. R. , Richter W. J.
Published: May 2005

The potential of tandem mass Spectrometry (MS/MS) as a stand‐alone technique in the structural analyses of an oviposition‐deterring pheromone (ODP, 1) is reviewed. Two facets of the salt‐like glycolipid structure of 1 were of major interest in this context: the substitution pattern of the lipid backbone (15‐glucosyioxy‐8‐hydroxypalmitate) and, more specifically, the configurational identity of the sugar portion (glucopyra nose). Throughout this study, trideuterioacetyl derivatives of ODP (1 → pentakis(trideuterioacetyl)‐ODP la) and the reference substrates were used. Probing of the sugar moiety by fast atom bombardment (FAB) and both low‐ and high‐energy collision‐induced dissociation (CID) of B2‐type sugar ions surprisingly failed as a single exception within a larger number of glycosidic substrates subjected to this approach. However, electrospray ionization (ESI) of la with the formation of the sugar ions in the gas phase by ‘first‐stage’ CID before mass selection circumvented this difficulty and provided an unambiguous and sensitive probe for sugar stereochemistry. When studying the ODP molecule as a whole, FAB‐generated M‐like ions such as [M − H]−, [M + Na]+ and [M − H + 2Na]+ were subjected to high‐energy CID using a four‐sector tandem mass spectrometer. Analyses of simple model substrates such as the 12‐trideuterioacetoxystearate anion facilitated the interpretation of the distinct charge‐remote fragmentation (CRF) behaviour of la. Whereas all M‐like species provided complete records of the lipid portion of la and its oxygenation pattern, only the sodiated cations allowed reliable location of the individual substituents. In these latter species complementary series of ‘sequence ions’ were observed that incorporated either the taurine or the sugar terminus and thus reflected CRF for both alternatives of terminal charge fixation.
Ortho effect in the mass spectrometric behaviour of N(pyrimidin‐4‐yl)aminobenzoic acids and their methyl esters
Authors: Plaziak Adam S. , Spychala Jaroslaw , Wójtowicz Hanna , Langer Jerzy J. , Thiel‐Pawlicka Halina , Golankiewicz Krzysztof
Published: May 2005

Ortho‐. meta‐ and para‐isomers of N‐(pyrimidin‐4‐yl)aminobenzoic acid and their methyl esters were investigated by electron impact mass Spectrometry. Their fragmentation was found to be strongly dependent on the position of the substituent in the aminobenzoic moiety. Two different kinds of ortho effect were studied and confirmed with the aid of deuterium‐labelled derivatives.
Mass‐analysed ion kinetic energy and collisionally induced dissociation mass spectra of clusters of acetylated xylo‐oligosaecharides with protonated ammonia and methylannine
Authors: Kovàčcik V. , Hirsch J. , Kováč P. , Grützmacher H.‐Fr.
Published: May 2005

Per‐O‐acetylated methyl glycosides of D‐xylan‐type di‐ and trisaccharides were studied by mass‐analysed ion kinetic energy (MIKE) and collisionally induced dissociation (CID) mass Spectrometry using protonated ammonia and methylamine, respectively, as reaction gases in chemical ionization (CI). The oligosaccharides form abundant cluster ions, [M + NH4]+ or [M + CH3NH3]+, and the main fragmentation of these ions in the MIKE and CID spectra is the cleavage of interglycosidic linkages. Thus, CI (NH3) or CI (CH3NH2) spectra in combination with the MIKE or CID spectra allow the molecular masses, the masses of monosaccharide units and the branching point in oligosaccharides to be established. In the case of disaccharides, it is possible to distinguish the (1 → 2) linkage from the other types of linkages.
Daughter ion mass spectra of 11‐pentafluorobenzyl ester derivatives of 11‐dehydiothromboxane B2 and B3
Authors: Ferretti Aldo , Flanagan Vincent P.
Published: May 2005

Collisionally activated decomposition (CAD) mass spectra of the [M – C6F5CH2⋅]− ions of 1‐methyl cster‐11‐pentafluorobenzyl ester‐9,12,15‐tris(trimethylsilyl) and 9,12,15‐tris(ethyldimethylsilyl) ether derivatives of 11‐dehydrothromboxane B2 are presented and discussed. The spectra are interpreted with the aid of those of a corresponding 3,3,4,4‐tetradeutero compound and of an analogous derivative of 11‐dehydrothromboxane B3. Proposed fragmentation pathways are based on internal consistency of data from all four compounds. The migration of a trimethylsilyl or an ethyldimethylsilyl group is the salient feature of all the CAD spectra.
Collisional activation of metal cationized and deprotonated triterpenoids: Charge remote fragmentations
Authors: Madhusudanan K. P. , Singh Chandan
Published: May 2005

The collisional activation spectra of lithiated and bariated cations and deprotonated anions of the triterpenoic acids hederagenin and oleanoic acid and their acctyl derivatives were examined. On collisional activation these precursors undergo similar charge‐remote fragmentations including ring cleavage reactions and loss of substituents from the ring furthest from the site of charge. The presence of a double bond in ring C induces charge‐remote retro‐Diels–Alder reaction in these molecules.
Use of deuterium–hydrogen exchange to characterize the fragmentation pathways of arteether and its metabolites in a thermospray mass spectrometer
Authors: Chi Hsien Tao , Baker John K.
Published: May 2005

Whereas the thermospray mass spectra of most compounds consist of only the pseudo‐molecular ion with little fragmentation, the thermospray mass spectra of arteether (a cyclic endoperoxide) and its metabolites are relatively complex. Assignments of structures to individual fragments from normal spectra was particularly ambiguous because of uncertainties as to which fragments arose from ammonium ion or methanol adducts. In this study, these assignments could be resolved through the comparison of the regular spectrum with the deuterium‐exchange spectrum (in an ND4O2CCH3–CD3OD–D2O mobile phase) achieved using ‘sandwiched slug’ injection technique. The mass spectra of arteether and four of its metabolites all showed [M + ND4]+ pseudo‐molecular ions with greater than 91% H/D exchange, indicating a high efficiency with a minimal use of deuterated mobile phase. Most fragments showed H/D exchange rates in the 70–90% range and the isotope shift of individual spectral lines (ΔM) was found to be extremely useful in determining the structure of the fragment.
Californium‐252 time‐of‐flight mass spectrometry of synthetic porphyrins
Authors: Tarnaud Eric , Robic Nadine , Gaudemer Alain , Bied‐Charreton Claude , Deprun Claude
Published: May 2005

Mass spectra of synthetic porphyrins were recorded using a 252Cf Time‐of‐flight mass spectrometer (TOF 21). They proved to be very useful for obtaining structure probes on porphyrins for which very little information was available owing to the presence of paramagnetic ions or to badly resolved NMR spectra.
Continuous‐flow fast atom bombardment mass spectrometry: A concept to improve the sensitivity
Authors: Hau J. , Schrader W. , Linscheid M.
Published: May 2005

For application of continuous‐flow fast atom bombardment (CFFAB), an ion source for a sector field mass spectrometer was designed which gives improved sensitivity and much better long‐term stability than a source with standard ion optics. The optics are based on two sets of static quadrupoles and a conical ion extraction device. It was shown that the gain in sensitivity has to be assigned mainly to the reduction of the chemical background in the CFFAB mass spectra. The reason for this reduction appears to be the exclusion of matrix fragment ions sputtered from the outer parts of the FAB target, whereas the center is continuously refreshed by the liquid emerging the capillary. The benefits of using this source were demonstrated in the course of the determination of the drug ifosfamide to a level of 1.5 ng cm−3 using selected ion recording and in the analysis of a Gramicidin S sample, where a minor component at a level of ∼1 pmol was detected.
Mechanism of electron impact ionization‐induced halogen elimination from 2‐methyl‐2‐bromosuccinates
Authors: Bornstein D. , Mandelbaum A. , Vidavsky I. , Domon B. , Mueller D. R. , Richter W. J.
Published: May 2005

The electron impact‐induced halogen elimination from 2‐methyl‐2‐bromosuccinates occurs only in the one of the two isomeric methyl ethyl esters in which the ethoxycarbonyl group is remote from the halogen, in analogy with the corresponding previously reported halosuccinates. However, the occurrence of debromination in dimethyl 2‐methyl‐2‐bromosuccinate contrasts with the behaviour of dimethyl bromosuccinate, indicating different mechanisms for this process in the two systems. Collision‐induced dissociation (CID) and deuterium labelling studies led to the conclusion that a hydrogen transfer from the 2‐methyl group to a carbonyl precedes the elimination of Br˙ from dimethyl 2‐methyl‐2‐bromosuccinate, resulting in a protonated dimethyl itaconate structure for the [M – Br]+ ion. An analogous process is the major route leading to [M – Br]+ ion from 1‐methyl‐4‐ethyl 2‐methyl‐2‐bromosuccinate. In this case deuterium labelling and CID measurements indicated a significant contribution of methyl ethyl citraconate and possibly mesaconate owing to partial operation of a mechanism similar to that reported for 1‐methyl‐4‐ethyl 2‐bromosuccinate.
Ion‐pair (X+ + Y−) formation from photodissociation of the interhalogen molecules BrCl, ICl and IBr
Authors: Kaur Devinder , Yencha Andrew J. , Donovan Robert J. , Kvaran Agust , Hopkirk Andrew
Published: May 2005

Excitation functions for both positive and negative ions (X+ + Y−), formed by photodissociation in the vicinity of the onset of molecular ionization, for the jet‐cooled interhalogen systems BrCl, ICl and IBr are reported. The overall shape of the excitation functions indicates that a number of overlapping Rydberg systems are accessed leading to dissociation. From analyses of the ion‐pair excitation functions of the three molecules, by means of simulation calculations, the dominant Rydberg systems involved are found to be X(2Π3/2)cnsσ and X(2Π1/2)cnsσ: other weaker Rydberg systems, with configurations X(2Π3/2)cnpπ, A(2Π3/2)cnpπ, A(2Π1/2)npπ, A(2Π3/2)cnsσ and A(2Π1/2)cnsσ are also found to be present. It is concluded that the formation of ion pairs occurs by the same process in all three interhalogens, i.e. via predissociation of bound Rydberg states by ion‐pair states.
Electron affinities of naphthalene, anthracene and substituted naphthalenes and anthracenes
Authors: Heinis Thomas , Chowdhury Swapan , Kebarle Paul
Published: May 2005

The determination of electron transfer equilibria A− + B = A + B− in the gas phase, with a pulsed‐electron high‐pressure mass spectrometer, leads to ΔG1°, ΔH1°, and ΔS1° values. These can be converted into the free energy, enthalpy and entropy changes, ΔGa°(B), ΔHa°(B) and ΔSa°(B), for the reaction e + B = B−, since the corresponding values for the reference compounds A are known. Results were obtained for 18 substituted naphthalenes, anthracene and substituted anthracenes. The results are compared with some theoretical predictions and the corresponding reduction potentials in solution. Rate constants for 13 exoergic electron‐transfer reactions were also measured. These were found to be close to the ADO collision rates.
Reduced isotopic scrambling in neutralization–reionization mass spectra
Authors: Drinkwater Donald E. , McLafferty Fred W.
Published: May 2005

Facile ion isomerization compromises isotopic position characterization by mass spectrometry, particularly for hydrocarbons. For example, hydrogen atom loss does not provide such characterization for [C6D5CH3]+˙ ions from electron impact ionization of toluene‐ar‐d5, as this loss is preceded by 89% H/D scrambling. Similarly, the corresponding low‐energy molecules formed from these ions by neutralization with Hg yield, on reionization, mass spectra that exhibit 78% scrambling. This is true for reionization to either positive or negative ions, collection of neutralized products scattered at larger angles and after collisional activation of the fast toluene neutral species. However, when these ions are neutralized with Cs vapor to form excited (∼5 eV) toluene molecules, half of the resulting losses occur before H/D scrambling. The resulting neutralization–reionization mass spectra are thus more useful for isomeric isotopic characterization. The method is not effective for ions such as [styrene]+˙ with an isomerization pathway(s) requiring far less energy than that for direct dissociation.
Metastable ion study of organosilicon compounds VI—triethoxymethylsilane and tetraethoxysilane
Authors: Tabei Eiichi , Mori Shigeru , Okada Fumio , Tajima Susumu , Ogino Kazuo , Tanabe Hirotaka , Tobita Seiji
Published: May 2005

The fragmentations of triethoxymethylsilane ((C2H5O)3SiCH3 (1)) and tetraethoxysilane ((C2H5O)4Si (3)) induced by electron impact were investigated by mass‐analysed ion kinetic energy (MIKE) spectrometry and a deuterium‐labelling study. These molecular ions begin to fragment by the loss of methyl, ethyl and/or ethoxy radicals. Almost complete scrambling of methylene hydrogen takes place in these resultant intermediate ions, prior to the elimination of acetaldehyde molecule. The fragmentations of [1]+˙ and [3]+˙ were compared with those of the corresponding carbon analogues, 1,1,1‐triethoxyethane ((C2H5O)3CCH3 (2)) and tetraethoxymethane ((C2H5O)4C (3)), respectively.
Conformational effect on gas‐phase protonation and NH4+ clustering of 1,2‐diols
Authors: Bouchoux Guy , Jezequel Sylvie , Penaud‐Berruyer Florence
Published: May 2005

Ab initio molecular orbital calculations at the MP2/6–31G*//3–21G level are reported on conformers of neutral ethane‐1,2‐diol (ethylene glycol; 1), its protonated from 1H+ and the ammonium adduct [1NH4]+ for an OCCO dihedral angle (θ) of 0–180°. The proton affinity (PA) of 1 was determined in ion cyclotron resonance bracketing experiments to be 820 ± 3 kJ mol−1. An adduct stabilization energy of 134 kJ mol−1 was calculated for [1NH4]+. Total optimization at the 3–21G level of cis‐ and trans‐cyclopentane‐1,2‐diol (2 and 3) and their protonated forms 2H+ and 3H+ showed distorted envelope structures with θ values of 47.2°, 73.4°, 33.0° and 58.0°, respectively. The calculation predicts PA(2) = 845 kJ mol−1 and PA(3) = 815 kJ mol−1.
Estimation of the polarizability of gaseous ions by ion trap mass measurements
Authors: Bortolini O. , Catinella S. , Traldi P.
Published: May 2005

Significant mass displacements from the expected instrumental value have been observed in ion‐trap experiments on several ionic species. This phenomenon has been extensively investigated and interpreted as the result of an interaction between the analyte and the radio‐frequency field present within the ion trap. Depending on the chemico‐physical characteristics of the analytes, deformation of the electron shell and forced alignment of the permanent dipoles may be induced. These two effects can be separated allowing an estimation of the polarizability related to the permanent dipoles for gaseous ions.
Mass spectrometry of transition metal π‐complexes. 40—(η4‐Norbornadiene)‐(η5‐cyclopentadienyl)rhodium derivatives
Authors: Zagorevskii D. V. , Chen Hongwen , Holmes J. L. , Nekrasov Yu. S. , Chizhevski I. T. , Rastova N. V. , Kolobova N. E.
Published: May 2005

Electron impact mass spectra of substituted norbornadienecyclopentadienylrhodium complexes have been studied. The decompositions of molecular ions are (i) metal–ligand bond rupture, (ii) norbornadiene skeleton destruction, (iii) substituent or hydrogen atom elimination from the norbornadiene moiety and (iv) radical or neutral molecule elimination from the substituent(s) on the diene ligand. Norbornadiene ligand loss occurs more easily than loss of the cyclopentadienyl ring. Elimination of C2H2R and C2H3 from the diene ligand leads to the formation of rhodocenium or its corresponding substituted derivatives. It is proposed that bridging CC bond rupture followed by migration of the endo‐H atom around the six‐membered ring precedes the loss of the substituent. Some decomposition pathways of the norbornadiene ligand are explained in terms of specific interaction between the metal atom and substituent.
7H‐benz [kl]acridin‐7‐ylium closed‐shell ion produced from 1,8‐bis(phenylamino)naphthalenes under electron impact: Tandem mass spectrometric structure elucidation
Authors: Rentzea Marina , Rimmler Gösta , Neugebauer Franz A.
Published: May 2005

Not only strongly basic aromatic amines such as ‘proton sponges’ show characteristic [M – Me2NH – H]+ peaks corresponding to cyclization to stable heterocyclic ions under electron impact. The fragmentation of the title compounds, which are weak bases, leads to [M – RNH2 – C6H5]+ heteroaromatic ions. These are the 7‐phenyl‐7H‐benz[kl]acridine radical cation and the delocalized stable 7H‐benz[kl]acridin‐7‐ylium ion as shown by unimolecular metastable ion spectra, collision‐induced decomposition (CID) tandem mass spectrometry (MS/MS) and accurate mass measurements. The high‐collision‐energy CID tandem mass spectra of these ions are perfectly superimposable on those of the ions produced by the reference substance, 7‐phenyl‐7H‐benz[kl]acridine obtained as a by‐product in the Ullmann phenylation of 1,8‐diaminonaphthalene. This combination of MS/MS experiments also provides strong support for the gas‐phase reaction mechanism leading to the benz[kl]acridine ions and for the structures of these ions.
Kinetic energy effects in an ion ensemble subjected to mass‐selective isolation and resonance excitation: A simulation study
Authors: March Raymond E. , Weir Mark R. , Tkaczyk Martin , Londry Frank A. , Alfred Roland L. , Franklin Anthony M. , Todd John F. J.
Published: May 2005

A simulation study is described of the behaviour of ions confined in a quadrupole ion trap during each of two separate operations of a tandem mass spectrometric experiment. The two operations are those of mass‐selective ion isolation and mass‐selective resonance excitation to the point of ion ejection from the ion trap. The method of mass‐selective ion isolation simulated is that of consecutive ion isolation. Simulation data indicate that the collisional history of the ions prior to the isolation process can greatly influence the degree to which ions survive this process. Simulation data for mass‐selective resonance ejection are compared with experimental data obtained with a Finnigan‐MAT ion trap mass spectrometer. In each operation, the facility with which ions absorb energy from the field within the ion trap, whether this field is derived from the R.F. drive potential or a supplementary potential, can determine the extent to which ions are retained within the ion trap during the two mass‐selective operations described.
Tandem mass spectrometer for ion–molecule collision studies
Authors: Ardelean P. , Cuna C. , Ioanoviciu D. , Dunca F. , Malz L. , Petrut M.
Published: May 2005

A variable‐angle tandem mass spectrometer designed and constructed in order to perform angle‐resolved energy distribution experiments required for the investigation of ion–molecule reaction mechanisms is described. The performance of the instrument was tested using the CH4+–CH4 system.
Electron impact mass spectra of polycyclic aromatic compounds with several types of pyridino‐ and benzobenzanthrone skeletons
Authors: Abliz Zeper , Aoki Junji , Ueda Toyotoshi , Kan Teruo , Takekawa Minoru , Iwashima Satoshi
Published: May 2005

Electron impact mass spectra were measured for five isomers of pyridinobenzanthrones and three isomers of benzobenzanthrones. The fragmentation pattern and intensity of M2+, [M – H]+, [M – CO]i+, [M – CO – H(or 2H)]i+ and [M – CO – HCN]i+ (i = 1, 2) ions indicated remarkable differences and very interesting features according to the isomers with or without nitrogen and condensation positions of a pyridino or benzo ring to the benzanthrone skeleton. Further, the competition of decompositions through [M – H]+, [M – CO]+˙ or [M – HCN]+˙ ions was confirmed by the observation of metastable ions and the appearance energies of fragment ions. Interesting observations from these results were expulsion of an H atom in close proximity to the area around an OC group, a weak bonding interaction between sp2 CH and an OC group, inducing specific hydrogen rearrangement, and characteristic charge localization on heteroatoms.
Reactions within and between adjacent dimethylamino groups: Collision‐induced dissociation tandem mass spectrometric study of the 1,9‐bis(dimethylamino)phenalenium cation
Authors: Rentzea Marina , Hofmeister Jörg , Staab Heinz A.
Published: May 2005

The electron impact (EI) ionization‐induced fragmentation pathways of the new 1,9‐bis(dimethylamino) phenalenium cation [1]+ were investigated. The peri‐dimethylamino substituents of [1]+ are incorporated in a trimethine cyanine substructure and show strong steric interactions. A mechanism is proposed for the unusual elimination of CH3NCH2, HN(CH3)2 and (CH3)3N from [1]+ and for the accompanying cyclizations to heterocyclic ions: prior to fragmentation, the intact cation [1]+ rearranges, by reciprocal CH3 and H transfers, to new isomeric cations which decompose subsequently in a characteristic way. A wealth of consistent information on dissociation pathways and fragment structures is provided by collision‐induced dissociation tandem mass spectra, collision‐induced dissociation mass‐analysed ion kinetic energy spectra and exact mass measurements of the salt cation and of its primary fragment ions. The liquid secondary ion mass spectrum of [1]+ is very similar to its EI mass spectrum.
Electron impact mass spectrometry of some 6‐substituted tetrazolo[1,5‐c]pyrimidin‐5(6H)‐ones
Authors: Płaziak Adam S. , Celewicz Lech , Ciszewski Krzysztof , Golankiewicz Krzysztof
Published: May 2005

The electron impact mass spectra of 6‐methyltetrazolo[1,5‐c]pyrimidin‐5(6H)‐one, its 7‐ and 8‐methyl derivatives, three 8‐halo derivatives and two related nucleosides are reported. On the basis of the high‐resolution data and detected metastable ions, the fragmentation routes of their molecular ions are proposed. Coexistence of the tautomeric forms of the title compounds of cyclic (tetrazole) or linear (azide) structure can be suggested owing to the fragmentation pathways identified for the bases. Decomposition of the related nucleosides lies in the breaking of nucleoside bonds to produce the appropriate base and sugar fragments.
Differences in the keto–enol equilibrium of [M + H]+ ions of bupropion formed by electron impact and fast atom bombardment ionization
Authors: Johnson Robert L. , Taylor Lester C. E.
Published: May 2005

The fragmentation of the protonated molecular ion of bupropion produced by collisionally induced decomposition is shown to depend on the ionization method used to form the [M + H]+ ion. The daughter ion products do not depend on the energy of decomposition, i.e. high‐ or low‐energy collisions, but on the ratio of the keto‐enol equilibrium as influenced by the ionization process.
Secondary isotope effects in the mass spectra of C2D5OC2H5 and CD3CH2OC2H5
Authors: Russell Morley E.
Published: May 2005

Secondary isotope effects were examined in the loss of methyl from the molecular ions of C2D5OC2H5 and CD3CH2OC2H5 for ion source processes and collisional activation (CA) processes. In the ion source loss of CH3 was slightly favored over loss of CD3, but in CA the CH3 loss was favored to a much larger extent than expected. A possible explanation is given which invokes an energy distribution function peaked near the appearance energy for the methyl loss process.
Usefulness of field desorption mass spectrometry in determining molecular masses of carotenoids, natural carotenoid derivatives and their chemical derivatives
Authors: Takaichi Shinichi
Published: May 2005

Field desorption (FD) mass spectrometry was applied to the determination of the molecular masses of carotenoids, natural carotenoid derivatives and their chemical derivatives. All the carotenoids examined gave the molecular ion as the base peak with negligible fragment ions. Carotenoid glucoside and its fatty acid monoester were successfully determined without acetylation, whereas carotenoic acids (carboxylate and sulphate) needed to be converted into methyl esters prior to analysis. The applicable ranges of molecular masses and polarity were very wide. In addition, carotenoid glycoside gave only [M]+˙ without [M + H]+˙ and [M + cation]+˙. The numbers of carbonyl groups, primary and/or secondary hydroxyl groups and total hydroxyl groups could be directly determined according to the increase in mass units of the carotenoids after chemical reduction, acetylation and trimethylsilylation, respectively. Owing to the negligible fragment ions, FD analysis was also suitable for carotenoids containing small amounts of impurities or other carotenoids. Hence this technique is useful for determining the molecular masses of carotenoids and the number of modifiable groups in carotenoids.
Simplified electron ejection in Fourier transform ion cyclotron resonance mass spectrometry by suspended trapping
Authors: Cooper Brian T. , Buckner Steven W.
Published: May 2005

Suspended trapping is used to eject electrons in negative‐ion Fourier transform ion cyclotron resonance (FT‐ICR) mass spectrometric experiments. In contrast to electron ejection by resonant excitation of the trapping motion, suspended trapping involves allowing the electrons to escape along the z‐axis (perpendicular to the trap plates) while the trapping potential is briefly removed. The duration of this event is sufficiently short (∼10 μs) so that ion losses are negligible; the overall effect is that of a ‘high‐pass mass filter’. Suspended trapping is simpler to implement and more generally applicable to various cell geometries than resonant electron ejection. The effectiveness of the suspended trapping technique is not compromised by the anharmonicity of the potential well in ‘elongated’ ICR traps, but depends simply on the time it takes the electrons to escape the cell. Finally, a small, positive offset potential (∼+0.25 V) applied to the trap plates during the suspended trapping event increases the efficiency of the ejection.
Collisions of fluorocarbon ions at solid surfaces: Electronic excitation, surface‐induced dissociation and chemical sputtering
Authors: Ast T. , Riederer D. E. , Miller S. A. , Morris M. , Cooks R. G.
Published: May 2005

Collisions of C3F at self‐assembled hydrocarbon, deuterated hydrocarbon and fluorocarbon surfaces yield fragment ions which are characteristics of both electronic excitation and vibrational excitation. Direct electronic excitation is indicated by loss of F˙, which has been shown previously to be diagnostic of this type of excitation process. Electronic excitation is favored by low‐energy collisions at the hydrocarbon surface. Even the change to the corresponding deuterated surface produces a large effect in favor of the normal vibrational excitation process. This change in mechanism with the nature of the target shows up as a dramatic isotope effect in the surface‐induced dissociation (SID) mass spectra. The control over the excitation process exhibited by the effective mass of the target is probably exerted through its effect on the relative velocity of the collision partners. The fluorinated surfce is more effective than the others in conversion of translational into internal energy and in minimizing ion loss through neutralization and other processes which compete with SID. The fluorinated surfaces yield spectra that are largely free from chemical sputtering, a process which occurs even at ultra‐high vacuum for stainless‐steel surfaces which are not rigorously cleaned. The internal energy deposition associated with chemical sputtering increases with increaisng collision energy. Several of the fluorocarbon fragment ions generated from perfluoropropylene have also been examined at self‐assembled monolayer surfaces and they are well behaved in their SID and chemical sputtering reactions. This in contrast to the low efficiency of SID and high sputtering efficiency observed in previous studies at uncharacterized multi‐layer hydrocarbon‐covered surfaces.
Role of different 5‐substituents on the mass spectrometric behaviour of uracil
Authors: Favretto Donata , Traldi Pietro , Celon Eloisa , Resnati Giuseppe
Published: May 2005

The influence of different 5‐substituents on the mass spectrometric behaviour of uracil was systematically studied by means of mass‐analysed ion kinetic energy spectrometry. By applying this technique to the molecular ions and the major primary product ions formed by loss of HNCO, the electron impact‐induced fragmentation patterns of a series of substituted uracils could be elucidated. In addition to the common decomposition processes, distinctive fragmentation routes were identified for some compounds, and a rationale for the observed behaviour is given based on the electronic properties of the substituents.
Elimination of acetic acid from protonated 4,5‐diacetoxyphenanthrene and 2,2′‐diacetoxybiphenyl: An example of an ion chemistry proximity effect
Authors: Orlando M. , George M. , Gross M. L.
Published: May 2005

Protonated 4,5‐diacetoxyphenanthrene and 2,2′‐diacetoxybiphenyl dissociate, owing to the interaction of the two acetoxy groups, by eliminating a molecule of acetic acid. This novel proximity effect, which occurs for a fast atom bombardment‐produced closed‐shell ion, was examined in detail using tandem mass spectrometric methods. This process, which was first observed in the decompositions of acetylated complex natural products such as stentorin and hypericin, may serve as a general process for determining the proximity of hydroxyl groups in polycyclic aromatic compounds.