bluuebunny/crossref_metadata_2025 huggingface dataset:
Oligosaccharide characterizations by fast atom bombardment mass spectrometry. Fragmentation study in relation to the substituent at the reducing end
Authors: Bosso C. , Heyraud A. , Patron L.
Published: May 2005

A systematic investigation of oligosaccharides (cello‐oligosaccharides, malto‐oligosaccharides, their corresponding alditols and methylmaltosides) was undertaken using fast atom bombardment mass spectrometry. Experimental conditions were defined in order to obtain characteristic fragmentation in relation to the structure of the oligomers. The role of substituents at the reducing end in the fragmentation process was demonstrated.
Ion‐Neutral complexes from protonated propyl phenyl ethers. Gas‐phase solvolysis versus elimination‐readdition
Authors: Kondrat Richard W. , Morton Thomas Hellman
Published: May 2005

Ion‐neutral complexes, well attested as intermediates in the expulsion of alkenes from M+⋅ and MH+ ions from primary alkyl phenyl ethers, are shown to intervene in the decomposition of the MH+ ion of a secondary alkyl phenyl ether, (CD3)2CHOPh. Chemical ionization (CI) (methane reagent gas)‐mass‐analysed ion kinetic energy spectroscopy (MIKES) shows ions of both m/z 96 and 97, indicating that the proton deposited by the CI reagent exchanges with the methyl deuterium atoms. The ratio of daughter ion intensities, as well as the proportions of ions of m/z 95, 96 and 97 from the MH+ of CD3CH2CD2OPh, agree with predictions based on the gas‐phase solvolysis mechanism, in which [i‐Pr+ PhOH] complexes form from the protonated parent via simple bond heterolysis. An alternative mechanism, elimination‐readdition, would proceed via [propene PhOHD+] complexes. This latter mechanism predicts a ratio of daughter ion intensities that is very different from gas‐phase solvolysis and which disagrees with experiment. The elimination‐readdition pathway is effectively ruled out, while the gas‐phase solvolysis mechanism is reinforced.
Gas‐Phase ring‐chain tautomerism in 1,3‐oxazines. Does it exist?
Authors: Vainiotalo Pirjo , Fülöp Ferenc , Pihlaja Kalevi
Published: May 2005

Gas‐phase ring‐chain tautomeric equilibria with eight 2‐phenyl‐substituted perhydro‐1,3‐oxazines and six 2‐aryl‐substituted l,2‐dihydro‐4H‐3,1‐benzoxazines were studied by recording their mass spectra Finder different conditions. Their fragmentation behaviour was also studied using metastable ion analysis and exact mass measurement. For the monocyclic compounds the existence of tautomerism was apparent and it resembled that found in non‐polar solvents. In contrast, benzoxazines gave little evidence for the presence of the open‐chain forms.
Factors affecting immonium ion intensities in the high‐energy collision‐induced decomposition spectra of peptides
Authors: Madden T. , Welham K. J. , Baldwin M. A.
Published: May 2005

Each amino acid in a peptide has a characteristic immonium ion (H2N+CHR), the presence of which in a mass spectrum can indicate the presence of that amino acid. High‐energy collision‐induced decomposition studies on small peptide ions formed by fast atom bombardment showed the relative intensities of these immonium ions to be dependent on the relative positions of the amino acids in the peptide chain: C‐terminal, N‐terminal or in‐chain. Evidence in favour of competition in the formation of immonium ions is presented.
Evaluation of nitric oxide chemical ionization mass spectra of substituted benzenes
Authors: Daishima Shigeki , Lida Yoshio , Kanda Fujihiro
Published: May 2005

Nitric oxide chemical ionization mass spectra of substituted benzenes obtained with the Townsend discharge technique were studied. There were four kinds of base peaks in the mass spectra, i.e. [M + NO]+˙, M+˙, [M − H]+ and [M − OR]+ (R = H, CH3). The formation of the specific ion [M + NO]+˙ was highly dependent on the kind of substituent, and it was produced more abundantly in the case of substitutions involving electron‐accepting groups. The measure of [M + NO]+˙ production was evaluated from the value of the ratio [M + NO]+˙/M+˙. In mono‐substitutions, it was clarified that the ratios of [M + NO]+˙/M +˙ were correlated with the Hammett substituent constant s̀p or the electrophilic substituent constant s̀p+. Monosubstitutions (C6H5R) and toluene substitutions (CH3C6H4R) could be classified into six groups in terms of base peak species, [M + NO]+˙/M+˙ ratios and substituents. In disubstitutions, the mass spectral patterns were governed by the combination of substituents. Mass spectral distinctions among ortho, meta and para isomers could be made in many cases.
Novel fragmentation of N‐diisopropyloxyphosphoryl dipeptides and tripeptides by fast atom bombardment mass spectrometry
Authors: Zhao Yu‐Fen , Zhang De‐Qing , Xue Chu‐Biao , Zeng Jia‐Ning , Ji Gai‐Jiao
Published: May 2005

Positive ion fast atom bombardment mass spectrometry of N‐diisopropyloxyphosphoryl dipeptides and tripeptides showed a novel cleavage pattern in that only the N‐phosphoryl fragment ions gave intense peaks while the C‐terminal series of ions was suppressed. The base peak was the N‐phosphoryl imino ion responding to the N‐terminal residue. These advantages are superior to those of other types of N‐protecting groups.
Site of gas‐phase methylation of l‐phenyl‐2‐aminopropane
Authors: Zagppey Herman , Fokkens Roel H. , Ingemann Steen , Nibbering Nico M. M. , Florencio Helena
Published: May 2005

The regioselectivity of methyl cation transfer from (CH3)2F+, (CH3)2Cl+ and (CH3)3O+ to 1‐phenyl‐2‐aminopropane was studied by Fourier transform ion cyclotron resonance in combination with collision‐induced dissociation and neutralization‐reionization mass spectrometry of the stable [M + CH3]+ ions formed in a chemical ionization source. The (CH3)2F+ ion transfers a methyl cation to the NH2 group and the phenyl ring with almost equal probability. Predominant CH3+ transfer to the NH2 group is observed for the (CH3)2Cl+ ion whereas the (CH3)3O+ ion reacts almost exclusively at the amino group. The preference for methylation at NH2 is discussed in terms of a lower methyl cation affinity of the phenyl ring than of the amino group and the existence of an energy barrier for methylation of the phenyl moiety.
A study of some imidazo[l,5‐a]benzodiazepin‐6‐ones by electron impact mass spectrometry. characterization by tandem mass spectrometry of a distonic fragment ion
Authors: Rubino Federico Maria , Zecca Luigi , Mascaro Paolo , Hunkeler Walter
Published: May 2005

The mass spectra of several imidazo[l,5‐a]benzodiazepin‐6‐one derivatives of neuropharmacological significance were determined in order to establish their decomposition paths under electron impact. A novel distonic fragment ion was observed and it was possible to demonstrate by consideration of metastable ions and by tandem mass spectrometry that it undergoes isomerization to the corresponding classical structure.
Improved tuning and calibration in liquid chromatography/thermospray mass spectrometry using acetic acid cluster ions
Authors: Saar Jacob , Haimberg Marcela
Published: May 2005

Tuning and calibration of a thermospray ion source can cause rapid contamination of the source, and can have the disadvantage of introducing substances or solvents that are not used in the subsequent analytical work on the mass spectrometer. The use of aqueous 0.05 M ammonium acetate alone to produce acetic acid clusters for calibration in the mass range up to m/z 800 is reported. A low temperature of the vaporizer and the source block is used in order to maintain the clusters formed. The low temperature makes possible a very good signal‐to‐noise ratio, since the only ions formed are clusters of the general formula [(CH3COOH)m(NH3)n(H2O)pNH4]+. Owing to the use of the ammonium acetate mobile phase, no interference from other sources was observed, e.g. clusters of solvents with ammonium acetate or impurities.
Structural characterization of isomeric triazolocoumarins by high‐ and low‐energy collision spectrometry of M+˙, [M + H]+ and [M − H]− species
Authors: Evans C. , Traldi P. , Chilin A. , Pastorini G. , Rodighiero P.
Published: May 2005

Two monometayl‐ and four dimethyl‐triazolocoumarin isomers were characterized by their electron impact mass spectra and by low‐energy collision experiments performed on molecular ions M+˙ and other fragment ions with an ion‐trap mass spectrometer. High‐energy collision‐activated dissociation measurements were performed on the protonated [M + H]+ and deprotonated [M − H]− molecular ion obtained by fast atom bombardment and M+˙ species produced by electron impact ionization on a double‐focusing, reverse‐geometry instrument. The data obtained allowed unequivocal structural identification of all the compounds investigated.
Mass spectra of some 2‐(p‐R2‐phenyl)‐indole‐3‐carboxaldehyde derivatives
Authors: Cortés C. Eduardo , Martinez Roberto , Gomez Martha B. Gutierrez
Published: May 2005

The mass spectra of eight new substituted 2‐(p‐R2‐phenyl)‐indole‐3‐carboxyaldehydes which have potentially useful pharmacological properties, are presented.
A McLafferty rearrangement in an even‐electron system: C3H6 elimination from the α‐cleavage product of tri‐n‐butylamine
Authors: Budzikiewicz Herbert , Bold Peter
Published: May 2005

It is shown by deuterium labelling, linked‐scan measurements and collision activation that the [M‐C3H7˙]+ (α‐cleavage) ion in the electron impact ionization spectrum of tributylamine loses C3H6 with transfer of one hydrogen specifically from the γ‐position. The experimental data point towards a mechanism which involves the intermediate formation of a distonic diradical ion from an excited α‐cleavage ion which then eliminates the neutral alkene.
Evidence that gas‐phase ion‐molecule reactions are responsible for the behaviour of crown ethers under fast atom bombardment conditions
Authors: Curcuruto Ornella , Traldi Pietro , Moneti Gloriano , Corda Luciana , Podda Gianni
Published: May 2005

The fast atom bombardment mass spectrometry of some crown ethers shows the formation of both [M + H]+ and [M − H]+ ions, paralleling behaviour already observed using electron impact ionization. The study of these oily samples with and without a glycerol matrix, trifluoroacetic acid or alkali metal salts, suggests that the ionization process does not occur in the condensed phase, but in the selvedge region by gas‐phase ion‐molecule reactions in accordance with the ‘gas‐phase explosion model’. Positive‐ion chemical ionization experiments support this proposal.
Caesium fluoride as a mass calibrant in fast atom bombardment mass spectrometry
Authors: Rubino F. M.
Published: May 2005

Caesium fluoride was shown to afford advantages over caesium iodide as a mass‐calibration compound for fast atom bombardment mass spectrometry.
Relative intensities of metastable peaks measured with B/Elinked scan and metastable defocusing techniques
Authors: Rashkes Yakov W. , Sirotenko Elena G. , Milgrom Yurij M.
Published: May 2005

The ratios (A) of metas table‐ and parent‐ion peak heights measured by me testable defocusing and the B/E inked scan technique have the same order of magnitude. This was established for the M+ → [M ‐ 15]+ and M+ → [M − OR1]+ (R1 = H, Me, Ac) transitions in the mass spectra of diterpene alkaloids with a licoctonine skeleton. The A values were demonstrated to depend on the position of the eliminated group in the parent molecule. The A values can also be employed as a criterion for the identification of daughter‐ion reaction configurations.
Mass spectra of N‐arylaminosulphonylcarbethoxydiazoacetamides
Authors: Lebedev Albert T. , Bakulev Vasily A. , Kolobov Mikhail Yu.
Published: May 2005

The electron impact mass spectra of N‐arylaminosulphonylcarbethoxydiazoacetamides were studied. On the basis of high‐resolution mass spectrometric data, mass‐analysed ion kinetic energy Spectrometry and linked scan experiments a detailed scheme of the fragmentation is proposed. A number of possibilities of charge Iocalization are revealed in the complex decomposition processes of the molecular ions.
Thermal effects on the mass spectra of benzophenone oximes obtained by gas chromatography/electron ionization mass spectrometry
Authors: Ma Yee‐Chung , Munson Burnaby
Published: May 2005

Benzophenone oxime and substituted benzophenone oximes can be pyroiyzed to the imines to a small extent in the heated transfer line from the gas chromatograph to the mass spectrometer source and to a large extent in the hot injection port of a gas chromatograph at high temperatures using the splitless mode of sample injection. The pyrolysis of the oximes to the imines appears to be largely a surface reaction and does not form the benzophenones as pyrolysis products. Decomposition of benzophenone oxime to benzophenone was produced by another reaction at the front of the chromatographic column. Thermal isomerizaton of benzophenone oxime to benzanilide was not observed under these conditions.
Mass spectrometry of pyrimidine derivatives: Electron impact‐induced decomposition of molecular ions of 4‐amino‐substituted and 4‐amino‐disubstituted 1,2‐dihydro‐1‐methylpyrimidin‐2‐ones
Authors: Plaziak Adam S. , Celewicz Lech , Ciszewski Krzystof , Golankiewicz Krzysztof
Published: May 2005

Electron impact (EI) mass spectra of fourteen 4‐amino‐substiruted 1,2‐dihydro‐1‐methylpyrimidin‐2‐ones are reported. The EI‐induced decomposition of their molecular ions is significantly dependent on the chemical nature of the substituents. The routes of mass decomposition established suggest the presence of the tautomeric forms in the gas phase of some investigated compounds.
Mass spectra of picolinic, nicotinic and isonicotinic acids and of their respective N‐oxides
Authors: de Oliveira Silvana M. , de Giovani Wagner F. , Romero José Ricardo , Miller Joseph
Published: May 2005

Mass spectra of picolinic, nicotinie and isonicotinie acids and of their respective N‐oxides are presented. Picolinic acid and its N‐oxide demonstrate the facile loss of carbon dioxide and low‐intensity molecular ions. Fragmentation is relatively simple. Nicotiuic and isonicotinic acids show very similar fragmentation patterns. For both, the molecular ion is the base peak. The fragmentations of nicotinic acid N‐oxide and of isonicotinic acid N‐oxide are more complex than those of the previous four compounds, but are similar to each other.
Time‐dependence of the isotope effects in the unimolecular dissociation of tertiary amine molecular ions
Authors: Ingemann Steen , Kluft Els , Nibbering Nico M. M. , Allison Colin E. , Derrick Peter J. , Hammerum Steen
Published: May 2005

The intramolecular secondary isotope effects on the α‐cleavage of deuterium‐labelled N‐methyldipentylamine radical cations have been studied as a function of ion lifetime by field ionization kinetics. The isotope effects observed are all normal and increase in magnitude with increasing ion lifetime, with the exception of the δ‐labelled compound which shows an inverse effect (predominant loss of the labelled radical) at times shorter than 10−9 s, and a normal effect at longer times. The isotope effects reflect differences in zero‐point energies of the transition states as well as the influence of slight reductions of isotope‐dependent frequencies on the state sums–a statistical weight effect. The latter is particularly important at high ion energies and is the primary reason for the occurrence of the inverse isotope effect. The time dependence of the normal and inverse isotope effect is reproduced by QET/RRKM calculations.
Electron impact mass spectra of some dioximes of o‐diacyl benzenes
Authors: Kotali Antigoni
Published: May 2005

The electron impact mass spectra of the new synthesized dioximes of o‐diacyl benzenes (2) are reported. In addition to the molecular ion, characteristic peaks appear at values corresponding to the [M − OH] +, [M − NOH]+ and [M − NHOH]+ ions. No initial dehydration of the molecular ion has been observed.
Use of bond orders and valences for the description and prediction of primary fragmentation processes
Authors: Somogyi Árpád , Gömöry Ágnes , Vékey Károly , Tamás József
Published: May 2005

Some approaches and examples are shown to demonstrate the usefulness of inherently ‘classical’ parameters, such as bond orders and valences derivable from quantum mechanical wavefunctions, in the description and prediction of mass spectral primary fragmentation processes.
Fast atom bombardment mass spectrometry of ionic gold(I) and gold(III) carbene derivatives: An investigation of the formation of [M – H]+ species
Authors: Banditelli G. , Bandini A. L. , Pacchioni G. , Minghetti G. , Seraglia R. , Traldi P.
Published: May 2005

Fast atom bombardment (FAB) mass spectrometry of the gold(I) and gold(III) derivatives, {Au[C(Y)–NHAr]2}+X− and {Au[C(Y)–NHAr]2I2} + X− (Y =OC2H5 or NHAr; X− = CIO4− or BF4−; Ar = p‐CH3C6H4) has led to the detection, for the alkoxyamino derivatives only, of [M–H]+˙ molecular species. The mechanism of the formation of these unusual species has been studied with respect to the oxidation state of gold, nature of the matrix, matrix acidity and ligand structure. The energetics of two possible alternative mechanisms has been studied by means of ab initio theoretical calculations. Both experimental and theoretical data indicate that [M–H]+˙ formation is due to the reaction of M+ with H+‐philic and/or H˙‐philic species produced from the matrix by FAB. Whatever the operative mechanism, the [M–H]+˙ formation is to be considered a FAB‐induced oxidative process.
Stereochemical studies by mass spectrometry: C15Nuphar alkaloids
Authors: Bortolini O. , Fantin G. , Curcuruto O. , Traldi P. , Iwanow A. , Wróbel J. T.
Published: May 2005

Representative C15 Nuphar alkaloids, containing the quinolizidine system, were studied by high‐resolution mass spectrometry and metastable‐ion decomposition analysis. The appearance with N‐oxide species of ions at m/z 168, useful in ascertaining the stereochemistry of the quinolizidinic ring junction, are also discussed.
Electron impact mass spectrometric investigation of pyrrole mono‐, di‐ and tri‐carboxylic acids
Authors: Costa Carlo , Bertazzo Antonella , Allegri Graziella , Catinella Silvia , Traldi Pietro
Published: May 2005

The electron impact‐induced fragmentation processes of pyrrole‐2‐, ‐3‐, ‐2,3‐, ‐3,4‐, ‐2,5‐ and ‐2,3,4‐carboxylic acids were investigated with the aid of metastable ion, collisional and deuterium labelling experiments. The general behaviour of these compounds is discussed in detail, together with the reasonable structures of the more relevant fragment ions.
Mass spectrometry in stereochemical problems. 6 — The case of mono and di‐substituted norbornanes
Authors: Curcuruto O. , Favrctto D. , Traldi P. , Ajo D. , Cativiela C. , Mayoral J. A. , Lorez M. P. , Fraile J. M. , Garcia J. I.
Published: May 2005

The mass spectrometric behaviour of pairs of stereoisomeric mono‐ and di‐substituted norbornanes, namely bicyclo[2.2.1]heptane‐2‐endo‐ and ‐exo‐carboxylic acid, methyl bicyclo[2.2.1]heptane‐2‐endo‐ and ‐exo‐carboxylate, 2‐exo‐acetamidobicyclo[2.2.1]heptane‐2‐endo‐ and 2‐endo‐acetamidobicyclo[2.2.1]heptane‐2‐exo‐carboxylic acid and methyl 2‐exo‐acetamidobicyclo[2.2.1]heptane‐2‐endo‐ and 2‐endo‐acetamido‐bicyclo[2.2.1]heptane‐2‐exo‐carboxylate was studied in detail with particular emphasis on characterization of the stereoisomers. The fragmentation patterns, studied with the aid of mass‐analysed ion kinetic energy spectrometry, were supported by semi‐empirical MO–SFC calculations, performed using the AM1 method included in the AMPAC program.
Dissociative charge exchange of C3F6
Authors: Habibi‐Goudarzi Sohrab , Kotiaho Tapio , Cooks R. G. , Ast T.
Published: May 2005

Charge exchange of neutral C3F6 by a variety of atomic and molecular ions in the 1 to 25 eV range of collision energies is used to characterize the energies associated with formation of [C3F6]+˙. The internal energy of the nascent [C3F6]+˙ ion, assessed by observing the degree to which it fragments, increases with the recombination energy of the charge‐exchange reagent. The existence of excited states of the reagent ions is identified from the fragmentation behaviour of [C3F6]+˙ in the cases of [CS2]+˙, NO+, O2+˙, [NH3]+˙ and possibly [CH4]+˙. In addition, the data confirm that the [C3F6]+˙ parent ion fragments from both the ground state and a long‐lived isolated electronic state. The latter is populated by near‐resonant charge transfer. Translational excitation contributes relatively little to internal excitation of the charge‐exchanged product ion and even less in the case of the isolated state.
Aryl cations: Searching for and assigning structures to [C7H5]+ isomers
Authors: Bissonnette Martine C. , George M. , Holmes John L.
Published: May 2005

The energetics and mass spectral characteristics of a number of [C7H5]+ ions have been examined. No compelling evidence could be found to show that the 2‐cyclopropaphenyl cation was produced by loss of bromine from the ionized 2‐bromo derivative. It was proposed that the ethynylcyclopentadienyl cation may be the global minimum on the [C7H5]+ hypersurface.
Interannular proton exchange and fragmentation of carbonyl‐protonated benzophenones
Authors: Sun Jing , Grützmacher Hans‐Friedrich
Published: May 2005

Benzopbenones a initially protonated at the carbonyl group were prepared by electron‐impact induced dissocation of 1,1‐diphenylpropanols (compounds 1‐5). These protonated ketones decompose in the ion source and the second field‐free region of a reversed geometry mass spectrometer by proton migration to one of the phenyl groups and subsequent elimination of benzene. In the case of derivatives substituted by methoxy groups and trifluoromethyl groups respectively, the proton migrates predominantly to the more bask benzene ring, resulting in the elimination of anisole in the former case and of benzene in die latter case. A study of protonated benzopbenones labelled at the phenyl ring and at the carbonyl group shows that only a few interannular H/D exchange steps precede the fragmentation. This is observed not only for metastable ions in the magnetic sector instilment but also for ions of long lifetimes investigated by Fourier‐transform‐ion cyclotron resonance (FT‐ICR) Spectrometry. This is in contrast to the arene elimination from protonated 1,ω‐dipbenylalkanes and related polyphenylalkanes which fragment by complete positional exchange of all hydrogen atoms at the aromatic rings. The special behaviour of protonated benzophenones is attributed to a low barrier for the decomposition of a chemically activated arenium ion b, which arises from the initial proton transfer. Once b is formed, it decomposes quickly without much interannular proton exchange.
Investigation of aliphatic dienes by chemical ionization with nitric oxide
Authors: Budzikiewicz H. , Blech St. , Schneider B.
Published: May 2005

It is shown that the position of the double bond close to the hydrocarbon end of an aliphatic diene functionalized at C(1) can readily be determined by chemical ionization with NO+. Owing to the low abundance of the ions characteristic for the position of the other double bond, its localization may be difficult. Measurement of the chemical ionization (nitric oxide as reagent gas) spectra of the corresponding epoxides or collision activation studies can help.
Characterization of synthetic N‐acetylcysteine conjugates by positive‐ and negative‐ion 252Cf plasma desorption mass spectrometry
Authors: Pittenauer Ernst , Pachinger Anton , Allmaier Günter , Schmid Erich R.
Published: May 2005

N‐Acetylcysteine and nine N‐acetylcysteine conjugates of synthetic origin were characterized by positive‐ and negative‐ion plasma desorption mass Spectrometry. For sample preparation the electrospray technique and the nitrocellulose spin deposition technique were applied. The fragmentation of these compounds, which are best seen as S‐substituted desaminoglycylcysteine dipeptides, shows a similar behaviour to that of linear peptides. In the positive‐ion mass spectra intense protonated molecular ion peaks are observed. In addition, several sequence‐specific fragment ions (A+, B+, [Y + 2H]+, Z+), immonium ions (I+) and a diagnostic fragment ion for mercap‐turic acids (RM+) are detected. The negative‐ion mass spectra exhibit deprotonated molecular ions and in contrast only one fragment ion corresponding to side‐chain specific cleavage ([RXS]−) representing the xenobiotic moiety. In the case of a low alkali metal concentration on the target, cluster molecular ions of the [nM + H]+ or [nM ‐ H]− ion type (n = 1‐3) are observed. The analysis of an equimolar mixture of eight N‐acetylcysteine conjugates shows different quasi‐molecular ion yields for the positive‐ and negative‐ion spectra.
Temperature effects in mass spectrometry. Estimation of thermal energies of organic molecules
Authors: Turecek Frantisek
Published: May 2005

Thermal energies of gaseous organic molecules, relevant to unimolecular dissociations of odd‐ and even‐electron ions, are estimated by ab initio/RRHO and empirical calculations. Thermal energies can be estimated with good accuracy by integration of molar heat capacities obtained from quadratic least‐squares fits. Thermal energies in gaseous n‐alkanes, alkanols, cholesterol, polyethylene glycols and oligopeptides are calculated and compared with estimates based on the equipartition principle.
Mass spectra of some 2‐(o‐R1‐phenyl)‐indole‐3‐carboxaldehyde derivatives. II
Authors: Cortés C. Eduardo , Martínez Roberto , Ramírez José I.
Published: May 2005

The electron impact mass spectra of thirteen new substituted 2‐(o‐R1‐phenyl)‐indole‐3‐carboxaldehydes which have potentially useful pharmacological properties, ate presented.
Measurement of initial translational energies of peptide ions in laser desorption/ionization mass spectrometry
Authors: Pan Ying , Cotter Robert J.
Published: May 2005

The initial kinetic energy distribution of [Arg]‐vasopressin molecular ions generated by matrix‐assisted UV laser desorption/ionization was measured using a delayed ion extraction, linear time‐of‐flight mass spectrometer. Energy distributions of the nicotinic acid matrix ions, with or without the presence of peptide, were also measured. These were compared with the kinetic energy distribution of gramicidin‐S ions using IR laser desorption. The measured molecular ion kinetic energy distribution from vasopressin is much broader than that from gramicidin‐S, and is characterized by a high‐energy tail that most likely results from entrainment of anlayte ions in the higher velocity matrix ions and fragments as they leave the surface.
Examination of Ortho effects in the collisionally activated dissociation of closed‐shell aromatic ions
Authors: Donovan Tracy , Brodbelt Jennifer
Published: May 2005

The collisionally activated dissociation of a variety of isomeric disubstituted aromatic ions formed by ion–molecule reactions were examined in order to characterize ortho effects in closed‐shell systems. Closed‐shell ions of methoxyacetophenone, hydroxyacetophenone, methoxyphenol, anisaldehyde and hydroxybenzaldehyde were formed by proton transfer, methyl addition or methyne addition by using dimethyl ether or ethylene oxide as chemical ionization reagents, and then the structures of these adducts were studied by deuterium‐labelling methods and by collisionally activated dissociation techniques in a triple quadrupole mass spectrometer or a quadrupole ion trap. Typically, the meta and para isomers have qualitatively similar dissociation spectra which reflect the types of dissociation reactions observed for the corresponding monosubstituted aromatic ions. The predominant dissociation pathways of the [M + H]+ and [M + 15]+ ions are directed by the electron‐withdrawing substituents, whereas the major dissociation pathways of the [M + 13]+ ions are related to the electron‐releasing substituent. In contrast, the dissociation routes of the corresponding ortho isomers are dramatically different. This is attributed to the opportunity for functional group interactions of the ortho isomers which facilitate alternative pathways.
Electron impact mass spectra of 1‐methyl‐3‐(2‐benzothiazolylhydrazono)‐2‐indolinones
Authors: Varma R. S. , Singh A. P. , Singh S. P.
Published: May 2005

A study of the fragmentation of l‐methyl‐3‐(2‐benzothiazolylhydrazono)‐2‐indolinones on electron impact reveals that the major processes involve NN bond fission and the competing loss of CO from the molecular ion.
Studies in organic mass spectrometry. 12–Electron impact ionization mass spectra of some 3‐nitropyrroles
Authors: Ceraulo Leopoldo , Ferrugia Mirella , Sprio Vincenzo
Published: May 2005

The positive‐ion electron impact ionization mass spectra of eight substituted 3‐nitropyrroles were examined. The major fragment ions arise by ortho interactions between the 3‐nitro group and the 2‐methyl or 2‐aryl group.
Electron impact mass spectrometry of diethyl 2‐oxysubstituted alkylphosphonates—a remarkably regiospecific α‐cleavage
Authors: Modro T. A. , Mphahlele M. J.
Published: May 2005

The major electron impact induced fragmentation of 2‐hydroxyphosphonic esters, XCH2CH(OH)CH2PO3Et2 (and their O‐derivatives) involves the C(2)–C(3) α‐cleavage, yielding the XCH2· radical and the oxocarbonium ion, +HO = CHCH2PO3Et2. No evidence for a competitive C(1)–C(2) α‐cleavage was obtained, and the results suggest a stabilizing effect of the phosphonyl group on the α‐oxocarbonium system.
Mass spectrometric differentiation of huperzinine, N,N‐dimethylhuperzine A and N‐methylhuperzine B
Authors: Hu Peifeng , Cross Michael L. , Yuan S. Q. , Wei T. T. , Lu Y. Q.
Published: May 2005

The newly isolated Lycopodium alkaloids huperzinine, N,N‐dimethylhuperzine A and N‐methylhuperzine B were studied by high‐resolution and tandem mass Spectrometry. Differentiation of these subtly different isomers from each other and from the general class of Lycopodium alkaloids can be achieved by taking advantage of the structure‐specific fragment ions formed upon electron ionization (El) or collisional activation of these alkaloids. β‐Obscurine was identified as an impurity component in the N‐methylhuperzine B sample and contributed to the El mass spectrum. The previously published El mass spectrum of N‐methylhuperzine B is likely to be that of a mixture of N‐methylhuperzine B and β‐obscurine. The presence of the impurity can now be readily recognized on the basis of two characteristic fragment ions of m/z 215 and 187.
Gas‐phase reactions of mono‐ and dichlorophenols
Authors: Mattina M. J. Incorvia , Sears L. J.
Published: May 2005

Reactions occurring within the high‐pressure mass spectrometer source during argon‐enhanced negative‐ion mass Spectrometry (NIMS) of mono‐ and dichlorophenols result in the formation of adduct ions. The reactants for the formation of the adduct ions are derived solely from the chlorophenol. High‐resolution accurate mass ‐measurements of the adducts and comparison of the argon NIMS of the phenols with the argon‐enhanced NIMS of authentic chlorinated phenoxyphenol and dichlorodioxin suggest that gas‐phase intermolecular and intramolecular nucleophilic substitutions are occurring. The products of the source reactions reflect the stability of the gas‐phase species involved and may be compared with the photolysis and pyrolysis reaction products of chlorophenols, chlorinated phenoxyphenols and chlorophenates reported in the literature.
Electron impact mass spectra of enamine esters, ketones and nitriles
Authors: Ayyangar N. R. , Lahoti R. J. , Daniel Thomas , Sudalai A.
Published: May 2005

The behaviour of some enamine‐esters, ‐ketones and ‐nitriles under electron impact has been investigated by means of low‐resolution mass Spectrometry.
Mass spectrometric studies of phosphodiesters linked to oxysterols and nucleosides, a family of biologically potent oxygenated sterols
Authors: Pannecoucke Xavier , Dorsselaer Alain Van , Luu Bang
Published: May 2005

Negative‐ion fast atom bombardment mass spectra of five compounds resulting from combinations between oxysterols and nucleoside analogues linked by phosphodiester bonds are presented and interpreted. This method seems to be the most appropriate for elucidating the structure of these complex, labile and non‐volatile phosphate‐containing molecules which exhibit important antitumour and/or immunosuppressive activities.
Ion‐trap detector electron impact mass spectrometry: Practical considerations
Authors: Vella Alfred J.
Published: May 2005

An investigation of the quality of mass spectra obtainable by the Finnigan ion‐trap detector (ITD) and on how this quality may depend on sample size is described. For compounds which are not very thermolabile or too prone to fragmentation, near‐normal spectra can be expected if the sample sizes do not exceed amounts of the order of 100 ng. Analyte loads which generate acceptable total ion current chromatograms with narrow‐bore capillary columns (about 500 ng) could still produce ITD mass spectra having enhanced quasi‐molecular ions, [M + 1]+, abnormal distributions of peak intensities and unusual fragments. Even under optimum conditions, certain analytes, e.g. acyclic alkanes, n‐alkanols and pyridines, will manifest spectral characteristics which are strictly typical of the ITD. In favourable cases, the formation of quasi‐molecular ions can be exploited for relative molecular mass determination. Even under conditions of self‐chemical ionization, the ITD spectra of most analytes generally retain enough electron impact mass spectral character to be readily recognizable by inspection or by library algorithms.
Characterization of phospho‐proteins in bovine and buffalo caseins using atmospheric pressure ionization mass spectrometry
Authors: Casetta Bruno , Bonner Ron , Shushan Bori , Fior Gianni
Published: May 2005

The specific bovine and buffalo caseins have been characterized with the aim of using atmospheric pressure ionization mass spectrometry as an alternative to electrophoretic and immunological methods in the detection of the fraudulent addition of bovine milk to buffalo milk used in the production of speciality cheeses.
Experimental investigation of double ionization to ground and electronically excited states of chlorobenzene, 1,2‐, 1,3‐ and 1,4‐dichlorobenzene, 1,2,3‐, 1,2,4‐ and 1,3,5‐trichlorobenzene, 1,2,3,4‐and 1,2,4,5‐tetrachlorobenzene and pentachlorobenzene dications
Authors: Harris F. M. , Jackson P. J. , Rontree J. A. , Griffiths W. J.
Published: May 2005

Double‐charge‐transfer spectrometry was used to measure double‐ionization energies to ground and electronically excited states of various chlorobenzenes. Since OH+ was the projectile ion used in these experiments, it is probable that triplet states of the dications were populated because of spin conservation in the double‐electron‐capture reactions which are the basis of this type of spectrometry. The lowest double‐ionization energies for all the molecules studied are within ±0.3 eV of 25.9 eV, except that for 1,3‐dichlorobenzene, which is at 26.6 eV. In general, double‐ionization energies to three higher lying states (or groups of states) were measured for each molecule. The energies of these states are the same, within experimental uncertainties, for the three trichlorobenzenes, two tetrachlorobenzenes and pentachlorobenzene dications, suggesting that they have the same or very similar distributions of triplet‐state energies.
Time‐dependent mass spectra and breakdown graphs: 15—toluene‐d8
Authors: Ohmichi N. , Gotkis I. , Steens L. , Lifshitz C.
Published: May 2005

The ion storage time in the cylindrical trap of a pbotoionization mass spectrometer has been extended to ∼500 ms. Time‐resolved photoionization efficiency (PIE) curves were meaured for [C7D8]+ and [C7D7]+ for toluene‐d8 and for the ion‐molecule reaction product [C8D9]+. PIE curves were modeled by k(E) dependences via RRKM/ QET calculations based on a model by Huang and Dunbar, with critical energy E0 = 2.13 eV and a 1000 K activation entropy ΔS≠ = −14.6 e.u. No energy range was found, even under long storage times, for which [C7D7]+ is pure tropylium, Tr+. The results are interpreted via the case C behaviour in isomerizing ions, due to Baer and co‐workers, according to which Tr+ and [benzyl]+, Bz+, are formed at equal rates for energies in excess of both of their dissociation limits. Dissociation is suppressed at internal energies lower than ∼2.S eV due to radiative decay in the infrared region. Dissociations observed at photon energies lower than ∼11.3 eV (8.8 eV ionization energy +2.5 eV internal energy) are ascribed to the offsetting effects of an intrinsic kinetic shift of ∼0.4 eV and the thermal energy distribution in the molecular ions.
Unusual fragmentation of 1,1,2,2,3,3‐hexamethylindan. Methyl group equilibration and multi‐step skeletal rearrangements in the [M  CH3]+ ions prior to the formation of t‐C4H9+ and other fragment ions
Authors: Kuck Dietmar , Mehdizadeh Ahmad
Published: May 2005

Based on the surprising observation of an intense C4H9+ (m/z 57) peak in the electron impact mass spectrum, the fragmentation of 1,1,2,2,3,3‐hexamethylindan (2) was studied by mass‐analysed ion kinetic energy Spectrometry of its deuterium‐labelled analogues. While methyl loss from ions [2]+˙ occurs with high selectivity (92%) from the positions 1 and 3 without any rearrangement, ions [2  CH3]+ undergo complete equilibration of the five methyl groups as intact entities. Subsequent multi‐step skeletal rearrangement of the [2 ‐ CH3]+ ions leads to formation of ferf‐butyl ions and to the loss of isobutene and propene, again without concomitant hydrogen exchange. Several kinetic isotope effects and also probably a thermodynamic isotope effect associated with each of these fragmentation processes have been found and their origin is discussed. The possibility of the formation of ion‐neutral complexes [t‐C4H9+ C10H10] aud [s‐C3H7+ C11H12] is considered on the basis of the labelling and reactivity pattern.
Some aspects of isobutane and ammonia chemical ionization for the analysis of volatile esters and phenylpropanoids occurring in essential oils
Authors: Lange G. , Schultze W.
Published: May 2005

The fragmentation reactions of some terpenoid esters and pbenylpropanoids under the conditions of isobutane and ammonia chemical ionization (CI) arc discussed. The esters show different behaviour with these two gases with respect to determination of the relative molecular mass and information about the structure of the molecules. The structural isomers of the phenylpropanoids can unequivocally be distinguished with both isobutane and ammonia CI. Cis/trans isomers of the phenylpropanoids show virtually identical CI spectra.
Fragmentation behaviour of alkylated thiophene‐1,1‐dioxides,
Authors: Budzikiewicz H. , Lange D.
Published: May 2005

It is shown that thiophene‐1,1‐dioxides carrying an alkyl chain in the 2‐ and 3‐positions can be readily distinguished by the characteristic fragmentation mode of the latter, viz. benzylic cleavage of the side‐chain with back‐transfer of two hydrogen atoms ([M  ˙CnH2n−1]+). By deuterium labelling it is shown that the migrating hydrogens come very specifically from the γ‐ and δ‐positions. Since alkylated thiophenes are important geological markers, a ready differentiation of the two types by gas chromatography/mass spectrometry is possible in this way.
Characterization of Z‐blocked isomeric dipeptides by fast atom bombardment tandem mass spectrometry and kinetic energy release measurements
Authors: Mammoliti Ezio , Sindona Giovanni , Uccella Nicola
Published: May 2005

Fast‐ and slow‐reacting, protonated, Z‐blocked (Z = benzyloxycarbonyl) phenylalanylphenylalanine and alanylpbenylalanyl diasteromeric dipeptides undergo decarboxylation through two competing pathways assisted by the migration of the urethane benzyl group either to the terminal or to the amidic nitrogens. The reaction mechanism has been proved by tandem mass spectrometric experiments. The different kinetic energy released associated with CO2 elimination allows the distinction of the S,S from the R,S isomers by moss‐analysed ion kinetic‐energy experiments.
Metastable fragmentation of somatostatin‐14 (SS‐14) and a series of SS‐14 analogs formed with liquid secondary ion mass spectrometry: Observation of fragment ions which involve unsymmetric disulfide bridge cleavage concomitant with peptide chain cleavage
Authors: Craig A. Grey , Rivier Jean E.
Published: May 2005

Somatostatin‐14 (SS‐14) and several SS‐14 analogs were analyzed using liquid secondary ion mass spectrometry (LSIMS). The observed isotope distributions showed low levels of [H2‐SS‐14] (reduced SS‐14). The daughter‐ion spectra of the protonated molecule ions of SS‐14 and several SS‐14 analogs contained a number of metastable fragment ions. Two fragments in these spectra were assigned to cleavage of the peptide chain concomitant with unsymmetric cleavage of the disulfide bridge. Single alanine‐substituted analogs of SS‐14 were used to confirm these assignments, while single D isomer‐substituted analogs of SS‐14 were used to investigate the dependence of the cleavages on conformation.
Fast atom bombardment mass spectra of iodonium salts
Authors: Schurz Helen H. , Busch Kenneth L.
Published: May 2005

Positive‐ion fast atom bombardment mass spectra and linked‐scan tandem mass spectra were measured for aromatic iodonium salts. The mass spectra usually contain the intact cation of the iodonium salt as the base peak, fragment ions of lower abundance resulting from simple cleavages or rearrangements, and a characteristic loss of atomic iodine. High‐level semi‐empirical calculations suggest that an obtuse ringI+ring angle facilitates loss of atomic iodine through concomitant ringtoring bond formation.
Electron impact mass spectrometry of isomeric [(5‐N‐methyl) and (12‐N‐methyl)]‐11‐(o‐ and p‐R‐aniline)‐5H‐dibenzo [b, e] [1,4]diazepines
Authors: Cortés C. Eduardo , Cortés R. Eduardo , Rojas Raymundo
Published: May 2005

The mass spectra of twelve isomeric [(5‐N‐methyl) and (12‐N‐methyl)]‐11‐(o‐ and p‐R‐aniline)‐5H‐dibenzo [b, e] [l,4]diazepines which have potentially useful pharmacological properties are presented.
Fast atom bombardment positive‐ion mass spectra of 1,2,2‐tris(sulfonyl)hydrazines
Authors: Giordano Giuseppe , Shyam Krishnamurthy , Sartorelli Alan C. , McMurray Walter J.
Published: May 2005

Several 1,2,2‐tris(sulfonyl)hydrazines, conceived as prodrugs of 1,2‐bis(sulfonyl)hydrazines and synthesized as potential antineoplastic and trypanocidal drugs, were analyzed by mass Spectrometry as part of the confirmation of the structure of these compounds. Since these compounds showed activity against several transplanted animal tumors, an understanding of the mass spectral behavior of these agents is important to gain information should clinical trials and metabolic studies be undertaken. In all spectra, protonated molecular ions were observed. Collision activation resulted in considerable fragmentation in the fast atom bombardment spectra. Rearrangement ions formed by elimination of substituted diimides from the middle of the molecule were observed. Other rearrangements involving the alkyl substituent and sulfonyl oxygen also occurred.
Fragmentation behavior of disaccharides during desorption–ionization
Authors: Carroll James A. , Lebrilla Carlito B.
Published: May 2005

The fragmentation behavior of native and singly derivatized protonated disaccharides were examined by fast ion bombardment Fourier transform mass spectrometry to determine the origin of various fragment ions produced during desorption–ionization. The lack of interfering matrix ions in this technique allowed the investigation of model disaccharides. Three major product ions were observed, corresponding in mass to a loss of H2O, a loss of a monosaccharide unit and a combination of both losses. The oxygen of the lost H2O molecule originates from an oxygen attached to the anomeric carbon. The other two product ions come from two different monosaccharide units and are due to competing processes. The relative ion intensities of these two fragment ions are governed by the basicities of the fragments. The basicity of the reducing end increases when the hemiacetal is converted into the methyl glycoside. This increase in basicity is due to the increased size of the alkyl group and the ability of the alkyl group to prevent the opening of the reducing glycosidic ring.
Protonation susceptibility of functional groups: A new parameter for interpreting chemical ionization mass spectra of bifunctional organic compounds
Authors: Nakata Hisao
Published: May 2005

A new parameter, the protonation susceptibility (PS), of functional groups in the chemical ionization mass spectrometry of bifunctional organic compounds is presented. In terms of quasi‐equilibrium theory of unimolecular decomposition of the molecular protonated ion of [MH]+, the relative PS corresponds to the relative area under P(E) curves of [MH]+ ions that have a proton at different functional groups. Numerical evaluation of the PS values of pertinent functional groups was made by using particularly selected compounds. The results clearly indicate that PS is independent of proton affinity (PA).
Fast atom bombardment mass spectra of telluronium salts
Authors: Fu Gui‐Xiang , Zhou Zhang‐Lin , Yu Lu , Huang Yao‐Zeng
Published: May 2005

The fast atom bombardment (FAB) mass spectra of telluronium salts were studied. The spectra exhibit the intact cation (C+) and cluster ions ([M + C]+). The principal fragment ions in the FAB mass spectra of telluronium salts are [RTe]+, [R2Te]+˙, [R2Te − H]+, [RTeR′]+˙, and [RTeR′ + H]+. When the anion was [BPh4]−, interesting cluster ions such as [M + C − BPh3]+ appeared.
Metastable ion study of organosilicon compounds. Part V—tetramethoxysilane and trimethoxymethylsilane
Authors: Tabei Eiichi , Mori Shigeru , Okada Fumio , Tajima Susumu , Ogino Kazuo , Okawara Yuzuru , Tobita Seiji
Published: May 2005

The fragmentations of tetramethoxysilane ((CH3O)4Si (1)) and trimethoxymethylsilane ((CH3O)3SiCH3 (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 CH3 or CH3O. These fragmentations are followed by the loss of an aldehyde molecule (H2CO), as commonly observed in the mass spectra of alkoxysilanes. Almost complete scrambling of the methoxy hydrogens takes place in the metastable molecular ion, [1]+˙, prior to the decomposition. On the other hand, a moderate extent of scrambling of the hydrogens takes place in [3]+˙. The fragmentations of [1]+˙ and [3]+˙ were compared with those of the corresponding carbon analogues, tetramethoxymethane ((CH3O)4C (2)) and 1,1,1‐trimethoxyethane ((CH3O)3CCH3 (4)), respectively.
Investigation of some pentasubstituted 1,4‐dihydropyridines by means of fast ion bombardment, chemical ionization and electron impact mass spectrometry
Authors: Hamdan M. , Scandola M. , Tarzia G.
Published: May 2005

Positive fast ion bombardment, positive chemical ionization (CI+) and positive electron impact (EI) ionization mass spectrometry were used to investigate a number of relatively large and structurally related organic molecules. Some of the major dissociation pathways observed in the CH4‐CI+ mass spectra are not present under NH3‐CI+ conditions, but are obtained in the collision‐induced dissociation (CID) spectrum of the 50 eV MH+ molecular ion, formed in the latter reaction. The resemblance between the EI mass spectra and their fast ion bombardment counterparts, the effect of changing the energy of the bombarding Cs+ ion beam over the range 2–16 keV and the different degrees of internal excitation of ions formed in different CI reagent gases are discussed.