bluuebunny/crossref_metadata_2025_split huggingface dataset:
Optimized production of the acylium diagnostic ions in the chemical ionization NO+ mass spectra of long‐chain monoolefins
Authors: Einhornt J. , Malosse C. 
Published: May 2005

AbstractA recent reinvestigation of the reactivity of NO+ towards straight‐chain monoolefinic compounds revealed that the characteristic acylium ions, previously reported for alkenyl acetates and related compounds, could also be obtained from alkenes and alkenoic acids (or esters). In this study, the influence of the sample pressure and that of NO on the production of the acylium ions was investigated, leading to disappearance graphs indicative of a strong dependence on these experimental factors. This gives a further explanation for previous apparent discrepancies in the literature and the optimum conditions of use for double‐bond location in a variety of substituted or unsubstituted monoolefins.
Mass spectra of t‐butyloxycarbonyl (BOC)‐protected peptides
Authors: Vairamani M. , Srinivas R. , Rao G. K. Viswanadha , Nagaraj R. , Reddy G. Laxma , Saberwal G. 
Published: May 2005

AbstractAnalytically useful mass spectra of t‐butyloxycarbonyl protected tetra‐ and pentapeptides can be obtained under chemical ionization conditions at a source temperature of 250‐270 °C without the use of a reagent gas. The mass spectrum of die thermally labile amino acid arginine could also be recorded under the same conditions.
Hydroxylation of selected hydrocarbon ions on reaction with methanol in the gas phase
Authors: Dolnikowski Gregory G. , Allison John , Watson J. Throck 
Published: May 2005

AbstractThe ion‐molecule reactions of selected hydrocarbon cations with methanol which lead to the production of hydroxylated odd‐electron molecular ions in the high‐pressure ion source of a mass spectrometer or in the central quadrupole of a tandem quadrupole mass spectrometer are described. A wide variety of hydrocarbon cations were investigated, including aliphatic and aromatic cations; of these, only those having a vacant site on an aromatic system appear to undergo the hydroxylation reaction in high yield. A mechanism is proposed for the formation of the molecular ion of phenol from the ion‐molecule reaction involving the phenyl cation with methanol. In addition, thermochemical data are provided which support the formation of the postulated species.
Influence of collision gas on doubly charged ion mass spectra
Authors: Regalado J. R. , Holbrook W. M. , Bostwick D. B. , Moran T. F. 
Published: May 2005

AbstractThe influence of the collision gas on doubly charged ion mass spectra of a selected number of hydrocarbons has been examined. Relative abundances of various product ions in 2E spectra, resulting from charge exchange collisions of doubly charged hydrocarbon ions, do not vary drastically as the collision gas is varied. However, the absolute intensities of these doubly charged ion mass spectra increase significantly when the collision gas is changed from argon to methane to isobutane. Tbese observations are rationalized in terms of a multichannel diabatic curve crossing model.
Tuning and calibration in thermospray liquid chromatography/mass spectrometry using perfluorinated alkyl acids and their ammonium salts
Authors: Stout Steven J. , daCunha Adrian R. 
Published: May 2005

AbstractOf the several approaches used to interface liquid chromatography with mass spectrometry, the thermospray interface has evolved as the most popular and applicable for the analysis of polar and labile organic compounds. Since a separate ion source must be used for thermospray, separate tuning and calibration are required. Unfortunately, current approaches to tuning and calibration suffer from serious shortcomings, most notably rapid contamination of the ion source. Recent reports have shown that this shortcoming can be overcome by using acetic acid‐ammonia cluster ions or trifluoroacetic acid–ammonia cluster ions for tuning and calibration. In the latter approach, the tuning solution could also be used in the negative ion mode of operation but suffers from concentration of most of the ion current in one ion. The use of perfluorinated alkyl acids and their ammonium salts to generate intense high‐mass negative ions for tuning and calibration to m/z 2000 is reported. Additionally, the ammonium salts of the longer chain perfluorinated acids offer an enhanced high‐mass response in the positive ion mode of operation.
Thermospray mass spectrometry of N‐methylcarbamates
Authors: Saar Jacob , Salomon Avraham 
Published: May 2005

AbstractThe thermospray mass spectrometry (TSP/MS) of five N‐methylcarbamates is presented. This is the first time that ions other than [M + H]+ and [M + NH4]+ have been reported using positive TSP/MS. Protonation of ROCONHCH3 yields the [CH3NH2CO]+· ion, with formation of the ion–molecule adduct [ROCONHCH3 · CH3NH2CO]+· through elimination of CO+· from [CH3NH2CO]+·, and the adduct [M + 75]+·, [ROCONHCH3 · OCONH2CH3]+·, is also obtained.
Negative ion liquid secondary ion mass spectrometry of carbamate‐linked oligodeoxynucleosides. II
Authors: Laramée James A. , Arbogast Brian , Stirchak Eugene P. , Weller Dwight D. , Deinzer Max L. 
Published: May 2005

AbstractCarbamate‐linked Oligodeoxynucleosides, in which the backbone consists of carbamate and N‐methylcarbamate linkages, have been analyzed by negative ion liquid secondary ion mass spectrometry. Bidirectional sequence‐determining fragmentations are postulated to occur from a common radical anion intermediate that is produced by capture of an ionizing electron by the neutral sample molecule. Fragmentation reactions appear to be related to whether a proton or methyl group is present on the amide nitrogen.
Collisionally induced dissociation mass spectrometric studies of perfluorinated 1H‐heptane, tert‐butanol, 2‐butyltetrahydrofuran and isopropyl bromobutyl ether
Authors: Huang Sunkwei , Tuinman Albert 
Published: May 2005

AbstractHigh‐energy collision‐activated dissociation in connection with mass‐analyzed ion kinetic energy spectrometry (CAD/MIKES) was employed to probe the structures of some ions generated by methane chemical ionization (CI) and negative ion chemical ionization (NICI) of the title compounds. CAD/MIKES results show that the [M  H]− ion of lH‐perfluorobeptane and the [O(CF2)4Br]− ion of perfluoroisopropylbromobutyl ether are stable. The methane CI of these fluorocarbons also showed that the expulsion of HF molecules appears to be a major driving force for further fragmentations.
Differentiation of diastereoisomeric terpenoid alcohols by electron impact and negative ion chemical ionization associated with collision‐induced dissociation. A fourier transform ion cyclotron resonance study
Authors: Decouzon Michéle , Gal Jean‐François , Geribaldi Serge , Rouillard Michel , Sturla Jean‐Michel 
Published: May 2005

AbstractElectron impact ionization‐collision‐induced dissociation (EI‐CID) and negative ion chemical ionization‐collision‐induced dissociation (NICI‐CID) experiments have been performed on the molecular or quasi‐molecular ions (M+· or [M ‐ H]−) of series of terpenoid alcohols, using a Fourier transform ion cyclotron resonance spectrometer. These terpenes belong to the p‐menthane family and bear a hydroxyl group in various positions relative to the isopropyl or isopropenyl substituent (positional or stereochemical isomers). In the case of positional isomers, different CID spectra were always obtained. Within a given diastereoisomeric series, stereochemical differences were also observed in both NICI‐CID and EI‐CID experiments.
Application of dicyandiamide as a matrix additive in fast atom bombardment mass spectrometry
Authors: Caldwell G. W. , Reitz A. B. , Masucci J. A. 
Published: May 2005

AbstractDicyandiamide (DCDA) is used as a chemical additive in the fast atom bombardment (FAB) matrix 3‐mercaptopropane‐l,2‐diol (thioglycerol) and propane‐l,2,3‐triol (glycerol). It is demonstrated that DCDA can be used to generate adduct ions [M + H + DCDA]+ for a variety of common organic functional groups to confirm the molecular ion [M + H]+. It is particularly useful for aromatic and alkyl amines and these compounds were therefore investigated in greater detail. Primary and secondary amines on heating react with DCDA to produce biguanides. DCDA can be used as a derivatizing reagent, but the reaction times are typically longer than 12 h and, therefore, it has limited utility. Biguanides can be detected at the nanogram level in full‐range FAB mass spectral analysis.
Spontaneous fragmentations of protonated benzaldimines mediated by intermediate ion‐neutral complexes
Authors: Grützmacher Hans‐Friedrich , Zalfen Ursula 
Published: May 2005

Abstract4‐Methoxymethylbenzaldimmonium ions (a) and the corresponding N‐methylated ions (b) and N,N‐dimethylated ions (c) were easily generated in the ion source by electron impact‐induced dissociation from 1‐(4‐methoxymethylphenyl)ethylamine and its N‐methylated derivatives. The spontaneous fragmentations of metastable ions a‐c and of specifically deuterated derivatives in the second field‐free region of a VG ZAB‐2F mass spectrometer were studied by mass‐analysed ion kinetic energy Spectrometry. The formation of an amino‐p‐quinodimethane radical cation by loss of the methoxy group is observed for all ions. In the case of a and b carrying at least one proton at the immonium group, competing fragmentations are the loss of CH2O and CH3OH, respectively, and the formation of ions CH3OCH2 +, m/z 45, and C7H7 +, m/z 91. Deuterium‐labelling experiments indicated the migration of a proton from the protonated imino group of a and b to the aromatic ring followed by the loss of methanol from the methoxymethyl side‐chain or protolysis of the bond to either side‐chain to form ion‐neutral complexes, in close analogy with the reactions of the corresponding protonated benzaldehydes. The intermediate ion‐neutral complexes dissociate eventually by internal ion‐neutral reactions resulting in the loss of CH2 O and the formation of C7H7 +, respectively.
Location of double‐bond position in tetradecenols without chemical modification by mass spectrometry
Authors: Horiike Michio , Gu Yuan , Hiranio Chisato 
Published: May 2005

AbstractTwelve positional isomers of tetradecenol were analysed by conventional combined gas chromatography/mass Spectrometry without any chemical derivatization for the elucidation of the double‐bond position. The spectra were interpreted in terms of similarity of mass spectral patterns based on a fuzzy reasoning method, in which the relative abundances of selected predominant fragment ions were chosen as standard parameters and similarity indices were devised. The method was tested with pure alcohols and enabled the double‐bond position to be located with acceptable accuracy.
Experimentally determined and calculated values of the energies required to form doubly charged ions of the bromomethanes CH3Br, CH2Br2 and CHBr3
Authors: Griffiths W. J. , Harris F. M. , Parry D. E. , Reid C. J. , Ballantine J. A. 
Published: May 2005

AbstractTwo experimental techniques were used to determine the double ionization energies of CH3Br, CH2Br2 and CHBr3. In one, these energies were measured directly by double‐charge‐transfer spectroscopy. In the other, charge stripping of [CH3Br]+, [CH2Br2]+ and [CHBr3]+ ions was investigated and the ionization energies of the singly charged ions were measured. The double ionization energies of the molecules obtained by adding known single ionization energies of the molecules to the single ionization energies of the ions were in good agreement with those determined by double‐charge‐transfer spectroscopy. The relevant mean values from the two techniques were 28.9 ± 0.5, 27.5 ± 0.5 and 29.1 ± 0.5 eV for the double ionization energy of CH3Br, CH2Br2 and CHBr3, respectively. The results of ab initio calculations using second‐order Møller‐Plesset perturbation theory were in good agreement with the observed double ionization energies; they were consistently slightly lower than the experimental values.
Assigning structures to isomeric [C5H10]+ ions: The generation of ionized ethylcyclopropane from pentan‐1‐ol and 1‐chloropentane
Authors: Harnish D. , Holmes J. L. , Lossing F. P. , Mommers A. A. , Maccoll A. , Mruzek M. N. 
Published: May 2005

AbstractThe charge‐stripping mass spectra of the ten C5H10 isomers and of cyclopropane and propene have been re‐evaluated. Oxygen is the preferred collision gas for the former group and helium for the latter pair. A con bined study of the low‐energy mass spectra, charge‐stripping mass spectra and appearance energy measurements had to the conclusion that loss of H2O from ionized pentan‐1‐ol and loss of HCl from ionized 1‐chloropentane both predominantly produce ionized ethylcyclopropane as the fragment ion. For the alcohol, a 1,4‐elimination followed by an energetically favoured 1,2‐H shift is involved, whereas for the halide a direct 1,3‐elimination obtains.
Determination of the isomeric composition of an ionic mixture using collision cross‐sections
Authors: Yoon Bo Un , Kim Myung Soo 
Published: May 2005

AbstractA theory has been developed for the determination of the isomeric composition of an ionic mixture. The probability theory describing the collisionally activated decomposition (CAD) which was developed previously provided a general foundation for the present theory. Quantification was based on the cross‐sections for the collisional production of daughter ions as observed in the mass‐analysed ion kinetic energy Spectrometry (MIKES). Experimental details for the implementation of the theory have also been developed. The method has been applied to the case of C2H4O+· generated from butane‐l,3‐diol, which is known to be a mixture of more than one isomeric structure. The results seem to be far superior to those based on previous methods, as evidenced by the excellent internal consistency.
Matrix effects on the fast atom bombardment mass spectra of palladium complexes
Authors: Mallis Larry M. , Scott William J. 
Published: May 2005

AbstractIn an attempt to identify and characterize the intermediates involved in multi‐step palladium catalyzed coupling reactions, under fast atom bombardment (FAB) conditions, the selection of a matrix to enhance ion formation without degrading the palladium complex is critical. In general, it is observed that the analysis of tetrakis(triphenylphosphine)palladiurn(0) using glycerol, m‐nitrobenzyl alcohol or o‐nitrophenyl octyl ether as the FAB matrix compound produces several ions which correspond to complexes of the type PdxLyOz+ (L = PPh3; x = 1‐4; y = 1‐4; z = 0‐2), in addition to clusters containing one or more matrix molecules. FAB mass spectra generated using triethanolamine‐ or tetramethylene sulfone (sulfolane) are observed to contain ions related to the palladium(0) complex with little or no interference from ions related to the oxidation or reduction processes.
Metastable ion study of organosilicon compounds. Part III—trimethoxyphenylsilane
Authors: Tajima Susumu , Iida Hiroyuki , Tobita Seiji , Okada Fumio , Tabei Eiichi , Mori Shigeru 
Published: May 2005

AbstractThe unimolecular decomposition of trimethoxyphenylsilane (1) was investigated by mass‐analysed ion kinetic energy (MIKE) spectrometry, deuterium‐labelling studies and from high resolution data. The characteristic fragmentations of metastable molecular ion of 1 were losses of C6H6 and C7H7· with rearrangements. Almost complete H/D scrambling occurred in the molecular ion prior to these decompositions. The other important fragmentation routes corresponded to expulsions of CH3O· and C6H5·. These fragmentations were followed by consecutive elimination of an H2CO molecule, as commonly observed in the mass spectra of alkoxysilanes. In these fragmentation processes, H/D scrambling increased as the internal energy of the molecular ion was lowered. The fragmentations of 1 were compared with those of its carbon analogue, α,α,α‐trimethoxytoluene.
Charge‐Reversal mass spectra of enolate ions of some open‐chain and cyclic ketones for structure identification
Authors: Sürig Thomas , Grützmacher Hans‐Friedrich 
Published: May 2005

AbstractThe charge‐reversal (CR) mass spectra of the enolate ions of heptanal and ten isomeric heptanones, of cyclohexanone, of cycloheptanone, of isomeric methylcyclohexanones, of isomeric ethylcyclohexanones and of the iso meric monoterpene ketones camphor, fenchone, pulegone and thujone were obtained by deprotonation using OH− under chemical ionization conditions followed by collision of the [M − H] − ions with helium in the second field‐free region of a VG ZAB 2F mass spectrometer. The CR mass spectra were evaluated by similarity index (SI) values. Characteristic of the CR mass spectra of the open‐chain enolates are fragment ions formed by α‐cleavage. However, the CR mass spectra are dominated by peaks of small hydrocarbon ions, particularly in the case of cyclic and bicyclic enolates. The CR mass spectra of enolates of linear heptanones differing in the position of the carbonyl group can be easily correlated with the structure of the parent ketone. The CR mass spectra of enolates of isomeric heptan‐2‐ones differing only in the degree of branching of the alkyl group are similar, but can be distinguished by the SI values. The CR mass spectra of the enolates of the isomeric cyclic and bicyclic ketones studied are more or less identical and cannot be used for structural assignment.
Benzene as a selective chemical ionization reagent gas
Authors: Allgood Charles , Lin Yi , Ma Yee‐Chung , Munson Burnaby 
Published: May 2005

AbstractDilute mixtures of C6H6 or C6D6 in He provide abundant [C6H6]+· or [C6D6]+· ions and small amounts of [C6H7]+ or [C6D7]+ ions as chemical ionization (CI) reagent ions. The C6H6 or C6D6 CI spectra of alkylbenzenes and alkylanilines contain predominantly M+· ions from reactions of [C6H6]+· or [C6D6]+· and small amounts of MH+ or MD+ ions from reactions of [C6H7]+ or [C6D7]+. Benzene CI spectra of aliphatic amines contain M+·, fragment ions and sample‐size‐dependent MH+ ions from sample ion‐sample molecules reactions. The C6D6 CI spectra of substituted pyridines contain M+· and MD+ ions in different ratios depending on the substituent (which alters the ionization energy of the substituted pyridine), as well as sample‐size‐dependent MH+ ions from sample ion‐sample molecule reactions. Two mechanisms are observed for the formation of MD+ ions: proton transfer from [C6D6]+· or charge transfer from [C6D6]+· to give M+·, followed by deuteron transfer from C6D6 to M+·. The mechanisms of reactions were established by ion cyclotron resonance (ICR) experiments. Proton transfer from [C6H6]+· or [C6D6]+· is rapid only for compounds for which proton transfer is exothermic and charge transfer is endothermic. For compounds for which both charge transfer and proton transfer are exothermic, charge transfer is the almost exclusive reaction.
Mass spectra of heterocyclic compounds VI. 3,4‐dihydro‐1H‐2,3‐benzothiazine 2,2‐dioxides
Authors: Zinczuk Juan , Bravo Rodolfo D. , Orazi Orfeo O. , Corral Renée A. 
Published: May 2005

AbstractThe mass fragmentation behaviour of 3,4‐dihydro‐1H‐2,3‐benzothiazine 2,2‐dioxides was studied. The rationalizations suggested are supported by accurate mass measurements, metastable evidence and deuterium labelling.
Stable γ‐distonic oxonium ions: R\documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\rm O}\limits^ + $\end{document}HCHR′ĊH2CHR″ and their characteristic reaction
Authors: Milliet Arielle , Sozzi Georges 
Published: May 2005

AbstractThe γ‐distonic radical ions R\documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\rm O}\limits^ + $\end{document}CHR′CH2ĊHR″ and their molecular ion counterparts R\documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\rm O}\limits^{{\rm + } \cdot } $\end{document}CHR′CH2CH2R″ have been studied by isotopic labelling and collision‐induced dissociation, applying a potential to the collision cell in order to separate activated from spontaneous decompositions. The stability of CH3\documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\rm O}\limits^ + $\end{document}HCH(CH3)CH2ĊHCH3, C2H5\documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\rm O}\limits^ + $\end{document}HCH(CH3)CH2ĊHCH3, CH3\documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\rm O}\limits^ + $\end{document}HCH(CH3)CH2ĊH2, CH3\documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\rm O}\limits^ + $\end{document}HCH2CH2ĊHCH3 and C2H5\documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\rm O}\limits^ + $\end{document}HCH2CH2ĊHCH3, has been demonstrated and their characteristic decomposition, alcohol loss, identified. For all these γ‐distonic ions, the 1,4‐H abstraction leading to their molecular ion counterpart exhibits a primary isotope effect.
Intermediate ion structures in the fragmentation of metastable 3‐methylbutan‐2‐ol radical cations
Authors: George M. , Holmes John L. 
Published: May 2005

AbstractIonized 3‐methylbutan‐2‐ol displays four low‐energy fragmentations, loss of CH3· and C3H7· and loss of CH4 and C3H8, the latter pair being produced by metastable ion decompositions. The electron‐impact, metastable‐ion and collision‐induced dissociation mass spectra of 13C and 2H‐labelled isotopomers have been recorded, together with appearance energy measurements. It was found that the fast (ion source) losses of CH3· and C3H7· involved only simple bond cleavages between C(1) and C(2) and between C(2) and C(3), respectively, and without any positional interchange of isotopes. The loss of C3H8 produces ionized vinyl alcohol containing only C(l) and C(2). The H atoms involved are only those attached to C(1) and C(3). In deuterium‐labelled analogues, the deuterium is preferentially located in the propane, e.g. metastable CD3CH(OH)CH(CH3)2 yields predominantly C3H6D2. On the basis of all the observations, it is proposed that low‐energy molecular ions can form a stable proton‐bridged molecule‐radical complex, , and that this key intermediate is responsible for the isotope distribution in propane loss and also for the relatively low importance of the lowest energy dissociation, the simple C(1)C(2) bond cleavage.
New rules concerning the formation of protonated amino acids from protonated dipeptides using the proton affinity order determined from collisionally activated decomposition spectra
Authors: Isa Kimio , Omote Toshiko , Amaya Mitsutaka 
Published: May 2005

AbstractThe use of the order of the proton affinities of natural α‐amino acids for the explanation of the sequence of dipeptidcs using the collisionally activated decomposition mass spectra of protonated dipeptides ions is discussed. New rules are given concerning the formation of protonated amino acid ions from protonated dipeptide ions using the proton affinity order determined by means of fast atom bombardment tandem mass spectrometry for Gly * M2, M1 * Gly, Leu * M2, and M, * Leu systems, where M1 and M2 are the N‐terminal and C‐terminal sides of the dipeptide, respectively.
Fast atom bombardment mass spectra of stibonium salts
Authors: Yu Lu , Fu Gui‐xiang , Liao Yi , Xu Chao‐Wei , Huang Yao‐Zeng 
Published: May 2005

AbstractThe positive‐ion fast atom bombardment (FAB) mass spectra of stibonium salts have been studied. The spectra exhibit an abundant intact cation (C+) and fragment ions resulting from the loss of R, R′ or stable neutral species from the cation. The principal fragment ions in the FAB mass spectra of stibonium salts are [R3Sb]+·, [R2Sb]+, [R2SbH2]+, [RSbR′]+, [RSbH]+, [RSb − H]+ and [R2SbR']+·. In most cases, [ M + C] + cluster ions were detected. When the anion was bromine, the adduct ions [M + (R − H)Sb]+, [C + (R‐H)]+ and [ C + (R′ − H)]+ were also observed, whereas when the anion was [BPh4]−, interesting cluster ions such as [M + (BR′ ‐ H)]+ and [M + (BR′ − 3H)]+ appeared.