bluuebunny/crossref_metadata_2025_split huggingface dataset:
Mass spectrometric behaviour of cyclopentane‐and cyclohexane‐condensed pyrimidinediones under electron impact
Authors: Himottu Marja , Pihlaja Kalevi , Bernáth Gábor , Stájer Géza , Vainiotalo Pirjo 
Published: May 2005

AbstractMass spectral fragmentations of four cyclopentane‐condensed cis‐pyrimidinediones and of six cyclohexane‐condensed cis‐ or trans‐pyrimidinediones were examined using metastable ion analyses and exact mass measurements. The fragmentation patterns of all of these compounds were clearly different and also cis‐ and trans‐fused isomers were easy to distinguish from each other by their mass spectra. In spite of the differences in their mass spectral fragmentations, all compounds formed phenylisocyanates (m/z 119 and 153) and anilines (m/z 93 and m/z 127), the structures of which were verified by collision‐induced dissociation experiments.
Differentiation of stereoisomers with electron impact mass spectrometry: (E)‐ and (Z)‐α‐hydroxyoximes
Authors: Łożyński Marek , Rusińska‐Roszak Danuta 
Published: May 2005

AbstractThe electron impact mass spectra of 5,8‐diethyl‐7‐hydroxydodecan‐6‐one (Z)‐oxime and (E)‐oxime provide a basis for distinguishing these stereoisomers.
Comparison of mass spectrometric methods for studying thermally labile compounds: Rifapentine
Authors: Vékey Kàroly , Edwards Duncan M. F. , Zerilli Luigi F. , Màk Marianna , Tamàs Jòzsef , Raverdino Vittorio , Selva Antonio 
Published: May 2005

AbstractResults of 16 different mass spectrometric ionization and sample‐introduction methods are compared for the case of a thermally very labile antibiotic, rifapentine. These suggest that extensive thermal decomposition occurs during evaporation when the sample can come into contact with hot metal parts, usually the source housing. The intensity of the molecular ion and the extent of fragmentation depend on various parameters, such as the ionization process, positive or negative‐ion detection and the type of sample introduction. The most informative methods for rifapentine seem to be ‘in‐beam’ electron impact, negative ionization with particle beam and direct liquid introduction interfaces and positive‐ and negative‐ion fast atom bombardment.
Positive‐ion mass spectra and collision‐induced dissociation of some 2,3‐didehydro amino acids
Authors: Hamdan Mahmoud , Tarzia Giorgio , Balsamini Cesarino , Spadoni Gilberto , Curcuruto Ornella , Traldi Pietro 
Published: May 2005

AbstractThe positive‐ion mass spectra of a number of didehydro amino acids, ionized by electron impact and/or thermospray, and collision‐induced dissociation spectra taken at collision energies of a few electron volts and keV have been performed on multiple quadrupole and reversed geometry sector instruments. Observed differences in the mass spectra and in the fragmentation patterns are explained in terms of different isomeric structures, different internal excitation energies and different ion transit times between the ion source and the collision cell. Molecular ions of unhydrated amino acids are efficiently formed both by electron impact and thermospray, whilst molecular ions of the hydrated compounds are formed more efficiently by the latter technique. The present investigation demonstrates that the use of different ionization techniques combined with mass spectrometry/mass spectrometry measurements at different collision energies yields a wealth of information relevant to structural characterization of this important class of molecules.
Nature of methyl cation bonding to dihydroxybenzenes elucidated using an ion trap mass spectrometer
Authors: Nourse B. D. , Brodbelt J. S. , Cooks R. G. 
Published: May 2005

AbstractMethylation of the isomeric dihydroxybenzeres using the dimethylfluoronium ion ([CH3FCH3]+) was studied in a quadrupole ion trap mass spectrometer. The products were characterized by tandem mass spectrometry using collision‐activated dissociation. A comparison of the daughter ion spectra of the methylated products with those of model ions, generated by protonation of substituent‐ and ring‐methylated analogs, demonstrates that a mixture of methylated products is generated. Included are structures in which the methyl is σ‐bonded to the ring and others with σ‐bonds to the heteroatom, the latter being favored in catechol and hydroquinone. The energy‐resolved daughter ion spectra for the methylated isomers, acquired by varying the amplitude of the a.c. voltage used to excite resonantly the mass‐selected ions, support these conclusions regarding the site of methylation.
Ion‐neutral complexes and the proton‐bound dimer of acetone
Authors: Hunter John A. , Johnson Chris. A. F. , Parker John E. , Smith Gerry P. 
Published: May 2005

AbstractHigh‐ and low‐energy collision‐induced dissociation, and multi‐photon infrared dissociation spectra of the proton‐bound dimer of acetone all show the formation of protonated‐acetone and an acetone molecule as the only dissociation products. In the present paper evidence is presented that the proton‐bound dimer of acetone can exist as three isomeric ion‐neutral complexes, two of which may interconvert. The dissociation channels and energetics of these three complexes are modelled using the MINDO/3 quantum chemical method.
Influence of experimental conditions on the liquid secondary ion mass spectra of sulfonated azo dyes
Authors: Richardson Susan D. , Thruston Alfred D. , McGuire John M. , Baughman George L. 
Published: May 2005

AbstractTwo monosulfonated and eight disulfonated azo dyes of varying relative molecular mass were examined by liquid secondary ion mass spectrometry (LSIMS). The effects of matrix, concentration, primary beam energy, and mode of operation were addressed in order to optimize sample ionization, whilst minimizing interference from matrix ions. Seven matrices were investigated: glycerol, thioglycerol, 3‐nitrobenzyl alcohol, diethanolamine, 2‐hydroxyethyl disulfide, a 1:1 (v/v) mixture of 2‐hydroxyethyl disulfide and thioglycerol, and a 1 : 3 (v/v) mixture of dithioerythritol and dithiothreitol. Of these matrices, 3‐nitrobenzyl alcohol produced LSIMS spectra that exhibited the most intense sample ions and the least inteiference from matrix ions. Minimum concentrations of 0.4 μg/μl and 4 μg/μl (dye in matrix) were necessary to produce useful full‐scan spectra for monosulfonated azo dyes and disulfonated azo dyes, respectively; maximum sample ion intensities were obtained with concentrations ranging from 20 μg/μl to 60 μg/μl. A primary ion beam (cesium) of 10 to 15 kV produced the greatest secondary ionization efficiency, and a negative‐ion analysis mode produced more useful spectra than those obtained in the positive‐ion mode.
Elimination and rearrangement reactions in the electron impact ionization mass spectrometry of 2,4,5,5‐tetrasubstituted 1,2,4‐triazolidine‐3‐thiones
Authors: Pihlaja Kalevi , Mäki Esa , Schulze Klaus , Richter Christian 
Published: May 2005

AbstractThe electron impact mass spectra of 2,4,5,5‐tetrasubstituted l,2,4‐triazolidine‐3‐thiones exhibited, in addition to four main routes of fragmentation, a reaction leading to the formation of 5‐alkyl‐l,2,4‐triazoline‐3‐thiones via an elimination of HR4 (R3 ≤ R4 are the substituents at C(5)) or via a McLafferty‐type reaction from the rearranged molecular ion in the case of the 5,5‐spiro derivatives. Substitution at N(2), N(4) and/or C(5) had a decisive effect on the contribution of the alternative reaction routes. Some fragments via the triazoline‐thione structure were also formed.
Matrix‐assisted laser desorption of neutral organic molecules
Authors: Kinsel Gary R. , Lindner Josef , Grotemeyer Jürgen 
Published: May 2005

AbstractResults of initial investigations of matrix‐assisted laser desorption (LD) of neutral molecules are presented. The investigations were performed using gramicidine D as the test molecule, since both the wavelength‐dependent LD beharioor and the ionization and fragmentation behaviour of the pure material had been studied previously. Comparisons between previously reported results for the pure compound and the matrix mixtures used in these studies are made. The results show that, whereas no signal could be observed from the pure sample material at non‐resonant desorbing wavelengths, addition of a strongly absorbing matrix to the sample initiated LD of abundant intact neutral sample molecules. The results are discussed in the light of previous studies of the LD mechanism and support an explosive, mechanically driven model for the LD process.
Fragmentation of ion–molecule adducts of transition metal ions with aromatic ring‐containing nitriles in the gas phase
Authors: Chen Lin‐Zhi , Miller Jack M. 
Published: May 2005

AbstractGas‐phase ion–molecule reactions of transition metal ions, M+ (M+ = Ni+, Co+, Fe+ and Mn+), with six aromatic ring‐containing nitriles were investigated in a modified fast atom bombardment (FAB) source. It is shown that the monoadduct, (Ph(CH2)nCN)–M+, is one of the most abundant ion–molecule reaction products. The main fragments in the FAB source are the [C7H7]+ and [C8H9]+ ions, and their formation is shown to involve metal ion insertion into the nitriles rather than direct bond cleavage from the ‘free’ or complexed nitriles after FAB ionization. An intramolecular oxidation–reduction reaction, giving [C7H7]+, is found in the metastable and collisionally induced dissociations of benzyl nitrile adducts accompanied by neutral MCN formation, but not seen for longer chain samples. An ortho effect is observed in the elimination of HCN from the 2‐methylbenzyl nitrile adduct ions. This reaction dominates the metastable ion spectrum of the adduct of Mn+, whereas metal detachment is nearly the major process for the other complexes of Mn+. The different bond‐insertion selectivities of the metal ions are also shown.
Competition between substitution (SN2), elimination (E2) and addition elimination (AE) reactions in the gas Phase
Authors: Haib J. , Stahl D. 
Published: May 2005

AbstractThe competition between substitution (SN2), elimination (E2) and addition–elimination (AE) reactions in the gas phase has been studied by using OH− and NH2− as nucleophiles reacting with esters of acetylenedicarboxylic acid of general formula RO(O)CCCC(O)OR′. By selectively varying R and R′ it was possible to show that the E2 reaction predominates over SN2 and that the relative contributions of the three reactions with OH− follow the decreasing order AE > E2 > SN2, whereas for NH2− it is E2 > AE > SN2. The E2 reaction is discussed in terms of substituent effects, relative acidity of the different β‐hydrogens and geometry of the transition state. For the AE reaction a leaving group order for this class of compounds was established.
Ion—molecule chemistry of pyrene in an ion‐trap mass spectrometer
Authors: Nourse B. D. , Cox K. A. , Cooks R. G. 
Published: May 2005

AbstractThe quadrupole ion‐trap mass spectrometer is used to investigate aspects of the ion‐molecule chemistry of the pyretic molecular radical cation (M+), the [M  H]+ ion and the [M  H2]+˙ ion. Cycloaddition and alkyl halide addition reactions with the reagents pyrene, methyl iodide, ethyl iodide, isopreue and 2‐iodopropane are investigated. The pyrene molecular radical cation is remarkably unreactive while the closed shell [M  H]+ ion is highly reactive and the [M  H2]+˙ ion shows intermediate reactivity. Analogies are found between the behaviour of the pyrene molecular radical cation and the corresponding [M  H]+ ion on the one hand, and the benzene radical cation and the phenylium ion on the other. The total lack of reactivity of the M+˙ ion is attributed to π‐delocalization of the radical and the cation over the large aromatic system. Addition of isoprene to the [M  H]+ and [M  H2]+˙ ions of pyrene occurs via cycloaddition reactions. A characteristic fragmentation of each adduct ion is methyl radical loss and evidence obtained using pyrene‐d10 indicates that the product in the case of [M  H]+ is an ionized indene. Addition of methyl iodide, ethyl iodide and 2‐iodopropane to the [M  H]+ ion of pyrene occurs to give an iodonium product (C16H9–I+–R) which fragments by loss of I˙ or CH3˙ to give the methylpyrene or iodopyreue product ions. Reactions of ethyl iodide and 2‐iodopropane with the dehydropyrene ion, [M  H2]+˙, give primarily an HI addition product, together with small contributions from the intact adducts. Evidence is provided suggesting that in this case the HI and alkyl halide molecules add across a CC bond rather than forming an iodine‐bound adduct. An experiment in which nine consecutive isolation and activation steps (MS10) are used to couvert the [2M  H]+ adduct, C32H, to C32H˙ exemplifies the intriguing ion chemistry and the stability of the carbon skeleton of the adduct ions.
Application of gas chromatography/mass spectrometry to steroid analysis in equine sports: Problems with enzyme hydrolysis
Authors: Houghton E. , Grainger L. , Dumasia M. C. , Teale P. 
Published: May 2005

AbstractIn steroid analysis in biological fluids, cleavage of conjugates is an essential step which can be achieved by either enzymatic or chemical hydrolysis. Where conjugation with both glucuronic acid and sulphate occurs, then the use of the enzyme preparation from Helix pomatia, containing both β‐glucuronidase and aryl sulphatase activities, would appear to be advantageous. However, it has been shown that the sulphatase enzymes of Helix pomatia do not hydrolyse 17β‐sulphates and that other enzymatic activities also present in the preparation can give rise to artefact formation with certain steroids.The artefacts produced from incubation of dehydroisoandrosterone with the enzyme preparation from Helix pomatia have been identified by gas chromatography/mass spectrometry (GC/MS) as androst‐4‐ene‐3,17‐dione, androsta‐4,6‐diene‐3,17‐dioue, androst‐4‐ene‐3,6,17‐trione and 6‐hydroxyandrost‐4‐ene‐3,17‐dione. Incubation of androst‐5‐ene‐3,17‐diol produced a similar series of compounds with a 17‐hydroxy function. Semi‐quantitative GC/MS analysis has been used to determine the extent of these transformations in the presence of increasing amounts of the Helix pomatia preparation. Quantitative conversion in buffer can be obtained but the results from incubation in urine showed a marked modifying effect with minimal artefact formation. The enzyme preparation from Escherichia coli does not yield any artefacts and results are presented for the optimization of its use in the hydrolysis of the glucuronic acid conjugate of 5α‐estrane‐3β,17α‐diol, the major metabolite of nandrolone in the horse.
Collisionally activated dissociation of 2,4,6‐triphenylpyridinium cations
Authors: Katritzky Alan R. , Malhotra N. , Dega‐Szafran Zofia , Savage G. Paul , Eyler John R. , Watson Clifford H. 
Published: May 2005

AbstractThresholds for the appearance of fragment ions allowed the estimation of threshold fragmentation energies (TFE) for the collisionally activated dissociation (CAD) in the gas phase of laser‐desorbed pyridine‐ring substituted N‐benzylpyridinium cations to form pyridine and a carbocation. p‐Methylbenzylpyridinium cation underwent an alternative CAD into pyridinium cation and the p‐quinodimethane. The TFE are discussed in comparison with the energy differences (ΔΔHf = ΔHf(Py) + ΔHf(R+) − ΔHf(Py +R) calculated by the AM1 method to provide strong evidence for benzyl to tropylium cation rearrangement in an ion‐molecule pair.
Methane positive‐ion chemical ionization mass spectra of phenols
Authors: Iida Yoshio , Daishima Shigeki , Shibata Akihiro 
Published: May 2005

AbstractPositive‐ion chemical ionization mass spectra for 48 phenols were measured using methane as the reagent gas in order to clarify their characteristics. The ion species obtained were almost identical with those generated in alkyl‐benzenes except for dehydrated ions produced from MH+ and adduct ions, in particular compounds such as pyrocatechol. Specific ions such as C6H7O+ (m/z 95) and C8H11O+ (m/z 123) in phenol derivatives (C6H4 · OH · R; R = CnH2n + 1, n ≥ 3) and [C7H9O]+ (m/z 109) and C9H13O+ (m/z 137) in cresol derivatives (C6H3 · OH · CH3 · R) were formed, respectively, by alkene elimination reaction from MH+ and [M + C2H5]+. The characteristic [M + 13]+ and [M + 15]+ ions observed in several phenols were identified as [M + C3H5 – C2H4]+ ([M + CH]+) and [M + C3H7 – C2H4]+ ([M + CH3]+), respectively, by tandem mass spectrometry.
Tandem mass spectrometry of aminated fullerene derivatives
Authors: Davey Simon N. , Tetler Lee W. , Leigh David A. , Moody Andrew E. 
Published: May 2005

AbstractThe products of the reaction between fullerenes (C60/C70) and dimethylamine were investigated by fast atom bombardment (FAB) mass spectrometry and tandem mass spectrometry (MS/MS). The FAB mass spectrum shows peaks corresponding to the addition of up to eight dimethylamine species, exclusively to C70. MS/MS reveals an unusual fragmentation pattern. The mass spectrum of the reaction products, together with a number of tandem mass spectra, are shown.
Study of the major fragmentation pathways of cypermethrin and related synthetic insecticides using tandem mass spectrometry
Authors: Fleet Ian A. , Tetler Lee W. , Monaghan John J. 
Published: May 2005

AbstractFragmentation pathways of the synthetic pyrethroid cypermethrin and four structurally related insecticides were investigated using a tandem quadrupole mass spectrometer incorporating a hexapole collision cell under positive‐ion electron impact ionization conditions. Conventional mass spectrometry using the first quadrupole analyser only and tandem mass spectrometry on selected precursor ions and product ions, and also constant neutral loss scan experiments, were used. Mechanisms and fragmentation pathways are proposed to explain the inherent stability of ions associated with the benzylphenoxy portion of this class of insecticide.
Ion–molecule reactions and dissociation of glycols in a quadrupole ion trap mass spectrometer: Evidence of intramolecular interactions
Authors: Eichmann Erika S. , Brodbelt Jennifer S. 
Published: May 2005

AbstractPolyethylene glycols react with CH3OCH2+ ions from dimethyl ether to form [M + 13]+ products. The [M + 13]+ ions are stabilized by intramolecular interactions involving the internal ether oxygen atoms and the terminal methylene group. Collisionally activated dissociation (CAD), including MSn and deuterium labeling experiments show that fragmentation reactions involving intramolecular cyclization are predominant. Scrambling of hydrogen and deuterium atoms in the ion‐molecule reaction products is not indicated. The CAD spectra of the [M + 13]+ ions provide unambiguous assignment of the glycol size.
Formation and identification of ionized and neutral cumulenes, RNCCCNH, by tandem mass spectrometry
Authors: Flammang Robert , Laurent Sophie , Flammang‐Barbieux Monique , Wentrup Curt 
Published: May 2005

AbstractUsing a combination of mass spectrometric techniques, it is shown that 5‐amino‐4‐cyanoisoxazole molecular ions (1+˙), lose isocyanic acid HNO, not fulminic acid, HCN → O. Metastable ion fragmentations (unimolecular and collision induced) and deuterium‐labelling experiments are in agreement with the formation of a cumulenic structure, HNCCCNH (3a+˙). The hitherto unreported molecules HNCCCNH are also shown to be stable when formed in the low‐pressure gas phase of the mass spectrometer by using the technique of neutralization–reionization mass spectrometry. The arguments developed for the characterization of 3a+˙ have also been extended to the methylated and phenylated analogues 3b+˙ and 3c+˙ [RNCCCNH+˙, R = CH3 or C6H5]. On flash‐vacuum pyrolysis at 700°C, 1 also loses HNCO producing the cumulene 3a, which is in turn readily tautomerized into malononitrile via wall collisions.
Rearrangements in metastable ion decompositions of protonated propylamines
Authors: Audier Henri E. , Morton Thomas Hellman 
Published: May 2005

AbstractDecomposition of nPrNH3+ to NH4+ does not occur via vicinal elimination. Hydrogen transfer takes place from all positions of the alkyl chain. Intermediacy of either an ion–neutral complex. [iPr+ NH3], or rearrangement to iPrNH3+ is required. SCF calculations were used to probe the potential energy surface. There is a minimum corresponding to [iPr+ NH3], in which the nitrogen lone pair points towards the machine hydrogen and is 2.1 Å away from it, and another, less stable, minimum corresponding to a hydrogen‐bonded structure, H3N …︁ H3CCHCH3+, in which one methyl hydrogen is 2.0 Å from the nitrogen. Density of states estimates suggest that avibrationally excited complex can live for the order of 100 ps before either collapsing to iPrNH3+ or yielding NH4+ and propene.
Unimolecular reaction dynamics from kinetic energy release distributions. 1—dissociation of bromobenzene ions
Authors: Lorquet J. C. , Leyh B. 
Published: May 2005

AbstractPreliminary data on a new method for extracting dynamic data from the kinetic energy release distribution of metastable fragment ions are presented. This method can give information concerning the energy threshold of the reaction and the energy dependence of the rate constant (i.e. its logarithmic derivative). It was applied to bromine loss from bromobenzene cations.
On the sodium and lithium ion affinities of some α‐amino acids
Authors: Bojesen Gustav , Breindahl Torben , Andersen Ulla N. 
Published: May 2005

AbstractThe decomposition of 59 different cluster ions (generated by fast atom bombardment) consisting of two different amino acids and a sodium ion was analysed. The only fragment ions of significant abundance could be assigned to sodium ion‐bound amino acids. Assuming that the most abundant ion in the fragment ion spectrum corresponds to the amino acid with the highest sodium ion affinity (SIA), the 20 common α‐amino acids could be ordered with increasing sodium ion affinity as follows: Gly, Ala, Cys, Val, (Leu, Ile), Ser, Met, Thr, (Phe, Pro), Asp, Tyr, (Glu, Lys), Trp, Asn, Gln, His, Arg. Quantitative determinations were carried out by comparison of the lithium ion affinity (LIA) of Ala with that of dimethylformamide (DMF) in a fragment ion scan of the ion‐bound dimer Ala—Li+—DMF. LIA(Ala) was calculated from LIA(Ala) = LIA(DMF) – (1/C)ln[I(AlaLi+)/I(DMF—Li+)], where the constant C was estimated from measurements of proton‐bound amine–amino acid clusters. From fragment ion analysis of nine other Li+‐bound α‐amino acid dimers, the following lithium ion affinities were obtained: Gly 51.0, Ala 52.6, Sar 53.5, α‐aminobutyric acid 53.7, glycine methyl ester 54.7 and Val 54.8. SIA(Ala) was estimated to be 75% of the lithium ion affinity and from fragment ion analysis of ten Na+‐bound α‐amino acid dimers the following sodium ion affinities were obtained: Gly 37.9, Ala 39.4, α‐aminobutyric acid 40.3, Val 41.0, glycine methylster 41.0 and Sar 41.2.
Direct peptide profiling of single neurons by matrix‐assisted laser desorption–ionization mass spectrometry
Authors: van Veelen P. A. , Jiménez C. R. , Li K. W. , Wildering W. C. , Geraerts W. P. M. , Tjaden U. R. , van der Greef J. 
Published: May 2005

AbstractPeptide profiles of single neurons in Lymnaea stagnalis were directly characterized by matrix‐assisted laser desorption–ionization mass spectrometry. The mass analysis was performed after minor pretreatment and without any separation steps. Good‐quality spectra were obtained of several cell types and also other tissues. The results were compared with the results of conventional peptide chemical methods. In addition to many known peptides, several new peptides were identified. The method provides new opportunities for studying peptide compositions at the single‐cell level, which is shown to have many advantages.
Alkylation in electron impact mass spectrometry of hydrobromides of 2‐alkylthioorotic acids
Authors: Wyrzykiewicz E. , Bartkowiak G. 
Published: May 2005

AbstractThe mass spectral fragmentations of eight 2‐alkylthioorotic acids and their hydrobromides were investigated. Fragmentation pathways, the elucidation of which was assisted by accurate mass measurements and metastable transitions, are proposed. It was found that there is evidence in the electron impact mass spectra of the hydrobromides of 2‐alkylthioorotic acids of intermolecular transfer of an alkyl group.