bluuebunny/crossref_metadata_2025_split huggingface dataset:
Relative cyanide cation (+CN) affinities of pyridines determined by the kinetic method using multiple‐stage (MS3) mass spectrometry
Authors: Yang Sheng S. , Bortolini Olga , Steinmetz Annick , Cooks R. Graham 
Published: May 2005

AbstractIon–molecule reactions occurring in a pentaquadrupole mass spectrometer are used to generate and characterize ions in which one or two pyridine molecules are bound by a +CN cation. Cyanide cation binds strongly to the nitrogen atom of pyridine to generate a mono‐adduct, which undergoes pyridine exchange reactions and from which one can generate the dipyridine adduct in low abundance. The dimeric ions have two structures, loosely bound and covalently bound, and both fragment to yield the constituent cyanide‐bound monomers. In the case of dimers comprised of meta‐substituted alkylpyridines, there is a quantitative correlation between relative cyanide cation affinity, as measured using the kinetic method, and literature values of relative proton affinities. These dimers fragment analogously to the corresponding H+‐ and Cl+‐ bound dimers, and on this basis are assigned analogous structures, viz. the loosely bound form Py1+CNPy2. Semi‐empirical molecular orbital calculations show that both pyridines are bound to the carbon atom of the cyanide cation. Making the assumption that the effective temperatures of the activated cyanide‐bound dimers are similar to those of the corresponding Cl+‐ and H+‐bound dimers, relative +CN cation affinities are estimated to be 1.5 kcal mol−1 (3‐MePy), 1.7 kcal mol−1 (4‐MePy), 2.6 kcal mol−1 (3‐EtPy), 3.5 kcal mol−1 (3‐n‐BuPy) and 3.6 kcal mol−1 (3,5‐diMePy), all expressed relative to pyridine (1 kcal = 4.184 kJ). A linear relationship between the relative +CN affinity and relative proton affinity (PA) is derived as Δ +CN affinity (kcal mol−1) = 0.78 (ΔPA), with the assumption that the +CN dimer effective temperature is 600 K. The estimated uncertainty is 0.5 kcal mol−1. Relative +CN affinities of pairs of pyridines are smaller by ca. 1 kcal mol−1 than the corresponding Cl+ affinities. Dimers in which one of the pyridines is meta‐chlorine‐ or para‐alkyl‐substituted have the covalently bound, ring‐carbon‐substituted structure, in which the +CN group is attached to the pyridine nitrogen and the second pyridine molecule is bound to a ring carbon. The fragmentation of these isomeric dimers yields the corresponding monomers, in addition to other minor ions, but the distribution of the cyanide cation between the two pyridines does not correlate with Cl+ affinity or proton affinity. In the special cases of the 3‐methylpyridine–3‐n‐butylpyridine and the 4‐methylpyridine–pyridine cyanide cation adducts, both the loosely bound dimer and the covalently bound adduct are generated and distinguished by their fragmentation behavior. Evidence for the formation of the covalently bound, ring‐carbon‐substituted structure was also obtained in semi empirical AMI calculations.
Formation of buckministerfullerene phenylene derivatives in the gas phase
Authors: Kan Steven Z. , Byun Yong G. , Lee Samuel A. , Freiser Ben S. 
Published: May 2005

AbstractThe gas‐phase chemistry of Fe(C6H4)n+ (n = 1–6) with C60 is studied by using Fourier transform ion cyclotron resonance mass spectrometry. The formation of some ionic phenylene derivatives and metallacyclic derivatives of C60 is observed. Specifically, Fe+, generated by laser desorption, reacts with chlorobenzene to form iron‐benzyne, FeC6H4+, which initiates further reactions with chlorobenzene to form Fe(C6H4) and (C6H4). Fe(C6H4) react with C60 to form metalated fullerene derivatives, C60Fe(C6H4). C60Fe(C6H4) undergo a demetalation reaction with chlorobenzene to yield the fullerene phenylene derivatives C60(C6H4), 8 and 9, through formation of CC bonds with C60. CID experiments and kinetic analysis indicate that each of the C60Fe(C6H4) species consists of a single isomer, presumably the metallacycles 12 and 14. Consistent with the typical reactions of metal‐benzyne complexes with alkenes in the condensed phase, these metallacyclic structures are believed to be formed through coupling of one of the double bonds at the 6,6 ring junction in C60 with an FeC σ bond of Fe(benzyne)+. These results are consistent with the notion that C60 acts like an electron deficient alkene rather than an aromatic molecule, and suggest a possible synthetic route to prepare this type of metallo‐C60 derivatives in the condensed phase. Finally, ligand displacement reactions yield a bond dissociation energy of D°(Fe+C60) = 44 ± 7 kcal/mol.
Solanum alkaloids. 132—Electron impact mass spectrometry of solanidane N‐oxides
Authors: Quyen Le Thi , Schmidt Jürgen , Schreiber Klaus 
Published: May 2005

AbstractThe electron impact mass spectra of nine solanidane N‐oxides show, in addition to the known typical fragmentation pattern of the solanidane moiety, the fragment ions [M – C5H9]+ and [C6H12NO]+, due to thermal Cope syn‐eliminations caused by the N‐oxide function and subsequent cleavage of the bonds between C(22) and C(23) and between C(20) and C(22), respectively, in the so‐obtained cyclic N,N‐dialkylhydroxylamines.
Sample morphology effects in matrix‐assisted laser desorption/ionization mass spectrometry of proteins
Authors: Westman A. , Huth‐Fehre T. , Demirev P. , Sundqvist B. U. R. 
Published: May 2005

AbstractMillimetre‐sized crystals of 2,5‐dihydroxybenzoic acid and 3,5‐dimethoxy‐4‐hydroxycinnamic acid (sinapinic acid) were grown from a cytochrome c/matrix solution. Effects of sample exposure to UV laser irradiation on the matrix‐assisted laser desorption ionization mass spectra are reported for such single crystals. The exposure was varied by irradiating the same sample spot with different numbers of UV‐laser pulses. The ion yield and mass resolution were monitored as a function of the sample exposure. Further, the minimum deposited laser energy needed for protein ion production (the threshold energy) for single crystals was determined for incidence angles between 35° and 60° with respect to the target surface normal. The results were compared with those obtained for polycrystalline samples containing micrometre‐sized crystals.
Internal energy distribution of benzene molecular ions in surface‐induced dissociation
Authors: Vékey Károly , Somogyi Árpád , Wysocki Vicki H. 
Published: May 2005

AbstractThe so‐called ‘deconvolution’ method has been used to determine the internal energy distribution of molecular ions of an organic compound, benzene, excited by collisions with self‐assembled monolayer surfaces formed on gold. The average internal energy was found to increase linearly with the laboratory collision energy. The kinetic energy–internal energy (T–V) conversion was 17% for the octadecanethiolate monolayer and 28% for the 2‐(perfluorooctyl)‐ethanethiolate monolayer surface. The results are similar to those obtained for metal carbonyl projectiles, though they indicate somewhat higher energy conversion. In addition, excitation of the projectile ion well beyond 20 eV internal energy is observed.
Mass spectrometric characteristics of two novel series of ring‐C monounsaturated tricyclic terpenes found in Tasmanian tasmanite
Authors: de Almeida Azevedo Débora , de Aquino Neto Francisco Radler , Simoneit Bernd Rolf Tatsuo 
Published: May 2005

AbstractElectron impact and methane chemical ionization mass spectra were measured for two homologous series of monounsaturated tricyclic terpenes, Δ9(11) and Δ13(14). The double bond position was inferred by interpretation of their mass spectra, comparisons with the known saturated and ring‐C monoaromatic series, published mass spectrometric data on other terpenoids and MM2 calculations. The distributions of Δ13(14)‐ and Δ9(11)‐monounsaturated tricyclic terpene isomers were shown by theory and from experimental data to be dependent on the chain length at position 14. These two series coexist in the same geological sample. Δ9(11)‐monounsaturated tricyclic terpenes can be derived from the Δ13(14) compounds by isomerization of the double bond. The Δ9(11)‐monounsaturated tricyclic terpene series extends from C19 to C40 and the Δ13(14) series from C21 to C40. The diastereomers >C28 for both series could be resolved by gas chromatography.
Studies in organic mass spectrometry. Part 17—Formation of phenol radical ions by rearrangement of the molecular ions of some N‐arylthiophenecarboxamides and ‐benzamides
Authors: Ceraul Leopoldo , De Maria Paolo , Ferrugia Mirella , Foti Salvatore , Saletti Rosaria , Spinelli Domenico 
Published: May 2005

AbstractIt has been shown by exact mass measurements and collision‐induced dissociation mass‐analysed ion kinetic energy spectra that the structure of the m/z 124 ion observed in the mass spectra of N‐(4‐methoxyphenyl)thiophene‐2‐carboxamide, N‐(4‐methoxyphenyl)thiophene‐3‐carboxamide, N‐(4‐methoxyphenyl)‐5‐nitrothiophene‐3‐carboxamide and N‐(4‐methoxyphenyl)benzamide is identical with that of the molecular ion of 4‐methoxyphenol. This ion becomes abundant in metastable energy window reactions. A probable mechanism for its formation is discussed.
Dualorthointeraction in 2‐substituted‐3‐(2‐methylphenyl)‐4(3H)‐quinazolinones and their thio analogues under electron impact conditions
Authors: Ramana D. V. , Kantharaj E. 
Published: May 2005

AbstractCompetingorthointeractions, involving the CX and theortho‐methyl substituent on the 3‐phenyl moiety, resulting in the eliminations of˙CH3and˙OH/˙SH from the molecular ions of 2‐substituted‐3‐(2‐methylphenyl)‐4(3H)‐quinazolinones and their thio analogues, were observed. An intramolecular aromatic substitution of the heteroatom of CX at theortho‐carbon of the 3‐phenyl moiety ejecting the methyl group and a hydrogen transfer from the same ortho‐methyl substituent to the heteroatom of CX resulting in the expulsion of˙XH are envisaged for the dualorthointeraction. Another expected fragmentation process observed in these compounds is the transfer of the aryl group from the 3‐position of the heterocycle to the heteroatom of CX leading to the elimination of ArX˙from the molecular ions. The proposed fragmentation processes and the ion structures are supported by high‐resolution data,B/EandB2/Elinked‐scan spectra, collisionally activated decompositionB/Espectra and deuterium isotopic labelling.
Mass spectrometry of thio analogues of pyrimidine bases: Correlation of the intensities of the M+˙ and selected fragment ions of o‐(m‐ and p‐)substituted benzylthiouracils
Authors: Wyrzykiewicz E. , Nowakowska Z. 
Published: May 2005

AbstractThe mass spectral fragmentations of sixteen new 2‐and 4‐o‐(m‐ and p‐)substituted benzylthiouracils and o‐(m‐ and p‐)substituted 2,4‐dibenzylthiouracils with NO2 and CI substituents in the benzyl groups were investigated. Fragmentation pathways are proposed on the basis of accurate mass and metastable transitions measurements. The correlation between the abundances of the M+˙ and the selected fragment ions of investigated compounds is discussed. The data obtained create the basis for distinguishing structural isomers.
Rearrangement processes of negative ions in the gas phase: [M  Hal]− ions in halogenated azobenzenes. Resonance stabilization of negative ions
Authors: Muftakhov M. V. , Vasil'ev Yu. V. , Masunov V. A. , Takhistov V. V. , Ponomarev D. A. 
Published: May 2005

AbstractIonization efficiency curves for [M  X]− ions from p‐XC6H4NNC6H5 molecules (XF, Cl, Br) have been registered in the energy range 0–9 eV with appearance energies 3.3, 4.1 and 3.2 ± 0.2 eV, respectively. The heats of formation of 17 isomeric C12H9N− ions have been estimated using isodesmic reactions. The possible mechanism of isomerization of molecule ions leading to various isomeric [M  X]− ions is represented. The resonance stabilization of both negative and positive ions, questioned for negative ions by some workers, was confirmed by measuring appearance energies of conjugated ions [M  H]− and [M  (CCl2 + CI)]− or [M  Me]+ and [M  CCl3]+ coming from p‐MeC6H4OR (R or Me) and 4‐Methyl‐4‐trichloromethylcyclohexa‐2,5‐dienone, respectively.
Liquid secondary ion mass spectra and fast atom bombardment mass spectra of diquaternary pyridinium oxime salts
Authors: Kunkel Gary J. , Busch Kenneth L. , Dunphy Richard , Burinsky David J. , Barak Ruth , Bel Peter , Amitai Gabriel , Vincze Adam 
Published: May 2005

AbstractPositive‐ion mass spectra of diquaternary pyridinium oxime salts were measured using fast atom bombardment and liquid secondary ion mass spectrometry in different laboratories to establish both the characteristic behavior and the spectral variability of this class of compounds. Molecular ions observed in these mass spectra include the one‐electron reduced doubly charged cation, the deprotonated double charged cation and the anion‐reduced doubly charged cation. Common fragment ions include the products of simple cleavages along the aliphatic bridge between the heterocyclic rings. Concomitant loss of hydrogen and cyclization of the bridge can occur, along with losses of OH, NOH and CHNOH from various fragment ions. A nitrobenzyl alcohol matrix generally gave superior results to glycerol and thioglycerol in all laboratories, although the use of additive surfactant acids such as p‐toluenesulfonic acid or camphorsulfonic acid in glycerol could provide useful results.
Linear energy correlation in the low‐energy tandem mass spectra of protonated tripeptides Xxx–Gly–Gly but failure for Gly–Xxx–Gly
Authors: Morgan Daniel G. , Bursey Maurice M. 
Published: May 2005

AbstractThe backbone cleavages of protonated tripeptide ions of the series Xxx–Gly–Gly, where Xxx–Gly, Ala, Val, Leu, Ile, Phe, Tyr, Met, Pro and Trp, were studied in a hybrid tandem mass spectrometer. C‐Terminal y‐type ions and N‐terminal a‐ and b‐type ions were noted. A linear relationship between log (intensity of y2 divided by the sum of all other product ion intensities) and the proton affinity of the N‐terminal amino acid substituent was found for the series Xxx–Gly–Gly: as the proton affinity of the N‐terminal residue increases, the fraction of y2 ion formation decreases. The series of protonated tripeptides Gly–Xxx–Gly, where Xxx = Gly, Ala, Leu, Phe, Tyr, Met and Trp, were also studied.
A molecular orbital description of aromatic cluster ions produced in continuous‐flow fast atom bombardment
Authors: Jarvis V. M. , Moran T. F. 
Published: May 2005

AbstractCluster ions from the continuous‐flow fast atom bombardment of several pure, liquid aromatics were examined. Most of the aromatics cluster as (M)n+; however, aromatic bases such as pyridine and aniline also form (M)nH+ ions. The abundance of both (M)n+ and (M)nH+ cluster ions decreases rapidly as n increases. The semi‐empirical molecular orbital PM3 method was used to examine energetics of cluster ion formation, binding energies of several aromatic dimer ions and structures of stable cluster ions observed in the desorption process.
Plasma desorption mass spectrometry of small straight‐chain and cyclic alkenes
Authors: Betts Robert L. , Park Melvin A. , Schweikert Emile A. 
Published: May 2005

AbstractThe plasma desorption mass spectra of straight‐chain and cyclic alkenes and cyclic alkadienes were examined to gain a better understanding of the influence of structure on mass spectral characteristics. The results are compared with electron impact data because the excitation and ionization mechanisms are influenced by electronic transitions, and are also compared with chemical ionization data because of the possibility that ion–molecule reactions may occur during the desorption process. Several ions related to the molecular ion by gain or loss of hydrogen are produced in all spectra. For plasma desorption, our data suggest that energy dissipation in the solid phase influences the intensity of these ions. A chemical ionization‐like process is proposed to explain the gain or loss of hydrogen atoms. The spectra of conjugated and unconjugated cyclooctadienes give evidence of the formation of benzene‐like ions. The fragment ions produced from these compounds indicate an electron impact‐like fragmentation mechanism, while fragments from other compounds suggest a chemical ionization‐like fragmentation process.
Dimethyl ether and dimethyl‐d6 ether chemical ionization mass spectrometry of polynuclear aromatic hydrocarbons
Authors: Burrows Elizabeth P. 
Published: May 2005

AbstractDimethyl ether (DME) chemical ionization mass spectrometry of a number of polynuclear aromatic hydrocarbons (PAHs) gave rise to a variety of fragment–molecule adduct ions resulting from ion–molecule reactions with the reagent gas. In 18 out of 22 cases, it was possible to differentiate among non‐nitrogenous PAHs on the basis of the identities and relative abundances of these adduct ions alone. For 14 nitrogen‐containing PAHs, adduct ion profiles were less distinct and differentiation among isomers was limited but possible in certain cases. With DME‐d6 as the reagent gas, the corresponding perduterio adduct ions were seen in substantially reduced abundances relative to their unlabeled counterparts, and there was no scrambling of deuterium. For the majority of the non‐nitrogenous PAHs and all of the nitrogen‐containing PAHs the most abundant ion was the methoxymethylene cation [M + 45]+. Collision‐induced dissociation studies of these ions demonstrated that fragmentation can take place according to three major pathways.
Electrospray mass spectral studies of aromatic diazonium salts and diazotates
Authors: Broxton Trevor J. , Colton Ray , Traeger John C. 
Published: May 2005

AbstractElectrospray (ES) mass spectra were observed for a series of aryldiazonium cations and the intact ions were observed. Collisionally activated decompositions lead to facile loss of nitrogen to form the corresponding aryl cations. Comparisons of the proportion of intact and fragment ions for each cation at a constant collisional energy lead to an order of relative stability for the diazonium cations which is similar to that determined in solution by chemical methods. Negative‐ion ES mass spectra were observed for the intact ions for the corresponding diazotates. Like the diazonium cations, they also readily lose nitrogen in collisionally activated decompositions to give the phenolate anions [OAr]−.
Ion source for electrohydrodynamic mass spectrometry
Authors: Dülcks Th. , Röllgen F. W. 
Published: May 2005

AbstractEarly in the development of electrohydrodynamic mass spectrometry (EH‐MS), it was realized that ion source performance improved when the sample liquid was supplied discontinuously to the capillary emitter. Based on this realization, an ion source was designed that operates without an external sample supply system. Its essential part is a metal capillary that serves both as the liquid reservoir and the field anode and is mounted exchangeably on a pushrod. As the liquid flow is field induced, the flow rates are extremely low, in the range of 0.2 nl min−1. Thus, in spite of high analyte concentrations needed, sample consumption is only a few picomoles per mass scan. Moreover, the emission of larger droplets is avoided, which contributes to the stability of the ion signal. As the capillary emitter is mounted on a standard emitter carrier known from field desorption (FD) MS, the new ion source is compatible with conventional FD ion sources. EH mass spectra of analytes could be obtained from substances whose solubility in glycerol was>0.5 mol l−1. The substances investigated with the new ion source include sugars, amino acids, peptides and an antibiotic. The general characteristics of the mass spectra are essentially the same as those known from other EH ion sources. Besides abundant solvent cluster ions, only cationated or protonated molecules of the analytes could be detected, frequently with one or more solvent molecules attached to the ions. Fragment ions were not observed.
Collection of ion‐trap mass spectra of sulfonylurea pyrolysis products
Authors: Galletti Guido C. , Dinelli Giovanni , Chiavari Giuseppe 
Published: May 2005

AbstractThe pyrograms of 14 sulfonylureas, i.e. herbicides characterized by high biological activity and low application dose are discussed and the mass spectra of over 30 relevant pyrolysis products as obtained with a heated filament pyrolyzer interfaced to a capillary gas chromatograph/ion‐trap detector mass spectrometer are presented. Such a data compilation is useful for diagnostic purposes for both intact suflfonylureas and their metabolites after degradation in soil, because metabolites and pyrolysis products are often identical and most of their mass spectra are lacking in commercially available mass spectral libraries. The performance of the ion‐trap detector based on the quality of the mass spectra is briefly discussed.
Proton transfer reactions of multiply charged peptide and protein cations and anions
Authors: Loo Rachel R. Ogorzalek , Smith Richard D. 
Published: May 2005

AbstractTwo types of gas‐phase proton transfer reactions were examined with electrospray ionization‐generated peptide and protein ions; (i) bases reacting with multiply protonated molecules and (ii) acids reacting with multiply deprotonated molecules. For reactions of type (i) with bases spanning a range of proton affinities, the proton transfer reaction rate was observed to increase with increasing proton affinity of the charge transfer reagent. Proton transfer was not observed for the low proton affinity reagents (ethyl acetate, acetonitrile and water). These studies also qualitatively measured for the first time the temperature dependences for reactions with multiply charged peptides and proteins. Negative temperature dependences were observed for the weaker bases and positive dependences for the stronger bases. A negative temperature dependence was also observed in the reaction of propionic acid with [M – nH]n− ions. Two hypotheses are proposed to explain the data. In the first, negative temperature dependences are attributed to slightly exothermic reactions, while the positive dependences may reflect contributions from a competing clustering pathway, a pathway which could be more dominant with the heavier reagents. Alternatively, the positive temperature dependences may reflect the barrier in the reaction coordinate arising from the repulsion of like‐charged ions, while negative temperature dependences could reflect a cluster‐mediated reaction in which charge delocalization lowers the barrier to proton transfer. In the latter cases, clustering is invoked with the lower proton affinity reagents because of the higher concentrations employed.