bluuebunny/crossref_metadata_2025 huggingface dataset:
Internal energy distribution of benzene molecular ions in surface‐induced dissociation
Authors: Vékey Károly , Somogyi Árpád , Wysocki Vicki H.
Published: May 2005

The 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

Electron 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

It 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

Competingorthointeractions, 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

The 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

Ionization 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

Positive‐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

The 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

Cluster 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

The 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

Dimethyl 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

Electrospray (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

Early 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

The 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

Two 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.
Mass fragmentographic assay for 25‐hydroxyvitamin D in plasma without derivatization: Enhanced sensitivity for metabolites of vitamins D2 and D3 after pre‐column dehydration
Authors: Coldwell Ruth D. , Trafford D. J. H. , Makin H. L. J.
Published: May 2005

A mass fragmentographic method for the measurement in plasma of underivatized, dehydrated 25‐hydroxyvitamin D2 and 25‐hydroxyvitamin D3 was developed. Quantitative dehydration of vitamin D metabolites was achieved prior to gas chromatography using a new high‐temperature injection system and a small precolumn packed with aluminium powder in the injection port, followed by mass fragmentography on an inexpensive bench‐top mass spectrometer. Plasma (2 ml) was incubated with hexadeuteriated 25‐hydroxyvitamin D3 prior to acetonitrile extraction and purification using cartridges pre‐packed with microparticulate silica using reversed‐ and normal‐phase solvent systems. After purification, capillary gas chromatography mass spectrometry was carried out following dehydration of the secosteroids on the aluminium power pre‐column at 400°C. High‐intensity dehydrated molecular ions were produced which were used for selected ion monitoring. The assay sensitivity for 25‐hydroxyvitamin D was approximately 1 ng ml−1. The intra‐assay variation was less than 7% and the recovery of added standard was quantitative. It is suggested that this method may be used to provide target values for much needed quality control schemes to monitor assays routinely used in the estimation of 25‐hydroxyvitamin D. The behaviour of a number of other hydroxylated vitamin D metabolites, when injected without derivatization on to a gas chromatographic column, was also investigated.
Quantitative bioanalysis using matrix‐assisted laser desorption/ionization mass spectrometry
Authors: Jespersen S. , Niessen W. M. A. , Tjaden U. R. , van der Greef J
Published: May 2005

The application of matrix‐assisted laser desorption/ionization mass spectrometry (MALDI‐MS) for quantitative analysis was investigated with the use of internal standards. Three peptides/proteins in the mass range 1000–12000 were tested and the effect of various internal standards was evaluated. Horse cytochrome c was used as an internal standard for bovine cytochrome c, melittin for renin and an undecapeptide B analogue was employed as an internal standard for the decapeptide A. A linear response was found between the measured peak height ratio and the applied amount of analyte when an appropriate internal stanard was used. The quantitative abilities of MALDI‐MS were finally applied to the determination of the drug amperozide in plasma. The biological samples were prepared for analysis using liquid–liquid extraction prior to MALDI‐MS. A linear calibration graph was obtained using the 13C4 stable isotopically labelled amperozide as an internal standard.
Identification of the metabolites of MX/2/120 in the guinea‐pig by high‐performance liquid chromatography/thermospray tandem mass spectrometry
Authors: Triolo Antonio , Bonelli Fabio , Agostini Orenzo , Bonacchi Graziano , Toja Emilio
Published: May 2005

The metabolism of MX/2/120, a new xanthine derivative endowed with potent and long‐lasting antibronchospastic activity, was investigated in guinea‐pig urine, plasma and bile after intravenous administration of 12.5 mg kg−1 by high‐performance liquid chromatography/tandem mass spectrometry with thermospray ionization. Following a first series of collisionally activated neutral losses and parent ion scan experiments performed on urine samples, potential quasi‐molecular ions of possible metabolites were identified, which were then analysed by collisionally activated fragment ion scans. A side‐chain carboxylated, a side‐chain hydroxylated and a xanthine‐ring demethylated metabolite, along with the unmodified drug, were identified. In urine, MX/2/120 and its hydroxylated metabolite were also present as glucuronic acid conjugates. In plasma and bile, only the unmodified drug was found. The structures of the identified metabolites were then confirmed by comparison with the authentic compounds prepared by synthesis.
Thin‐layer chromatography/laser desorption of peptides followed by multiphoton ionization time‐of‐flight mass spectrometry
Authors: Krutchinsky A. N. , Dolgin A. I. , Utsal O. G. , Khodorkovski A. M.
Published: May 2005

The location of the separated compounds of GlnTrp/GlyTyr and pentagastrin/gramicidin D peptide model mixtures on silica gel and cellulose thin‐layer chromatography plates has been examined by laser desorption multiphoton ionization time‐of‐flight mass spectrometry. The multiphoton ionization mass spectra of neutrals desorbed by sequential scanning of the thin‐layer chromatography plates versus the infrared laser spot allowed imaging of the distribution profile of the compounds. The method appeared to be promising for the analysis of thin‐layer chromatograms.
A mass‐spectrographic study of the isotopes of argon, potassium, rubidium, zinc and cadmium
Authors: Nier Alfred O.
Published: May 2005

A mass spectrograph is described with which a study of the isotopic constitution of argon, potassium, rubidium, zinc and cadmium has been made. A calculation is carried out which indicates that the radioactivity of potassium and rubidium can best be explained by assuming that it is K40 in the case of potassium and Rb87 in the case of rubidium which is undergoing decay.
Utility of nicotinoyl derivatives in structural studies of mono‐ and diacylglycerols by gas chromatography/mass spectrometry. Part 2
Authors: Zöllner P. , Lorbeer E.
Published: May 2005

The positional isomers of mono[(Z)‐9‐octadecenoyl] glycerol, di[(Z)‐12‐octadecadienoyl] glycerol were derivatized with nicotinic acid chloride hydrochloride. The resulting nicotinoyl derivatives were examined by gas chromatography/mass spectrometry. In their electron impact mass spectra, each methylene group and double bond of the alkyl chain is reflected by a fragmentation pattern in the high mass region. This is caused by radical‐induced cleavage of the alkyl chains following random hydrogen abstraction by the pyridine nucleus. An accurate determination of double bond positions in mono‐ and diacylglycerols is possible by characteristic spacings between abundant diagnostic ions in this fragmentation pattern.
Development and application of a gas chromatographic/mass spectrometric/mass spectrometric method for the determination of 5‐methoxyflavone in rat and dog plasma
Authors: Baker Timothy R. , Wehmeyer Kenneth R. , Kelm Gary R. , Tulich Linda J. , Kuhlenbeck Debra L. , Dobrozsi Douglas J. , Penafiel Jorge V.
Published: May 2005

A gas chromatographic/mass spectrometric/mass spectrometric method was developed for the determination of 5‐methoxyflavone in plasma. Optimized detection schemes for 5‐methoxyflavone readily allow a limit of quantification of 1 ng ml−1 in rat or dog plasma (1.0 ml sample volume). The complete analysis time (injection to injection) is less than 9 min and allows for rapid automated sample throughput. Additional advantages include a high degree of specifity and good accuracy and precision. This type of rapid tandem mass spectrometric assay has been found to be particularly useful in pharmaceutical discovery, since an assay for one compound can be quickly developed, utilized and then modified to determine analogs of similar structure. Application of this methodology to pilot preclinical pharmacokinetic studies of the drug indicated that it is rapidly absorbed and cleared, with an apparent terminal half‐life of about 15 min in dogs. Bioavailability in the two dogs tested ranged 33 to 72%, but was about 25% in rats.
Use of electrospray ionization and neutral loss liquid chromatography/tandem mass spectrometry in drug metabolism studies
Authors: Jackson P. J. , Brownsill R. D. , Taylor A. R. , Walther B.
Published: May 2005

The application of liquid chromatography/mass spectrometry (LC/MS) and LC/MS/MS with electrospray ionization to drug metabolism studies was investigated using S 9788 and various synthesized metabolic products as model compounds to assess the response characteristics with regard to compound lipophilicity and the influence of biological matrix components. The results obtained demonstrate the versatility of the electrospray ionization technique to analyse compounds of widely varying polarity and the power of MS/MS to identify unequivocally metabolic products. These techniques offer a very rapid screening procedure that can be used to identify metabolic products and thus provide important early metabolic information that can be used in the candidate drug selection programme. These procedures were then applied to an in vivo study sample and, using neutral loss MS/MS, it was possible to detect metabolites of S 9788 directly from a crude biological matrix (bile) without prior extraction or chromatography to confirm positively the identity of five important metabolites of S 9788 in the rat.
Identification of Fenton's reagent‐generated atrazine degradation products by high‐performance liquid chromatography and megaflow electrospray ionization tandem mass spectrometry
Authors: Arnold Scott M. , Talaat Rasmy E. , Hickey William J. , Harris Robin F.
Published: May 2005

High‐performance liquid chromatography megaflow electrospray tandem mass spectrometry (HPLC/ES‐MS/MS) with an on‐line radioisotope detector was used to identify [2,4,6‐14C] atrazine degradation products generated by treatment with Fenton's reagent (Fe2+ and H2O2). Fenton's reagent produced dealkylated and/or partially oxidized [2,4,6‐14C] atrazine products in preference to dechlorinated products. Seven major products were identified by collision‐induced dissociation spectra: 4‐acetamido‐2‐chloro‐6‐(isopropylamino)‐s‐triazine, 4‐amino‐2‐chloro‐6‐(isopropylamino)‐s‐triazine, 4‐acetamido‐2‐chloro‐6‐(ethylamino)‐s‐triazine, 6‐amino‐2‐chloro‐4‐(ethylamino)‐s‐triazine, 4‐acetamido‐6‐amino‐2‐chloro‐s‐triazine, 2‐chloro‐4,6‐diamino‐s‐triazine and the first report of 4‐acetamido‐2‐hydroxy‐6‐(isopropylamino)‐s‐triazine. HPLC/ES‐MS/MS provided a rapid method for identifying a wide range of atrazine transformation products in aqueous samples and obviated the need for fraction collection, extraction, and chemical derivatization of the more polar atrazine products. Furthermore, because analyte retention times in HPLC/UV and HPLC/ES‐MS/MS were similar, compound identities determined using the latter could be directly assigned to peaks in UV chromatograms.
Mass spectra of 1,3‐dithiaspiranes and 2‐aryl‐1,3‐dithianes
Authors: Shiue Gong‐Yih , Lin Shaw‐Tao , Kuo Yueh‐Hsiung , Chen Zong‐Shiow
Published: May 2005

The mass spectra of 20 1,3‐dithianes were studied. The fragmentation patterns including the loss of 74 u and 107 u and clearage of the substituent at C‐2 depended strongly on the nature of the substituents at that position. 2,2‐Diphenyl‐1,3‐dithiane undergoes an atypical fragmentation in which two hydrogens migrate from the phenyl ring, with the formation of a fluorene skeleton.
High‐sensitivity liquid chromatography–combustion isotope ratio mass spectrometry of fat‐soluble vitamins
Authors: Caimi Richard J. , Brenna J. Thomas
Published: May 2005

The sensitivity of high‐precision liquid chromatography/combustion isotope ratio mass spectrometry (LC/C‐IRMS) was improved by more than two orders of magnitude by modifications which permit optimization of flows. The lower limits for high precision are about 3 μg of analyte on‐column for flow injection and LC modes. Pneumatic aerosol spray coating was implemented and compared with simple dip coating. The signal enhancement for aerosol compared with dip coating is up fourfold at higher levels but drops to less than twofold at lower levels, while the dynamic range is extended at higher levels by fourfold at high sample load levels. LC separations for underivatized tocopherols, retinyl acetate and ergocalciferol are demonstrated with precision and accuracy of about δ13C < 2.5% for replicates. This work demonstrates sensitivity useful for a wide range of LC analyses and extends high‐precision LC/C‐IRMS to the determination of several fat‐soluble vitamins.
Linear free energy correlation in the low‐energy tandem mass spectra of sodiated tripeptides Gly‐Gly‐Xxx
Authors: Morgan Daniel G. , Bursey Maurice M.
Published: May 2005

The backbone cleavages of 14 sodiated tripeptides of the series Gly‐Gly‐Xxx, where Xxx = Gly, Ala, Val, Leu, Ile, Phe, Tyr, Met, Glu, Pro, Trp, Lys, His and Arg, were studied in a hybrid tandem mass spectrometer. A C‐terminal y‐type ion of the form y1 + Na + H was noted in all cases studied. N‐Terminal bn + Na + 17, bn + Na ‐ H and an + Na – H ions, along with internal fragments, were also noted. Because information on sodium affinities of amino acids is limited, the sodiated tripeptides studied were compared not only with the rank ordering of amino acid sodium affinities, but also on the basis of available proton affinities. A linear relationship between log[(y1 + Na + H)/(b2 + Na + 17)] and the proton affinity of the C‐terminal amino acid substituents was found: as the proton affinity of the C‐terminal residue increases, the fraction of y1 ion formation increases. When the C‐terminal substituent was more basic than Trp, the correlation does not hold, probably because the highly basic amino acids, Lys, His, and Arg, are cationized on the side‐chain instead of on the terminal amino group.
Comparison of [5,5,5‐2H3]leucine and [ring‐2H5]phenylalanine tracers for the measurement of human apolipoprotein B100 kinetics
Authors: Maugeais C. , Ouguerram K. , Maugeais P. , Simoneau C. , Gardette J. , Magot T. , Krempf M.
Published: May 2005

Incorporation of amino acids labeled with stable isotopes in apoliproproteins is used to estimate kinetic aspects of lipoprotein metabolism. In this study two deuterated tracers, [5,5,5‐2H3]leucine and [ring‐2H5]phenylalanine, were compared. Isolation and acid hydrolysis of apolipoproteins are required for mass spectrometric analysis. When apolipoprotein B100 of very low density liproproteins was prepared with this procedure, a loss of deuterium was observed on deuterated phenylalanine with 10 and 6 M HCl hydrolysis but not with deuterated leucine or when 4 M HCl hydrolysis was used. This study stre sses the effect of acid hydrolysis on [ring‐2H5]phenylalanine. This tracer must be used with caution in studies of specific protein synthesis.
Influence of the matrix on the analysis of small oligoribonucleotides by fast atom bombardment mass spectrometry
Authors: Wolter Marek A. , Engels Joachim W. , Montanarella Luca , Tilio Roberto , Facchetti Sergio
Published: May 2005

The analysis of oligonucleotides by mass spectrometry should give information on both the molecular mass and sequence. Fast atom bombardment mass spectrometry gives both in one step. Until now glycerol, thioglycerol and triethanolamine have been used as matrices for the analysis of oligonucleotides by fast atom bombardment mass spectrometry (FABMS), but there have been no comparative studies for matrix selection for these specific analytes. In this work, the influence of diethanolamine, glycerol, 1‐thioglycerol and triethanolamine on the analysis of unprotected trimer up to heptamer oligoribonucleotides was studied using negative‐ion FABMS on a sector‐type mass spectrometer. Collision‐induced dissociation MS/MS measurements were performed and the fragmentation patterns in MS and MS/MS were compared.
Interconversions of C5H10O+· ions with the oxygen on the first, second and third carbons: Approximately 60 communicating isomers
Authors: McAdoo David J. , Hudson Charles E.
Published: May 2005

The structures of the C4H7O+ and C3H6O+· dissociation products from selected C5H10O+· isomers with the oxygen on the first, second and third carbons were determined. The first product is CH3C(OH)CHCH2+ and the second is CH3C(OH+)CH2⋅ and CH3⋅CHCHOH+ in various proportions. These results demonstrate that ions with the oxygen on the first and third carbons isomerize partially to isomers with the oxygen on the second carbon. This and C5H10O+· isomers expected to be accessible to each other suggest that there are traversable pathways between about 60 C5H10O+· isomers, demonstrating how extensive interconversions of aliphatic radical cations can be.
Profiling 19‐norsteroids. I—tandem mass spectrometric characterization of the heptafluorobutyryl ester and pentafluorobenzyloxime heptafluorobutyryl ester derivatives of 19‐nortestosterone using collisionally activated dissociation
Authors: de Boer D. , Bensink S. N. , Borggreve A. R. , van Ooijen R. D. , Maes R. A. A.
Published: May 2005

Tandem mass spectrometric methods for the identification of 19‐nortestosterone (estr‐4‐en‐17β‐3‐one) are described and evaluated. The fragmentation reactions of the heptafluorobutyryl (HFB) and pentafluorobenzyloxime heptafluorobutyryl (PFBOHFB) ester derivatives of 19‐nortestosterone in particular were studied for the purpose to select characteristic ions. The HFB ester was analyzed by collisionly activated dissociation (CAD) following electron impact in order to fragment the steroid nucleus. Cleavage of the A‐ring, i.e. the ring containing the keto function, was prominent. The formation of A‐, A/B‐ and D‐ring fragments was also typical for this type of derivative. The PFBOHFB ester was formed to create a derivative, which could capture electrons and be analyzed in the electron‐capture negative chemical ionization (ECNCI) mode. Besides fragmentations originating in the groups coupled to the steroid by derivatization, no prominent steroid nucleus fragmentations were observed by CAD following ECNCI. Accordingly, of both methods only CAD following EI of the HFB derivative of 19‐nortestosterone provided a characteristic MS/MS procedure for the identification of 19‐nortestosterone.
Profiling 19‐norsteroids. II—tandem mass spectrometric characterization of the heptafluorobutyryl ester and pentafluorobenzyloxime heptafluorobutyryl ester derivatives of 19‐norandrosterone using collisionly activated dissociation
Authors: de Boer D. , Bensink S. N. , Borggreve A. R. , van Ooijen R. D. , Maes R. A. A.
Published: May 2005

Tandem mass spectrometric methods for the identification of 19‐norandrosterone (3α‐hydroxy‐5α‐estran‐17‐one) are described and evaluated. The fragmentation reactions of the heptafluorobutyryl (HFB) and pentafluorobenzyloxime heptafluorobutyryl (PFBOHFB) ester derivatives of 19‐norandrosterone (3α‐hydroxy‐5α‐estran‐17‐one) in particular were studied for the purpose to select characteristic ions. The HFB ester was analyzed by collisionly activated dissociation (CAD) following electron impact in order to fragment the steroid nucleus. The formation of D‐ring fragments, i.e. the ring containing the keto function, was typical for this type of derivative. Cleavages of fragments with an intact D‐ring were also prominent. The PFBOHFB ester was formed to create a derivative, which could capture electrons and be analyzed in the Electron Capture Negative Chemical Ionization (ECNCI) mode. Besides fragmentations originating in the groups coupled to the steroid by derivatization, also characteristic D‐ring fragments were observed by CAD following ECNCI. Accordingly, of both methods evaluated only CAD following EI of the HFB derivative of 19‐norandrosterone provided a characteristic MS/MS procedure for the identification of 19‐norandrosterone under the conditions studied.
Special feature: Perspective. Mass spectrometric peptide and protein charting
Authors: Feistner Gottfried J. , Faull Kym F. , Barofsky Douglas F. , Roepstorff Peter
Published: May 2005

Six years after coining the term ‘mass spectrometric (MS) peptide charting’ for the component analysis of peptide mixtures in a whole tissue, body fluid, or an extract thereof, we offer our current perspective of this field. Matrixassisted laser desorption/ionization and electrospray ionization have replaced plasma desorption and fast atom bombardment as ionization methods of choice. At the same time, the upper mass range has been extended to now include most peptides and proteins of interest to research on cell‐cell communication. In addition to qualitative aspects, quantitative applications of MS charting have become important. In combination with new database search algorithms, on‐line liquid chromatography‐tandem mass spectrometry promises greater dividends from MS charting than are achievable with molecular mass matching alone. We discuss what is and is not yet possible, and consider foreseeable means for overcoming current limitations. Our intent is to encourage researchers in the biological and medical sciences to take advantage of this powerful methodology in their various fields of endeavor.
Detection and characterization of native β‐endorphin1–31 in bovine pituitary using electrospray ionization, liquid secondary ion and tandem mass spectrometry
Authors: Yan Lin , Tseng Jih‐Lie , Desiderio Dominic M.
Published: May 2005

The molecular ion of intact β‐endorphinbovine, 1–31 (BE), which was extracted from bovine pituitary, was determined by electrospray ionization mass spectrometry. Liquid secondary ion mass spectrometry determined the molecular masses of three peptides produced by trypsin digestion of BE, and tandem mass spectrometry was used to determine the amino acid sequence of the tryptic peptide BE20–24. These data, in combination, were used to characterize BE in bovine pituitary.
Ammonia chemical ionization mass spectrometry of substituted phenylpropanoids and phenylalkyl phenyl ethers
Authors: van der Hage Erik R. E. , Weeding Tina L. , Boon Jaap J.
Published: May 2005

The ammonia chemical ionization (NH3/CI) spectra of phenylpropanoids and substituted phenylalkyl phenyl ethers containing α‐hydroxy or α‐carbonyl functional groups are discussed. Fragmentation reactions which occur in the temperature range 180–450°C are examined to model pyrolysis mass spectrometric experiments of lignin. Hydroxycinnamyl alcohols and α‐hydroxy phenylalkyl phenyl ethers show abundant [M + H − H2O]+ elimination ions and to a lesser extent [M + NH4 − H2O]+ substitution ions while hydroxycinnamic acids and α‐carbonyl phenylalkyl phenyl ethers show predominantly [M + H]+ and [M + NH4]+ ions. The interpretation of functional group information is facilitated by using trideuterioammonia (ND3) and [15N] ammonia (15NH3) as reagent gases. Labile hydrogens undergo essentially complete exchange upon ND3/CI and the number of hydroxyl functional groups is readily determined by comparison of the [M + NH4]+ and [M − nH + nD + ND4]+ adduct ions. Incomplete HD exchange is observed for enolizable and aromatic protons.
Fast atom bombardment tandem mass spectrometry of the anti‐parasitic agent pentamidine and its oxygenated metabolites
Authors: van Breemen Richard B. , Jiang Ou , Tidwell Richard R. , Hall James Edwin , Brewer Thomas G.
Published: May 2005

Although pentamidine (1,5‐bis(4′‐amidinophenoxy)pentane) is currently in use for the treatment of a variety of parasitic infections, including acquired immune deficiency syndrome‐related Pneumocystis carinii pneumonia, its metabolism is still under investigation. Positive‐ion fast atom bombardment mass spectrometry was used with high‐energy collision‐activated dissociation (CAD) and linked scanning at constant B/E to obtain tandem mass spectra of protonated molecules of pentamindine and seven synthetic oxygenated derivatives, which are known metabolites of pentamidine. Charge‐initiated fragmentation produced abundant fragment ions of m/z 120 and 137 and loss of neutral ammonia from the protonated analyte that characterized the amidinophenoxy group. The structures of isomeric 2‐hydroxypentamidine, 3‐hydroxypentamidine and N‐hydroxypentamidine could be distinguished based on charge‐remote fragmentation that produced a series of fragment ions of the pentyl chain and permitted the exact location of the hydroxyl group in each molecule to be determined. Next, tandem mass spectra were obtained and the charge‐initiated and charge‐remote fragmentation discussed for four other metabolites of pentamidine, including N,N′‐dihydroxypentamidine, 5‐(4′‐amidinophenoxy)pentanoic acid, 5‐(4′‐amidinophenoxy) pentan‐1‐ol, and p‐hydroxybenzamidine. Finally, tandem mass spectrometry was used to identify pentamidine and three pentamidine metabolites contained in high‐performance liquid chromatographic (HPLC) fractions from rat liver perfusate and rat urine following treatment with pentamidine. Pentamidine metabolites identified in rat urine and liver perfusate using mass spectrometry and HPLC retention times included 2‐hydroxypentamidine, 3‐hydroxypentamidine and 5‐(4′‐amidinophenoxy)pentanoic acid.
Reactions of selected molecular anions with oxygen
Authors: Knighton W. B. , Bognar J. A. , Grimsrud E. P.
Published: May 2005

An investigation of the gas‐phase reactions of molecular oxygen with the molecular anions of 17 compounds formed by resonance electron capture was undertaken using a pulsed e‐beam high‐pressure mass spectrometer. The molecular anions of sulphur hexafluoride, perfluromethylcyclohexane, cis‐ and trans‐perfluorodecalin, m‐chloronitrobenzene, o‐, m‐and p‐fluoronitrobenzene and o‐, m‐ and p‐dinitrobenzene were found to be unreactive towards oxygen. Those of o‐ and p‐chloronitrobenzene, penta‐ and perchlorobenzene, perfluorobenzene, and perfluorotoluene were found to react readily with oxygen. The second‐order rate constants for these reactions are shown to bear an inverse dependence on temperature. The reactions involving o‐ and p‐chloronitrobenezene and penta‐and perchlorobenzene proceed via a branched mechanism by which an ion of the type [M + O − Cl]− and Cl− ion are simultaneously produced. A greater variety of negative ions are formed in the reactions of the molecular anions of perfluorobenzene and perfluorotoluene with oxygen. The electron affinities of pentachlorobenzene (0.7 eV) and perchlorobenzene (1.0 eV) are also reported for the first time.
Micropore membrane inlet mass spectrometer probes suitable for measurement of tissue surface gas tensions
Authors: Baumgardner James E. , Quinn John A. , Neufeld Gordon R.
Published: May 2005

New membrane inlet mass spectrometer (MIMS) probes are described that feature a micropore in a flat metal surface filled with a polymer membrane (Krytox high‐vacuum fluorinated grease). In vitro assessment of spatial resolution, time response, stirring effect and calibration are reported. The small membrane area for this MIMS results in spatial resolution of about 30 μm, adequate for measuring gas tensions at an exposed tissue surface in experimental studies of tissue oxygenation and tissue gas exchange. These probes offer a unique combination of minimal stirring effect and rapid response speed for measurements of gas partial pressures in the per cent range in aqueous solutions. Several gases, including oxygen, carbon dioxide, helium, sulfur hexafluoride and argon, permeate the polymer membrane to give a detectable signal, and the membrane is highly impermeable to water. Membrane dimensions were calculated from time response characteristics and the measured gas sample rate for argon. The membrane area was independently confirmed by direct assessment of spatial resolution. This MIMS is highly linear, has an excellent signal‐to‐noise ratio and offers practical advantages over electrode approaches to the measurement of gas tensions in aqueous solution.
Normal and inverse electron demand Diels–Alder cycloaddition of protonated and methylated carbonyl compounds in the gas phase
Authors: Lu L. , Yang S. S. , Wang Z. , Cooks R. G. , Eberlin M. N.
Published: May 2005

Protonated and methylated quinones, α,β‐unsaturated ketones and aldehydes and saturated ketones all react to form cycloaddition products with butadiene. The reagent ions are generated by chemical ionization (CI) and react at nominally zero kinetic energy with butadiene in an r.f.‐only quadrupole of a pentaquadrupole mass spectrometer. In selected cases, the product ions were characterized by sequential product ion dissociation (triple stage mass spectrometry [MS3]). The activated dicarbonyl ions, such as protonated quinone and protonated 4‐cyclopentene‐1,3‐dione, are more reactive than the protonated α,β‐unsaturated carbonyl compounds and the protonated saturated ketones. The methylated ions are less reactive than their protonated analogs. MS3 spectra of the quinone and α,β‐unsaturated carbonyl adducts and ab initio calculations of product ion stability are interpreted as indicating Diels–Alder cycloaddition at the carbon–carbon double bond. Benzoquinones and the α,β‐unsaturated ketones are also good dienophiles in solution. The differences in reactivity between these two groups of reactant ions, between the protonated and methylated ions and between individual members of each of these groups are ascribed to differences between the HOMO and LUMO orbital energies (ΔE) of the diene and reactant ion, respectively. The correlations observed between the cycloaddition reactivity and the energy gap indicate that normal Diels–Alder reactions occur for the quinones and α,β‐unsaturated ions. Correlations between ion–molecule reactivity and the HOMO–LUMO energy gaps also extend to the protonated saturated ketones, where MS3 studies confirm that cycloaddition occurs at the carbon–oxygen double bond. In all cases, when the proton affinity of the conjugate base of the dienophile is close to that of the diene, proton transfer between the diene and the dienophile becomes a major competitive process; this in turn decreases the cycloaddition yield. Gas‐phase inverse electron demand Diels–Alder reactions are studied using methylated 2‐butenone as diene and several neutral alkenes as dienophile. Higher reactivity is achieved with electron‐donating alkenes as dienophiles, in agreement with observations made in solution chemistry on inverse electron demand Diels–Alder reactions.
Linear energy correlations and failures in the low‐energy tandem mass spectra of protonated N‐benzoylated tripeptides: Tools for probing mechanisms of CAD processes
Authors: Morgan Daniel G. , Bursey Maurice M.
Published: May 2005

The backbone cleavages for three series of protonated N‐benzoyl tripeptide ions were studied in a hybrid tandem mass spectrometer: (i) benzoyl‐Gly‐Gly‐Xxx, where Xxx = Gly, Ala, Val, Leu, Ile, Phe, Tyr, Met, Glu, Pro and Trp, (ii) benzoyl‐Gly‐Xxx‐Gly, where Xxx = Gly, Ala, Leu, Phe, Tyr, Met and Trp, and (iii) benzoyl‐Xxx‐Gly‐Gly, where Xxx = Gly, Ala, Val, Leu, Ile, Phe, Tyr, Met, Pro and Trp. C‐Terminal y‐type ions and N‐terminal a‐ and b‐type ions were noted in all three cases. For benzoyl‐Gly‐Gly‐Xxx, a linear relationship between log (y1/b2) and the proton affinity of the C‐terminal amino acid substituents was found: as the proton affinity of the C‐terminal residue increases, the fraction of y1 ion formation increases. A similar relationship was noted for the benzoyl‐Xxx‐Gly‐Gly tripeptides between log (y2/b1) and the proton affinity of the N‐terminal amino acid substituent: as the proton affinity of the N‐terminal residue increases, the fraction of b1 ion formation increases. For the series benzoyl‐Gly‐Xxx‐Gly, these relationships did not hold true. These observations point to similar reaction pathways throughout the benzoyl‐Gly‐Gly‐Xxx series and also similar pathways throughout the benzoyl‐Xxx‐Gly‐Gly, but pathways that are substituent dependent for benzoyl‐Gly‐Xxx‐Gly. The increased correlation coefficients for benzoyl‐Gly‐Gly‐Xxx and benzoyl‐Xxx‐Gly‐Gly when compared with the free tripeptides, suggest that fewer interfering competitive reactions exist, as fewer possibilities for internal hydrogen bonding exist in the N‐benzoyl derivatives versus the free compounds.