bluuebunny/crossref_metadata_2025_split huggingface dataset:
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

AbstractAlthough 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

AbstractAn 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

AbstractNew 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

AbstractProtonated 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

AbstractThe 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.
Doubly charged positive ions of chromium hexacarbonyl and molybdenum hexacarbonyl: Calculated and measured electronic‐state energies
Authors: Harris F. M. , Jackson P. J. , Rontree J. A. , Andrews S. R. , Parry D. E. 
Published: May 2005

AbstractDouble‐charge‐transfer spectroscopy was used to measure the double‐ionization energies of chromium hexacarbonyl and molybdenum hexacarbonyl molecules to triplet electronic states of the corresponding dications. The spectra were interpreted using data calculated using a modified MSXα method. The measured double‐ionization energy to the ground triplet state is 22.8 ± 0.5 eV for Cr(CO)6 and 22.4 ± 0.5 eV for Mo(CO)6; both values match, within experimental error, an earlier measurement of 22.8 ± 0.5 eV for W(CO)6. The spectra for the three hexacarbonyls are remarkably similar, probably reflecting that the electronic structures of the three molecules are almost identical in the valence region. The similarity is reflected in the calculated data; the Coulomb repulsions between the two positive holes which characterize the dictations' states are 4.54, 4.44 and 4.45 eV for Cr(CO), Mo(CO) and W(CO), respectively. These values correspond to the repulsive energy for two single charges separated by just over 3 Å, this separation being consistent with the size of the molecules.
High‐performance liquid chromatography/thermospray mass spectrometry of some prostaglandins of the F series
Authors: Abián J. , Gelpí E. 
Published: May 2005

AbstractThermospray (TSP) mass spectra and chromatographic characteristics of the prostanoids PGF2α, 6‐keto‐PGF1α, 2,3‐dinor‐6‐keto‐PGF1α, and their methyl esters and methoximes are reported. The spectra of these compounds are dominated by ions of the type [M + H +xNH3 ‐ nH2O]+ in the positive‐ion mode and [M ‐ H + xAcOH – nH2O]− in the negative‐ion mode (n ranges from 0–4 and x is 0 or 1). The relative abundances of these ions depend on the particular structure, source and interface temperatures and eluent composition. In addition, these compounds show losses of 44 mass units, mainly due to the loss of the C‐10–C‐11 moiety, as demonstrated by deuterium labelling of PGF2α. Methoximated derivatives of 6‐keto‐PGF1α also show low‐abundance ions due to fragmentation in the position α to the methoxime group. The liquid‐phase equilibria of tautomers of 2,3‐dinor‐6‐keto‐PGF1α or products thereof which direct its particular chromatographic behavior, can be effectively blocked by methoximation of the keto group thus improving its detectability. Detection limits of 20 ng on‐column may be obtained for this derivative. Adsorption and hydrolysis in the interface are the principal factors responsible for this relatively high detection limit.
Mass spectrometric evidence for the formation of silaethene accompanying the fragmentation of a non‐ester silicon‐containing pyrethroid insecticide
Authors: Fleet Ian A. , Tetler Lee W. , Monaghan John J. 
Published: May 2005

AbstractThe non‐ester silicon‐containing pyrethroid SSI‐116 and its carbon analogue (ethofenprox, MTI‐500) 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. Accurate mass measurements on key ions were made using a high‐resolution double‐focusing mass spectrometer. Based on the experimental observations, mechanisms have been proposed to explain the major fragmentation pathways of SSI‐116 and ethofenprox. The novel expulsion of silaethene, CH2SiH2, as a neutral species from the silicon‐containing insecticide and the formation of an ion at m/z 135, isomeric with the fragment ion, [C9H11O]+, observed in the spectrum of its carbon analogue, have also been rationalized. Minor fragmentation pathways, found only in the silicon‐containing analogue, are also discussed.
Selective ion–molecule reactions of ether reagent ions with nucleoside antibiotics in a quadrupole ion trap
Authors: Alvarez Erwin J. , Brodbelt Jennifer S. 
Published: May 2005

AbstractThe analysis of a targeted group of nucleoside antibiotics has been accomplished through the use of selective ion‐molecule reactions and collision‐activated dissociation (CAD) techniques in a quadrupole ion trap. A series of homologous ether reagent ions generated from dimethyl ether, di‐n‐butyl ether and 2‐methoxyethanol were used as chemical ionization reagents. Because chemical ionization with dimethyl ether and di‐n‐butyl ether reagent ions did not provide selectivity and signal enhancement for the analysis of these biopharmaceuticals, a chemical ionization reagent with special hydrogen‐bonding capabilities was used. The reagent ion that showed the greatest promise is a product of 2‐methoxyethanol, CH3OCH2CH2OCH2 +. This highly reactive species, which reacts selectively with nitrogen‐containing compounds, can undergo both nucleophilic attack and anchoring via hydrogen bond formation between the methoxy oxygen and an acidic hydrogen of the nucleoside substrate. The reaction of the CH3OCH2CH2OCH2+ ion with each of the nucleoside antibiotics resulted in formation of [M + 13]+ and [M + 89]+ products. The CAD spectra indicated that the adducts are covalently bound species and that the nucleotide moiety dominates both the reactive and dissociative behavior of the nucleoside antibiotics.
Radical cation adduct formation between dihydroxybenzenes and ammonia under CI conditions
Authors: Madhusudanan K. P. 
Published: May 2005

AbstractUnder ammonia chemical ionization conditions, instead of the expected [M + H]+, and [M + NH4]+ and [M + N2H7]+ ions, hydroquinone gives rise to M+·, [M + NH3]+· and [M + 2NH3]+· ions, whereas resorcinol gives both series of ions. Catechol shows M+·, [M + NH3]+·, [M + NH4]+ and [M + N2H7]+ ions. The favourable ionization energy difference between ammonia and the dihydroxybenzenes leads to charge exchange and the resulting radical cations, being highly acidic, form clusters with the NH3. The effect of ion source parameters and mass‐analysed ion kinetic energy (MIKE) and collisional activation spectra confirm proton‐bound structures for [M + NH3]+· and [M + 2NH3]+ ions. Because of the proximity of the two OH groups, NH4+ attachment is favoured in catechol. The MIKE spectra of [M + H + Et2O]+ ions show that resorcinol has the highest proton affinity among the dihydroxybenzenes.
Identification of new metabolites of ifosfamide in rat urine using ion cluster technique
Authors: Wang Jeff J.‐H. , Chan Kenneth K. 
Published: May 2005

AbstractMetabolism of the anticancer drug ifosfamide was investigated in Sprague‐Dawley rats. Along with four known metabolites, namely N2‐dechloroethylifosfamide, N3‐dechloroethylifosfamide, alcoifosfamide and isophosphoramide mustard, four new urinary metabolites were identified utilizing combined techniques of chemical modification/derivatization, capillary gas chromatography/chemical ionization mass spectrometry (ammonia), deuterium‐labeling/ion cluster analysis and chemical synthesis. Secondary metabolites of N2‐dechloroethyl and N3‐dechloroethylifosfamide formed by 4‐hydroxylation, i.e. 4‐hydroxy‐N2‐dechloroethylifosfamide and 4‐hydroxy‐N3‐dechloroethylifosfamide, respectively, and their subsequent decomposition product, N‐dechloroethyliso‐phosphoramide mustard, were identified. Secondary dealkylation pathways of N2‐dechloroethylifosfamide and/or N3‐dechloroethylifosfamide were also demonstrated through characterization of N2,3‐didechloroethyl ifosfamide. The key active metabolite of ifosfamide, 4‐hydroxyifosfamide, was characterized as a cyanohydrin adduct for the first time.
Negative‐ion fast atom bombardment mass spectrometry of anionic ruthenium carbonyl cluster complexes
Authors: Chihara Teiji , Yang Lanping , Esumi Yasuaki , Wakatsuki Yasuo 
Published: May 2005

AbstractBis(triphenylphosphine)iminium salts of a series of high‐nuclear and anionic ruthenium carbonyl cluster complexes were characterized by use of the negative‐ion fast atom bombardment mass spectrometry. With a m‐nitrobenzyl alcohol matrix, all of the monoanionic cluster complexes gave relatively intense intact anion peaks [A]− and all of the dianionic cluster complexes examined gave protonated monoanion peaks [HA]−. In some cases weak adduct ions were observed, which arose from the reaction of the cluster anions with the matrix during the bombardment process. The predominant fragmentation process of intact ions was found to be sequential loss of CO ligands and no loss of methyl, allyl or iodo ligand was observed. However, dissociation of bromo ligand from [Ru6C(CO)16Br]− and fragmentation of acetyl groups in [Ru5C(CO)13I2(COMe)]− and 6C(CO)16(COMe)− were noted. Degradation of cluster metal frameworks of [HRu10C(CO)24]− and [Ru10C(CO)24]2− into [HRu6C(CO)16]− was observed. These fragmentation and degradation patterns are comparable to their reactions in solution.
Determination of plasma levels of exemestane (FCE 24304), a new irreversible aromatase inhibitor, using liquid chromatography/thermospray mass spectrometry
Authors: Allievi C. , Zugnoni P. , Benedetti M. Strolin , Dostert P. 
Published: May 2005

AbstractA high performance liquid chromatographic mass spectrometric method with thermospray ionization for the determination of concentrations of exemestane (6‐methylenandrosta‐1,4‐diene‐3,17‐dione, FCE 24304) in human plasma has been developed. The sensitivity of the method allowed the determination of exemestane concentrations as low as 1 ng ml−1. A suitable internal standard was used for quantification. The intra‐day precision (relative standard deviation, R.S.D.) ranged from 16.3% near to the lower limit of quantification to 0.3% close to the upper end of the calibration graph. The mean accuracy of the method was found to be 97.8% (R.S.D.=7%). Unlike a previously developed gas chromatographic/mass spectrometic method, the new method proved to be suitable for the determination of unchanged drug plasma levels in exemestane‐treated subjects.
Determination of various steroids in normal adrenal glands and adrenocortical tumours by liquid chromatography/atmospheric pressure ionization mass spectrometry
Authors: Komatsu Funito , Morioka Masaaki , Fujita Yukitoshi , Sugahara Kazunori , Kodama Hiroyuki 
Published: May 2005

AbstractSeven steroids in normal adrenal gland and those of patients with aldosteronoma or Cushing's adenoma were measured by liquid chromatography/mass spectrometry with an atmospheric pressure ionization interface system. Using this system, quasi‐molecular ions [M + H]+ of standard cortisol, corticosterone, 17α‐hydroxyprogesterone, 11β‐hydroxyandrostenedione and Δ4‐androstenedione and [(M + H) − H2O]+ ions of aldosterone and dehydroe‐piandrosterone were observed as their base peaks, and quasi‐molecular ions [M + H]+ and [(M + H) − H2O]+ ions of seven steroids were clearly observed in chromatograms of biological samples. The ratio of glucocorticoid (cortisol) to mineralocorticoid (corticosterone) content was measured, and found to be significantly lower for aldosteronomas and higher for Cushing's adenomas than for normal adrenals. These findings indicate that the method had suffficient sensitivity for the identification and simultaneous measurement of a variety of adrenal gland steroids.
Alkali metal cationization and its effect on the collision‐induced decomposition of taxol
Authors: Madhusudanan K. P. 
Published: May 2005

AbstractThe effect of alkali metal cationization on the collision‐induced decomposition of taxol is discussed. The facile elimination of H2O observed from the [M + H]+ ion does not occur from the corresponding [M + Met]+ ion. Some of the major decomposition pathways appear to be charge‐remote fragmentations involving eliminations of the functional groups on the taxane ring or the cleavage of the side‐chain with retention of the metal ion on either the side‐chain or the taxane ring. The collision‐induced decompositions of the lithiated side‐chain reflect multi‐site binding of the lithium ion with the basic centres in the side‐chain.
Recognition of cell‐wall peptide ligands by vancomycin group antibiotics: Studies using ion spray mass spectrometry
Authors: Lim Heng‐Keang , Hsieh Yin Liang , Ganem Bruce , Henion Jack 
Published: May 2005

AbstractNon‐covalent binding of antibiotics to their target ligands represents a form of molecular recognition which is of considerable contemporary interest in bioorganic and bioanalytical chemistry. The vancomycin antibiotics, including vancomycin and ristocetin, are a family of complex glycopeptides which bind specifically to the C‐terminal sequence X‐D‐Ala‐D‐Ala, where × is L‐lysine, L‐diaminopimelic acid, L‐alanine or L‐homoserine. It is shown that non‐covalent complexation of vancomycin and ristocetin with peptide ligands in solution, a key molecular recognition phenomenon in antibacterial chemotherapy, can be detected and analyzed in the gas phase by ionspray mass spectrometry. Using Nα,Nϵ‐diacetyl‐L‐Lys‐D‐Ala‐D‐Ala (Ac2KAA) as a representative ligand, it is further demonstrated that correlations of relative ion abundance with ligand concentrations in solution afford a direct method for measuring the binding constants of vancomycin and ristocetin complexes with target peptide sequences in bacterial cell wall. Results for ristocetin‐Ac2KAA (Ka = 6.25 × 105 l mol−1) and vancomycin‐Ac2KAA (Ka = 7.33 × 105 l mol−1, are in reasonable agreement with previously values [Ka = 5.9 × 105] and 1.5 × 106 l mol−1, respectively).