摘要:

AbstractSix 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‐tandemmass 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

ISSN:1076-5174    

DOI:10.1002/jms.1190300402

出版商:John Wiley&Sons, Ltd.    

年代:1995

数据来源: WILEY

摘要:

AbstractThe 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 pit

ISSN:1076-5174    

DOI:10.1002/jms.1190300403

出版商:John Wiley&Sons, Ltd.    

年代:1995

数据来源: WILEY

摘要:

AbstractThe 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 enolizabl

ISSN:1076-5174    

DOI:10.1002/jms.1190300404

出版商:John Wiley&Sons, Ltd.    

年代:1995

数据来源: WILEY

摘要:

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‐relatedPneumocystis cariniipneumonia, 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 constantB/Eto 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 ofm/z120 and 137 and loss of neutral ammonia from the protonated analyte that characterized the amidinophenoxy group. The structures of isomeric 2‐hydroxypentamidine, 3‐hydroxypentamidine andN‐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, includingN,N′‐dihydroxypentamidine, 5‐(4′‐amidinophenoxy)pentanoic acid, 5‐(4′‐amidinophenoxy) pentan‐1‐ol, andp‐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‐hyd

ISSN:1076-5174    

DOI:10.1002/jms.1190300405

出版商:John Wiley&Sons, Ltd.    

年代:1995

数据来源: WILEY

摘要:

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‐ andtrans‐perfluorodecalin,m‐chloronitrobenzene,o‐,m‐andp‐fluoronitrobenzene ando‐,m‐ andp‐dinitrobenzene were found to be unreactive towards oxygen. Those ofo‐ andp‐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 involvingo‐ andp‐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

ISSN:1076-5174    

DOI:10.1002/jms.1190300406

出版商:John Wiley&Sons, Ltd.    

年代:1995

数据来源: WILEY

摘要:

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 vitroassessment 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 so

ISSN:1076-5174    

DOI:10.1002/jms.1190300407

出版商:John Wiley&Sons, Ltd.    

年代:1995

数据来源: WILEY

摘要:

AbstractSteric and substituent effects can play large roles in influencing the outcomes of organic reactions. In this work, the use of ion‐molecule reactions of dibenzo‐16‐crown‐5 compounds (lariat ethers) by tandem mass spectrometry to probe the influence of the pendant groups on the selectivity of their gas‐phase reactions was evaluated. Lariat ethers are macrocyclic ethers with pendant substituents that have been developed as new types of hosts for molecular recognition. Dimethyl ether (DME) was the reactant chosen because of its well characterized reactivity with various organic substrates possessing different functional groups. Only those dibenzo‐16‐crown‐5 compounds with no or at most one substituent at the center carbon of the three‐carbon bridge form the diagnostic [M + 13]+product ion through a methylene substitution process. Dibenzo‐16‐crown‐5 compounds with geminal substituents on the center carbon of the three‐carbon bridge form the [M + 45]+ion, but not the characteristic [M + 13]+ion. Causative factors may be steric blocking of the reaction pathway by the geminal groups or a requirement for the presence of at least one hydrogen on the center carbon of the three‐center bridge for formation of the [M + 13]+ion. CAD, deuterium labelling, molecular orbital calculations and comparisons with model compounds provide additional information

ISSN:1076-5174    

DOI:10.1002/jms.1190300408

出版商:John Wiley&Sons, Ltd.    

年代:1995

数据来源: WILEY

摘要:

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. MS3spectra of the quinone and α,β‐unsaturated carbonyl adducts andab initiocalculations 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 MS3studies 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

ISSN:1076-5174    

DOI:10.1002/jms.1190300409

出版商:John Wiley&Sons, Ltd.    

年代:1995

数据来源: WILEY

摘要:

AbstractThe backbone cleavages for three series of protonatedN‐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‐Terminaly‐type ions andN‐terminala‐ andb‐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 theC‐terminal amino acid substituents was found: as the proton affinity of theC‐terminal residue increases, the fraction ofy1ion formation increases. A similar relationship was noted for the benzoyl‐Xxx‐Gly‐Gly tripeptides between log (y2/b1) and the proton affinity of theN‐terminal amino acid substituent: as the proton affinity of theN‐terminal residue increases, the fraction ofb1ion 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

ISSN:1076-5174    

DOI:10.1002/jms.1190300410

出版商:John Wiley&Sons, Ltd.    

年代:1995

数据来源: WILEY

摘要:

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)6and 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) 62+, Mo(CO) 62+and W(CO) 62+, respectively. These values correspond to the repulsive energy for two single charges separated by just over 3 Å, this separation being consistent with the siz

ISSN:1076-5174    

DOI:10.1002/jms.1190300411

出版商:John Wiley&Sons, Ltd.    

年代:1995

数据来源: WILEY