Electron ionization mass spectrometry of aryl- and fluoroalkyl-substituted palladium(II) β-diketonates and monothio-β-diketonates

Positive ion electron ionization mass spectra are presented for palladium(II) β-diketonates and monothio-β-diketonates of the general form PdII[RC(X)CHC(O)R′]2, where R = phenyl, 4-methoxyphenyl, 2-thienyl, or 2-naphthyl; R′ = trifluoromethyl, pentafluoroethyl, or n-heptafluoropropyl; and X = O or S. The mass spectral behavior is in sharp contrast to that of metals of the first transition series. The spectra of the β-diketonates are dominated by metal-containing ions that arise by migration of the R group from the ligand (L) to palladium, but there is no evidence for fluorine-to-metal transfer. These findings are consistent with HSAB theory. The strong tendency of palladium to form bonds with unsaturated carbon also leads to remarkably abundant metal-containing ions that arise by losses of CO or aryloxy radicals from [PdRL]+• ions. In contrast, in decompositions of ions in the spectra of the monothio-β-diketonates, migration of the R group is suppressed; competition for palladium dπ electrons by the sulfur donor makes palladium a poorer aryl group acceptor.

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Evaluating the Accuracy of the QCEIMS Approach for Computational Prediction of Electron Ionization Mass Spectra of Purines and Pyrimidines

Metabolites ◽

10.3390/metabo12010068 ◽

2022 ◽

Vol 12 (1) ◽

pp. 68

Author(s):

Jesi Lee ◽

Tobias Kind ◽

Dean Joseph Tantillo ◽

Lee-Ping Wang ◽

Oliver Fiehn

Keyword(s):

Mass Spectra ◽

Electron Ionization ◽

Ionization Mass ◽

Mass Spectral ◽

Electron Ionization Mass Spectra ◽

Spectral Libraries ◽

The Impact ◽

Mass Spectral Libraries ◽

Purines And Pyrimidines ◽

Similarity Scores

Mass spectrometry is the most commonly used method for compound annotation in metabolomics. However, most mass spectra in untargeted assays cannot be annotated with specific compound structures because reference mass spectral libraries are far smaller than the complement of known molecules. Theoretically predicted mass spectra might be used as a substitute for experimental spectra especially for compounds that are not commercially available. For example, the Quantum Chemistry Electron Ionization Mass Spectra (QCEIMS) method can predict 70 eV electron ionization mass spectra from any given input molecular structure. In this work, we investigated the accuracy of QCEIMS predictions of electron ionization (EI) mass spectra for 80 purine and pyrimidine derivatives in comparison to experimental data in the NIST 17 database. Similarity scores between every pair of predicted and experimental spectra revealed that 45% of the compounds were found as the correct top hit when QCEIMS predicted spectra were matched against the NIST17 library of >267,000 EI spectra, and 74% of the compounds were found within the top 10 hits. We then investigated the impact of matching, missing, and additional fragment ions in predicted EI mass spectra versus ion abundances in MS similarity scores. We further include detailed studies of fragmentation pathways such as retro Diels–Alder reactions to predict neutral losses of (iso)cyanic acid, hydrogen cyanide, or cyanamide in the mass spectra of purines and pyrimidines. We describe how trends in prediction accuracy correlate with the chemistry of the input compounds to better understand how mechanisms of QCEIMS predictions could be improved in future developments. We conclude that QCEIMS is useful for generating large-scale predicted mass spectral libraries for identification of compounds that are absent from experimental libraries and that are not commercially available.

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Electron Ionization Mass Spectra of N(O,S)-Isobutoxycarbonyl Isobutyl Esters of Amino Acids

European Journal of Mass Spectrometry ◽

10.1255/ejms.522 ◽

2002 ◽

Vol 8 (6) ◽

pp. 447-449 ◽

Cited By ~ 5

Author(s):

Tim G. Sobolevsky ◽

Alexander I. Revelsky ◽

Igor A. Revelsky ◽

Barbara Miller ◽

Vincent Oriedo

Keyword(s):

Amino Acids ◽

Mass Spectra ◽

Spectral Characteristics ◽

Aqueous Media ◽

Electron Ionization ◽

Ionization Mass ◽

Mass Spectral ◽

Ionization Mode ◽

Electron Ionization Mass Spectra

Mass spectra of N(O,S)-isobutoxycarbonyl isobutyl esters of 17 amino acids (L-alanine, glycine, L-valine, L-norvaline, L-leucine, L-isoleucine, L-norleucine, L-proline, L-asparagine, L-methionine, L-threonine, L-serine, L-phenylalanine, L-lysine, L-tryptophan, L-tyrosine and L-cystine) were obtained in the electron ionization mode. These derivatives were found suitable for the analysis of amino acids in aqueous media allowing proper identification and quantitation from the mass spectral characteristics.

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Electron ionization mass spectrometry of aryl- and fluoroalkyl-substituted nickel(II) β-diketonates and monothio-β-diketonates

Canadian Journal of Chemistry ◽

10.1139/v93-187 ◽

1993 ◽

Vol 71 (9) ◽

pp. 1450-1462 ◽

Cited By ~ 2

Author(s):

Mark L.J. Reimer ◽

John B. Westmore ◽

Manoranjan Das

Keyword(s):

Mass Spectra ◽

Hydrogen Transfer ◽

Electron Ionization ◽

Central Position ◽

Ionization Mass ◽

Aryl Group ◽

Molecular Ion ◽

Transfer Processes ◽

Mechanisms Of Formation ◽

Positive Ion

Electron ionization positive-ion mass spectra are reported for 18 substituted nickel(II) β-diketonates and monothio-β-diketonates, NiII(RCXCHCOR′)2, where X = O or S; R = phenyl, 2-thienyl, 5-methyl-2-thienyl, or 2-naphthyl; and R′ = difluoromethyl, trifluoromethyl, pentafluoroethyl, or n-heptafluoropropyl. Each mass spectrum contains a prominent molecular ion, [NiL2]+, which, for β-diketonates, fragments mainly by elimination of the odd-electron R′• species; the resulting ion decomposes by losses of one or more even-electron neutral species to yield ions containing nickel(II). In contrast, the major fragmentation of the molecular ion of monothio-β-diketonates is loss of NiIL to yield an abundant L+ ion. Furthermore, while most ions contain nickel(II), some prominent ions contain nickel(I); among these are [NiISC(R) = CH]+ and [NiI(HCCR)]+. Interesting ions are formed by hydrogen transfer processes. The [NiHL]+ ion is favored in the spectra of β-diketonates having a phenyl substituent, consistent with hydrogen transfer to the metal from the aryl group. On the other hand, the [Ni(L–H)]+ ion, favored for the monothio-β-diketonates, could be formed by hydrogen transfer from the central position of the chelate ring or from an aryl substituent. Alternative mechanisms of formation are discussed. Some minor ions are formed by fluorine transfer to nickel. The trends in their abundances are influenced by the hardness of nickel as an acid in its different oxidation states, under the influence of the ligand donor atoms, and by the hardness of the carbon atoms of the perfluoroalkyl substituents.

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