High-resolution mass spectra of two α,β-unssaturated γ-dilactones

The fragmentations of two α,β-unsaturated γ-dilactones in a mass spectrometer are studied. The main feature is conecutive carbon monoxide expulsions. Strong indication of ejection of a fragment C₂O₂ is presented, however. Masses were determined by the high resolution rechnique and metastable transitions were detected by defocusing. Corresponding deuterated dilactones were also studied to verify the fragmentation mechanism.     

The high resolution mass spectra of α,β-unsaturated and α-chloromercuri-α,β-unsaturated steroidal ketones

The high resolution mass spectra (500 eV) of some α,β-unsaturated steroidal ketones have been studied and compared with the spectra of the corresponding α-chloromercuri ketones. In the latter, the carbon-mercury bond frequently remains intact at the expense of the fission of two carbon-carbon bonds. The abundance of mercury-containing ions allows the use of the mercury atom fingerprint in confirming ring B fragmentation of the steroid nucleus at C(6)–C(7) and C(9)–C(10) for 5α-androst-1-ene-3,17-dione, 1,4-androstadiene-3,17-dione and their 2-chloromercuri derivatives; and at C(7)–C(8) and C(9)–C(10) for 1,4,6-androstatriene-3,17-dione, 1,4,6-androstarien-17 β-ol-3-one and their 2-chloromercuri derivatives. 2-Chloromercuri-1,4,6-androstatriene-3,17-dione and 2-chloromercuri-1,4,6-androstatrien-17 β-ol-3-one also give an abundant ion as the result of ring C fragmentation at C(8)–C(14) and C(11)–C(12), the chloromercuri group being replaced by a hydrogen atom. This ring C cleavage gives the only recognizable distinctive fragmentation ion for 1,4,6-pregnatriene-3,20-dione and 2-chloromercuri-1,4,6-pregnatriene-3,20-dione. For most of the mercurated steroids, the low resolution mass spectra (70 eV) are reported. In these spectra, the fragmentation patterns are similar to those obtained using the higher ionization energy employed for the high resolution spectra.     

Alkyl–oxygen bond formation in the mass spectra of α-chloromethyl aryl sulphones

When subjected to electron-impact, chloromethyl aryl sulphones (II, X = Cl) fragment predominantly by the loss of CH₂Cl from the molecular ion followed by the loss of SO₂ and in most cases the appropriate metastable peaks are present to confirm the transitions. In addition, alkyl–oxygen bond formation in the molecular ion was revealed by the presence of prominent peaks corresponding to the [R? ?-SO]⁺ ions. In most spectra no evidence for aryl–oxygen bond formation could be found and thus the presence of the chlorine atom was able to effectively reverse the direction of skeletal rearrangement reported for aryl methyl sulphones.     

Electron-impact mass spectra of nitromethylpyridines

Conclusions Under conditions of electron-impact mass spectrometry, nitromethylpyridines form molecular ions whose stability depends on the position of the substituent. The nature of the fragmentation of the molecular ions permits us to distinguish trinitromethyl from dinitromethyl substituents.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 12, pp. 2785–2787, December, 1985.     

Anomalies in the molecular ion region in the electron impact mass spectra of α- and β-hydroxyesters

In the electron impact mass spectra of some alkyl α- and β-hydroxyesters (introduced using the gas chromatography/mass spectrometry (GC/MS) technique), the absence of the molecular ion M^+· and the presence of the [M + 1]⁺ ion instead is observed. This phenomenon is especially characteristic of C₃? C₆ glycolates and diethyl malate, and is due to chemical auto-ionization—ion-molecule reactions in the high concentration gradient at the top of the GC peak. The existence of the [M ? 2]^+·, [M ?1]⁺ and M^+· ions in the mass spectra of other β- and α-hydroxyesters is discussed.     

The mass spectra of some α-lactams

The electron-impact induced fragmentation of eight aziridinones has been studied by conventional as well as by high resolution mass spectrometry. All α-lactams exhibit a molecular ion. The major primary step, in the fragmentation, is the ejection of carbon monoxide from the molecular ion. Ions of the general formula R₁? NC and R₂R₃C?O were found in the mass spectra of all α-lactams investigated. A skeletal rearrangement to rationalize these ions is proposed. The fragmentation of the molecular ion is affected by the N-substituent. Exact mass measurement and specific deuterium labeling indicate the absence of McLafferty rearrangement from either the N- or C-substituent.     

Negative ion mass spectra of a series of fluorinated β-diketones

Electron capture by and the subsequent fragmentation of a series of eleven fluorinated β-diketones of general formula CF₃COCH₂COR has been studied in an MS-50 mass spectrometer. Consecutive loss of two HF molecules from molecular anions occurs with all compounds, as does elimination of CHF₃ from [M ? H]^? ions. Elimination of CO occurs from either \documentclass{article}\pagestyle{empty}\begin{document}$ \left[{{\rm M - HF}} \right]_{}^{_.^ - } $\end{document} or \documentclass{article}\pagestyle{empty}\begin{document}$ \left[{{\rm M - 2HF}} \right]_{}^{_.^ - } $\end{document} ions for five compounds where R ? CF₃ or a cyclic substituent. Kinetic energy release in metastable transitions associated with these HF and CO eliminations has been measured. Intensities of various fragment ions are in part influenced by the ion source temperature. Interaction of \documentclass{article}\pagestyle{empty}\begin{document}$ \left[{{\rm O}} \right]_{}^{_.^ - } $\end{document} reagent ions with five of the β-diketones under chemical ionization conditions gave [M ? H]^? ions as the only significant ion-molecule reaction product.     

Electron-impact mass spectra of natural phenylethanoids

The electron-impact mass spectra of a number of phenylpropanoids and iridoid glycosides containing a phenylethanoid fragment in their structure have been studied. This has revealed features of the formation of fragments of 4-hydroxyphenylethyl and 3,4-dihydroxyphenylethyl alcohols and also of fragments of phenylethylamine and indolylethylamine derivatives present in the structures of the compounds investigated.     

Electron-impact mass spectra of natural phenylethanoids

The electron-impact mass spectra of a number of phenylpropanoids and iridoid glycosides containing a phenylethanoid fragment in their structure have been studied. This has revealed features of the formation of fragments of 4-hydroxyphenylethyl and 3,4-dihydroxyphenylethyl alcohols and also of fragments of phenylethylamine and indolylethylamine derivatives present in the structures of the compounds investigated.Samara State Medical Institute. All-Russian Scientific Research Institute of Medicinal and Aromatic Plants Scientific Production Combine, Moscow. Translated from Khimiya Prirodnykh Soedinenii, No. 4, pp. 506–509, July–August, 1994.     

The mass spectra of some α-aminooxy acids

The mass spectrometric behaviour of six simple α-aminooxy acids is described. Comparison is made with the electron-impact-induced fragmentation of the parent α-amino acids. The differences are in accordance with the observed

1 See Ref. 1.

chemical character of the α-aminooxy acids.     

Studies in organic mass spectrometry-XIII: Investigation of electron-induced isomerisation of αβ- and βγ-unsaturated esters

The mass spectral fragmentation of methyl esters of α,β- and β,γ-unsaturated carboxylic acids has been studied. Deuterium labelling, metastable ion analysis and high resolution mass spectrometry have been utilised to elucidate the mechanism of a number of fragmentations and to check possible double bond migration prior to fragmentation. Some breakdown modes were found to occur through double bond migration. Additional support was provided by application of the ‘Metastable Ion Characteristics’ method. Partial isomerisation of molecular ions must therefore be accepted.     

The mass spectra of six fluorinated β-diketones and their monothio analogues

The mass spectra of the fluorinated β-diketones RCOCH₂COCF₃ (R = Ph, p-FC₆H₄, p-ClC₆H₄, p-BrC₆H₄, p-MeC₆H₄ and 2-thienyl) and their monothio analogues RC(SH)?CHCOCF₃ have been obtained. The replacement of one oxygen by sulphur in the β-diketones brings about a greater complexity in the mass spectra. The β-diketones fragment by first losing a ·CF₃ radical and then successively lose CH₂?C?O and CO to yield \documentclass{article}\pagestyle{empty}\begin{document}${\rm [R}\mathop {\rm C}\limits^{\rm + } {\rm = O]} $\end{document} and [R]⁺. The monothio-β-diketones also fragment by an analogous reaction pathway: viz. the initial loss of ·CF₃ is followed by the successive loss of CH₂?C?O and CS to yield \documentclass{article}\pagestyle{empty}\begin{document}${\rm [R}\mathop {\rm C}\limits^{\rm + } {\rm = S]} $\end{document} and [R]⁺. However, they also fragment by two other pathways involving the initial loss of ·H and ·X (X=F, Cl, Br, Me), the latter occurring only with those monothio-β-diketones having R=p-XC₆H₄.     

An unexpected γ-hydrogen rearrangement in the mass spectra of di-ortho -substituted alkylbenzenes

In contradiction of long-accepted mass spectrometric dogma, the site-specific γ-hydrogen rearrangement is observed in alkylbenzenes in which both ortho positions are blocked with methyl substituents. Mass spectrometric studies of a series of five trimethyl- and three tetramethylisopentylbenzenes have shown that this rearrangement is only suppressed to a significant degree in those compounds in which all three positions ortho and para to the isopentyl group are blocked. Deuterium labelling has confirmed the γ-site-specific origin of the migrating H atom while metastable studies have been used to investigate the mechanism of the rearrangement process.     

MALDI imaging mass spectrometry of β‐ and γ‐crystallins in the ocular lens

Lens crystallin proteins make up 90% of expressed proteins in the ocular lens and are primarily responsible for maintaining lens transparency and establishing the gradient of refractive index necessary for proper focusing of images onto the retina. Age‐related modifications to lens crystallins have been linked to insolubilization and cataractogenesis in human lenses. Matrix‐assisted laser desorption/ionization (MALDI) imaging mass spectrometry (IMS) has been shown to provide spatial maps of such age‐related modifications. Previous work demonstrated that, under standard protein IMS conditions, α‐crystallin signals dominated the mass spectrum and age‐related modifications to α‐crystallins could be mapped. In the current study, a new sample preparation method was optimized to allow imaging of β‐ and γ‐crystallins in ocular lens tissue. Acquired images showed that γ‐crystallins were localized predominately in the lens nucleus whereas β‐crystallins were primarily localized to the lens cortex. Age‐related modifications such as truncation, acetylation, and carbamylation were identified and spatially mapped. Protein identifications were determined by top‐down proteomics analysis of lens proteins extracted from tissue sections and analyzed by LC‐MS/MS with electron transfer dissociation. This new sample preparation method combined with the standard method allows the major lens crystallins to be mapped by MALDI IMS.     

Rearrangements in the mass spectra of α-phenylcinnamic acid and its derivatives

The electron impact ionization and collisional activation mass spectra of α-phenylcinnamic acid and its derivatives have been studied. The loss of a phenylic hydrogen is not an important process in these molecules, unlike the unsubstituted cinnamic acids. However, in o-chloro-α-phenylcinnamic acid and its methyl and trimethylsilyl derivatives loss of Cl resulting in the formation of 2-substituted-3-phenylbenzopyrilium ion is an important fragmentation pathway. The rearrangement ions observed at m/z 118 and 107 in the Spectrum of α-phenylcinnamic acid have been found to have the structures of the M⁺˙ of benzofuran and PhCH?$ \mathop {\rm O}\limits^{\rm +} $H, respectively. The ion at m/z 121 in the spectrum of the methyl ester of α-phenylcinnamic acid has been found to have the structure PhCH?$ \mathop {\rm O}\limits^{\rm +} $Me.