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Characterization of [C4H5O]+ ions in the gas phase using their metastable ion and collisional activation spectra shows that the three isomeric ions HCC \documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\rm C}\limits^{\rm + } $\end{document}HOCH3, CH3O \documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\rm C}\limits^{\rm + } $\end{document}CCH2 and OCH3 related to the two stable [C3H3]+ cations [HCCCH2]+ and are stable for ≥ 10−5s. In contrast to the formation of cyclopropenium ions, it is found that the methoxy cyclopropenium ion is not generated from acyclic precursor molecules. The small but significant intensity differences found in the collisional activation spectra of [C3H3]+ ions generated from HCCCH2I and HCCCH2Cl possibly indicate the presence of [C3H3]+ ions of different structures. [ABSTRACT FROM AUTHOR]

Loss of an alkyl group X⋅ from acetylenic alcohols HCCCX(OH)(CH3) and gas phase protonation of HCCCOCH3 are both shown to yield stable HCC \documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\rm C}\limits^{\rm + } $\end{document}(OH)(CH3) ions. Ions of this structure are unique among all other [C4H5O]+ isomers by having m/ z 43 [C2H3O]+ as base peak in both the metastable ion and collisional activation spectra. It is concluded that the composite metastable peak for formation of m/ z 43 corresponds to two distinct reaction profiles which lead to the same product ion, CH3 \documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\rm C}\limits^{\rm + } $\end{document}O, and neutral, HCCH. It is further shown that the [C4H5O]+ ions from related alcohols (like HCCCH(OH)(CH3)) which have an α-H atom available for isomerization into energy rich allenyl type molecular ions, consist of a second stable structure, H2C \documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\rm C}\limits^{\rm + } $\end{document}C(OH)CH2. [ABSTRACT FROM AUTHOR]

Mass spectrometry‐based techniques can be applied to investigate collagen with respect to identification, quantification, supramolecular organization, and various post‐translational modifications. The continuous interest in collagen research has led to a shift from techniques to analyze the physical characteristics of collagen to methods to study collagen abundance and modifications. In this review, we illustrate the potential of mass spectrometry for in‐depth analyses of collagen. [ABSTRACT FROM AUTHOR]

From the NIST website and the literature, we have collected the Ionisation Energies (IE) of 3,052 and the Proton Affinities (PA) of 1,670 compounds. For 614 of these, both the IE and PA are known; this enables a study of the relationships between these quantities for a wide variety of molecules. From the IE and PA values, the hydrogen atom affinities (HA) of molecular ions M•+ may also be assessed. The PA may be equated to the heterolytic bond energy of [MH]+ and HA to the homolytic bond energy. Plots of PA versus IE for these substances show (in agreement with earlier studies) that, for many families of molecules, the slope of the ensuing line is less negative than -1, i.e. changes in the PA are significantly less than the concomitant opposite changes in IE. At one extreme (high PA, low IE) are the metals, their oxides and hydroxides, which show a slope of close to -1, at the other extreme (low PA, high IE) are the hydrogen halides, methyl halides and noble gases, which show a slope of ca. -0.3; other molecular categories show intermediate behaviour. One consequence of a slope less negative than -1 is that the changes in ionic enthalpies of the protonated species more closely follow the changes in the enthalpies of the neutral molecules compared with changes in the ion enthalpies of the corresponding radical cations. This is consistent with findings from ab initio calculations from the literature that the incoming proton, once attached to the molecule, may retain a significant amount of its charge. These collected data allow a comparison of the thermodynamic stability of protonated molecules in terms of their homolytic or heterolytic bond cleavages. Protonated nitriles are particularly stable by virtue of the very large hydrogen atom affinities of their radical cations. [ABSTRACT FROM AUTHOR]

Atherosclerosis is a lipid and inflammation-driven disease of the arteries that is characterized by gradual buildup of plaques in the vascular wall. A so-called vulnerable plaque, consisting of a lipid-rich necrotic core contained by a thin fibrous cap, may rupture and trigger thrombus formation, which can lead to ischemia in the heart (heart attack) or in the brain (stroke). In this study, we present a protocol to investigate the lipid composition of advanced human carotid plaques using matrix-assisted laser desorption ionization (MALDI) mass spectrometry imaging (MSI), providing a framework that should enable the discrimination of vulnerable from stable plaques based on lipid composition. We optimized the tissue preparation and imaging methods by systematically analyzing data from three specimens: two human carotid endarterectomy samples (advanced plaque) and one autopsy sample (early stage plaque). We show a robust data reduction method and evaluate the variability of the endarterectomy samples. We found diacylglycerols to be more abundant in a thrombotic area compared to other plaque areas and could distinguish advanced plaque from early stage plaque based on cholesteryl ester composition. We plan to use this systematic approach to analyze a larger dataset of carotid atherosclerotic plaques. [ABSTRACT FROM AUTHOR]