Application of self-ionization for enhancing stereochemical and positional effects from arylglycosides under electron ionization conditions in an ion trap mass spectrometer

Hybrid density functional theory study of fragment ions generated during mass spectrometry of 1,3-dioxane derivatives

It was recently reported that the cis,cis and trans,trans diastereoisomers of four 2(r)-R-2,4(R),6(S)-trimethyl-1,3-dioxane derivatives show distinct electron ionization mass spectra. As a possible explanation for this finding, the authors suggested that the ions generated during the mass spectrometry of these compounds could follow different fragmentation patterns that initiate from different ion conformations. In this report, hybrid density functional theory methods have been used to investigate the conformational preference of three ions involved in the mass spectrometry of some 1,3-dioxane derivatives. We found that there is indeed more than one stable ion conformation for each of the investigated ions. Energy profiles along the torsional coordinates connecting the conformers are presented, and factors influencing the relative stability of ion conformations are discussed.

Gas phase ion chemistry of the heterocyclic isomers 3-methyl-1,2-benzisoxazole and 2-methyl-1,3-benzoxazole

Different mass spectrometric methods, stable isotope labeling, and theoretical calculations have allowed us to structurally characterize and differentiate the isomeric ion structures produced by the two heteroaromatic isomers 3-methyl-1,2-benzisoxazole and 2-methyl-1,3-benzoxazole. The low-energy collision induced dissociation spectra of their molecular ions show large differences. Although both of them produce abundant loss of CO, that involves a carbon atom of the benzene ring, the 2-methyl-1,3-benzoxazole also shows abundant [M-CHO](+) ions at m/z 104, the intensity of which is quite low in the case of its isomer 3-methyl-1,2-benzisoxazole. In addition, MS/MS measurements of fragment ions show characteristic differences that allow distinction among the isomers depending on the original arrangement of the atoms in the five-membered ring. Theoretical ab initio calculations have allowed to determine chemico-physical properties of different ions and to propose a rationalization of the decomposition pathways followed by the two benz(is)oxazole isomers.

Gas phase reactivity of isomeric arylglycosides towards amines. A chemical ionization mass spectrometry and tandem mass spectrometry study

Chemical ionization mass spectrometry (MS) and tandem mass spectrometry (MS/MS) experiments have been performed for the structural characterization and isomeric differentiation of two series of C- and O-linked arylglycosides with potential antioxidant activity. Different amines have been used for producing gas phase chemical ionization. Depending on their proton affinity and steric hindrance, adduct ions with different stability are formed. The most stable adducts are produced by ethylamine and they have been extensively structurally characterized by experimental and theoretical approaches. Energy resolved chemical ionization tandem mass spectrometric experiments have allowed unambiguous characterization and differentiation of both the anomers differing at the configuration of the glycosidic C(1) atom, and regio- and structural isomers at extremely low concentrations, typical of mass spectrometry. This study has shown that amine chemical ionization mass spectrometry and MS/MS are powerful and versatile tools for the structural characterization of arylglycosides.