Fragmentation reactions of molecular ions and dications of indoleamines

Abstract

The combination of techniques such as two-dimensional mass spectrometry and mass analysed ion kinetic energy spectrometry (with and without collision gas) in the study of gas-phase ion chemistry of indole, gramine, tryptamine and serotonine enabled us to establish the fragmentation pathways of their singly-and doubly-charged molecular ions generated by electron impact. The measurement of the kinetic energy released in the charge separation reactions of the molecular dications produced information on the intercharge distance on the transition state for the fragmentation, assuming that it arises entirely from the coulombic energy released. For the singly-charged molecular ions of indoleamines, loss of the neutral molecule CH 2 =NR (R = H or CH 3), by hydrogen transfer from the amino (or methyl) group to the indole nucleus, is the only fragmentation occurring in the third field-free region of the mass spectrometer. Upon collision of the molecular ion with He gas, a competing process of bond cleavage by loss of the radical • CH 2 NH 2 (or • N(CH 3) 2 for gramine) is observed for tryptamine and serotonine. The doubly-charged ions dissociate by elimination of neutral molecules or radicals to generate doubly-charged fragment ions or by charge separation reactions. The intercharge distance, calculated from the kinetic energy released in the fragmentation, was, whenever possible, correlated with charge location in the ion.

Cycloreversion and other gas‐phase reactions of neutral and cationic pyrrolidine‐fused chlorins and isobacteriochlorins under ion bombardment and electrospray

“…31 In particular the loss of CH 3 þ from a doubly charged indoleamine cation has been described as occurring through partial location of the positive charge in the methyl group due to stretching of the bond prior to the separation of the two singly charged ions. 32 In the present case, although losses of a methylated aziridine cation and of a methylated imine cation from the doubly charged Chlorin and isobacteriochlorin gas-phase reactions 2609 similarity of the ESI-MS/MS spectra of the ions of m/z 975 for compounds I, IA and IB (Fig. 5).…”

Charge permutation reactions in tandem mass spectrometry

“…80,86 The amount of kinetic energy released can be calculated from the widths of peaks in ion kinetic energy spectra and the distance between the two charges at the moment of decomposition, estimated by 5,87 r Å D 14.40/KER eV can be used to infer information regarding the structures and geometries of precursor ions. 88,89 For example, the MIKE spectrum and B/E spectrum of the M 2C ion of indole 90 are shown in Fig. 7, where broad metastable peaks were observed due to the charge separation processes.…”

Characterisation and determination of indole alkaloids in frog‐skin secretions by electrospray ionisation ion trap mass spectrometry

“…LC coupled to electrospray ionisation (ESI) with tandem mass spectrometry has been used for the elucidation of indole‐3‐acetic acid metabolism in bacteria 7. Combinations of techniques such as two‐dimensional mass spectrometry and mass‐analysed ion kinetic energy spectrometry have been used to establish fragmentation pathways in the gas‐phase ion chemistry of indole, gramine, tryptamine and serotonin following production of molecular ions by EI 8. The need to determine the presence of biogenic amines in complex matrices such as fermented foods has led to the development of an LC method involving derivatisation with 3,5‐dinitrobenzoyl chloride and detection by mass spectrometry 9…”