Intriguing differences in the gas-phase dissociation behavior of protonated and deprotonated gonyautoxin epimers.

The aim of this study was to investigate the unusual gas-phase dissociation behavior of two epimer pairs of protonated gonyautoxins (GTX) following electrospray ionization in comparison to their deprotonated counterparts. The chemical structures of the investigated GTX1-4 variants vary in their substitution pattern at N-1 and the stereochemical orientation of the hydroxysulfate group at C-11 (11α for GTX1/2 versus 11β for GTX3/4). The direct comparison of mass spectra in positive and negative ion modes illustrated two distinct features: first, an intriguing difference between protonated 11α and 11β species, where 11α conformations exhibited almost complete dissociation of [M + H](+) ions via facile SO(3) elimination, while 11β species remained mostly intact as [M + H](+); and second, the lack of such differences for the deprotonated counterparts.