Collision-induced dissociation of protonated cyproheptadine: Ion-neutral complex mediated electron transfer versus hydride transfer reaction

Abstract

In this study, the gas-phase fragmentation of protonated cyproheptadine was investigated by electrospray ionization tandem mass spectrometry (ESI–MSn). Upon collision induced dissociation (CID), two most abundant fragment ions at m/z 196 and 197 were observed, assigned to the loss of toluene or benzyl radical respectively. The formation pathways of these two ions involved the cleavages of multi-bonds along with complicated skeletal rearrangement. In order to rationale the fragmentation, we proposed a mechanism involving an ion-neutral complex (INC) intermediate. Intra-complex hydride transfer or electron transfer lead to the formation of final product ions. Deuterium-labeled experiments, density functional theory (DFT) calculations and the breakdown curves also corroborate the proposed mechanism.