Isomer differentiation via collision-induced dissociation: The case of protonated a-, β2- and β3-phenylalanines and their derivatives

Abstract

A combination of electrospray ionisation (ESI), multistage and high-resolution mass spectrometry experiments is used to examine the gas-phase fragmentation reactions of the three isomeric phenylalanine derivatives, a-phenylalanine, b2-phenylalanine and b3-phenylalanine. Under collision-induced dissociation (CID) conditions, each of the protonated phenylalanine isomers fragmented differently, allowing for differentiation. For example, protonated b3-phenylalanine fragments almost exclusively via the loss of NH3, only b2-phenylalanine via the loss of H2O, while a- and b2- phenylalanine fragment mainly via the combined losses of H2ORCO. Density functional theory (DFT) calculations were performed..