Mass Spectrometry

Biography

Biography: Xinhua Guo

Abstract

Several unusual peptide fragment ions including b_n-44, c_n and b_n+H₂O ions are initially observed in the MS/MS spectrum of a singly charged deuterohemine N-terminated peptide (DhHP-6, Deuterohemin-βAHTVEK-NH₂). A detailed investigation on formation pathways of these characteristic ions are performed by using high resolution mass determination, H/D exchange, isotope labeling and density functional theory (DFT). Results indicate that the production of these ions is related to the presence of threonine (Thr) residue in the peptide. Also the N-terminal fixed charge carried by deuterohemine group may play a critical role for the activation of the hydrogen connecting with carbon, and McLafferty-type rearrangement reactions are proposed as the potential mechanism for explaining the generation of the b_n-CH₃CHO and c_n ions. In this study, we also propose a rearrangement fragmentation pathway for the production of b_n+H₂O ions from the Thr/Ser residue. In that case, the N→O acyl shift occurs to generate an ester intermediate which is the first and the most critical step, following that a further fragmentation of the ester isomer leads to the formation of b_n+H₂O ions. Detections of these diagnostic ions from the MS/MS spectra of sodiated Thr containing peptides further support the proposed charge-remote fragmentation pathways. Present work provides mechanism insights into the production of special ions, such as c_n and b_n + H₂O ions, in the low energy CID process.