Novel Fragmentation Processes of 2-Nitrobenzenesulfonyl Amino Acid Anions

Abstract

A library of 2-nitrobenzenesulfonyl (Ns) derivatives incorporating isotopic labels and a range of structural variations was prepared and characterized to investigate mass spectrometric fragmentation processes. Deprotonated Ns amino acids were formed readily by negative mode electrospray ionization. Collision induced dissociation experiments established precursor-product ion relationships and indicated a novel loss of an aryl ortho substituent (NO2, F, Cl or Br). In total, four distinct fragmentation pathways of Ns-alpha- and Ns-beta-amino acid anions were identified using isotopic labeling, structural variations of the Ns derivatives, and collision induced dissociation of ions generated in source. Overall, the observation of specific fragmentation pathways correlated with anion structure and ionization site. However, the observation of only one of four possible fragmentation processes in the mass spectrum of the Ns derivative of an amino dicarboxylic acid indicated that functional group interactions must also be considered in the interpretation and prediction of fragmentation processes.