Collision-induced dissociation of halide ion-arginine complexes: Evidence for anion-induced zwitterion formation in gas-phase arginine

摘要

We report the first low-energy collisional-induced dissociation studies of the X -?arginine (X - = F -, Cl -, Br -, I -, NO _3 -, ClO _3 -) series of clusters to investigate the novel phenomenom of anion-induced zwitterion formation in a gas-phase amino acid. Fragmentation of the small halide ion clusters (F -?arginine and Cl -?arginine) is dominated by deprotonation of the arginine, whereas the major fragmentation channel for the largest ion clusters (I -?arginine and ClO _3 -?arginine) corresponds to simple cluster fission into the ion and neutral molecule. However, the fragmentation profiles of Br -?arginine and NO _3 -?arginine, display distinctive features that are consistent with the presence of the zwitterionic form of the amino acid in these clusters. The various dissociation pathways have been studied as a function of % collision energy and are discussed in comparison to the fragmentation profiles of protonated and deprotonated arginine. Electronic structure calculations are presented for Br -?arginine to support the presence of the zwitterionic amino acid in this complex. The results obtained in this work provide important information on the low-energy potential energy surfaces of these anion-amino acid clusters and reveal the presence of several overlapping surfaces in the low-energy region for the Br -?arginine and NO _3 -?arginine systems.