Collision-Induced Dissociation of Halide Ion–Arginine Complexes: Evidence for Anion-Induced Zwitterion Formation in Gas-Phase Arginine
- Publication date
- 2012
- Publisher
Abstract
We report the first low-energy collisional-induced dissociation studies of the X<sup>–</sup>·arginine (X<sup>–</sup> = F<sup>–</sup>, Cl<sup>–</sup>, Br<sup>–</sup>, I<sup>–</sup>, NO<sub>3</sub><sup>–</sup>, ClO<sub>3</sub><sup>–</sup>) 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<sup>–</sup>·arginine and Cl<sup>–</sup>·arginine) is dominated by deprotonation of the arginine, whereas the major fragmentation channel for the largest ion clusters (I<sup>–</sup>·arginine and ClO<sub>3</sub><sup>–</sup>·arginine) corresponds to simple cluster fission into the ion and neutral molecule. However, the fragmentation profiles of Br<sup>–</sup>·arginine and NO<sub>3</sub><sup>–</sup>·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<sup>–</sup>·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<sup>–</sup>·arginine and NO<sub>3</sub><sup>–</sup>·arginine systems