Collision-Induced Dissociation of Halide Ion–Arginine Complexes: Evidence for Anion-Induced Zwitterion Formation in Gas-Phase Arginine

Abstract

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.

Assessing the impact of anion–π effects on phenylalanine ion structures using IRMPD spectroscopy

“…10,11 Anionic interactions may also stabilize isolated amino acid zwitterions. 12,13 These naturally adopt canonical isomers in the gas phase, 14,15 but oxalate and malonate are computationally predicted to cluster with zwitterionic glycine, 16 and halide-bound ArgX À zwitterions have been confirmed by infrared multiple photon dissociation (IRMPD) spectroscopy. 17 The current work similarly uses IRMPD spectroscopy to identify the structures of PheX À complexes (X = Cl À and Br À ) and five fluorinated derivatives (3-and 4-fluoro, 2,5-and 3,5-difluoro, and pentafluoro).…”

Complexation of halide ions to tyrosine: role of non-covalent interactions evidenced by IRMPD spectroscopy

“…However, anion complexation also relies on hydrogen bonding, iondipole interactions, and hydrophobic effects which in principle may also preferentially stabilize zwitterionic forms relative to their neutral, canonical counterparts. 3 In addition, other non-covalent contacts, including anion-π effects favored between π-acidic arenes and charge-diffuse anions, may contribute in stabilizing negatively charged adducts of (aromatic) amino acids. Recently, Infrared Multiple Photon Dissociation (IRMPD) spectroscopy, [4][5][6][7] a powerful tool to identify the structural and electronic features of various ionic species in the gas phase, [8][9][10][11][12][13][14] including mono- [15][16] and divalent- 17 metal-bound amino acids, has revealed canonical structures for halide adducts of glutamic acid, histidine, and phenylalanine.…”

Observation of Conformational Simplification upon N-Methylation on Amino Acid Iodide Clusters

“…Amino acids (AAs) are the building blocks of proteins and play a crucial role in living cells and biological processes. , All 20 proteinogenic AAs adopt zwitterionic structures with the N-terminus protonated and the C-terminus deprotonated under typical physiological conditions, whereas they exist in their canonical forms in the gas phase. − Previous studies have shown that the gaseous zwitterionic forms of AAs can be stabilized upon solvation and exist in AA-ion clusters, illustrating the remarkable molecular binding forces exerted by solvents and ions on AA structures. − AA-ion complexes are tractable both by first principle calculations and detailed spectroscopic characterizations, making them attractive models for probing fundamental intermolecular interactions important to the understanding of protein and ion function under biological settings.…”

“…Gas phase ion spectroscopy accompanied by high-level ab initio computations has proven to be a powerful means for determining biomolecule-ion structures, − but there are significant challenges regarding (1) how to experimentally populate energized isomers and (2) how to obtain spectroscopic signatures for distinguishing different but similar structures. We recently demonstrated in the Gly·I – case study that cryogenic “iodide-tagging” negative ion photoelectron spectroscopy (NIPES) coupled with an electrospray ionization (ESI) source is an effective approach for this purpose .…”