Mass spectrometric and computational study of gaseous L-glutathione non-covalent complexes

Sharifi, Mahsa (2024) Mass spectrometric and computational study of gaseous L-glutathione non-covalent complexes. Masters thesis, Memorial University of Newfoundland.

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Abstract

This study investigates the structures, energetics, and unimolecular reactions of glutathione complexes with various metal cations, including alkali metals, alkaline earth metals, transition metals, and heavy metals. Using sustained off-resonance irradiation collision-induced dissociation (SORI-CID) and infrared multiphoton dissociation (IRMPD) spectroscopy, combined with computational techniques, the research explores the coordination chemistry and dissociation dynamics of these metal-GSH complexes. Additionally, the study examines the dissociation behaviors of protonated amino acid-GSH complexes, correlating these findings with proton affinity data and kinetic parameters. Chapter 2 explores SORI-CID and IRMPD (or vibrational) spectroscopy results for [M(GSH)]⁺ complexes (where M is an alkali metal cation), highlighting differences in fragmentation behaviors linked to metal size and charge density. The study reveals that smaller cations like Li⁺ and Na⁺ lead to extensive fragmentation of glutathione, whereas larger cations like Rb⁺ and Cs⁺ predominantly result in the loss of glutathione itself. The lowest energy alkali metal-glutathione complexes are tetracoordinated, with the metal binding to the amino nitrogen and three carbonyl oxygens, while O2 interacts with the thiol and forms a hydrogen bond with the amine. The vibrational spectra for these structures are in good agreement with experimental IR spectra. In Chapter 3, the fragmentation patterns of doubly charged metal glutathione complexes are analyzed. SORI-CID results for metals including Mg²⁺, Ca²⁺, and Zn²⁺ reveal fragmentation pathways such as the loss of water, ammonia, and pyroglutamic acid. The IRMPD spectra and computational models offer detailed structural insights, showing that metal coordination affects the binding geometry and stability of these complexes. Chapter 4 investigates the dissociation dynamics of protonated glutathione complexes with various amino acids using BIRD experiments. Temperature-dependent studies reveal that arginine, with its high proton affinity, shows the most rapid dissociation, while lysine exhibits slower kinetics. The findings underscore the influence of amino acid side chain properties on dissociation mechanisms and provide a comprehensive understanding of their stability and reactivity. Overall, this thesis integrates experimental and computational approaches to elucidate the structural and dynamic properties of metal-GSH and amino acid-glutathione complexes, offering valuable insights into their fragmentation patterns, structural configurations, and reactivity under varying conditions.

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