The physical chemistry of gaseous protonated and metal cation-coordinated proline containing complexes studied by tandem mass spectrometry methods

Studying protonated or metal cationized amino acids and small peptides in the gas phase offers an opportunity to better understand these systems on a molecular level, not often afforded for macromolecules in solution. In the current thesis, proline containing complex ions were electrosprayed and isolated in an FTICR cell where their unimolecular chemistries, structures, and kinetics were explored using sustained off-resonance irradiation collision-induced dissociation (SORI-CID), infrared multiple photon dissociation (IRMPD) spectroscopy and blackbody infrared radiative dissociation (BIRD). These experiments were augmented by computational methods such as electronic structure, simulated annealing, master equation modeling and atoms in molecules (AIM) calculations. The purpose of the present study is to examine the gas phase structures of the proton- and sodium-bound proline amino acids. Later the unimolecular chemistries of the complexes of proline containing doubly charged first row transition and alkaline earth metals were explored. Finally, the structures and the energetics of the complexes containing isomeric ProLeu and LeuPro dipeptides bound alkali metal cations were discussed. Reasonable agreements between the experimental data obtained from IRMPD spectroscopy and BIRD results with the theoretical calculations for the lowest energy forms were achieved. In the following sections the influence of the size and identity of the metal cation, the gas-phase basicity of the amino acid, anchor site of each ligand and peptide sequence on the structures and energetics of molecules were considered