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Non-covalent Interactions in the Gas Phase: Infrared Spectroscopy and Nanocalorimetry of Ion-Biomolecule Complexes

  • Author(s): O'Brien, Jeremy Thomas
  • Advisor(s): Williams, Evan
  • et al.
Abstract

In this dissertation, experiments investigating the effects of non-covalent interactions on the structure and reactivity of gas-phase, ion-containing clusters, including ion-amino acid and ion-water complexes, are presented and discussed. Ions generated using electrospray ionization and analyzed using Fourier transform ion cyclotron resonance mass spectrometers at the University of California, Berkeley, and the FOM Institute for Plasma Physics Rijnhuizen in Nieuwegein, The Netherlands, are investigated using infrared photodissociation/infrared multiple photon dissociation (IRPD/IRMPD) spectroscopy, collision-induced dissociation, and electron capture dissociation (ECD). Using ion nanocalorimetry, the effect of varying the potential which controls the kinetic energy of the thermally generated electrons used for ECD experiments is determined to be minimal under typical experimental conditions. The results indicate that only a small population of electrons with near zero velocity relative to the trapped hydrated ions are captured and result in the observed ECD products. IRMPD spectra of proton-bound heterodimers containing valine and basic amines indicate that the structure of the heterodimer changes with increasing basicity of the amine suggesting that the structure of an amino acid in a proton-bound dimer may be different than in isolation which breaks an assumption made in the determination of gas-phase basicities using the kinetic method. IRMPD spectra of ion-amino acid complexes reported here reveal the effects of gas-phase acidity, ion polarity/charge state and ion size on the relative zwitterionic stability of the amino acids. The coordination numbers (CN) of hydrated divalent transition metals are determined using IRPD spectroscopy and photodissociation kinetics measurements. The CN of Cu2+ is lower than the other metal ions (CN = 4) due to Jahn-Teller effects brought about by the d9 electronic configuration of the ion. IRPD spectra of SO42- with up to 80 water molecules attached indicate that the structure induced by the dianion dominates over the intrinsic water-water interactions for clusters with up to 43 water molecules, well beyond the first solvation shell. The roles of ion charge state and cluster size in the structure of gas-phase "nanodrops" are investigated for the largest mass-selected ionic clusters for which IRPD spectra have been reported. Effects of ion charge state are observed for nanodrops containing up to ∼250 water molecules in contrast with recent reports that only the first solvation shell is affected by ions in aqueous solution.

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