Infrared Spectroscopy of Hydrated and Biomolecular Ions

Infrared Spectroscopy of Hydrated and Biomolecular Ions

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This dissertation reports experimental studies on the formation, reactivity, and structure of hydrated and biomolecular ions. Ions are formed using electrospray ionization and experiments are performed using Fourier-transform ion cyclotron resonance mass spectrometers and tunable infrared lasers in Berkeley and Nieuwegein, the Netherlands. Infrared action spectra of divalent calcium solvated by up to 69 water molecules reveal that the coordination number of the metal increases with cluster size and that the spectra of the largest clusters exhibit many similarities with spectra of condensed-phased water. Hydrated trivalent metal ions were observed for the first time and dissociation experiments show that the reactivity of these ions depend strongly on both metal ion identity and the number of solvating water molecules. The hydrogen-stretch infrared action spectrum of hexahydrated sulfate dianion contains spectral signatures for extensive inter-water hydrogen bonding, whereas a spectrum obtained previously in a lower-frequency region suggests that all six water molecules only donate hydrogen bonds to the metal ions. Hydrogen-stretch infrared action spectra of alkali metal cationized arginine that show that arginine changes from its nonzwitterionic to zwitterionic form with increasing metal ion size, with the transition in structure occurring predominantly between lithium and sodium. Infrared action spectra in the fingerprint region show that alkali metal cationized lysine and glutamine are nonzwitterionic, and that additional nonzwitterionic structures with additional hydrogen bonds are formed for complexes with the larger alkali metal ions. Similar spectra for alkaline earth metal ion cationized amino acids indicate that arginine, glutamine, proline, serine, and valine all adopt zwitterionic structures when complexed with divalent barium. Hydrogen-stretch action spectra of lithiated and sodiated arginine solvated by one water molecule provide compelling evidence that attachment of a single water molecule to this ion makes the zwitterionic form of arginine most stable. These studies provide detailed information on the effects of different amino acid side chains and metal ions on the relative propensity of amino acids to adopt zwitterionic and nonzwitterionic structures.Candidate structures were energy minimized with hybrid method density functional calculations (B3LYP) using the LACVP* and LACVP++** basis sets as implemented in Jaguar v. 6.5 (Schrodinger, Inc., Portland, OR). Vibrational frequenciesanbsp;...

Title:Infrared Spectroscopy of Hydrated and Biomolecular Ions
Author:Matthew Francis Bush
Publisher:ProQuest - 2008


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