Structural Influences of Noncovalent Interactions in the Gas Phase

摘要

The physical properties of molecules in solution, such as basicity and structure, depend on the cooperation and competition of noncovalent intra- and intermolecular interactions. Studying these interactions in the condensed phase is made difficult by the presence of competing influences from counterions and impurities. In the gas phase, however, specific ions, ion complexes and hydration states can be isolated and studied by Fourier transform mass spectrometry coupled with infrared (IR) laser spectroscopy. Using these two techniques, it is possible to isolate specific ions before inducing dissociation via absorption of IR photons. The extent of absorption at a given wavelength correlates to the relative abundance of product ions produced via dissociation, which can be measured using mass spectrometry. The absorption of IR photons only occurs at specific wavelengths depending on which functional groups are present and how their vibrational modes are influenced by interactions such as hydrogen bonding. Structural information is obtained from these spectra by interpreting the presence of certain bands and their frequencies. In addition, information can also be obtained by comparing the spectra from ions of interest to the spectra of reference ions, with known structures, or the simulated spectra of computed geometries. These types of studies provide valuable insight into how noncovalent interactions govern the structure of biomolecules and hydrogen-bonded networks. This dissertation reports experiments utilizing IR spectroscopy to study how waterion interactions can affect both the structure of an ion solvated by an aqueous nanodrop as well as the hydrogen-bonding network of the nanodrop itself. In addition, the structural effects of ion-peptide interactions, which are relevant to understanding how ions influence biological processes, are also investigated. (Abstract shortened by ProQuest.).