| dc.description.abstract | Our understanding of many biological processes requires knowledge
about biomolecular structure and weak intra- and intermolecular
interactions (e.g. hydrogen bonding). Both molecular
structure and weak interactions can be directly studied by
far-infrared (or THz) spectroscopy, which probes low-frequency
molecular vibrations. In this thesis I present the results of experimental
and theoretical investigations of far-infrared vibrations
in small aromatic molecules of biological relevance. To enable a
direct comparison with theory, far-infrared spectroscopy was performed
in the gas phase with a conformer-selective IR-UV ion-dip
technique. The far-infrared spectra of molecules containing a peptide
(-CO-NH-) link revealed that the low-frequency Amide IV-VI
vibrations are highly sensitive to the structure of the peptide moiety,
the molecular backbone, and the neighboring intra- and intermolecular
hydrogen bonds. The study of far-infrared spectra of
phenol derivatives identified vibrations that allow direct probing
of strength of hydrogen-bonding interaction, and a size of
a ring closed by the hydrogen bond. Furthermore, benchmarking
theory against the experimental data identified advantages
and disadvantages of conventional frequency calculations for
the far-infrared region performed with ab initio and density functional
theory. For example, the conventional approaches were not
able to reproduce strongly anharmonic vibrations such as aminoinversion
in aminophenol. Instead, a double-minimum potential
model was used for this vibration, and successfully described
the experimental spectra of aminophenol. The results presented
in this thesis can assist the interpretation of far-infrared spectra
of more complex biomolecules, pushing forward low-frequency
vibrational spectroscopy for efficient structural analysis and the
studies of weak interactions. | sv |
