Theoretical and experimental investigation into the IR-VUV ion dip spectroscopy of amino acids and analogue systems

Clawson, Keven James, author
Bernstein, Elliot, advisor
Bartels, Randy, committee member
Fisher, Ellen, committee member
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Amino acids are among the fundamental building blocks of life, and as such have been, and continue to be, of much interest for study. While gas phase spectroscopic studies can be very useful in obtaining information about molecular species (in this case various naturally occurring amino acids), the use of computational and theoretical methods can aid these studies in providing a more complete understanding of the properties and behaviors of these species. Here presented are the results of IR-VUV ion dip spectroscopy, coupled with a high-level theoretical examination of the spectroscopic results, including MP2 and CASSCF calculations. In IR-VUV ion dip spectroscopy, the isolated neutral molecules are ionized by a single photon of 10.5 eV energy 118 nm. If the neutral ground state amino acids are exposed to IR radiation prior to ionization, an IR spectrum can be determined by observation of the ion intensity of the different fragment mass channels. Species specifically studied include numerous naturally occurring aliphatic and aromatic amino acid species, and amino acid analogue species. In the case of the aliphatic amino acids, conformer specific decomposition pathways are observed spectroscopically, and further elucidated both through the study of III amino acid analogue species and through high level multiconfigurational CASSCF calculations. It is shown that upon ionization, the localized character of the charge, coupled with the geometry of the neutral parent molecule, directs the decomposition reaction of the molecule. In simple, small aliphatic amino acid and analogue species, these factors are unique to the conformation of the molecule, leading to conformer specific decomposition chemistry. In the amino acid species, the localized charge tends to occur either on one of the available moieties (carboxylic acid, amine, etc.), or on the carbon-carbon bond, depending on the conformer. The IR-VUV ion dip spectra obtained from the aromatic amino acid species, however, clearly demonstrate different photodecomposition behavior in the aromatic species when compared to the simple, smaller aliphatic species. The conformer specific chemistry which was observed in the smaller molecules was not evident in the aromatic species. This is likely due to the aromatic moiety containing the lowest energy, localized ion state for the molecule which does not lead to ion fragmentation. Thus, the conformer specific decomposition chemistry observed in the non-aromatic species is no longer observed in those species which contain an aromatic moiety.
2010 Fall.
Includes bibliographic references.
Covers not scanned.
Print version deaccessioned 2022.
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Far ultraviolet radiation
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