UBC Theses and Dissertations
Exploring the conformational landscape of amino acids in solid parahydrogen matrices through ab initio calculations Carlson, Colton Dean
It is well known that amino acids are the building blocks for proteins, and as such, likely played a critical role in the origin of biological life. When in the solid phase, or in solution, amino acids take on a zwitterionic form, enabling a plethora of stabilizing intermolecular interactions. However, prior to understanding amino acids in the bulk phase, one must first characterize them in their neutral form. Due to the conformational flexibly and thermal instability of amino acids, this is best accomplished through the use of high-resolution matrix isolation Fourier transform spectroscopy in conjunction with high level ab initio calculations. The vibrational spectrum of alpha-serine is reported for the first time within a solid parahydrogen matrix, in which ten conformers were identified, thereby supporting the claim that solid parahydrogen matrices are superior to other noble gas matrices for the analysis of highly flexible molecules. Assignment of the vibrational transitions was accomplished through the use of quantum chemical calculations at both the DFT and MP2 levels of theory. Additionally, preliminary TD-DFT calculations indicate that the first singlet excited state of alpha-alanine is a dissociative state, in which, upon excitation alpha-alanine forms the hydrocarboxyl (HOCO) and ethylamine radicals through a Norrish type I pathway. Interestingly, it is predicted that both the first and second singlet excited states are dissociative states for alpha-alanine conformers displaying strong hydrogen bonds between the carboxyl hydrogen and amine lone pair, indicating that noncovalent interactions play a substantial role in both the ground and excited state potential energy surfaces of amino acids.
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