This thesis project investigates two of the mechanisms that have been postulated to explain the origin of the molecular homochirality found in living systems. These mechanisms are i. the Yamagata-Rein Hypothesis, which predicts that the weak neutral currents between electrons and nucleons result in a Parity-Violating Energy Difference (PVED) between a pair of molecular enantiomers; and ii. the Vester-Ulbricht Hypothesis, which predicts that the β-particles produced during weak force mediated nuclear β-decay interact differently with each of a pair of molecular enantiomers. Both hypotheses predict a small enantiomeric excess and theorise that such an excess might have been the prebiotic chiral influence that led to homochirality, which is generally accepted to be a prerequisite for biology. It is found that those PVED computations carried out the coupled-perturbed level of theory are approximately one order of magnitude larger than those previously computed at the entry-level uncoupled-perturbed level of theory. The results computed as part of this thesis project include the first to apply Density-Functional theory to the computation of the PVED. The coupled-perturbed Hartree-Fock and Kohn-Sham computations of the PVED are found to be in good agreement with recent related computational studies. The hypersensitivity of the PVED to small conformational changes, coupled to the difficulties in knowing the aqueous phase structure of even small chiral biomolecules such as α-alanine, means that it is difficult to make any unambiguous conclusions regarding which of a pair of biomolecular enantiomers might have been favoured by the PVED in a probiotic regime. These results do indicate that the largest β-asymmetries are generated in the forward scattering regimes and that the sign of the asymmetries may change suddenly as the energy of the incoming β-particle increases so as to allow the removal of electrons from successive molecular orbitals during the impact ionisation of the molecule.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:604912 |
| Date | January 2003 |
| Creators | Hyde, G. |
| Publisher | University of Cambridge |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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