New insights into biomolecule polymerization under plausible primordial earth conditions: Implications for the origin of life
Parker, Eric Thomas
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The origin of life on Earth is amongst the greatest scientific mysteries. The Miller-Urey experiment brought legitimacy to studying life's origins and ushered in the era of prebiotic chemistry. Much focus in prebiotic chemistry has been on monomer organic synthesis. Consequently, polymerization of simple species into more complex biomolecules remains a major challenge. Therefore, this thesis investigates the transition from organic building blocks to simple polymers. In this thesis, a standard protocol for performing prebiotic simulation experiments was established to study organic synthesis under various mimicked primitive conditions. The formation of amino acids from such experiments was compared to that of Titan simulation reactions, illustrating these prebiotic experiments are good analogs of possible abiotic chemistry elsewhere and that such synthesis is robust under numerous possible cosmochemical environments. In addition to performing original experiments, archived samples from Stanley Miller’s unreported 1958 cyanamide experiment were analyzed to evaluate abiotic amino acid polymerization via the plausible prebiotic condensing reagent cyanamide. The analyses revealed the experiment with added cyanamide induced amino acid polymerization. Repeating the experiment confirmed peptide synthesis. Aqueous heating experiments determined polymerization is encouraged by amino acid synthesis intermediates and cyanamide dimerization. The plausibility of amino acid/alpha-hydroxy acid polymerization to form depsipeptides (mixed amide/ester linkages) was studied by developing a liquid chromatography-tandem mass spectrometry method to analyze a suite of alpha-hydroxy acids. The method was applied to prebiotic mixtures and indicated the monomers glycine, alanine, and aspartic, glutamic, glycolic, lactic, malic, and alpha-hydroxyglutaric acids are most pertinent for future depsipeptide studies. Finally, abiotic samples underwent simulated environmental cycling and were analyzed for depsipeptides. This work marked the first development of an analytical platform for depsipeptides using ion-pair chromatography, ion mobility spectrometry, and high resolution tandem mass spectrometry. This method tentatively identified the glycolic acid-aspartic acid/malic acid-glycine and malic acid-aspartic acid didepsipeptides, suggesting simple depsipeptides may form upon environmental cycling of complex mixtures. This thesis expands our knowledge of the range of chemical and environmental conditions that could have supported polymer synthesis on the primordial Earth and probably elsewhere.