Date of Award

Spring 1-1-2018

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Chemistry & Biochemistry

First Advisor

Veronica Vaida

Second Advisor

Joel D. Eaves

Third Advisor

Veronica M. Bierbaum

Fourth Advisor

Sheref S. Mansy

Fifth Advisor

Paul Ziemann

Abstract

Sunlight-driven reactions of organic molecules contribute to the environmental processing of organic compounds, including the generation of molecular complexity via aqueous chemistry. This thesis focuses on the aqueous photochemistry of α-keto acids, and the implications of this reactivity for environmental chemistry of both the early and modern Earth. Beginning with pyruvic acid, the simplest α-keto acid, I have investigated the photochemical mechanisms governing their reactivity in aqueous solutions. Even in very dilute solutions with low concentrations of pyruvic acid, covalently-bonded dimers and trimers are formed from the recombination of photochemically-generated radical species. These mechanisms are readily generalizable to α-keto acids as a class of molecules, as shown for a series of alkyl α-keto acids. α-Keto acids are also shown to be capable of acting as photo-initiators, driving reactions of non-photoactive species.

The photochemistry of α-keto acids is known to be particularly sensitive to reaction conditions. One example of this sensitivity is the observed pH dependence and its effects on relative product yields, which is due in part to changes in the extent of hydration and deprotonation. These observed changes are consistent within the expanded mechanistic framework for the reactivity of α-keto acids.

Even simple starting solutions of a single alkyl α-keto acid species become a complex mixture of oligomeric species upon photolysis. This is due to the formation of reactive intermediate species, which can further react in solution. The oligomers formed from this photochemistry are amphiphiles, many of which have two or three alkyl chains. The photoproducts generated from these alkyl α-keto acids are surface-active and spontaneously self-assemble into monodisperse, spherical aggregates over the course of photolysis, which has important environmental implications both for today and the early Earth. In the modern environment, this chemistry may contribute to the abiotic processes by which surface-active species are formed at the sea surface microlayer. The formation of such multi-tailed lipids and aggregates on the early Earth may help answer questions about how the first protocells evolved.

Available for download on Saturday, December 21, 2019

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