Exogenous and Endogenous Sources of Organic Compounds on the Early Earth: Investigating Carbonaceous Meteorites and Plausibly Prebiotic Complex Mixtures by Liquid Chromatography-mass Spectrometry

Open Access
Author:
Smith, Karen Elizabeth
Graduate Program:
Geosciences
Degree:
Doctor of Philosophy
Document Type:
Dissertation
Date of Defense:
November 19, 2013
Committee Members:
  • Christopher Howard House, Dissertation Advisor
  • James David Kubicki, Committee Chair
  • James Kasting, Committee Member
  • Philip C. Bevilacqua, Special Member
Keywords:
  • analytical chemistry
  • meteorites
  • mass spectrometry
  • liquid chromatography
  • geochemistry
Abstract:
The early Earth atmosphere was thought to have been composed mostly of nitrogen and carbon dioxide with low concentrations of reduced gases (H2, CH4, etc.). Laboratory experiments simulating endogenous chemistry of early Earth (i.e. spark discharge with neutral gas mixtures) produce low abundances of biologically relevant molecules, which may have been a problem for the origin(s) of life. Thus, an exogenous source (e.g., meteorites, comets, and interplanetary dust particles) that delivered organic molecules may have been important in facilitating prebiotic reactions on the early Earth. In Chapter 2, we investigated cyanide in a variety of meteorites by developing an analytical protocol that consisted of extracting a meteorite via acid-digestion and distillation using a gas-permeable membrane apparatus followed by chemical derivatization and analysis by liquid chromatography coupled to fluorescence detection and time-of-flight mass spectrometry. Cyanide is an important precursor for the synthesis of both amino acids and nucleobases. In Chapter 3, we investigated pyridine carboxylic acids in eight different CM2-type carbonaceous chondrites by liquid chromatography coupled to UV detection and high resolution Orbitrap mass spectrometry. Of particular interest was nicotinic acid (pyridine-3-carboxylic acid), which is a precursor to the coenzyme nicotinamide adenine dinucleotide (NAD), a ubiquitous molecule found in all living cells. Additionally, the synthesis of meteoritic pyridine carboxylic acids has yet to be determined. Therefore, we carried out laboratory studies of proton-irradiated pyridine in carbon dioxide-rich low-temperature ices to serve as a model of the interstellar ice chemistry that may have led to the synthesis of pyridine carboxylic acids. Examining the synthesis and inventory of small, biologically relevant molecules in carbonaceous meteorites is useful for understanding their availability on the early Earth; however, biopolymers (e.g., nucleic acids and proteins) are extremely large and complex in structure and such molecules are not found in meteorites. In Chapter 4, we investigated the reactivity of various nitrogen heterocycles with plausibly prebiotic complex mixtures produced from spark discharge experiments in order to understand their ability to form more complex (substituted or polymeric) structures. We also investigated nitrogen heterocyclic polymers produced from 5-hydroxymethyluracil and 5-hydroxymethylcytosine by liquid chromatography-high resolution Orbitrap mass spectrometry and theoretical calculations.