Investigating Hydrothermal and Radiation Effects on Nitrogen Heterocycles Relevant to Meteorite Parent Bodies

Abstract

supporting this research and my graduate studies. I would also like to thank the ELSI (Earth-Life Science Institute) Origins Network for supporting this research. I would especially like to thank Dr. Henderson (Jim) Cleaves who acted as my guide and colleague while conducting research at the Tokyo Institute of Technology in Japan. I consider him a friend now. In addition, I want to thank Ruiqin Yi, Mayuko Nakagawa, and Kyoko Akiyama for their hard work and their help guiding me through working in a foreign laboratory. Thank you to Dr. Aaron Burton and Dr. Darren Locke at NASA Johnson Space Center for analyzing NH4CN polymers by TMAH GC-MS and providing the data for me to analyze. I would like to thank Dr. Karen Smith for reading and editing my thesis. Finally, I would like to thank the faculty and staff in the Department of Chemistry and Biochemistry including those on my thesis committee who helped me throughout graduate school. I'm proud to say Boise State University is my alma mater for both my B.S. and M.S. degrees in Chemistry. Prof. Callahan…you know what you did. I blame all this-the research, the travel, the conferences, continuing to pursue a doctorate, and this dissertation ON YOU!!! vi ABSTRACT Organic compounds in meteorites were likely transformed by a variety of processes on the asteroid parent body including aqueous, thermal, and radiolytic alteration. Previous studies have identified a suite of purine nitrogen heterocycles in carbonaceous chondrites (a class of meteorites) and determined that their likely origin was due to cyanide chemistry. The thesis research described here consisted of two parts: investigating thermal effects on aqueous ammonium cyanide reactions and the production/survivability of organics (Chapter 2) and investigating gamma radiation effects on purine nitrogen heterocycles to understand how prolonged radiation exposure influenced the distribution and abundance of nitrogen heterocycles measured in meteorites today (Chapter 3). A temperature study of 1 M ammonium cyanide was conducted from room temperature to 200 °C (temperatures similar to the aqueous alteration of some carbonaceous chondrites) using a high-pressure reaction vessel. The resulting liquid supernatant and water insoluble cyanide (hetero)polymer were isolated and analyzed by attenuated total reflectance Fourier transform infrared spectroscopy and thermochemolysis gas chromatography-mass spectrometry using tetramethylammonium hydroxide or highperformance liquid chromatography with UV detection (HPLC-UV). A strong correlation was observed between thermochemolysis products of cyanide polymers and the initial reaction temperature-production of aromatic compounds increases and nitrogen containing compounds decrease with respect to increasing reaction temperature. The data presented in this thesis suggests that the polymer may be a less efficient source of nitrogen vii heterocycles when produced at high temperatures. HPLC-UV analysis showed that the supernatant of heated NH4CN reactions is a complex mixture containing m...