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Metal and Mineral Catalyzed Organic Photochemistry in Modern and Prebiotic Environments

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Metal and Mineral Catalyzed Organic Photochemistry in Modern and Prebiotic Environments Metal and mineral catalyzed organic photochemistry in modern and prebiotic environments By David Michael Mangiante A dissertation submitted in partial satisfaction of the requirements for degree of Doctor of Philosophy in Earth and Planetary Science In the Graduate Division Of the University of California, Berkeley Committee in charge: Professor Jillian Banfield Doctor Benjamin Gilbert Professor Walter Alvarez Professor Laura Lammers Summer 2016 Abstract Metal and mineral catalyzed organic photochemistry in modern and prebiotic environments by David Mangiante Doctor of Philosophy in Earth and Planetary Science University of California, Berkeley Professor Jillian Banfield, Chair Minerals and metals serve important roles in the organic geochemistry of natural environments. Mobility of organics, catalysis of degradation, and redox catalysis are among the processes affected by minerals. With the addition of ultraviolet light a new suite of photo-induced redox reactions is possible including reductive and oxidative ligand-to- metal/mineral charge transfer. Such reactions allow for novel chemistry that has relevance to the modern Earth as well as the pre-biotic origin of life. This thesis describes processes by which electrons transfer between minerals/metals and organic ligands relevant to natural systems as well as the origins of life. I present evidence of ultrafast electron transfer and the production of radical intermediates essential to deducing redox reaction mechanisms. I also present methods for communicating understanding of interfacial chemistry to the public that promote engagement in science. This thesis is broadly applicable to those interested in mineral organic photochemistry, electron transfer, the origin of life, and science teaching methods. I probed the chemistry between organic molecules and minerals/metals, using pump/probe transient absorption (TA) spectroscopy to observe the dynamics of electrons and vibrational modes at timescales ranging from picoseconds to nanoseconds. This technique can be conducted in solution and can be highly sensitive to intermediate reaction products. I examined the photolysis of the metal carboloto, ferric oxalate, under UV irradiation using mid-infrared TA spectroscopy in both D2O and H2O. Ferric oxalate is a model molecule for natural systems and is used to measure photo flux due to its well-characterized quantum efficiency. However, the mechanism of its photolysis is debated. This was the first time the intermediates of ferric oxalate photolysis were observed using techniques sensitive to the vibrational states of organic molecules. I observed the rapid intramolecular charge •– transfer and the production of CO2 and tentatively CO2 . Additionally, we observed intermediate states that we interpret to be CO2 disassociating from ferrous iron, a signature never before reported. Investigations of photo-induced electron transfer were expanded to ZnS nanoparticles and fumarate. Fumarate is an intermediate metabolite in the tricarboxilic acid (TCA) cycle, which is a part of core metabolism in modern organisms. It undergoes a two- electron reduction to form succinate. Reductive versions of the TCA cycle may have been important for the origin of prebiotic metabolism. I measured the effect of adsorbed fumarate on the electronic states of photo-excited ZnS and observed electron transfer both at short (<1 ps) and long (>1 ns) timescales. Additionally, I observed an electronic signature tentatively attributed to fumarate radical, which persisted for at least 8 nanoseconds. The appearance of a long-lived radical intermediate product and the rapid initial electron transfer 1 from the mineral to the organic suggests that ZnS could be a viable catalyst for prebiotic metabolism on the early Earth. To better educate students on the importance of mineral surface chemistry I designed and implemented a classroom experiment wherein students performed electrolysis of water using mineral electrodes. The experiment emphasized both the mineral catalysis and mineral redox chemistry, which occur at the solid/liquid interface. Concepts in interfacial chemistry are often difficult to exhibit, making this teaching tool unique and useful. Students were guided through a set of investigations and constructed their understanding through observations and sharing of ideas. The experiment was successfully implemented in a college level mineralogy course. 2 for my mother i Acknowledgements The practice of a graduate student is to learn about the world in which we live, to interact with great thinkers from the past, and, most importantly, to grow alongside talented and intelligent people. Throughout my time in graduate school, I have come to realize that the thoughtful and emotional connections with people around me are worth more to me than any facts I may learn or personal successes I may have. Firstly I thank my committee Jill, Ben, Walter, and Laura. You all inspire me though your hard work and dedication to your craft and the innovative energy you bring to a difficult and sometimes sterile profession. Jill and Walter you have been mentors and teachers for me and I admire the way you inspire excitement in your students. Jill, you have always helped me to see through sometimes muddy thoughts and “cut the crap” to get to the point. Your kindness and generosity has never gone unnoticed, even when I am a troublemaker. Ben, kind, calm, and thoughtful attitude has propelled through the most difficult times in my tenure as a graduate student. I have learned so much from you as both a scientist and a person and I will always cherish the relationship we have had. The support of my mother, father, and brother has be a constant and ever-present force in my life, for which I am forever grateful. Your unconditional belief in me pushes me to always keep trying. I am so lucky to be a part of a strong and robust community of graduate students in the Earth and Planetary Science department at UC Berkeley. The amazing people that saw me in like Ved and Dave as well as the lovely youngsters who see me leave like Chelsea, Alex, and Jesse have all helped bring life to graduate school. My friends, my family away from home, I love you all. Carolina, Ian, Patrick, Claire, Brent, Alicia, Jesse, Matthew, Pam, Lori, Sanne, and Daniela you all mean so much to me. We have shared so much history together. Wherever you are in the world I will always support you. Alice, you have always inspired me to feel and participate in the world around me. Your commitment to teaching as a life practice is reflected in me. Jenny, you always reminded me that thinking and communicating about science was my passion. Katherine, your constant belief in me was motivation to finish my dissertation. I respect your strength and perseverance. I will always aspire to your grit. The Exploratorium has been a home to me for my entire tenure as a graduate student. I have learned and grown so much as a person in amongst its people, exhibits, and the public. Thank you to Melissa, Dave, Sarah, Marcus, Fran, Stephanie, Kelly, and Deirdre. Thank you to all of my students throughout the years, it was my pleasure to learn with you. Never stop teaching. ii CONTENTS 1 Introduction 1 1.1 What is life? ....................................................................................................................... 1 1.2 Conceptual frameworks for the origin of life ............................................................... 1 1.3 Top down: Chemical systems active in modern organisms that could have been important in the pre-biotic earth ............................................................................................. 1 1.3.1 Catalysis is a key biological capability ................................................................ 1 1.3.2 Origin of Life Theory: RNA World ................................................................... 1 1.3.3 Core metabolic may record chemical cycles available on the early Earth .... 2 1.4 Bottom up: What ingredients for life were present on the Early Earth? ................. 2 1.4.1 Organic material on the early Earth ................................................................... 2 1.4.2 Minerals and metals as energy sources and catalysts on the early Earth ...... 3 1.4.3 Origin of Life Theory: Iron-Sulfur World ........................................................ 3 1.4.4 Mineral Catalysis with UV light .......................................................................... 3 1.4.5 Origin of Life Theory: Minerals as Prebiotic Photocatalysts ......................... 3 1.5 Overview of dissertation ................................................................................................. 4 1.5.1 Ultrafast spectroscopy .......................................................................................... 4 1.5.2 The photolysis of ferric oxalate .......................................................................... 4 1.5.3 Teaching electrochemistry ................................................................................... 4 1.6 Works cited ........................................................................................................................ 5 2 Mechanism of Ferric Oxalate Photolysis 7 2.1 Abstract ............................................................................................................................... 7 2.2 Introduction ...................................................................................................................... 7 2.3 Materials
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