Thesis defence

Title : « Mineral spirits: The redox transformations of CO2 & CH4 mediated by Fe2+/3+ oxyhydroxide “green rust” minerals »

Composition du jury

Rapporteurs

Laurent CHARLET, Professeur Emérite, Université de Grenoble Alpes

Abderrazak EL ALBANI, Professeur, Université de Poitiers

Examinateurs

Anabella IVANCICH, Directrice de Recherche, CNRS

Christian RUBY, Professeur, Université de Lorraine

Simon DUVAL, Membre invité, Chargé de recherche, CNRS

Michael J. RUSSELL Membre invité, Professeur Emérite, Université de Turin

Président du Jury

François GUYOT, Professeur, Sorbonne Université

Directeurs de thèse

Daniel FERRY Directeur de thèse, Chargé de recherche, CNRS

Wolfgang NITSCHKE Co-encadrant de thèse, Directeur de recherche, CNRS

Abstract :

Extant biological metabolism is powered by the efficient transfer of electrons between carbon species and coordinated metal atoms within specially evolved enzymes. However, this redox mechanism is not unique to biology as naturally occurring metals and mineral scaffolds conduct cryptic electron transfer throughout the environment. This abiotic redox cycling of carbon by minerals drove the geochemical evolution of marine and terrestrial environments prior to life, and it is implicated in its emergence. Structural homology between the lattice coordination of certain reactive minerals and enzymatic reaction centers suggests a geochemical transition between abiotic and biological chemical systems. This thesis explores this hypothesis and identifies the unique layered nanomineral Fe2+/Fe3+ oxyhydroxide ‘green rust’ as a potential candidate for this transition due to its impressive electron transfer and versatile ionic exchange properties. We experimentally demonstrate the novel redox chemistry of Fe-oxyhydroxide green rust (GR) minerals towards CO2 and CHgases under a barrage of conditions (e.g. pressure, temperature, UV irradiation) and characterize the reactions via spectroscopic and spectrometric analysis (e.g. XRD, Raman, FTIR, XPS, NMR, and GC-MS). We identify various products formed from the reduction of CO2 and oxidation of CH4 mediated by Fe-oxyhydroxide GR, supporting the hypothesis that life emerged from reactive minerals that mediate complex organic chemistry pathways mimicking extant carbon fixation metabolisms. Additionally, certain products formed by GR mediated carbon redox have strong implications over early climate forcing and the nature of the abiotic controls over the development of the biosphere.

Key words : redox, iron oxyhydroxide, green rust, reactive mineral, methane oxidation, carbon dioxide reduction, climate, origin of life