Preformed Complex Organic Molecules from the Matrix of Magnetic Minerals

Grant #: NNX10AR81G
Senior Scientist: Friedemann Freund

The hard, dense solid state of magmatic minerals is a medium, in which organic synthesis can take place. When minerals crystallize from magmas laden with H2O, CO/CO2, N2, H2S etc, the gas/fluid-phase components become incorporated, forming oxyanion complexes, best known among them OH (hydroxyl) and CO3^2(carbonate). Thermodynamically, solid state solubility is highest at the crystallization point but decreases with decreasing temperature. During cooling, the exsolution becomes so sluggish that the mineral H2O/CO/CO2/N2/H2S solid solution drifts out of thermodynamic equilibrium and becomes supersaturated. Electronic rearrangements lead to a redox conversion whereby the biogenic elements H, C, N, S etc become reduced while lattice O2 oxidizes from the valence 2 to the valence 1¿. To the extent that the chemically reduced H, C, N, S etc. are diffusively mobile, they will exsolve (segregate). Segregation sites are grain surfaces, dislocations and other structural defects. There, the biogenic elements form polyatomic Cn-H-O-N-S entities, so-called organic protomolecules. In the lab we can extract them from mineral powders crushed under clean condition. Since the assembly of Cn-H-O-N-S entities in the solid matrix occurs under metastable conditions, it is independent of the redox potential, meaning that - on the early Earth - their formation is decoupled from the redox potential of the atmosphere/hydrosphere. We have so far identified glycolamide, a short-chain dicarboxylic (succinic) acid, medium-chain length carboxylic acids, and whole families of stereochemically controlled, oxygen-rich compounds (some S-containing) with molecular weights up to 600 amu. We propose an in-depth study of the formation of these Cn-H-O-N-S entities in the matrix of laboratory-grown MgO and gem-quality olivine crystals from the upper mantle, using IR spectroscopy and ultrahigh resolution mass spectrometry of solvent extracts from crushed powders. The work is relevant to prebiotic chemistry in the Exobiology Program.