The formation of a cell membrane was a critical moment in the origin of life. Amphiphillic molecules will self-assemble into bilayer vesicles in aqueous solution, but only under a certain set of conditions (concentration, pH, ionic strength, etc). One of the most plausible pre-biotic systems in which these conditions are met are briny pools formed near hydrothermal vents, where organic compounds in aqueous solution are in contact with mineral surfaces. Notably, clay minerals have been shown to promote the aggregation of pre-biotically available amphiphiles and increase the rate at which they form vesicles. However, there are almost no specific physical or chemical properties of clay surfaces that have been correlated with increased rate of vesicle formation. Interactions between amphiphiles and clay surfaces will depend on the clay layer charge, the charge location, the surface area, delamination properties of the clay layers, the hydrophilicity of the surface, and a host of solution properties. In our study, we attempt to provide some mechanistic clarity by testing the hypothesis that clays charge-balanced by more hydrophillic cations will promote formation of membrane-like bilayers. Natural montmorillonite clays from the Clay Mineral Society Source Clays Repository were purified to isolate the clay fraction and saturated with Cs+ (ΔhydH = -264 kJ/mol), tetramethylammonium (TMA; ΔhydH = -133 kJ/mol), and Ca2+ (ΔhydH = -1577 kJ/mol). The self-assembly of decanoic acid (C10H20O2) was studied in aqueous solution using UV-Vis spectroscopy to monitor the micelle-to-vesicle transition in the presence and absence of our three montmorillonite clays. A second set of studies examining vesicle formation from a thin film of decanoic acid rehydrated in the presence of our clays using fluorescence spectroscopy will also be presented.

Role of cation hydrophobicity in mineral-assisted membrane formation

2019 Spring National Meeting

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