LAUSR

3012-Pos Board B220 Molecular Interactions of Lipids and Mineral Surfaces Brenda L. Kessenich1, John S. Loring2, Sarah L. Keller1, James J. De Yoreo2,3. Chemistry, University of Washington, Seattle, WA, USA, Pacific Northwest National Laboratory, Richland, WA, USA, Materials Science and Engineering, University of Washington, Seattle, WA, USA. Lipid assembly at mineral surfaces is a poorly understood phenomenon that reflects underlying lipid-lipid and lipid-substrate interactions, both of which are expected to be sensitive to hydration/dehydration cycles and have the potential for significant environmental impacts. Organic matter derived from plants and microbes represents a large and poorly constrained terrestrial carbon pool that is stabilized through the interaction with mineral surfaces via an unknown mechanism. The lipid fraction is particularly interesting as it impacts parameters such as soil water repellency and its assembly on mineral surface may inhibit digestion by microbial attack and consequent mobilization of carbon. Furthermore, determination of molecular-scale interaction mechanisms of lipids and mineral surfaces may help elucidate the role of minerals in formation of pre-biotic membranes. To understand lipid-mineral interaction and assembly, as well as the impact of hydration/dehydration cycles, we are using infrared spectroscopy and atomic force microscopy (AFM) to observe humidity-dependent conformation and morphology for model systems of DOPC, DSPG, and DSPE on mica, montmorillonite, and kaolinite. Lipid morphology observed via both fluorescence and AFM is found to be heterogeneous in both liquid and air, with some dependence on the type of lipid headgroup. AFM data also suggest that bilayers are the dominant unit of dry lipid structures on mineral surfaces, contrasting prior hypotheses in the soil science field for transformation to monolayer structures. Preliminary measurements of contact angle vs lipid coverage suggest both a sharp increase in hydrophobicity at low coverage and oscillatory variations as coverage is increased beyond that of a full bilayer. Changes are seen in both photoinduced force microscopy and attenuated total reflectance infrared spectroscopy with varying humidity that may reflect changes in conformation. The relationship between these changes and both contact angle and soil water repellency are the subject of current research.