COLL 539 |
| Robert Hazen1, Hugh Churchill1, David Sholl2, and H Teng3. (1) Geophysical Laboratory, Carnegie Institution of Washington, 5251 Broad Branch Rd. NW, Washington, DC 20015, (2) Department of Chemical Engineering, Carnegie Mellon University, Pittsburgh, PA 15213, (3) Department of Earth and Environmental Sciences, The George Washington University, Washington, DC 20052 |
| Chemical interactions at the interface between crystalline mineral surfaces and aqueous solutions play a central role in numerous natural processes, including weathering and soil formation, pH buffering, hydrothermal ore deposition, biofilm formation, catalytic organic synthesis, and the uptake and release of both organic and inorganic species that affect water quality. Selective adsorption of chiral organic molecules onto chiral mineral surfaces is of special interest in origin-of-life studies, because selection and concentration of chiral organic species on mineral surfaces may have facilitated the transition from geochemistry to biochemistry. Studies of amino acids adsorbed onto chiral crystalline surfaces of calcite (CaCO3) and quartz (SiO2) reveal two factors that influence selective adsorption. First, adsorption is strongly dependent on the charge difference between the mineral surface and the amino acid. Maximum adsorption is observed for amino acids with isoelectric points that differ significantly from the point of zero charge of the mineral surface. Selective adsorption may also depend on the fortuitous conformity of an amino acid with a specific crystalline surface structure. Chiral adsorption, for example, requires three noncolinear points of attraction between molecule and surface. Different crystallographic faces, therefore, will display different adsorption behavior. We have measured selective adsorption on specific crystal faces of calcite and quartz. These observations underscore the necessity of studying well documented single crystal faces, in contrast to powdered mineral samples employed in many previous studies. |
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Chiral Surfaces
Division of Colloid and Surface Chemistry |