HR: 0800h
AN: B21B-0870    [Abstracts]
TI: Nanoscale controls of inorganic impurities and peptides on shape modification during calcite growth
AU: * Dove, P M
EM: dove@vt.edu
AF: Virginia Tech, Department of Geosciences, Blacksburg, VA 24060 United States
AU: De Yoreo, J J
EM: deyoreo1@llnl.gov
AF: Lawrence Livermore National Laboratory, Department of Chemistry and Materials Sciences, Livermore, CA 94551 United States
AB: Many organisms produce crystalline structures during controlled biomineralization that exhibit complex topological forms. These biominerals often express facets or pseudofacets that are not found on crystals grown from pure solutions in the laboratory. This modification of growth shape, whether by inorganic and organic modulators, is generally explained within the paradigm of "stereochemical recognition". According to this model, stereochemical matching of the growth modulator to the molecular structure of these new and otherwise unexpressed faces, stabilizes the formation of new faces to result in a new crystal shape. This idea, however, was developed primarily from bulk crystallization experiments and geometrical models that focused on interactions between impurities and atomic planes of the newly expressed faces. Over the last several years, we have reported nanoscale investigations of how small molecule modifiers (Mg, Sr, amino acids) interact with calcite surfaces during growth. Low concentrations of these `simple' impurities have significant shape-modifying effects. While the observed mechanisms of growth modification are highly diverse, in all cases, it is clear that the source of shape modification always arises from step-specific interactions that alter either the equilibrium properties of the crystal (step edge and bulk free energy) or the kinetics of step motion. The resulting macroscopic shape changes can be traced to these effects at steps on existing faces rather than to stereochemical matching to and thermodynamic stabilization of new faces. Molecular modeling shows that the essential reason for this is that steps provide non-planar environments in which non-planar modifiers can form contacts to both the lower terrace and the step riser. Our findings provide a mechanism-based understanding of shape modification. This is essential as biomineralization studies advance to investigate more complex studies of systems that employ long-chain polypeptides or the full proteins found in vivo. In these systems, we suspect that the inherently non-planar nature of steps also provides an environment in which multiple bonding accommodations provide a large binding energy for non-planar growth modifiers.
DE: 1045 Low-temperature geochemistry
DE: 1050 Marine geochemistry (4835, 4850)
DE: 1055 Organic geochemistry
DE: 0400 Biogeosciences
SC: Biogeosciences [B]
MN: 2004 AGU Fall Meeting