Nita Sahai
University of Wisconsin
Biominerals are nanocomposite materials, where the organic molecules exert strict control over the mineral crystal shape, size, orientation, and hierarchical self-assembly, lending biominerals their unique mechanical, optical, magnetic, and chemical properties. Examples include apatite (Ca 5 (PO 4 ) 3 OH) in bones; calcite (CaCO 3 ) produced by marine algae called coccolithophorids, foraminifera, and other organisms; and opaline silica (SiO 2 ) formed by algae called diatoms.
The unique shape and size of biomineral crystals, not found in their inorganic counterparts, is determined by the expression of high-energy faces that are stabilized by interactions with organic molecules. Understanding the physical-chemical interactions at the organic/mineral/ water interface can provide �biomimetic� synthesis routes for novel materials with emergent properties in biomedical and technological applications. The discovery of mineral crystals with unique morphologies may also serve as tantalizing �biosignatures� on Mars and other extraterrestrial environments. Furthermore, biogenic calcite and silica production provide significant sinks for atmospheric CO 2 , so that identifying the genetic biomineralization pathways may provide avenues for engineered CO 2 sequestration strategies.
We have used Molecular Mechanics/Molecular Dynamics simulations to examine the role of small organic acids and amino-acids on calcite dissolution promotion/growth inhibition which, ultimately, control crystal shape and size. We find that both thermodynamic and kinetic processes at defects sites are responsible for the unique biomineral morphology features. Thus, understanding the fundamental physical-chemical controls on biomineralization, from atomic and nano through continuum levels, have implications for a wide range of scientific endeavors from the evolution of life to carbon cycling and biotechnology.
Coccolithophorid bloom (cyan) in the Bering Sea as seen from satellite (b). An individual coccolith, composed of uniquely oriented and self-assembled CaCO 3 plates (c), each of which behaves optically as a single-crystal. Molecular model of succinate adsorbed at a hydrated step on the calcite {104} face (d).
Friday, October 31st at 4:00 PM
Room L211, Technological Institute
Refreshments are served at 3:30 PM
