HR: 15:10h
AN: B43G-06    [Abstracts]
TI: Investigating the Physical Basis of Amorphous Precursor Transformation to Calcite Using Patterned Alkanethiol Surfaces
AU: * Wang, D
EM: wangdb@vt.edu
AF: Department of Geosciences, Virginia Tech, Blacksburg, VA 24061, United States
AU: Wallace, A
EM: afw@vt.edu
AF: Department of Geosciences, Virginia Tech, Blacksburg, VA 24061, United States
AU: Han, T Y
EM: han5@llnl.gov
AF: Chemistry, Materials, Life Sciences Directorate, Lawrence Livermore National Labs, Livermore, CA 94550, United States
AU: Lee, J R
EM: lee204@llnl.gov
AF: Chemistry, Materials, Life Sciences Directorate, Lawrence Livermore National Labs, Livermore, CA 94550, United States
AU: Hailey, P D
EM: hailey4@llnl.gov
AF: Chemistry, Materials, Life Sciences Directorate, Lawrence Livermore National Labs, Livermore, CA 94550, United States
AU: De Yoreo, J J
EM: deyoreo1@llnl.gov
AF: Chemistry, Materials, Life Sciences Directorate, Lawrence Livermore National Labs, Livermore, CA 94550, United States
AU: Dove, P M
EM: dove@vt.edu
AF: Department of Geosciences, Virginia Tech, Blacksburg, VA 24061, United States
AB: Increasing evidence from X-ray Absorption Spectroscopy and Environmental Scanning Electron Microscopy (ESEM) studies of biominerals extracted from calcifying organisms show that amorphous calcium carbonate (ACC) plays a key role in the initial formation of carbonate minerals and in shaping them into complex morphologies. Echinoderms and possibly a wide variety of other organisms, use ACC as a precursor phase. The ACC is first formed within spatial and temporally controlled environments such as vesicles, followed by a subsequent onset of mineralization that transforms the precursor into a fully crystalline material. Recent studies on sea urchin embryos have shown that during this transformation, ACC develops short-range order that resembles calcite before fully crystallizing. While this "non-traditional" process is recognized, the mechanisms and factors that govern this transformation remain poorly understood. Of particular interest are the roles of water, and the functional group chemistry of surfaces and macromolecules within mineralization environments. To investigate these questions, we have developed an experimental approach using ESEM that allows us to control impurity concentration, surface functionality and water content through the degree of water condensation. Patterned self-assembled monolayers (SAM) of hydrophilic moieties with domains of approximately 25 microns in diameter are used to form an array of micro-reactors. ACC particles with known composition are then deposited on the patterns. Condensing water in the ESEM initializes the transformation of ACC to calcite. Our results show that in saturated water vapor, ACC swells, but no obvious faceting of the material occurs. It is only in bulk water, via dissolution/crystallization, where the calcite grown on carboxyl-terminated surfaces is found with the often-observed \{013\} nucleation face. We use this insight to understand the role of the different chemical moieties on ACC to calcite transformation by measuring nucleation rates with time resolved experiments in the ESEM using bulk water. Preliminary evidence shows a markedly lower nucleation rate on hydroxyl versus carboxyl surfaces suggesting that hydroxyl functionalized surfaces do not promote the nucleation of calcite thus stabilizing the amorphous phase.
DE: 0400 BIOGEOSCIENCES
DE: 0419 Biomineralization
SC: Biogeosciences [B]
MN: 2007 Fall Meeting