HR: 1340h
AN: B13A-1043    [Abstracts]
TI: Observations of Nucleation and Early Stage Growth of Amorphous Silica on Carboxyl-Terminated Model Biosubstrates
AU: * Wallace, A F
EM: afw@vt.edu
AF: Virginia Tech, Department of Geosciences, Blacksburg, VA 24061 United States
AU: Dove, P M
EM: dove@vt.edu
AF: Virginia Tech, Department of Geosciences, Blacksburg, VA 24061 United States
AB: Over Earth history, organisms have developed the ability to control the nucleation and growth of a broad range of nanocrystalline and amorphous materials. The formation of amorphous biosilica is of particular interest because silicifiers sequester gigatons of silica annually, and suppress dissolved silica levels in the ocean to current low levels. The ecological success of marine diatoms, which are arguably the most important silicifiers, places them alongside marine calcifiers as major players in the sequestration of organic carbon. Thus, the biologically mediated formation of amorphous silica plays a key role in the global cycling of silicon and carbon. During controlled biomineralization, nucleation typically occurs in designated locations. There is a substantial body of evidence suggesting that macromolecules in the cellular environment determine these locations by acting as templates to provide energetically favorable sites for the onset of mineral and amorphous material nucleation. In diatoms, silica formation is likely initiated through heterogeneous nucleation on functional portions of macromolecules inside the Silica Deposition Vesicle (SDV). Previous studies of silica nucleation have implicated multiple chemical moieties associated with the constituent amino acids and sugars of polysaccharides, proteins, and glycoproteins as probable sites for in vivo surface nucleation and patterning. These investigations have usually employed complex macromolecules that exhibit multiple functionalities, and un-characterized solution compositions, thus rendering a quantitative analysis of kinetic and thermodynamic processes impossible. The objective of this research is to experimentally test kinetic and thermodynamic controls exercised by surface moieties on silica nucleation. Our experimental model system uses synthetic organic substrates designed to mimic key features of the interfacial regions between the surrounding cellular environment and the amorphous silica surface. While controlling solution chemistry, we can make in situ measurements of nucleation and early stage growth at these interfaces with Atomic Force Microscopy (AFM). Preliminary experiments show that at pH 4 to 7, and supersaturations of 0.76 to 1.45 (σ = ln([H₄SiO₄]/K_sp)), silica nucleates on carboxyl-terminated areas of the surface, that are less than 30 nm in diameter. The nuclei evolve during early stages of growth to spread over the surface into a sheet like form.
DE: 0400 BIOGEOSCIENCES
DE: 0419 Biomineralization
DE: 1055 Organic and biogenic geochemistry
SC: Biogeosciences [B]
MN: Fall Meeting 2005