March 17, 2004
FRONTIERS IN MATERIALS SCIENCE
VINSE COLLOQUIUM SERIES
Dr. Daniel MorseAbstract. With a precision of nanostructural control that exceeds present human capabilities, biological systems fabricate 3-d multifunctional high-performance silicon-based materials at low temperatures and near-neutral pH. The fundamental molecular mechanisms of silica production in sponges and diatoms are now being elucidated, and aspects of these processes are being harnessed for industrial and technological processes. Working with the silica needles produced by marine sponges, our laboratory discovered that proteins we named "silicateins" catalyze and structurally direct the polymerization of silica from silicon alkoxides at neutral pH and low temperature. The silicateins are true enzymes, closely related to a well-known family of hydrolases. Site-directed mutagenesis of the cloned recombinant DNAs coding for the silicateins confirmed the mechanism of silicatein-mediated catalysis, and has been used to increase the rate of catalysis as well. These studies identified the catalytic groups on the protein, and enabled the synthesis of self-assembling biomimetic polymers that incorporate the functionalities identified as essential for catalysis, yielding new structure-directing catalysts of polymerization. The silicateins and their biomimetic counterparts catalyze structure-directing synthesis from a wide range of precursors, yielding inorganic silica, organically substituted silsesquioxanes (silicones) with a wide range of organic functionalities and organometallic silsesquioxanes.
Institute for Collaborative Biotechnologies
California NanoSystems Institute and the Materials Research Laboratory
University of California, Santa Barbara
"Biocatalytic Routes to Structure-Directed Nanofabrication of Siloxanes, Organometallics and Semiconductors"
We recently discovered that the silicateins also catalyze and structurally direct the hydrolysis and polycondensation of molecular precursors of metallo-oxanes such as titanium dioxide and the oxides of gallium, zinc, cobalt and ruthenium. These are the first reported examples of enzyme-catalyzed, nanostructure-directed synthesis of semiconductors. Interaction with the template-like protein surface stabilizes polymorphs of these materials (e.g., anatase titanium dioxide and a spinel form of gallium oxide) otherwise not formed at low temperatures. In some cases, interaction between the condensing metallo-oxane and the protein results in preferential alignment of the resulting nanocrystallites, suggesting a pseudo-epitaxial relationship between the mineral crystallite and specific functional groups on the templating protein surface. We now are using genetic engineering in concert with physical analyses to identify and harness these structure-directing determinants to develop improved catalytic and nanostructure-directing biomimetic interfaces. Potential uses are under investigation for optical, electronic and biomedical applications.