Poly-L-Lysine Mediated Fractal Titania Structures
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0921-T05-24
Poly-L-Lysine Mediated Fractal Titania Structures Laura A. Sowards1, Kristi M. Singh1,2, Lawrence F. Drummy1, Linda S. Kasten1,3, Melanie M. Tomczak1,2, and Rajesh R. Naik1 1 Biotechnology Group, Air Force Research Laboratory, 3005 Hobson Way, WPAFB, OH, 45433 2 UES, Inc, Dayton, OH, 45432 3 UDRI, Dayton, OH, 45469 ABSTRACT We demonstrate the use of Poly-L-lysine to mediate the mineralization of fractal titania structures. Reproducible structures formed by 2D DLA are prepared on various substrates when the proper length and concentration of poly-L-lysine are present.
INTRODUCTION Biomineralization occurs in many biological organisms in order to create specialized inorganic structures.1 The transformation of inorganic molecules into nanoand microstructured components is controlled in vivo by the organic matrix. This ability of proteins to direct the assembly of inorganic components into sophisticated functional structures at ambient conditions has motivated intense research efforts in developing methods that mimic the recognition and nucleating capabilities found in biological systems.1-3 Silicatein, a protein isolated from the glassy spicules of a marine sponge, has been shown to catalyze and structurally direct the hydrolysis and condensation of a variety of metal alkoxides.3 Another example is the silaffin proteins from diatoms, which are capable of precipitating silica.4 In addition, polypeptides like poly-L-lysine (PLL) can also be used in the precipitation of silica.5 In a recent report by Morse and co-workers, silicateins have been demonstrated to catalyze the formation of TiO2 using a watersoluble titanium congugate, titanium (IV) bis(ammonium lactato) dihydroxide (TiBALDH) precursor solution.6 The titanium dioxide formed by the biocatalytic method was found to differ from that obtained by conventional alkali catalysis or thermal pyrolysis. The use of biotemplates for the formation of metal oxides avoids the use of harsh reaction parameters such as high temperature or extreme pH. In this study, we report on the formation of fractal titania structures mediated by PLL. Exposure of a diluted precursor TiBALDH solution to PLL resulted in the formation of a white precipitate composed of a network of particles of amorphous titania. The cationic PLL template possibly serves to concentrate the TiBALDH precursor through the combination of electrostatics and hydrogen bonding, via the lactate ligand of the precursor, to promote polycondensation. The formation of fractal titania structures was also found to be dependant on PLL chain lengths. Intrigued by the nano- and microscale ordering of these structures, we investigated if we could direct or alter their formation by changing the reactants, substrate or reaction conditions.
EXPERIMENTAL DETAILS
Materials TiBALDH (Aldrich), ammonium lactate (Aldrich), and poly-L-lysine (Sigma) were prepared with deionized water. The poly-L-lysine (PLL) solutions were prepared at 10 mg/ml. Ammonium lactate, 20 wt. % in water, and titania particles (< 5 microns) were pur
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