Spermidine and spermine catalyze the formation of nanostructured titanium oxide

Naturally occurring polyamines putrescine, cadaverine, spermidine, and spermine are analogues of the species-specific long-chain polyamines found in diatoms. Scanning electron microscopy and energy-dispersive spectroscopy show that the reactions of a soluble Ti(IV) precursor with spermidine and spermine, but not putrescine or cadaverine, produce nanostructured irregular polyhedra of titanium oxide. At 25 degrees C, the average size of the particles formed with spermidine is 400 +/- 150 nm, and with spermine, 140 +/- 50 nm. Although the particles are X-ray amorphous at room temperature, annealing studies reveal that the particles adopt crystallinity at higher temperatures characteristic of anatase (TiO2). The major portion of the biopolyamines is not coprecipitated with the solid but is left in solution. Kinetic measurements reveal an initial fast step followed by two slower phases of reaction. At 25 degrees C, k(1obs) and k(2obs) for the reaction with spermidine are 5 x 10(-3) s(-1) and 3.6 x 10(-4) s(-1), respectively, and for spermine, 4.8 x 10(-3) s(-1) and 4.2 x 10(-4) s(-1), respectively. Taken together, the data suggest spermidine and spermine are biocatalysts for the precipitation of nanostructured titanium oxide.