Peptide- and long-chain polyamine-induced synthesis of micro- and nanostructured titanium phosphate and protein encapsulation

Poly(allylamine) (a mimic of biopolyamines) and the R5 peptide (a repeat unit of a silaffin protein isolated from a diatom) induce the formation of mineralized titanium from soluble titanium(IV) precursors. These reactions proceed under mild aqueous conditions. Scanning electron microscopy shows that the nanometer to micrometer diameter particles induced by poly(allylamine) are spherical under a range of conditions, while those induced by the R5 peptide include spheres and fused structures. Dynamic light scattering experiments confirm the SEM results and reveal that the particles range in size from 2 nm to 5 mu m. The surface charge is negative at neutral pH. Energy dispersive X-ray spectroscopy shows the composition to be primarily titanium, oxygen, and phosphorus. The solids are amorphous at room temperature by powder X-ray diffraction but the material induced by poly(allylamine) converts to cubic crystalline TiP2O7 with annealing to 800 degrees C. Infrared spectroscopy suggests that the biomolecule mineralization inducers are encapsulated in the solid. Discrete poly(allylamine)-induced spheres are formed only between pH 7-9.5, with polydispersity strongly dependent on pH. The surface of the poly(allylamine)-induced spheres becomes smoother at higher reaction temperatures. Green fluorescent protein can be immobilized in the solid induced by poly(allylamine) but not R5 peptide under the conditions examined.