TiO2 sphere-tube-fiber transition induced by oligovaline concentration variation

L-Valine-based oligopeptides with the general structure Z-(L-Val)(n)-OMe or -OH (n = 1-4) form stable organogels in a variety of solvents, including the inorganic liquid tetraethylorthosilicate. The acid form Z-(L-Val)(n)-OH is a less efficient gelator than the methyl ester, but forms stable organogels in aromatic solvents and di- and trichloromethane. In all cases the peptides form micrometer long helical fibers with a beta-sheet structure. IR and X-ray diffraction show that the peptides have closely related structures in the crystalline state and the fibers in the organogels. The gels are efficient templates for the fabrication of complex titania architectures on a (sub)micron length scale: at low peptide concentrations titania spheres form and at higher concentrations one-dimensional shapes like hollow titania tubes or titania fibers are observed. The tubes are stable towards calcination whereas the fibers (partially) transform into spherical or even bulk particles.