Inheritance of the Secondary Structure of Keratin During Crystallization of Titanium Dioxide under Hydrothermal Conditions Using Wool Fibers as a Biotemplate

The paper discusses experimental results concerning the probable inheritance of the secondary structure of the polypeptide chain of wool keratin used as a biotemplate by titanium dioxide through topochemical reaction and crystal nucleation during crystallization under hydrothermal conditions. Sheep wool fibers were impregnated with a solution containing titanium hydroxocomplexes. Samples of native wool, wool-TiO₂ hybrid material, and TiO₂ crystalline powders were characterized using X-ray diffraction, IR spectroscopy, thermal analysis (DSC and TG), and scanning electron microscopy. X-ray studies revealed that diffuse halos characteristic of the secondary structure of wool (containing α-spiral and β-folded keratin configurations) at 2θ = 8.7° and 19.6° are preserved both for hydrothermally impregnated wool and after annealing at 600°C and 800°C, albeit with a shift towards smaller angles of 2θ = 6.3° and 13.2°. This suggests stretching of keratin fibers during hydrothermal impregnation and preservation of crystallinity domains of the secondary structure in annealed samples, representing a mixture of well-crystallized phases of anatase and rutile. The interpretation of this effect is based on the assumption that TiO₂ crystallization centers are located along the turns of the α-helix or folds of the β-structure, replicating these structures in a certain spatial arrangement. Nucleation is attributed to the interaction of monomeric forms of titanium hydroxocomplexes with carbonyl and carboxyl groups of the polypeptide chain, followed by growth of anatase and rutile crystallites via olation/oxolation reactions under hydrothermal conditions.