Morphology and molecular dynamics of hard α-keratin based micro-tubes by 1H and 13C solid-state NMR

We have obtained keratin-based micro-tubes by heating keratin fibres at temperatures above 240 °C under nitrogen atmosphere. The morphology and molecular mobility for micro-tubes prepared at 245 and 300 °C from fibres emptied of cortical material were investigated by 1H and 13C NMR spectroscopy, 1H spin-diffusion and 13C longitudinal relaxation in the rotating frame ( T 1 ρ C ). The micro-tubes have a three-phase morphology given by rigid, interfacial and amorphous fractions similar to the cuticle with the largest content of the rigid domain for the micro-tube obtained at 300 °C. Proton spin-diffusion experiments reveal that the rigid domain sizes are comparable in both 245 and 300 °C micro-tubes, but the 300 °C ones have larger chain disorganization. 13C NMR investigation shows the significant presence of beta-sheet morphology in micro-tubes that is strongly enhanced by the thermal treatment.