The morphology and molecular mobility changes of the side chains for hard α-keratin due to oxidative and reductive/oxidative treatments for temperatures around the DSC denaturation peak were investigated by 1H, 13C, and 129Xe NMR spectroscopy and 1H spin diffusion. Proton wide-line spectra were used to obtain the phase composition (rigid, interface, and amorphous fractions) and molecular dynamics of each phase. Proton spin diffusion experiments using a double-quantum filter and initial rate approximation were employed to obtain the dependence of the rigid domain sizes on chemical treatments and denaturation temperatures. A drastic reduction in the rigid domain thickness takes place for the reductive/oxidative treatment. The keratin mobility gradient in the interfacial region at different denaturation temperatures was measured for hard α-keratin from 1H spin diffusion data. 13C CPMAS spectra were used to provide a detailed examination of the effects of the chemical treatments especially on the disulfide bonds. Thermally polarized 129Xe spectra suggest the existence of voids in the hard α-keratin induced by the reductive and oxidative treatment. The surface of the hard α-keratin fiber surface is probed by the laser hyperpolarized 129Xe. A qualitative model describing the changes induced in hard α-keratin protein by chemical transformation was developed and could be correlated with the changes in domain thickness, phase composition, and molecular dynamics.
ASJC Scopus subject areas
- Physical and Theoretical Chemistry
- Surfaces, Coatings and Films
- Materials Chemistry