Morphology and molecular dynamics of hard α-keratin under pressure by 1H and 13C solid-state NMR

The effect of uniaxial pressure on phase composition, aminoacid side-chain and backbone dynamics, as well as rigid domain sizes of hard α-keratin from human fingernail clippings was investigated by 1H solid-state and 13C cross-polarization MAS NMR spectroscopy. Proton spin–diffusion NMR experiments revealed that the rigid-domain sizes increased upon compression. The 13C carbonyl resonance components were shown to be very sensitive to the transition of α-helices to β-sheets induced by uniaxial compression. Carbon-13 longitudinal relaxation in the rotating frame showed dynamic heterogeneity of aminoacid residues especially during the α-helix to β-sheet transition.