Probing the molecular-level signature of chemical pretreatment in α-keratin by employing solid-state NMR measurements.

The molecular-level signature of chemical pretreatment in α-keratin was revealed by employing advanced solid-state NMR spectroscopic techniques, like 13C CPMAS, 13C 2DPASS ssNMR, 1H-13C HETCOR, and NMR relaxometry. The chemical pretreatment process disrupts the disulfide linkage associated with the cystine residue of α-helix. It was revealed by 13C CPMAS spectral analysis that the FWHM of C8 nuclei (which represents the Cβ carbon of cross-linked cystine and leucine) is reduced, which is the signature of the increment of motional degrees of freedom. Any alteration in motional dynamics of pretreated α-keratin was further quantified by measuring the 13C spin-lattice relaxation time at chemically and crystallographically distinct carbon nucleus sites. It is noticeable that for each site, the motional dynamics is enhanced due to pretreatment, which is the signature of breaking the robust structure of α-keratin. Complementarily, the 1H-13C HETCOR measurements showed that the cross-peak contours corresponding to C8 nuclei were getting narrower due to pretreatment, further supporting the enhancement of the motional degrees of freedom of α-keratin. These types of investigations provide the local electronic environment and nuclear spin dynamics of 13C nuclei in α-keratin, essential for designing and developing novel biomimetic materials derived from animal-based feedstocks.