Morphology and Molecular Mobility of Fibrous Hard α-Keratins by¹H,¹³C, and¹²⁹Xe NMR

Abstract

The morphology and molecular mobility changes of the side chains for hard alpha-keratin due to oxidative and reductive/oxidative treatments for temperatures around the DSC denaturation peak were investigated by (1)H, (13)C, and (129)Xe NMR spectroscopy and (1)H 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 alpha-keratin from (1)H spin diffusion data. (13)C CPMAS spectra were used to provide a detailed examination of the effects of the chemical treatments especially on the disulfide bonds. Thermally polarized (129)Xe spectra suggest the existence of voids in the hard alpha-keratin induced by the reductive and oxidative treatment. The surface of the hard alpha-keratin fiber surface is probed by the laser hyperpolarized (129)Xe. A qualitative model describing the changes induced in hard alpha-keratin protein by chemical transformation was developed and could be correlated with the changes in domain thickness, phase composition, and molecular dynamics.

Morphology and side-chain dynamics in hydrated hard α-keratin fibres by 1H solid-state NMR

“…The value of the excitation/ reconversion times used in the DQ dipolar filter was s = 7 ls. It corresponds to the rising region of the DQ build-up curve for each sample [8,9].…”

“…A simple procedure to obtain domain sizes is that based on the initial-rate approximation [9,13]. We made the following assumptions: (i) Three phases morphology of hard a-keratin (Fig.…”

“…Only the first three components were used for dehydrated keratin sample. The three phase morphology was also used for keratins under thermal denaturation and chemical treatments [8,9]. The fractional composition is shown Fig.…”

Sex-related chemical differences in keratin from fingernail plates: a solid-state carbon-13 NMR study

“…In particular, previous 13 C CP/MAS NMR papers have been devoted to the interpretation of the carbon-13 spectra, characterization of native and modied keratins, elucidation of the a-keratin structure, testing its dependence on stretching, heating and chemical treatment, analysis of the a-helix and b-sheet regions and observation of their mutual transitions, monitoring disulphide bonds breaking under various conditions, thermal and reductive/oxidative denaturation, assessment of crystalline and amorphous regions, characterization of molecular dynamics and so on. 8,[26][27][28]33,[36][37][38][39][40][41][42][43] The studies were made on human and horse hair, human stratum corneum, horse hoof and sheep wool.…”

Solid state NMR of isotope labelled murine fur: a powerful tool to study atomic level keratin structure and treatment effects

“…Multinuclear solid state NMR has been used to study the phase composition (rigid, amorphous and interface fractions) and aspects of the reductive/oxidative processes involving disulphide linkages. In hard α-keratin, disulfide reduction followed by alkylation trapping decreases a signal near 40 ppm, assigned to Cys β-carbon (Baias et al 2009). …”