Thermal Denaturation of Hydrated Wool Keratin by 1H Solid-State NMR

Alterations promoted by acid straightening and/or bleaching in hair microstructures

Human hair is a biopolymer constituted mainly of keratin intermediate filaments, lipids, pigments and water. Cosmetic treatments usually interact with the hair at the molecular level, inducing changes in its components and modifying the physicochemical and mechanical properties of the fibers. Here, the effect of acid straightening on the morphology and ultrastructure of Caucasian hair was investigated by a group of complementary experimental methods: wide-, small- and ultra-small-angle X-ray scattering; high-resolution 3D X-ray microscopy; quasi-elastic neutron scattering and inelastic neutron scattering; thermogravimetry-mass spectrometry; and differential scanning calorimetry (DSC). X-ray diffraction patterns showed that acid straightening associated with a flat iron (∼180°C) changed the cortex of the fiber, shown by denaturation of the intermediate filaments (measured by DSC). The increase in the spacing of the lipid layers and the observation of the dehydration behavior of the fiber provided indications that water may be confined between these layers, while neutron spectroscopy showed alterations in the vibration mode of the CH2 groups of the lipids and an increase of the proton (H+) mobility in the hair structure. The latter may be associated with the extremely low pH of the formulation (pH ≃ 1). Additionally, this investigation showed that bleached hair (one-time bleached) is more damaged by the action of acid straightening than virgin hair, which was shown by a threefold increase in the percentage of total porosity of the tresses. The obtained results demonstrate that the investigation approach proposed here can provide very important thermodynamic and structural information on induced changes of hair structure, and certainly can be applied for the evaluation of the action mode and efficiency of cosmetic treatments.

Mechanism of human nail poration by high-repetition-rate, femtosecond laser ablation

Optical poration, or drilling, of the human nail has the potential to drastically improve transungual drug delivery. However, this approach is accompanied by thermal damage to the nail tissue surrounding the laser radiation-created pore. In this paper, fluorescence microscopy has been employed to quantitatively evaluate thermal damage to the nail induced by laser ablation with 80 MHz, nanojoule, femtosecond pulses delivered via a hollow-core fibre. An empirical relation has been established between the intensity of the resulting fluorescence signal and temperature to which the nail was exposed. Using this relationship, detailed temperature maps have been created of the areas surrounding the pores, enabling the mechanism of poration to be better understood. It was deduced that plasma-mediated ablation is primarily responsible for nail tissue ablation at the centre of the pore, while cumulative photothermal processes dominate at the pore edges. It is concluded, furthermore, that temperature mapping represents a useful new tool with which to optimise the process of nail poration. The method is potentially generic and may be applicable to other biological materials.

A comprehensive and comparative study of the internal structure and dynamics of natural β-keratin and regeneratedβ-keratin by solid state NMR spectroscopy

Structure and dynamics of natural and regenerated chicken feather β-keratin were investigated by ¹³C cross-polarization (CP) magic angle spinning (MAS) solid state nuclear magnetic resonance (SSNMR) spectral analysis, ¹³C and ¹H spin-lattice relaxation time measurements, and ¹³C two dimensional phase adjusted spinning sidebands (2DPASS) MAS SSNMR measurements. Chemical shift anisotropy (CSA) parameters of both natural and regenerated chicken feather β-keratin were extracted by using 2DPASS MAS SSNMR experiment. The beauty of 2DPASS MAS SSNMR experiment is it can correlate the isotropic and anisotropic dimension with the help of shearing transformation and two dimensional Fourier Transformation. Molecular correlation time at each and every magnetically inequivalent carbon site of both natural and regenerated chicken feather β-keratin were also determined. The change in molecular dynamics of structural protein after pretreatment was monitored by 2DPASS MAS SSNMR and ¹³C relaxation measurement. This type of comprehensive study will provide the information about the interrelation between the structure and dynamics of structural protein and will also shed light in the way of developing methods for conversion of animal by-products to novel product.

The structure of the "amorphous" matrix of keratins

Various keratin fibers, particularly human hairs, were investigated by transmission electron microscopy, TEM, solid-state ¹H NMR and Transient Electro-Thermal Technique, TET. The results converge to suggest that the matrix of keratin fiber cortex, far from being amorphous, has a well-defined nano-scale grainy structure, the size of these grains being around 2-4nm. The size of the grains appears to strongly depend on the chemical treatment of the fiber, on the temperature and on the relative humidity of the environment, as well as on the physiological factors at the level of fiber production in follicle. By suggesting an organization at the nano-scale of the protein chains in these grains, likely to be Keratin Associated Proteins, the results challenge the view of matrix as a homogeneous glassy material. Moreover, they indicate the potential of further investigating the purpose of this structure that appears to reflect not only chemical treatments of keratins but also biological processes at the level of the follicle.

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

The carbon-13 solid-state NMR reveals chemical differences in fingernail keratin between young, healthy males and females.

The effects of anticalcification treatments and hydration on the molecular dynamics of bovine pericardium collagen as revealed by 13C solid-state NMR

This article describes a solid-state NMR (SSNMR) investigation of the influence of hydration and chemical cross-linking on the molecular dynamics of the constituents of the bovine pericardium (BP) tissues and its relation to the mechanical properties of the tissue. Samples of natural phenethylamine-diepoxide (DE)- and glutaraldehyde (GL)-fixed BP were investigated by (13)C cross-polarization SSNMR to probe the dynamics of the collagen, and the results were correlated to the mechanical properties of the tissues, probed by dynamical mechanical analysis. For samples of natural BP, the NMR results show that the higher the hydration level the more pronounced the molecular dynamics of the collagen backbone and sidechains, decreasing the tissue's elastic modulus. In contrast, in DE- and GL-treated samples, the collagen molecules are more rigid, and the hydration seems to be less effective in increasing the collagen molecular dynamics and reducing the mechanical strength of the samples. This is mostly attributed to the presence of cross-links between the collagen plates, which renders the collagen mobility less dependent on the water absorption in chemically treated samples.

Stabilization of collagen by cross-linking with oxazolidine E-resorcinol

Cross-linking agents play an important part in the physical properties of collagen based biomaterials. This paper describes the stabilization of type I collagen using an oxazolidine E-resorcinol compound. It is shown by NMR and elemental analysis techniques that oxazolidine E undergoes ring opening to form an N-methylol intermediate form and then reacts with the hydrogen bonds of resorcinol. Oxazolidine E-resorcinol compound treated collagen fibers are shown by DSC analysis to be more thermally stable than simple oxazolidine E-resorcinol treated collagen. Treated collagen fibers showed shrinkage temperature around 98 degrees C implying that the oxazolidine E-resorcinol compounds impart thermal stability. Circular dichroism revealed that there is no major alteration in the structure of collagen after treatment with the compound. The study demonstrates that the involvement of hydrogen bonding and hydrophobic interaction as the principal mechanisms for stabilization of collagen by oxazolidine E-resorcinol compounds.

Morphology and molecular mobility of fibrous hard alpha-keratins by 1H, 13C, and 129Xe NMR

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.