Eur. Phys. J. Special Topics 229, 2825–2832 (2020)
https://doi.org/10.1140/epjst/e2020-900217-4

Regular Article

Human hair: subtle change in the thioester groups dynamics observed by combining neutron scattering, X-ray diffraction and thermal analysis

¹ Institute of Physics, University of São Paulo, São Paulo, 05508-090, SP, Brazil
² Academic Unit of Physics, Federal University of Campina Grande, Campina Grande, 58429-900, PB, Brazil
³ Niels Bohr Institute, University of Copenhagen, 2300 Copenhagen, Denmark
⁴ Radiation Technology Center, Nuclear and Energy Research Institute, São Paulo, 05508-000 SP, Brazil
⁵ Faculty of Pharmaceutical Sciences, University of São Paulo, São Paulo 05508-000, SP, Brazil
⁶ ISIS Facility, Rutherford Appleton Laboratory Chilton, Oxfordshire OX11 0QX, UK
⁷ Department of Materials, University of Oxford, Parks Road, Oxford, UK
⁸ European Spallation Source ESS ERIC, P.O. Box 176, 221 00 Lund, Sweden

^* e-mail: cibelelima@usp.br

Received: 3 October 2019
Accepted: 29 July 2020
Published online: 16 November 2020

Abstract

Hair analysis plays an important role in forensic toxicology and biomonitoring tests. However, cosmetic treatments cause changes to the hair. Thus, a better understanding of the hair’s structure and the factors that influence its composition is critical. It is known that oxidative treatments modify the hair chemical, structural and mechanical properties. These treatments also cause degradation of the melanin as well as of the structures present in the hair cuticle and cortex. Considering that the literature is unanimous regarding the increase in hydrophilicity and porosity promoted in human hair by bleaching, in this work we investigated how this oxidative damage is triggered. By combining several techniques, inelastic and quasi-elastic neutron scattering, differential scanning calorimetry, thermal gravimetric analysis and X-ray diffraction, we were able to connect the chemical and structural changes to a subtle dynamic modification of the proton mobility in the hair fibers. In addition, alterations in the thermal behavior evidenced a small denaturation of α-keratin intermediate filaments and a slight decrease in the amount of confined water in the hair fibers. Moreover, data obtained by neutron spectroscopy indicated that bleaching attacks the thioester groups of the proteins causing larger proton mobility of the hydrogenous components (water, protein and/or lipids).