Protein structural changes in keratin fibers induced by chemical modification using 2‐iminothiolane hydrochloride: A Raman spectroscopic investigation

For the purpose of investigating in detail the influence of chemical modification using 2‐iminothiolane hydrochloride (2‐IT) on keratin fibers, the structure of cross‐sections at various depths of white human hair, treated with 2‐IT and then oxidized, was directly analyzed without isolating the cuticle and cortex, using Raman spectroscopy. In particular, the β‐sheet and/or random coil content (β/R) and the α‐helix (α) content in human hair fibers were estimated by amide I band analysis. The SS band intensity, amide III (unordered) band intensity, and β/R content existing from the cuticle region to the center of cortex region of virgin white human hair remarkably increased by performing the chemical modification using 2‐IT. On the other hand, not only the SS band intensity, but also SO band intensity existing throughout the cortex region of the bleached (damaged) white human hair increased by performing chemical modification using 2‐IT. In particular, β/R content existing throughout the cortex region of the bleached white human hair decreased, while the skeletal CC stretch (α) band intensity at 935 cm −1 and the α content remarkably increased. This indicates a secondary structural change from the random coil form to the α‐helix form in the proteins existing throughout the cortex region. From these experiments, we concluded that the formation of new disulfide (SS) groups resulting from chemical modification using 2‐IT induced the secondary structural changes of proteins existing throughout the cortex region. © 2005 Wiley Periodicals, Inc. Biopolymers 79: 173–184, 2005 This article was originally published online as an accepted preprint. The “Published Online” date corresponds to the preprint version. You can request a copy of the preprint by emailing the Biopolymers editorial office at biopolymers@wiley.com