Raman spectroscopy and electronic microscopy structural studies of Caucasian and Afro human hair

Abstract

Human hair fibre is subjected to various structural modifications due to the application of chemicals such as dyes, shampoos and bleaches and/or physical procedures such as heating, and often more than one procedure is performed on the same hair. The present work aims to analyze the changes incurred in hair samples of two ethnic groups, namely Caucasian and Afro, before and after different treatments such as thermal, bleaching and straightening. In addition to observing the damage caused by each treatment separately, the study of samples that received all three treatments was carried out. For molecular structural characterization, the Raman vibrational spectroscopic technique was used and scanning electron microscopy (SEM) was used for morphological analysis of the hair fibres. This investigation has shown, through vibrational spectroscopy, that several important bonds have been modified, such as the S-S, C-S, C-C and S-O bonds as well as the secondary structures of proteins that have indergone changes in their conformation as a result of the treatment. Hair from the two ethnic groups showed small differences in relation to each applied treatment. Excessive heat generated a higher rate of Raman spectral band intensity changes when compared to the other treatments and it was observed that the action of several treatments on the same hair fibres resulted in even more pronounced structural changes. Finally, scanning electron microscopy showed that each treatment caused a different morphological deformation pattern on the capillary surface of the human hair.

Study on Keratin/PEGDA Composite Hydrogel with the Addition of Varied Hair Protein Fractions

“…From the FTIR spectra of both keratin fractions (Figure c), the absorption peaks at 1600–1700, 1540, and 1240 cm –1 were the typical amide I, II, and III, respectively . The peaks observed around 3500 cm –1 were the standard bond of the N–H stretching vibration. , The strong band at 1070 cm –1 reveals the S–O asymmetric stretching and symmetric vibration of cysteine-S-sulfonate residues. , Other peaks observed at 995 cm –1 for KAPs and 961 cm –1 for KIFs might be associated with disulfide bonds in keratins, while the band around 661 and 614 cm –1 for KAPs and KIFs, respectively, might represent C–S stretching vibrations. − Finally, the peaks at 835 cm –1 for KAPs and 841 cm –1 for KIFs suggest the N–H out-of-plane bending. , …”

“…In addition, an amide II peak at 1540 cm –1 was identified arising from the vibrations of the amide bond caused by bending (N–H) and stretching (C–N). It is important to note that the ring vibrations or −S–S– stretching mode of the disulfide group in hair keratin is related to the massive band in the 600–1200 cm –1 range. − As shown, more of the KAPs content observed leads to a bigger size of the peaks, corresponding to high disulfide bond contents and the signature nature of KAPs with high sulfur matrix structures . Additionally, according to Figure S.2 in section S.4, when the FTIR spectrum of keratin gel is compared to that of keratin-PEGDA gel, we can observe the presence of the free thiol group of the KAPs/KIFs proteins in Figure S.2a, which may cross-link with PEGDA via thiolene reactions and lead to a decrease in SH and a new S–C bond formation in Figure S.2b.…”

Host factors that shape the bacterial community structure on scalp hair shaft

“…Coating the hair surface with wax may decrease the cell numbers of specific genera, including Lawsonella , and Moraxella . Furthermore, it has been reported that treatment with chemicals such as dyes and bleach damages hair fibres 27 . In particular, the cell membrane complex of scalp hair is reported to be very vulnerable to chemical treatments 28 .…”

How different is human hair? A critical appraisal of the reported differences in global hair fibre characteristics and properties towards defining a more relevant framework for hair type classification

“…Recent spectroscopic studies have explored the variations in relative protein content representing the Intermediate Filament (IF) and Keratin Associated Proteins (KAPs) fractions. In summary, higher content of random coil and disorganized structure was reported (understood as amorphous and random coil mix) in African versus Caucasian hair [35], in hair from African countries versus African American and Jamaican [16] and in Asian versus blond Caucasian hair [36]. As the studies did not provide clear descriptions of the tested hair, the observed effects could be resulting from other variables such as donor age, hair damage, etc.…”