Abstract:

Objective Analysis of disulfide bonds content and its conformation is essential to study the microstructural changes in wool. Some of the currently used chemical testing methods are both time-consuming and labor-intensive, and also cause damage to the fiber during testing, together with inaccurate results sometimes. Raman spectroscopy analysis provides fast, simple, reproducible, and non-destructive and qualitative analysis, and this research proposes to analyze disulfide bonds and conformation content of wool using Roman spectroscopy.

Method To investigate the effect of different methods such as ultrasound, reduction and oxidation on the disulfide bonds and conformational changes of wool. The disulfide bonds and the conformation of wool were analyzed non-destructively using laser confocal microscopic Raman spectroscopy. The effects of laser wavelength, laser intensity, scanning time, objective size, and morphological structure on the measurement results of wool fibers were analyzed in detail. The testing conditions of laser Raman spectroscopy on wool fibers were optimized. A comparative analysis of the disulfide bonds and conformational changes of wool fibers was also carried out.

Results The results showed that the better Raman measurement conditions for wool fibers were excitation wavelength of 785 nm, laser intensity of 50 mW, scanning time of 20 s and 50× objective observation. The macromolecular structure of wool was not significantly changed by changing morphology. From the comparison of Raman spectra of fibers treated by different methods, it was found that the content of β-folding conformation decreased after ultrasonic treatment of wool fibers. The absorption peak of sulfhydryl group appeared at 2 569 cm^-1 after dithiothreitol treatment of wool fibers. The relative content of disulfide bonds in wool fibers was decreased to 28.9%, and the disulfide bonds were transformed from the intramolecular GGG configuration to the intermolecular GGT and TGT configurations. The protein macromolecules were converted from α-helical conformation to β-folded conformation. The treatment of wool fibers with hydrogen peroxide produced a new S—O absorption peak at 1 044 cm^-1, and the content of β-folded conformation decreased.

Conclusion Wool fibers were measured by laser confocal Raman spectroscopy, and the best test conditions were obtained by analyzing the Raman spectra at laser wavelength 785 nm, scanning time 20 s, laser intensity 50 mW and 50× objective. The macromolecular structure of wool was not significantly changed by changing morphology. After optimizing the test conditions, ultrasonic treatment and DTT reduction treatment were compared and analyzed. Raman spectra of wool fibers treated with H₂O₂ oxidation showed that the Raman spectra of fibers treated by different methods had a good response. Among them, the reduction treatment has the greatest influence on the disulfide bond and conformation of the fiber. The results show that Raman spectroscopy has great advantages such as simplicity, reproducibility, and being non-destructive compared with conventional wool disulfide bonds and conformational measurements.

Key words: wool, Raman spectroscopy, dithiothreitol, hydrogen peroxide, fiber structure, disulfide bood