Detection And Analysis Of Wool/cashmere Structure Based On THz-TDS

Wool/cashmere is a widely used protein fiber.Terahertz time-domain spectroscopy(THz-TDS)is a novel spectral technique.Studies have shown that the dynamic energy levels corresponding to the fluctuations of intermolecular interactions of biomolecules such as proteins are consistent with the time scale of the THz band.Based on THz spectroscopy,molecular interactions of protein fibers such as wool/cashmere can be detected.In this study,THz-TDS was used as the main characterization method,combined with quantum chemistry computational analysis methods,as well as infrared spectroscopy,Raman spectroscopy,and X-ray diffraction spectroscopy,to characterize and analyze the THz spectra of sulfur-containing amino acids and their derivatives,the oxidation/reduction reactions of cysteine/cystine,the internal structural changes of aged wool/cashmere,and the effect of Melanoidin dye on the structure of wool/cashmere.The main contents are as follows:(1)Firstly,THz-TDS was used to characterize the sulfur-containing amino acids and their derivatives in wool/cashmere,and the corresponding THz spectra were obtained.Then,the obtained spectra were further analyzed using quantum chemistry calculation methods to obtain information on the vibration modes and intermolecular interactions of molecules.The results showed that the absorption peaks of the THz spectra of sulfur-containing amino acids and their derivatives were mostly derived from the collective vibration of molecules in the crystal cell,and the crystal structure and intermolecular interactions also affected the absorption peaks of the THz spectra.Among them,the crystal structure of the sample would affect the position of the absorption peak,and the intermolecular interactions would affect the absorption intensity.Therefore,THz spectroscopy can characterize the differences in molecular interactions of similar substances.(2)The disulfide bonds in wool/cashmere affect the stability of their structures,and disulfide bonds exist in cystine.At the molecular level of amino acids,the reduction/oxidation of cystine/cysteine involves the breakage and rearrangement of disulfide bonds.After clarifying that THz spectroscopy can reflect the molecular interactions of sulfur-containing amino acids and their derivatives,this paper used THz spectroscopy to study the oxidation/reduction of cysteine/cystine.The results showed that the change in the concentration of the product cystine during the oxidation process of cysteine was in accordance with Lambert-Beer’s law,indicating that THz spectroscopy can be used to monitor the oxidation/reduction process of cysteine/cystine.In addition,by changing the temperature and p H value during the oxidation of cysteine,the following conclusions were drawn: the oxidation temperature and rate were positively correlated,and the stronger the alkalinity of the environment,the faster the oxidation rate of cysteine.This part of the study realized the monitoring of the oxidation/reduction process of cysteine/cystine at the level of small molecules,providing a new method for the study of disulfide bond breakage and rearrangement in wool/cashmere.(3)The aging process of wool/cashmere is also accompanied by the breakage and rearrangement of disulfide bonds in the space.By comparing the terahertz spectroscopy,Raman spectroscopy,and X-ray diffraction spectra of aged wool/cashmere samples,the following conclusions can be drawn: the degree of aging of wool/cashmere can be detected by utilizing the corresponding terahertz spectroscopic absorption coefficients of aged samples.The change of disulfide bonds during the aging of wool/cashmere leads to an increase in the disorder degree inside the fiber,resulting in a gradual decrease in the crystallinity and intermolecular interaction strength of wool/cashmere,as manifested by a decrease in the spectral absorption coefficient.This study confirms the feasibility of analyzing the degree of internal structural damage of wool/cashmere caused by aging by utilizing the information on intermolecular interaction strength provided by terahertz spectroscopic technology,and provides a theoretical basis for using terahertz spectroscopic technology to study the internal structural changes of protein fibers.(4)The dyeing process also affects the internal structure of fibers.In this study,the internal structural changes of wool/cashmere before and after melanoidin dyeing were investigated using terahertz spectroscopic technology.The results showed that the more reducible glucose isomers caused relatively greater damage to the internal structure of wool/cashmere,as manifested by a decrease in fiber crystallinity and intermolecular interaction,leading to a corresponding decrease in the terahertz spectroscopic absorption coefficient.At the same time,according to the terahertz spectroscopic analysis results,it can be seen that the interaction strength between the dye molecules and fibers during melanoidin dyeing is greater than that of commonly used acid dyes.This not only indicates that terahertz spectroscopic technology can sensitively monitor the changes in overall interaction strength in wool/cashmere,but also confirms the feasibility of applying terahertz spectroscopic technology to the study of conformational changes in biological macromolecules.