Conformation Transition of Bombyx mori Silk Protein Monitored by Time-Dependent Fourier Transform Infrared (FT-IR) Spectroscopy: Effect of Organic Solvent

The conformation transition from random coil and/or helix to beta-sheet of silk protein is the most important step in the formation of silk fiber in nature as well as by artificial spinning. Time-dependent Fourier transform infrared (FT-IR) spectroscopy was used in this research to monitor such a conformation transition process induced by the organic solvents methanol, ethanol, propanol, isopropanol, and acetone. The kinetics of beta-sheet formation of regenerated Bombyx mori silk fibroin in these organic solvents was obtained by the Delta absorbance-time curve from the time-dependent difference infrared spectra. The results showed that the conformation transition rate of silk fibroin was methanol > ethanol > acetone > propanol > isopropanol, which is in accordance with the polarity of these organic solvents. In connection with the mechanical properties and morphologies of regenerated silk fibers using these organic solvents as coagulation bath reported in the literature, we may conclude that the conformation transition rate of silk protein in the organic solvent is very important in wet-spinning to produce high-performance regenerated silk fibers.