The effect of water on the conformation transition of Bombyx mori silk fibroin

Near-infrared spectroscopy (NIR) and differential scanning calorimetry (DSC) were used to investigate temperature-induced changes in the secondary structure and hydration of reconstituted Bombyx mori silk fibroin, with and without freezing water, by looking at regenerated silk fibroin films with a range of water content. We suggest that freezing water facilitates the movement of peptide chains and thus contributes to the conformational transition at 60 °C. The structural changes during heat treatment were analyzed by the two-dimensional correlation method. It was found that the band at 4600 cm−1 consists of complex overlapping components due to different secondary structure elements which compose the protein architecture. Thus, this band could be used as a sensitive probe to estimate the conformations of silk fibroin. By monitoring the variations of the spectral components dynamically, an NIR procedure for tracking the conformational transition of silk fibroin was established.