It has been proved that time-resolved total reflectance FT-IR spectroscopy is a useful tool for investigating acetic acid diffusion in silk fibroin film and conformational transition of silk fibroin. Acetic acid could induce the construction of highly dominating content of β-sheet conformation in the silk fibroin film, in addition, the kinetic curve of organic solvent diffusion was similar to that of conformational transition as both processes reached equilibria at the same time. The access of acetic acid into the silk fibroin architecture appeared to be a necessary step in which the organic solvent could interact with silk protein, breaking its original hydrogen bond and inducing re-alignment of peptide chains. Furthermore, the content of water appeared to be an important factor in this dynamic system.

Key words: silk fibroin, acidity-basicity, diffusion, β-sheet, dynamic process