Study on secondary structural transition of nano‐TiO2 modified silk fibroin composite films by two‐dimensional Raman correlation spectroscopy and solid‐state 13C‐NMR spectroscopy

By a sol-gel processing, the nano-TiO2/silk fibroin (SF) composite films were prepared. One-dimensional (1D) Raman, two-dimensional (2D) correlation Raman spectroscopy, and C-13 cross-polarization magic-angle-spinning nuclear magnetic resonance (C-13 CP-MAS NMR) were used to characterize the structural evolution of SF as the nano-TiO2 content increased from 0 to 0.4 wt%. The experimental data demonstrated that the secondary structures in the pure SF film and nano-TiO2/silk fibroin (SF) composite films were random coil, -helix and -sheet structures. The nano-TiO2 particles formed in the SF films might induce partial structural transitions from random coil and Silk I (-helix) to Silk II (-sheet). The transition identified by 2D-Raman correlation spectra was the following order: silk I-like structure, silk I (-helical structure), Silk II-like structure, and Silk II (-sheet structure). POLYM. COMPOS., 36:121-127, 2015. (c) 2014 Society of Plastics Engineers