IR spectra, representing typical absorption
bands sensitive to the molecular conformation of
silk fibroin, were used by many researchers to
determine the conformation of silk fibroin. The
absorption bands at 1660 (amide I), 1540 (amide
II), and 1235 cm21 (amide III), which were assigned
to the random coil structure of silk fibroin,
shift to 1630, 1530, and 1265 cm21
, in accordance
with the structural changes into b-sheet conformation.10–13
Nakamura et al.14 reported that IR spectra of
fibroin and a fibroin/chitosan blend showed the
characteristic peaks of a random coil structure of
fibroin. On the other hand, other researchers4–6
reported that the conformational transition of silk
fibroin to a b-sheet structure was induced by chitosan.
It is uncertain if the chitosan components
affect the conformation of silk fibroin in the fi-
broin/chitosan blend. In our study, because the
fibroin/chitosan blend films were treated with
methanol and the conformation of silk fibroin
changed to the b-sheet structure, IR spectra of the
blend films showed all the characteristic bands of
chitosan and the b-sheet structure of silk fibroin.