Structure and molecular conformation of tussah silk fibroin films: Effect of methanol



Structural changes of tussah (Antheraea pernyi) silk fibroin films treated with different water-methanol solutions at 20°C were studied as a function of methanol concentration and immersion time. X-ray diffraction measurements showed that the α-helix structure, typical of untreated tussah films, did not change for short immersion times (2 min), regardless of methanol concentration. However, crystallization to β-sheet structure was observed following immersion of tussah films for 30 min in methanol solutions ranging from 20 to 60% (v/v). IR spectra of tussah films untreated and methanol treated for 2 min exhibited strong absorption bands at 1265, 892, and 622 cm−1, typical of the α-helix conformation. The intensity of the bands assigned to the β-sheet conformation (1245, 965, and 698 cm−1) increased for the sample treated with 40% methanol for 30 min. Raman spectra of tussah films with α-helix molecular conformation exhibited strong bands at 1657 (amide I), 1263 (amide III), 1106, 908, 530, and 376 cm−1. Following α → β conformational transition, amide I and III bands shifted to 1668, and to 1241, 1230 cm−1, respectively. The band at 1106 cm−1 disappeared and new bands appeared at 1095 and 1073 cm−1, whereas the intensity of the bands at 530 and 376 cm−1 decreased significantly. ©1995 John Wiley & Sons, Inc.