STRUCTURE AND MOLECULAR-CONFORMATION OF TUSSAH SILK FIBROIN FILMS - EFFECT OF METHANOL

Structural changes of tussah (Antheraea pernyi) silk fibroin films tre ated with different water-methanol solutions at 20 degrees C were stud ied as a function of methanol concentration and immersion time. X-ray diffraction measurements showed that the alpha-helix structure, typica l of untreated tussah films, did not change for short immersion times (2 min), regardless of methanol concentration. However, crystallizatio n to beta-sheet structure was observed following immersion of tussah f ilms 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 exhi bited strong absorption bands at 1265, 892, and 622 cm-l, typical of t he alpha-helix conformation. The intensity of the bands assigned to th e beta-sheet conformation (1245, 965, and 698 cm(-1)) increased for th e sample treated with 40% methanol for 30 min. Raman spectra of tussah films with alpha-helix molecular conformation exhibited strong bands at 1657 (amide I), 1263 (amide III), 1106, 908, 530, and 376 cm(-1). F ollowing alpha --> beta conformational transition, amide I and III ban ds shifted to 1668, and to 1241, 1230 cm(-1), respectively. The band a t 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. (C) 1995 John Wiley & Sons, Inc.