INVESTIGATION ON THE SECONDARY STRUCTURE OF SILK FIBROIN THREAD

Abstract

We investigated the secondary structure of silk fibroin thread by measuring attenuated total reflection spectra and circular dichroism spectra. In ATR absorbance curves of the silk fibroin thread, the amide I band has a strong absorption at 1616cm-1, which is ca. 10cm-1 lower than the wave number observed for the specimen in beta structure. The CD spectrum of the silk fibroin thread obtained immediately after spinning shows a negative band at ca. 225nm, which is different from that observed for the aqueous silk fibroin solution in beta structure. With regard to the results of the infrared dichroism of the drawn silk fibroin film obtained by casting the aqueous silk fibroin solution, silk fibroin in cross beta structure gives a negative band at 217nm, while the specimen in antiparallel beta structure gives negative band centered at ca. 225nm. These results imply that the crystalline regenerated silk fibroin gives the cross beta structure, while the silk fibroin thread which is produced by the larva of the moth gives antiparallel beta structure in which the degree of molecular orientation is extremely developed by the spinning action of the larva of the moth.