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Structural Transition of Bombyx mori Liquid Silk Studied with Vibrational Circular Dichroism Spectroscopy
Toshinori Morisaku1, Sho Arai, Kohzo Konno
1Department of Chemistry, Faculty of Science, Tokyo University of Science.
Abstract:
We investigated the structural transition from liquid silk to silk fibers with vibrational circular dichroism spectroscopy. Liquid silk showed a major right-handed optically active band at around 1650 cm(-1) and a minor one at around 1680 cm(-1). The former disappeared over time, while the intensity in the latter increased. With the former wavenumber, liquid silk mainly adopted a random-coil structure. In contrast, the latter may reflect an intermediate structure in the transition. Furthermore, two right-handed bands at around 1630 and 1660 cm(-1) appeared with the disappearance of the major band, and then the wavenumber of the former shifted to around 1620 cm(-1). The shift results from the decrease in the frequency of the CO stretching mode due to the stacking of the β-sheet that comprises fibers. The band at 1660 cm(-1) may reflect another intermediate structure due to its strong correlation with that at 1620 cm(-1) in terms of their temporal change in intensity.
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