SOLVENT-INDUCED AND MECHANICAL-TREATMENT-INDUCED CONFORMATIONAL TRANSITION OF SILK FIBROINS STUDIED BY HIGH-RESOLUTION SOLID-STATE C-13 NMR-SPECTROSCOPY

We have recorded 13C NMR spectra of silk fibroins from Bombyx mori and Philosamia cynthia ricini to examine solvent- (or diluent-) or mechanical-treatment-induced conformational transi-tio. First, 13C NMR spectra of silk I and II forms of the crystalline (Cp) fraction of B. mori fibroin and of a-helix and /3-sheet forms of P. c. ricini fibroin were recorded under improved spectral resolution than those previously reported. For the latter fibroin, two kinds of a-helical domains (stable and less stable a-helical domains consisting of longer and shorter Ala sequences, respectively) were distinguished in view of the substantial difference in the stability of helices between the solid and the solution. Hydration of B.mori fibroin resulted in a stabilization of silk I forms, asmanifested from the significant narrowing of peaks without inducing conformational transition. In c. ricini fibroin, however, hydration caused a partial conformational change from the less stable a-helix to the /9-sheet form, without any change in line widths. Furthermore, solvent-induced conformational change of B. mori fibroin from the “random coil” to the silk II form was examined and explained in terms of ease of dehydration by the solvent used. In additio, conformational change by mechanical treatments such as drawing and compression was also examined. © 1990, American Chemical Society. All rights reserved.