Bombyx mori silk fibroin liquid crystallinity and crystallization at aqueous fibroin-organic solvent interfaces

A banded morphology has been observed for Bombyx mori silk fibroin films ob tained from an aqueous-hexane interface; the period of the banding is appro ximately 1 mu m. Morphology and diffraction from different regions of the b anded structure suggest that it is a free surface formed by a cholesteric l iquid crystal. Truncated hexagonal lamellar crystallites of B. mori silk fi broin have been observed in films formed in the surface excess layer of fib roin at the interface between aqueous fibroin and hexane or chloroform. Bas ed on initial crystallographic evidence, a three-fold helical conformation has been ascribed to the fibroin chains within the crystals. The chain conf ormation and crystalline habit appear to be similar to the silk III structu re previously observed at the air-water interface (Valluzzi R, Gido SP. Bio polymers 1997;42:705-717; Valluzzi R, Gido S, Zhang W, Muller W, Kaplan D. Macromolecules 1996;29:8606-8614) but the crystalline packing is different. Diffraction data obtained for the crystallites are similar to diffraction behavior for a collagen-like model peptide. Diffraction patterns obtained f rom crystallized regions of the banded morphology can be indexed using the same unit cell as the hexagonal lamellar crystallites. Surfactancy of fibro in and subsequent aggregation and mesophase formation may help to explain t he liquid crystallinity reported for silk, which is long suspected to play a role in the biological silk spinning process (Valluzzi R, Gido SP. Biopol ymers 1997;42:705-717; Willcox, P. J.; Gido, SP, Muller W, Kaplan DL. Macro molecules 1996;29:5106-5110; Magoshi J, Magoshi Y, Nakamura S. In: Kaplan D , Adams W, Farmer B, Viney C, editors, Mechanism of Fiber Formation of Silk worm. Washington, DC: American Chemical Society 1994:292-310; Magoshi J, Ma goshi Y, Nakamura S. J Appl Polym Sci Appl Polym Symp 1985;41:187-204; Mago shi J, Magoshi Y, Nakamura S. Polym Commun 1985;26:309.). (C) 1999 Elsevier Science B.V. All rights reserved.