Structural analyses of silk fibroins based on the structures of oligoalanine, and periodic oligopeptides of L‐alanine and glycine using x‐ray diffraction and ¹³C solid‐state NMR methods

Abstract The structures of (A) 12 , (AAAG) 7 , (AAG) 10 , (AG) 15 , and (AGG) 10 were determined using x‐ray diffraction and 13 C sold‐state NMR methods after different solvent treatments to obtain knowledge about the structural changes of silk fibroins (SFs) from Samia cynthia ricini ( S.c.ricini ) and Bombyx mori ( B. mori ). Three solvent treatments were performed: precipitation from dialysis of LiSCN (LiSCN/Dialysis) or LiBr (LiBr/Dialysis) aqueous solutions, and drying from formic acid (FA) or trifluoroacetic acid (TFA) solutions. (AAAG) 7 and (AAG) 10 as models of S.c.ricini SF, formed antiparallel β‐sheet structure with staggered packing configuration and did not change after LiSCN/Dialysis or LiBr/Dialysis and FA treatments. (AGG) 10 formed 3 1 helix structure and did not change with these solvent treatments either. On the other hand, (AG) 15 as model of B. mori SF formed Silk I (type II β‐turn) structure after LiBr/Dialysis treatment and Silk II (lamellar packing) structure after FA treatment. Especially, B. mori SF seems useful for biomaterials.