title: Molecular Orientation Enhancement of Silk by the Hot-Stretching-Induced Transition from α-Helix-HFIP Complex to β-Sheet.
abstract: Enhancing the molecular orientation of the regenerated silk fibroin (RF) up to a level comparable to the native silk is highly challenging. Our novel and promising strategy for the poststretching process is (1) creating at first an α-helix-HFIP complex with a hexagonal packing as an intermediate state and then (2) stretching it at a high temperature to induce the helix-to-sheet structural phase transition. Here we show for the first time the significantly high stretching efficiency of the proposed technique compared with the conventional wet-stretching techniques and the successful achievement of higher crystalline orientation and higher Young's modulus compared even with the native silk. The detailed structural analysis based on the time-resolved simultaneous measurement of stress-strain curve, synchrotron X-ray scatterings, and FTIR has revealed the structural transition mechanism from the hexagonally packed α-helix-HFIP complex to the highly oriented β-sheet crystalline state as well as the critical level of crystal orientation needed for the helix-to-sheet transition.
authors.affiliation: Department of Future Industry-oriented Basic Science and Materials, Graduate School of Engineering, Toyota Technological Institute , Tempaku, Nagoya 468-8511, Japan.
authors.forename: Taiyo
authors.initials: T
authors.lastname: Yoshioka
authors.affiliation: Department of Future Industry-oriented Basic Science and Materials, Graduate School of Engineering, Toyota Technological Institute , Tempaku, Nagoya 468-8511, Japan.
authors.forename: Kohji
authors.initials: K
authors.lastname: Tashiro
authors.affiliation: Japan Synchrotron Radiation Research Institute , 1-1 Koto, Mikazuki-cho, Sayo-gun, Hyogo 679-5198, Japan.
authors.forename: Noboru
authors.initials: N
authors.lastname: Ohta
mesh_terms: D000818:Animals; D012831:Bombyx / Q000378:metabolism*; D005349:Fibroins / Q000737:chemistry*; D006358:Hot Temperature; D000072756:Protein Conformation, alpha-Helical; D000072757:Protein Conformation, beta-Strand; D017433:Protein Structure, Secondary; D047011:Silk / Q000737:chemistry*
chemical_list: D047011:Silk; D005349:Fibroins