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Int. J. Mol. Sci. 2016, 17(9), 1517; doi:10.3390/ijms17091517

Glycerin-Induced Conformational Changes in Bombyx mori Silk Fibroin Film Monitored by 13C CP/MAS NMR and 1H DQMAS NMR

Department of Biotechnology, Tokyo University of Agriculture and Technology, Koganei, Tokyo 184-8488, Japan
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Academic Editors: John G. Hardy and Chris Holland
Received: 15 June 2016 / Revised: 12 August 2016 / Accepted: 30 August 2016 / Published: 9 September 2016
(This article belongs to the Special Issue Silk-Based Materials: From Production to Characterization)
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Abstract

In order to improve the stiff and brittle characteristics of pure Bombyx mori (B. mori) silk fibroin (SF) film in the dry state, glycerin (Glyc) has been used as a plasticizer. However, there have been very limited studies on the structural characterization of the Glyc-blended SF film. In this study, 13C Cross Polarization/Magic Angle Spinning nuclear magnetic resonance (CP/MAS NMR) was used to monitor the conformational changes in the films by changing the Glyc concentration. The presence of only 5 wt % Glyc in the film induced a significant conformational change in SF where Silk I* (repeated type II β-turn and no α-helix) newly appeared. Upon further increase in Glyc concentration, the percentage of Silk I* increased linearly up to 9 wt % Glyc and then tended to be almost constant (30%). This value (30%) was the same as the fraction of Ala residue within the Silk I* form out of all Ala residues of SF present in B. mori mature silkworm. The 1H DQMAS NMR spectra of Glyc-blended SF films confirmed the appearance of Silk I* in the Glyc-blended SF film. A structural model of Glyc-SF complex including the Silk I* form was proposed with the guidance of the Molecular Dynamics (MD) simulation using 1H–1H distance constraints obtained from the 1H Double-Quantum Magic Angle Spinning (DQMAS) NMR spectra. View Full-Text
Keywords: Bombyx mori; silk fibroin; glycerin; solid state NMR Bombyx mori; silk fibroin; glycerin; solid state NMR
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MDPI and ACS Style

Asakura, T.; Endo, M.; Hirayama, M.; Arai, H.; Aoki, A.; Tasei, Y. Glycerin-Induced Conformational Changes in Bombyx mori Silk Fibroin Film Monitored by 13C CP/MAS NMR and 1H DQMAS NMR. Int. J. Mol. Sci. 2016, 17, 1517.

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