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Int. J. Mol. Sci. 2016, 17(9), 1517;

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
Author to whom correspondence should be addressed.
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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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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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).

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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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Int. J. Mol. Sci. EISSN 1422-0067 Published by MDPI AG, Basel, Switzerland RSS E-Mail Table of Contents Alert
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