Conformations and Intermolecular Interactions in Cellulose/Silk Fibroin Blend Films: A Solid-State NMR Perspective
作者：Donglin Tian, Tao Li, Rongchun Zhang,* Qiang Wu, Tiehong Chen, Pingchuan Sun,* and Ayyalusamy Ramamoor
關鍵字：Cellulose,Silk Fibroin,Solid-State NMR
論文來源：期刊
具體來源：Journal of Physical Chemistry B 2017, In Press
發表時間：2017年
Fabricating
materials with excellent mechanical performance from the natural renewable and
degradable biopolymers has drawn significant attention in recent decades due to
the environmental concerns and energy crisis. As two of the most promising
substitutes of synthetic polymers, silk fibroin (SF) and cellulose, have been
widely used in the field of textile, biomedicine, biotechnology, etc.
Particularly, the cellulose/SF blend film exhibits better strength and
toughness than that of regenerated cellulose film. Herein, this study is aimed
to understand the molecular origin of the enhanced mechanical properties for
the cellulose/SF film, using solid-state NMR as a main tool to investigate the
conformational changes, intermolecular interactions between cellulose and SF
and the water organization. It is found that the content of the β-sheet
structure is increased in the cellulose/SF blend film with respect to the
regenerated SF film, accompanied with the reduction of the content of random
coil structures. In addition, the strong hydrogen bonding interaction between
the SF and cellulose is clearly elucidated by the two dimensional (2D) 1H-13C
heteronuclear correlation (HETCOR) NMR experiments, demonstrating that the SF
and cellulose are miscible at the molecular level. Moreover, it is also found
that the -NH groups of SF prefer to form hydrogen bonds with the hydroxyl groups bonded to carbons C2 and C3 of
cellulose, while the hydroxyl groups bonded to carbon C6 and the ether oxygen
are less favorable for hydrogen bonding interactions with the -NH groups of SF.
Interestingly, bound water is found to be present in the air-dried cellulose/SF
blend film, which is predominantly associated with the cellulose backbones as
determined by 2D 1H-13C wideline-separation (WISE) experiments with spin
diffusion. This clearly reveals the presence of nanoheterogeneity in the
cellulose/SF blend film, although cellulose and SF are miscible at a molecular
level. Without doubt, these in-depth atomic-level structural information could help
reveal the molecular origin of the enhanced mechanical properties of the blend
film, and thus to establish the structure-property relationship, which could
further provide guidance for the fabrication of high performance
biopolymer-based materials.