Surface structural analysis of selectively 13C-labeled cellulose II by solid-state NMR spectroscopy

• Published in: Cellulose (London) 2020-03, Vol.27 (4), p.1899-1907
• Main Authors: Kita, Yusuke, Kusumi, Ryosuke, Kimura, Tsunehisa, Kitaoka, Motomitsu, Nishiyama, Yusuke, Wada, Masahisa
• Format: Article
• Language: English
• Subjects: Bioorganic Chemistry; Cellulose; Ceramics; Chemistry; Chemistry and Materials Science; Composites; Cross polarization; Crystal structure; Glass; Natural Materials; NMR spectroscopy; Organic Chemistry; Original Research; Phosphorylases; Physical Chemistry; Plates (structural members); Polymer Sciences; Solid state; Spectrum analysis; Structural analysis; Sustainable Development
• ISSN: 0969-0239; 1572-882X
• DOI: 10.1007/s10570-019-02896-x

The local structure on the surface of plate-like cellulose II oligomer crystals (CIIOCs) was investigated by NMR spectroscopy. CIIOCs with reducing ends that were selectively labeled with 13 C were enzymatically synthesized using cellodextrin phosphorylase. The solid-state 13 C cross polarization/magic angle spinning spectra of the 13 C-labeled CIIOCs clearly exhibited two resonance peaks (labeled as C1Rα and C1Rβ) derived from the C1 atoms of the reducing ends. The 2D 13 C double quantum/ 13 C single quantum homonuclear correlation spectrum indicated that two magnetically nonequivalent glucopyranose rings (Rα and Rβ units) coexisted at the reducing end units. The 1 H/ 13 C heteronuclear correlation spectrum suggested that there was a large difference between the local environments around the anomeric carbons of Rα and Rβ units. The abundance ratio of C1Rβ to C1Rα in the solid state was 4:1, whereas that of C1α and C1β in solution was 1:1. When the oligomer chains are packed in the cellulose II crystal, the reducing end units located on the surface of the plate-like crystal may tend to have β-anomeric structure, which would be more sterically stable than the α-anomeric structure.