We investigate theoretically the NMR response of twisted configurations of Iβ cellulose in the tg conformation. These finite helical angle structures were constructed by a mathematical deformation of zero-angle configurations obtained via the periodic density functional energy minimizations with dispersion corrections (DFT-D2). Subsequent calculations of the 13C nuclear magnetic resonance chemical shifts (δ13C) were compared with experimental findings by Erata et al. (Cellul Commun 4:128–131, 1997) and Kono et al. (Macromolecules 36:5131–5138, 2003). We determine the sensitivity of the NMR chemical shifts to helical deformation of the microfibril and find that a substantial range of helical angle, ±2 degrees/nm, is consistent with current experimental observations, with a most probable angle of ∼0.2 degree/nm. Through exhaustive combinatorial provisional assignments, we also demonstrate that there are different choices of the chemical shift (δ13C) assignments which are consistent with the experiments, including ones with lower deviations than existing identifications.
All Science Journal Classification (ASJC) codes
- Polymers and Plastics