Constraints on [Formula: see text] cellulose twist from DFT calculations of [Formula: see text] NMR chemical shifts

• Published in: Cellulose (London) Vol. 21; no. 6; pp. 3979 - 3991
• Main Authors: Shklyaev, Oleg E, Kubicki, James D, Watts, Heath D, Crespi, Vincent H
• Format: Journal Article
• Language: English
• Published: Dordrecht Springer-Verlag 01-12-2014; Springer Nature B.V
• Subjects: Cellulose; Chemical equilibrium; Combinatorial analysis; Configurations; Deformation; Density functional theory; energy; Macromolecules; Mathematical analysis; NMR; Nuclear magnetic resonance; nuclear magnetic resonance spectroscopy; Organic chemistry
• ISSN: 0969-0239; 1572-882X
• DOI: 10.1007/s10570-014-0448-3

We investigate theoretically the NMR response of twisted configurations of [Formula: see text] 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 [Formula: see text] nuclear magnetic resonance chemical shifts [Formula: see text] 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 [Formula: see text] assignments which are consistent with the experiments, including ones with lower deviations than existing identifications.