A DFT study of vibrational frequencies and ¹³C NMR chemical shifts of model cellulosic fragments as a function of size

Plane wave and molecular orbital density functional theory calculations with periodic models and oligomer fragments based on Iβ cellulose showed relationships among hydrogen bond (H-bond) lengths, angles, energies, and vibrational frequencies. Significantly, the ¹³C NMR chemical shifts (δ¹³C), glycosidic and hydroxymethyl torsion angles, H-bond vibrational frequencies, and H-bond geometries results all suggest the predominance of the crystallographic structure C rather than structure A of Iβ cellulose as reported by Nishiyama et al. (J Am Chem Soc 124(31):9074–9082, 2002). The results reported herein also clarified that the δ¹³C and δ¹³C′ data from Erata et al. (Cellul Commun 4:128–131, 1997) correspond to δ¹³C from the origin and center chains of cellulose, respectively. Moreover, this work discusses the use of cellulose oligomer fragments for their potential use in understanding cellulose assembly.