Higher Ordered Structure of Cellulose Predicted by Computational Chemistry

Cellulose Nanotube in Cyclohexane and Ethyl Acetate

Abstract

Nanotubes are remarkable nanoscale architectures for a wide range of potential applications. Recently, we have predicted a nanoscale, tubular structure of cellulose molecules (CelNT), through density functional theory (DFT) calculation. In the present paper, we report a molecular dynamics (MD) study of the theoretical CelNT models to evaluate their dynamic behavior in solution (cyclohexane or ethyl acetate). Based on the one-quarter chain staggering relationship predicted by DFT calculations, we constructed six CelNT models by combining the two chain polarities (parallel (P) and antiparallel (AP)) and three symmetry operations (helical right (H_R), helical left (H_L), and rotation (R)) to generate a circular arrangement of molecular chains. The tubular structure of the CelNT models quickly collapsed in ethyl acetate with cleavage of intermolecular hydrogen bonds, indicating that ethyl acetate was not appropriate for the solvent of CelNTs. The four models (P-H_R, P-H_L, P-R, and AP-R) retained the tubular form in cyclohexane and the P-R and AP-R models exhibited relatively continuous tubular forms with the largest binding energies. The structural features of the CelNT models in cyclohexane were characterized in terms of intermolecular hydrogen bond and the hydroxymethyl group conformation. Solvent structuring clearly occurred, suggesting that the CelNT models may stably disperse in cyclohexane.