The crystal structures of cellulose allomorphs can be characterized by stacking of the molecular chain sheets composed by hydrogen-bonded molecular chains. The present paper reports the systematic assessment of the structural stability of the isolated molecular chains sheets (4×8mer chains) extracted from the cellulose crystal allomorphs. (Fig.1) The structures of the molecular chain sheets were optimized by DFT calculations. As a comparable study, the crystal models with the finite dimensions (36 to 48×40mer chains) were examined by molecular dynamics (MD) calculations in solution state. The linear chain sheets of cellulose Iα and Iβ crystals exhibited the right-handed twist forms with similar extent, whereas the cellulose Iα crystal model displayed more distinct twist than the Iβ one, suggesting weaker inter-sheet interactions involved in the former crystal structure. While the DFT optimization completely deformed the structure of the (100) chain sheet of cellulose IIII crystal, the (1-10) chain sheet essentially retained the initial structure and so did the cellulose IIII crystal model during the MD calculations. The results suggested that the crystal structure was more appropriately described by the layered (1-10) chain sheets. The isolated (010) and (020) chain sheets of cellulose II crystal, both aligned in parallel in the crystal structure, twisted with the opposite chirality to each other. The isolated (110) chain sheet, on the other hand, was slightly deviated by the DFT optimization. The crystal structure of cellulose II was also characterised by the layered (010) and (020) chain sheets. The present DFT calculations may have revealed the interior stress along the (010) and (020) lattice planes so as to deviate to the opposite mode, which probably resulted in a moderate deformation of the crystal model in the MD calculations.1 Reference (1) Uto, T.; Mawatari, S.; Yui, T. J. Phys. Chem. B 2014, 118, 9313-9312

Structural stability of the molecular chain sheets composing the crystal structures of cellulose allomorphs: A theoretical study

249th National Meeting (2015)

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