Hydrogen disorder was demonstrated by X-ray and neutron diffraction studies on highly crystalline cellulose I but not for regenerated cellulose samples (II and IIII). Recently, classical molecular dynamics simulation found that an irreversible conversion from the experimental hydrogen bonding pattern (named HB A) to a new hydrogen bonding pattern (named HB B) under thermal treatment without changing in the main structural motif (such as orientation of O6). Rigorous DFT calculations based on various functional all revealed that the HB B is more energetically favorable than the original HB A. The energy landscape of four crystal allomorphs together two possible hydrogen bonding pattern is in the order of II(B) &lt; Iβ(A) &lt; IIII(B) &lt; Iα(A) &lt; IIII(A) &lt; II(A) &lt; Iα(B) &lt; Iβ(B). If a unit cell of cellulose IIII is considered as the size for an intermediate state structure, the two HB patterns can interconvert by a low energy barrier of 4~7 kcal/mol, through either the cooperative rotation of adjacent hydroxyl groups or the proton transfer mechanism.

Hydrogen disorder: the nature of crystalline cellulose

255th National Meeting (2018)

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