Molecular dynamics simulation of dehydration in cellulose/water crystals

It is well known that there are two crystal types for a cellulose/water complex: Na-cellulose IV and cellulose II hydrate. The water molecules in these crystals are released with increasing temperature and the hydrated models are then transformed into cellulose II crystals. Dehydration can be observed even when the cellulose/water crystal is soaked in water. In this study, we investigated the dehydration process in Na-cellulose IV and cellulose II hydrate using molecular dynamics simulations. In both crystals, as simulation time progressed, the water molecules were gradually released from the crystal while forming hydrogen bonds with the hydroxyl groups of cellulose. Interestingly, water molecules were released from the spaces between the molecular sheets formed by hydrophobic interactions. All hydroxyl groups existed on the surface of the molecular sheets. Therefore, it is reasonable to suggest that water molecules pass between the sheets. For Na-cellulose IV, the ratio of gt conformations was high. In addition, it was observed that water molecules were in the space between O6 and O3 on each adjacent molecular sheet forming hydrogen bonds during simulation. On the other hand, the gg conformations were mainly observed in cellulose II hydrate probably because of the presence of the O6 center dot center dot center dot O6 intermolecular hydrogen bond. During the simulation, the water molecules were present in the space between O2 and O3 while forming hydrogen bonds.