A molecular dynamics study of cellulose inclusion complexes in NaOH/urea aqueous solution

We investigated the dissolution state of cellulose in NaOH/urea aqueous solution using molecular dynamics simulations. All the components, including cellulose, NaOH, urea and H₂O were combined into one simulation. A clear and detailed description for the formation of cellulose inclusion complexes has been stated. The simulation results showed that the cellulose inclusion complexes exhibited anisotropic properties. In this system, the sodium ions and hydroxide ions located at the regions of hydroxyl and hydroxymethyl groups in cellulose molecules. However, the urea molecules occupied the faces of the hydrophobic pyranose rings. The hydrogen-bonding configuration and lifetime of hydrogen bonds in cellulose inclusion complexes were also systematically characterized. The spatial structure of inclusion complexes, the hydrogen-bonding interaction between cellulose and solvent molecules, the diffusive property of solvent molecules and the distribution of water-water angles in cellulose inclusion complexes were discussed in details. The NaOH, urea and H₂O molecules surrounding the cellulose chain within radial distance 0.35 nm have smaller diffusion coefficients than those in bulk state. The water-water angles provide a quantitative estimate of hydrophobic effect of cellulose.