The mechanism of cellulose solubilization by urea studied by molecular simulation

We used molecular dynamics simulation to model the effect of urea and thiourea on the solvent quality of aqueous solutions with respect to cellulose. A model system consisting of a periodically replicated cellulose molecule of effectively infinite degree of polymerization immersed in aqueous (thio-)urea solution was considered. Kirkwood-Buff theory, which relates the pair distribution functions to the concentration derivatives of the chemical potential, allowed the solubilization effect to be quantified in terms of the preferential binding of urea over water to the cellulose molecule. We found that urea is preferentially adsorbed on the hydrophobic faces of the anhydroglucose rings but has the same affinity as water to the hydroxyl groups. Thus, the simulations suggest that urea acts primarily by mitigating the effect of the hydrophobic portions of the cellulose molecule.