Density Functional Theory Study of the Cellobiose Model System for Unveiling Cellulose-Water Interactions to Enhance Dewatering and Drying.

Abstract

Understanding cellobiose-water interactions at a molecular level is essential to enhance dewatering and drying for advancing industrial applications of cellulosic materials. Using density functional theory, quantum mechanical (QM) simulations were conducted on a cellobiose model extracted from an I_β-cellulose chain to understand the strength and nature of hydrogen bonding with water molecules. Water molecules were positioned on cellobiose, and the resulting changes in bond lengths revealed that regions R3 and R2 exhibit stronger interactions with interaction energies of -58.3 and -49.0 kJ/mol, respectively, compared to R1 and R4. Localized molecular orbital energy decomposition analysis identified electrostatic forces as the primary contributor to cellobiose-water stability, with polarization and dispersion effects adding significant energy contributions. The hydrogen-bond strengths were also quantified using the intrinsic bond strength index for weak interactions, attaining values up to 2.0 au/Ų in regions R3 and R2, indicating strong hydrogen bonds. The water-bridging effect, commonly seen in molecular dynamics simulations, was found to enhance cellobiose-water interactions by shortening hydrogen-bond distances to as low as 1.8 Å in specific regions. Free energy of solvation for cellobiose-water cluster (cellobiose-(H₂O)₄) with four water molecules was calculated at -184.8 kJ/mol, showing the stabilizing effects of hydration. These findings provide valuable insights for improving industrial dewatering and drying processes in the forest product industry and establish a transferable QM framework for studying hydration energetics in complex biopolymers.