Molecular Dynamics Study on Hydrogen Bond Reconstruction and Conformational Stability of Sodium Alginate/Pectin Mixtures in Aqueous Solution

Sodium alginate (SA)/pectin (PEC) mixture polysaccharides possess tunable rheological properties and wide biomedical application prospects, while the atomic-scale mechanism of ratio-dependent hydrogen bond reconstruction and conformational stability remains unclear. Herein, 200 ns all-atom molecular dynamics simulations were performed on pure SA and three SA/PEC mixture systems with mass ratios of 11:1, 7:1, and 3:1. Microscopic conformational evolution, hydrogen bond networks, chain flexibility, diffusion kinetics, and thermodynamic characteristics were quantitatively analyzed. The results reveal that PEC incorporation triggers prominent hydrogen bond network reconstruction. SA-PEC hydrogen bonds gradually replace intrinsic SA-SA hydrogen bonds, increasing average hydrogen bond length and weakening single-bond interaction strength. With elevated PEC content, polysaccharide chains undergo obvious curling and contraction, accompanied by reduced radius of gyration, solvent-accessible surface area, and topological chain entanglement density. Despite the electrostatic repulsion between these two negatively charged polysaccharides, van der Waals interactions dominate the spontaneous thermodynamic association between SA and PEC and maintain composite structural stability. High PEC ratios raise the conformational transition energy barrier and drive the conversion of polysaccharide chains from extended to collapsed conformations, significantly improving molecular diffusion capacity and reducing solution viscosity. The normalized viscosity variation trend from simulations is highly consistent with macroscopic rheological measurements, which validates the reliability of the constructed simulation model. This study clarifies the atomic-scale mechanism of PEC regulating the rheological behavior and structural stability of SA/PEC solutions, providing theoretical guidance for the processing optimization and performance tuning of polysaccharide-based functional materials.