Investigating Fundamental Interactions between Pectin and Cellulose Nanocrystals: A Molecular Dynamics Simulation

Abstract Pectin and cellulose nanocrystals are the main biopolymers in the plant's prime cell walls. Despite extensive studies on the structure of prime cell walls of plants, limited information is known about the interaction between pectin and cellulose due to previous models placing pectin as a matrix and cellulose nanocrystals as a separate reinforcement component. However, recent developments in prime cell wall structure have shifted, and pectin is considered a part of the reinforcement structure. This work aims to provide fundamental information on the interaction between pectin and cellulose nanocrystals using molecular dynamic simulations. Interphase models consisting of two cellulose nanocrystals and a homogalacturonan pectin molecule are created to simulate the interfacial structure, including binding energy and hydrogen bonds. Friction and adhesion responses are predicted by moving one cellulose nanocrystal against the other. The results show that a pectin molecule increases the friction at the interphase by 14 and 8 times between CNC (200) and (110) surfaces, respectively, which is correlated to the significantly increased binding energies and interfacial hydrogen bonds, regardless of pectin's charge density. On the other hand, adhesion rises by 1.1 times but reduces to 1/5 with a pectin molecule between the CNC (110) and (200) surfaces, respectively, which is attributed to disrupted π-π interaction. The simulation results reveal the atomistic level interaction between pectin and cellulose nanocrystals, which is essential for designing nanocomposites that mimic the natural biocomposites of the plant's primary cell walls.