Quantifying acetylation-induced changes in the plant secondary cell wall structure and dynamics

Lignin and carbohydrate rich secondary plant cell walls are abundantly available in the biosphere, and is a notable renewable feedstock for biofuels, biomaterials with wide applicability. Particularly for construction applications, long-lived wood that is resistant to fungal degradation is highly desirable. Chemical modifications, such as acetylation, have been successfully demonstrated inhibit wood breakdown. X-ray fluorescence microscopy experiments have determined that acetylation hinders fungal attack by reducing moisture content while other experiments examining moisture-induced wood damage mechanisms observed that chemical transport through cell walls is reduced after acetylation. We investigate these hypotheses directly through molecular simulation, acetylating existing models for secondary plant cell wall structure to 5-18% weight-percent gain for additional acetylations on exposed hemicellulose and lignin hydroxyl groups. By comparing diffusive behavior for cell wall polymers, water, and select ions (Na+ and Fe3+), we can track the dynamics within the cell wall and identify the causal mechanisms for reduced transport and uptake by acetylated cell walls. We find that cell wall acetylation alone does not account for reduced transport. The most substantial changes in diffusion occur in a constant volume system where the additional acetylation displaces water, reducing the moisture content for the cell wall. Utilizing these simulations, we further analyze the interactions between ions and cell wall polymers and the evolution of water pockets within the structure. Ions interact more frequently with the acetyl group than the hydroxyl groups they replace, yielding to increased ion interactions on aggregate upon acetylation. These findings elucidate the molecular mechanism through which acetylation affects secondary plant cell wall at atomic resolution.