Probing Polymer Interactions in Softwood Cell Walls using Molecular Dynamics Simulation

Plant cell wall architecture and its molecular structure-property relationships are principal topics in plant cell research. The mechanical stress applied to fresh wood
can exceed the yield point without breaking the material, and the wood fully recovers its shape after the stress is removed. However, dried wood cannot deform beyond its elastic deformation limit, suffering brittle failure and breaking in experiments. Thus, water may play a crucial role alongside lignocellulose polymers, modulating polymer interactions and supporting the plant cell wall architecture. Here, we adapt an atomistic spruce secondary cell wall model based on experimental data to evaluate how hydration content influences polymeric interactions via molecular dynamic simulations. We use the softwood 'nolcc' model from our previously published work [Biomacromolecules 2025, 26, 6, 3395–3409] as the starting point for our new systems. The atomistic system comprises lignocellulose polymers (cellulose, hemicellulose, and lignin) that are the building blocks of structural and mechanical properties in this biomaterial. The major modification is the O-methylation of glucuronic acids in arabinoglucuronoxylan to increase the structural hydrophobicity of xylan side chains. Crucially, the DMSO:H₂O proportion was a key adjustment. DMSO serves as a tool to prepare systems with different water content, preventing vacuum spots and facilitating hydrophobic interactions. Although DMSO is not a natural component of plant cell walls, experimental evidence shows that DMSO-d6 favors lignin aggregation, and we expect it to potentially enhance lignin-lignin and lignin-carbohydrate interactions. Furthermore, DMSO is miscible with water in all proportions, acting as a cosolvent that allows testing hydrophobic effects at higher DMSO content without introducing phase transition artifacts in simulations. Therefore, we explore systems with DMSO molar fractions of 0.0 (only water), 0.25, 0.50, 0.75, and 1.0 (just DMSO) to elucidate water and hydrophobic effects on plant cell wall systems.