(360aq) Effect of Solvent Quality on Structure and Dynamics of Lignin in Solution

Due to significant aromatic content, lignin is an attractive source of valuable organic chemicals. As the majority the proposed lignin depolymerization are expected to be liquid-phase, it is imperative to understand the effect of solvent quality on the structure and dynamics of lignin. Here we use all-atom molecular dynamics simulations to understand the evolution of lignin structure as a function of concentration of methanol in methanol/water solution at different temperatures. We utilize two different lignin models, softwood that consists of guaiacyl (G) monomer, and hardwood that consists of heteropolymer containing guaiacyl:syringyl (S) with a 1.35:1 ratio. The presence of methoxy groups in the hardwood leads to a slightly higher value in the Flory exponent with increasing methanol concentration. Furthermore, softwood lignin adopts the ideal chain state in 80 mole% methanol solution while the hardwood adopts the same state in 40 mole% mixture at 300 K. We find that methanol preferentially solvates the nonpolar segments of the lignin polymer while water molecules solvate the polar functional groups. Thus, as the methanol concentration increases, methanol is able to better solvate lignin polymer leading to more extended configuration.