Mechanistic hydrogen bond mediated screening of hydroxyl functionalized additives for lignin condensation suppression

Hydroxyl functionalized additives (Ga-OHs) that can inhibit lignin re-polymerization have demonstrated significant potential in biomass resource conversion and utilization. However, the molecular mechanisms underlying this inhibitory effect remain poorly understood. This study systematically compares the lignin condensation inhibition capabilities of four hydroxyl functionalized additives with distinct functional group effects: salicylic acid, mannitol, 2-naphthol, and glycolic acid. Results indicate that lignin condensation inhibition is primarily associated with hydrogen bonding interactions formed between hydroxyl functionalized additives and oxygen containing functionalities on lignin side chains, while van der Waals interactions contribute as non-specific stabilizing contacts at the early stages. Rapid electron flow in short-chain compounds molecules stabilized the lignin structure. The strong hydrogen bond interaction between mannitol and oxygen groups in lignin branches (–80.38 kJ/mol) enhanced the stability of a separated lignin in a strong acidic environment, which resulted in a high β -O-4 content (up to 47.12 per 100 aromatic units). Here, we comparatively screened hydroxyl functionalized additives with different structures under dilute acid pretreatment and linked the quantitative outcomes of lignin condensation inhibition to density functional theory (DFT) validated noncovalent interactions. This work provides insight into the separation of low condensation lignin and informs the screening of additives with lignin condensation inhibition potential.