Beyond choline chloride: Molecular dynamics insights into tetraethylammonium chloride-based deep eutectic solvents for biomass delignification.

Rational design of deep eutectic solvents (DESs) for selective biomass fractionation requires molecular-level insights into how composition governs lignin-cellulose disruption. While choline chloride-based DESs dominate research, the choline hydroxyl group strongly sequesters chloride ions, limiting anion-mediated delignification. We present a systematic molecular dynamics investigation of tetraethylammonium chloride (TEACl)-based DESs, where the absence of hydroxyl functionality enhances chloride mobility, paired with urea (URE) or lactic acid (LAC) as hydrogen bond donors in binary systems, and 1,4-butanediol (BDO) in ternary formulations. All-atom simulations over 300 ns reveal distinct solvation mechanisms: urea-based DESs form stable solvation shells that moderately weaken cohesion, whereas lactic acid-based systems exhibit dynamic hydrogen-bond networks with high chloride recruitment, driving delignification through synergistic anion-HBD interactions. Ternary BDO incorporation further enhances chloride mobility and accelerates hydrogen-bond turnover. Critically, the TEACl:LAC:BDO system achieves the most pronounced reduction in lignin-lignin and cellulose-lignin interfacial bonds, significantly outperforming other formulations. Analyses establish that delignification efficiency correlates more strongly with dynamic hydrogen-bond exchange and chloride accessibility than with bulk viscosity or static solvation strength. These findings provide a comprehensive computational framework demonstrating that non-choline quaternary ammonium-based DESs with acidic, polyol-modified formulations enable superior biomass fractionation through enhanced ionic participation. These structure-performance relationships offer rational design principles for optimized green solvents in sustainable biorefinery applications.