Unveiling the solvent composition dependence of amine kinetics in DMSO-water systems: Stopped-flow intrinsic rate analysis with DFT/MD mechanistic validation

DMSO promotes primary/secondary amines and sustains tertiary amine kinetics. • DMSO enhances amine nucleophilicity by restructuring solvation shells and modulating N H interactions. • Destabilized transition states in DMSO lower activation barriers, promoting reaction activity. • Provides molecular insights for designing efficient water-lean CO 2 capture systems. The high energy demand associated with regeneration poses a significant bottleneck for conventional aqueous amine absorbents, rendering the R&D (Research and Development) of water-lean systems crucial for energy-efficient CO 2 capture. This study employs an integrated approach combining stopped-flow apparatus with multi-scale simulations to systematically investigate the intrinsic kinetic behavior of AP, EAE and MDEA in DMSO-H 2 O mixed solvents ([H 2 O]: 0–55 M for AP and EAE, 5–55 M for MDEA). Experimental results revealed distinct solvent-response profiles for the three amines: the intrinsic rate constant k 0 of AP increased monotonically with decreasing water content, peaking in pure DMSO; EAE exhibited a non-monotonic U-shaped trend with a kinetic minimum at 20 M water; whereas MDEA maintained a relatively stable kinetic profile. Molecular dynamics (MD) simulations indicated that DMSO restructures solvation shells to alleviate steric shielding effects and enhanced the electron density of the amine nitrogen, thereby improving local reactivity. Density functional theory (DFT) calculations further corroborated that DMSO lowered reaction activation barriers by destabilizing transition states through the attenuation of hydrogen-bond stabilization. This work elucidates the cooperative regulation mechanism involving DMSO solvent effects and electronic properties, providing a theoretical basis for the rational design of efficient water-lean CO 2 capture systems.