Elucidating the Molecular Mechanism of CO₂ Capture by Amino Acid Ionic Liquids

Amino acid ionicliquids have received increasing attentionasideal candidates for the CO2 chemisorption process. However,the underlying molecular mechanisms, especially those involving protontransfer, remain unclear. In this work, we elucidate the atomistic-levelreaction mechanisms responsible for carbamate formation during CO2 capture by amino acid ionic liquids through explicit ab initio molecular dynamics augmented by well-temperedmetadynamics. The resulting ab initio free-energysampling reveals a two-step reaction pathway in which a zwitterion,initially formed from the reaction between the anion of serine andCO(2), undergoes a kinetically facile intermolecular protontransfer to the O atom of the COO- moiety in thenearby serine. Further analysis reveals that the significantly reducedfree-energy barriers are attributed to enhanced intermolecular interactionbetween the zwitterion and serine, thus facilitating the kinetic favorabilityof the proton transfer, which governs the overall CO2 capturemechanism. This work provides valuable insight into the importantmechanistic and kinetic features of these reactions from explicitcondensed phase ab initio MD free-energy samplingof the CO2 capture process.