Mechanistic insights into competitive water-bridged proton transfer during CO₂ absorption via aqueous...

The dual mechanism of water-bridged proton transfer in the reaction between CO₂ and 3-(2-hydroxyethylamino)propan-1-ol (HEAP) is investigated using density functional theory (DFT) calculations. The proton transfer involved in CO₂ absorption via HEAP with varying number of water molecules is studied. The change in the energetics of the reaction due to two different hydroxy groups present at different carbon chains of the molecule is discussed. The studies revealed that the hydroxy groups of the alkanol amines are not only involved in the initial binding with CO₂ but also govern the energetics of the rate-determining step in the subsequent proton transfer by enhancing the efficiency of the CO₂ absorption process.

The geometry optimizations and the calculations of thermochemical properties of the reactants, intermediates, transition states, and products are carried out at M06-2X/cc-pVDZ level of theory using Gaussian 09 software. The bond critical point analyses are carried out using Multiwfn program to get insight into different types of interactions between various species involved.