Green CO₂-capture cluster model using bioengineering of carbonic anhydrase enzyme: QM and QM/QM' approach

The ongoing increase in anthropogenic CO₂ levels and global warming demonstrate serious risks to human society and the biosphere. Green CO₂ capture technologies that utilize the characteristics of enzymes such as carbonic anhydrase (CA), including low consumption, exceptional selectivity, and environmentally friendly nature, show significant promise. The hydration of CO₂ by the CA model was investigated using QM/QM' calculations. We performed a detailed theoretical study using density functional theory (B3LYP/6-31G* and B3LYP-D3/def2-TZPV/def2-ECP) by the cluster model approach. The hydration mechanisms were studied extensively in both gas and water solvent phases. Furthermore, explicit solvent effect was evaluated for water solvent using ONIOM (QM: QM') calculations, and all thermodynamic functions through the reaction path were calculated in different phases. The mechanism of CO₂ hydration exhibits the characteristics of an exothermic reaction, wherein the transition state resembles the reactant with a barrier height about of 6.35, 5.71, and 5.22 kcal.mol^- 1 for TS1, TS2, and TS3, respectively, in water solvent. These results reveal low energy barriers and favorable thermodynamic profiles in solvated environments. These findings support future research on CA hydration mechanisms and the development of a synthetic enzyme model, which may lead to a significant reduction of CO₂ emissions.