Computational Insights into the Activity of Transition Metals for Biomimetic CO2 Hydration

Density functional theory (DFT) calculations were carried out on five transition metals (Co, Ni, Pd, Rh, Ru) to test their activities toward the biomimetic carbon dioxide hydration reaction. Periodic plane-wave calculations demonstrated the formation of surface species in accordance with the mechanism of the reaction known for alpha-carbonic anhydrase action. To determine different activation barriers for the different elementary steps involved in the reaction, DFT calculations using a cluster model of transition metals with Gaussian-type orbitals were carried out. The periodic and cluster calculations were found to correspond to a mechanism of the reaction constitituting seven steps, namely, surface adsorption of H2O, deprotonation and surface OH formation, adsorption of CO2, OH attack on adsorbed CO2, proton transfer, H2O attack on surface HCO3- complex, and HCO3- displacement by H2O. The behaviors of the metals were found to be different in a vacuum and in the solvated state, with Co being the best potential candidate for the biomimetic CO2 hydration reaction in a vacuum and Ru being the best candidate for the reaction in solution.