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 α-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.