THEORETICAL INVESTIGATION OF THE CO2+OH--]HCO3- REACTION IN THE GAS AND AQUEOUS PHASES

For the CO2 + OH- --> HCO3- reaction in the gas phase, we have identified the minimum energy reaction path using high-level ab initio calculations. The gas-phase free energy profile at 298.15 K has been assembled by computing thermodynamic corrections, which are quite significant. The full thermodynamic cycles for this reaction in the gas and aqueous phases have been constructed. The main feature of the gas-phase results is that the reaction is activationless, which agrees with previous theoretical studies. We have also performed molecular dynamics free energy perturbation simulations on this system in an aqueous environment. Our results predict an aqueous free energy barrier (19.2 kcal/mol) which is induced by solvation effects. The ramifications of our results on the catalytic mechanism of carbonic anhydrase are discussed.