How water molecules modulate the hydration of CO2 in water solution: insight from the cluster-continuum model...

The hydration of CO(2) in water solution was investigated by the cluster-continuum model calculations with n = 1-8 water molecules. For n = 1-4 water molecules, all the reactions follow a concerted pathway to the hydration product directly. For n = 5-8 water molecules, all the reactions follow a stepwise mechanism and a labile H(3)O(+) intermediate is involved in reaction. The surrounding water molecules from the bulk solvent play a key role in the proton relay process, which can stabilize the charged transition state and the H(3) O(+) intermediate in reaction. Furthermore, if the proton transfer from H(3)O(+) to the carbonyl oxygen occurs, the hydration pathway will be followed. If there is a proton transfer from H(3)O(+) to the outer water phase through the water bridge, the dissociation product of HCO(3)(-) will be formed. The predicted reaction energetics by current cluster-continuum model calculations shows good agreement with the experimental values. Present calculations strongly suggest the suitable cluster-continuum model including more explicit water molecules highly required for reasonable and unbiased description of the proton relay mechanism for proton transfer related reactions in water solution.