Ab initio molecular dynamics study of the mechanism of proton recombination with a weak base

Despite its fundamental nature, many of the microscopic features of acid–base recombination remain poorly understood. In this work, we use ab initio molecular dynamics simulations to study the recombination of the proton with a weak base, the carbonate ion CO3(2–). Our simulations elucidate the network structure around CO3(2–) that provides a distribution of pathways over which recombination can occur. We observe that the penultimate neutralization step involves a correlated behavior of the transferred protons that is mediated by the water wires decorating the carbonate. These concerted proton transfers are coupled to collective compressions of these water wires. We show further that these processes are dynamically coupled to the reorganization of the water molecules hydrating the CO3(2–) ion. The insights from these simulations help to bridge the structural and dynamical complexity of the microscopic mechanisms with those of phenomenological models invoked by experiments in this field.