A Consistent Force Field for the Carboxylate Group

In the light of the important role played by the carboxylate group in bio- and coordination chemistry, its consistent and reliable parametrization for molecular simulations is crucial. The experimental vibrational spectra of three carboxylate anions (formate, acetate, and benzoate) both in the gas phase and in the condensed phase (as sodium salts) are interpreted on the basis of high-quality ab initio calculations. The interaction with the counterion (metal cation) is shown to be of major importance in the interpretation of the spectral features of the carboxylate group both in the solid state and in aqueous solution. Previous attempts to parametrize the carboxylate group within the molecular mechanics approach is critically reviewed, and a new set of the consistent valence force field parameters based on first principles calculations is proposed, which is able to reproduce accurately both the structure and the dynamics of the carboxylate moiety both free and coordinated with metal cations.