Hydrogen-Bonded Complexes of p-Hydrobenzoic Acid and Its Derivatives with a Polar Cosolvent in Supercritical Carbon Dioxide

The results of numerical modeling of p-hydroxybenzoic acid, methylparaben, and propylparaben solutions in methanol-modified supercritical carbon dioxide were presented. The composition, structure, and formation energy of the solute-cosolvent hydrogen-bonded complexes were determined. The duration of the existence of hydrogen bonds via individual paraben atoms was evaluated based on the data of Car-Parrinello ab initio molecular dynamics simulation, and the potential of mean force of interaction with methanol was calculated taking into account the medium. It was shown that, despite the presence of several potential centers of specific interaction, p-hydroxybenzoic acid and its derivatives form hydrogen bonds mainly via carboxyl and hydroxyl protons, respectively.