Hydrogen-bonded clusters and solvate structures in the supercritical CO2-water-o-hydroxybenzoic acid system: the car-parrinello molecular dynamics

Hydrogen-bonded clusters and solvate structures formed by o-hydroxybenzoic acid (o-HBA) and water in supercritical CO₂ were studied (T = 318 K, 348 K, ρ = 0.7 g/cm³). The atom-atom radial distribution functions, coordination numbers, average numbers of hydrogen bonds for individual atomic groups, and power spectrum were calculated by the Car-Parrinello molecular dynamics. Despite the high polarity of the cosolvent, the hydroxyl group of o-HBA predominantly forms intramolecular hydrogen bond, while hydrogen bonds with water involve only the atoms of carboxyl groups. The temperature effect on the stability of these bonds showed itself in different ways. The intermolecular interactions of o-HBA with carbon dioxide were found to be weaker than those with water. It was established that the Lewis acid-Lewis base interactions between CO₂ and the hydroxyl group of the solute increase with increasing temperature. Instantaneous configurations illustrating the temperature effects on the molecular structures were obtained.