Solvation of Hydroxybenzoic and Hydroxycinnamic Acids in Supercritical Carbon Dioxide: Formation of Hydrogen Bonds with a Polar Cosolvent

Selective solvation of ortho-hydroxybenzoic, meta-hydroxybenzoic, para-hydroxybenzoic, protocatechal, gallic, lilac, para-coumaric, and caffeic acids with a polar cosolvent (methanol) in supercritical carbon dioxide was studied at 318 K at a density of 0.7 g/cm3 and a methanol concentration of 3.5 mol % with conventional molecular dynamics. We studied the localization of a cosolvent in the nearest environment of a solute, the formation of cosolvent clusters around the solute, and the number and nature of hydrogen bonds between molecules of the solute and cosolvent. We also considered the structural features of hydrogen-bound complexes associated with a molecular structure of a solute (the number and the arrangement of hydroxyl groups, the substitution of hydroxyl hydrogen atoms with methyl moieties, and the presence of an ethylene group).