Solvation of salicylic acid in pure, methanol-modified and water-modified supercritical carbon dioxide: Molecular dynamics simulation

In the present work, solvation of the salicylic acid in pure, methanol-modified and water-modified (by adding 0.035 methanol or 0.0079 water mole fraction) supercritical carbon dioxide (sc-CO2) at 318 K and 0.7 g/cm(3) has been studied by computer simulation techniques. It was shown that solvation of salicylic acid in pure sc-CO2 is governed by electron donor-acceptor interactions and proceeds more slowly than in modified sc-CO2, where salicylic acid forms solvate complex with co-solvent by means of hydrogen bonding through carboxyl group. Salicylic acid hydroxyl group participates only in intramolecular hydrogen bond and does not interact with solvent molecules. The salicylic acid-co-solvent complexes are stable: the duration of their existence is much higher than lifetime of other hydrogen bonds in the fluid. The behavior of two co-solvents is different: methanol exists in the form of monomers and hydrogen-bonded dimers in the supercritical fluid, the water molecules tend to form microclusters with spatially-branched structure. (C) 2015 Elsevier B.V. All rights reserved.