Abstract
Liquid-liquid extraction is a key extraction process used to selectively separate different solutes. One of the most important extraction systems is the water-octanol interface used in the industry to classify solutes based on their hydrophilicity [1]. The hydrophilicity of a solute, measured experimentally by its partition coefficient log(P), is linked to the Gibbs energy of transfer, which governs the solute transfer between the aqueous and the organic octanol phases [2].This work deals with the prediction of the Gibbs energy of transfer of water molecules in water-octanol interfaces using Steered Molecular Dynamics (SMD), an out-of-equilibrium simulation technique for Molecular Dynamics. The SMD methodology uses a moving biasing harmonic potential to steer the water molecules from the aqueous phase to the organic phase, allowing for accurate sampling of the free energy landscape of the interface [3,4].Calculating the molecular orientation revealed that the octanol molecules at the interface organize themselves in a rigid bilayer structure, as previously observed [5], preventing the water transfer toward octanol. SMD simulations were carried out to determine the Gibbs energy barrier of this interface, allowing a preliminary calculation of the water solubility in octanol. [1] J. Sangster, J. Phys. Chem. Ref. Data, 1989, 18 (3), 1111–1229.[2] C. C. Bannan, et al. J. Chem. Theory Comput., 2016, 12 (8), 4015–4024. [3] L. Jami, et al. J. Chem. Phys., 2022, 157 (9), 094708. [4] C. Jarzynski, Phys. Rev. E, 1997, 56 (5), 5018–5035. [5] G. Benay, G. Wipff, J. Phys. Chem. B, 2013, 117 (4), 1110–1122.