Structure and hydrogen bonds of hydrophobic deep eutectic solvent-aqueous liquid-liquid interfaces

Hydrophobic deep eutectic solvents (DESs) emerge as candidates to extract organic substrates from aqueous solutions. The DES-aqueous liquid-liquid interface plays a vital role in the extraction ability of DESs because the nonbulk structure of interfacial molecules could cause thermodynamic and kinetic barriers. One question is how the DES compositions affect the structural features of the interface. We investigate the density profile, dipole moment, and hydrogen bonds of eight hydrophobic DES-aqueous interfaces using molecular dynamics simulations. The eight DESs are composed of four organic compounds: decanoic acid, menthol, thymol, and lidocaine. The results show the variations of dipole moment and hydrogen bond structure and dynamics at the interfaces. These variations could influence the extraction ability of DES through adjusting the partition and kinetics of organic substrates in the DES-aqueous biphasic systems. We also analyze the relationship between the variation of these interfacial features and the size and hydrophobicity of DES components.