Effect of nonpolar solute on the local structure of aqueous solution: Orientation-dependent integral equation study of nonpolar solute in rose water model

The presence of solute in water, even in small quantities, changes the properties of water. The ability of water molecules to form hydrogen-bonds is decisive for the structural and thermodynamic properties. When the solute is added to water, the network of hydrogen bonds is disrupted, changing the structure and properties of the water. In this work, we have used a simple two-dimensional rose water model together with orientation-dependent integral equation theory (ODIET) to gain insight into the effects of nonpolar solutes on the local structure of aqueous solutions. The theory shows good agreement with the radial distribution functions and enthalpies of solvation obtained with simulations, while improving the results of the orientation-averaged version of the theory. The advantage of the two-dimensional water model together with ODIET is that angle-dependent properties can be calculated relatively quickly and easily visualised. Using the potential of the mean force derivatives, the effect of added nonpolar solute on the local structure of the solution was investigated. Depending on the size of the solute, two different regimes of the effect of the solute on the structure of the solution were identified. Small solutes increase the tendency of water to form hydrogen-bonds and at the same time decrease solvation and association of the solute. On the other hand, large solutes have the opposite effect - they decrease the HB tendency of water and increase solvation and association of the solute. • Solvation of non-polar solute in rose model was studied by integral equation theory. • Two different regimes of the effect of the solute on the structure of the solution were identified. • The theory shows good agreement with the radial distribution functions and enthalpies of solvation obtained with simulations.