Free energy of solvation of solutes and their partition coefficients in methanol-water binary mixtures

A method is presented that permits semiquantitative estimation of the partitioning of any solute between any two media. The method is adapted to the simulation of multicomponent solvents. As an example, the free energies of solvation ΔGsolv,aqo in methanol-water binary mixtures and the partition coefficientsP for organic solvent—aqueous solvent were calculated. The organic solvents studied were 1-octanol, cyclohexane and chloroform. Linear relationships were observed between the relative dielectric constant and the volume fraction of methanol in mixtures with water. The four hydrocarbon models studied were hexane, cyclohexane, hexatriene and benzene. The results are in agreement with calculations carried out by the method of Leo et al. For hexane and cyclohexane, ΔGsolv,aqo and the three logP decrease with the volume fraction of methanol. However, hexatriene and benzene show the opposite trend. Parabolic or linear relationships are fitted for the volume fraction of methanol with ΔGsolv,aqo and the three logP.