Solubility and partitioning I: Solubility of nonelectrolytes in water.

On the basis of a semiempirical analysis, an equation was obtained that enables the estimation of the aqueous solubility of either liquid or crystalline organic nonelectrolytes: (see formula in text) where log PC and delta Sf are estimated from the chemical structure and MP is either known or experimentally determined. Analysis of this equation provides a means of assessing the role of crystal structure [as reflected by the melting point (MP) and the entropy of fusion (delta Sf)] and of the activity coefficient [as reflected by the octanol-water partition coefficient (PC)] in controlling the aqueous solubility of a drug. Techniques are also provided for estimating the entropy of fusion of organic compounds.