Characterization of lipophilicity scales using vectors from solvation energy descriptors

Lipophilicity scales were characterized by an approach using vectors provid ed from solvation energy descriptors (SED) of solutes such as an excess mol ar refraction, the dipolarity/polarizability, the hydrogen-bond acidity, th e basicity, and the McGowan characteristic volume. The five components of t he SED vector were obtained from the coefficients of the five SED terms of the linear solvation energy relationship (LSER) equation for the lipophilic ity scales. The analogy between two lipophilicity scales was expressed as t he angle between the two SED vectors, while the difference in the contribut ion of the five independent SEDs to these two lipophilicity scales was quan tified by the difference of the unit vectors of the SED vectors. These appr oaches were applied to several lipophilicity scales measured using microemu lsions, micelles, an immobilized artificial membrane column, and an octanol -water system. As a result, the quantitative classification of these scales was successfully carried but, and the difference in the scales was well ch aracterized. In addition, this vector approach was extended to the estimati on of the contribution of each constituent of the microemulsions to the lip ophilicity scale. Furthermore, some biological parameters such as skin perm eability and the distribution between blood and brain could be predicted by the summation of the SED vectors obtained from the chromatographic systems . These results suggest that complex biological systems can be expressed qu antitatively by simple chemical models with their SED vectors.