Determination of partition and binding properties of solutes to stratum corneum

The binding property of a number of relatively hydrophilic solutes to native and delipidized stratum corneum (SC) and their partition coefficients to extracted lipid have been measured by equilibration experiments to expand the current database which consisted of mostly hydrophobic solutes. Using the extended database, quantitative structure property relationships (QSPR) have been proposed for predicting the partition and binding coefficients of both hydrophobic and hydrophilic solutes to the SC protein, and lipid. Solute partition to the SC lipid is best fitted by PClip/w=Kow0.69 and solute binding to the SC protein is best described by PCpro/w=4.2Kow0.31. The two QSPR models of solute partition to the SC lipid and binding to the SC protein have been further combined into a two-phase model to predict the overall partition coefficient of solutes to the stratum corneum (Ksc/w). Our study not only extends the database of solute partition and binding properties of the SC to include hydrophilic solutes, but also demonstrates that the thermodynamic equilibrium properties of the SC partition and binding can be fitted with good accuracy by combining QSPR models with the multiphase and heterogeneous structures of the SC.