The hydrophobic fragmental constant approach for calculating log P in octanol/water and aliphatic hydrocarbon/water systems

Lipophilicity is a prime physicochemical parameter in describing both pharmacodynamic and pharmacokinetic aspects of drug action. Its quantitative descriptor (log P) is measured in or calculated for different model solvent systems depending on the respective scientific interest. The first part of this article focuses on the hydrophobic fragmental constant approach (Sigma f system) for octanol/water partitioning. The original approach and its revisions are presented, followed by recipes for the practical procedure of Sigma f calculations and a detailed description of how to apply the correction factor C-M. A Sigma f system for application in the study of aliphatic hydrocarbon/water (ahc/w) partitioning is described in the second part of the article. The current version is based on an optimized coupling of the ahc/w system with f constants for octanol/water partitioning. A total of 70 f(ahc) values are now available.