The log P algorithm
The calculation of the octanol-water partition coefficient (log P) is based on the XLOGP3-AA method [Cheng et al., 2007b].
XLOGP3-AA is an atom-additive method that calculates log P by adding up contributions from each atom in the given molecule. Each atom is categorized into one of the 83 basic atom types or the four terminal groups suggested by Cheng et al. The terminal groups are included to take the effects of the common cyano-, diazo-, nitro-, and nitro oxide-groups into account. In addition, two correction factors are included to account for intermolecular interactions: 1) internal hydrogen bonding, which can give rise to an increase in the hydrophobicity of a molecule, and 2) molecules containing an amino acid moiety to compensate for overestimation of log P in these cases.
The contribution of each atom type, terminal group, and correction factor has been found by multivariate regression analysis of molecules with known experimental log P values (see [Cheng et al., 2007b] for details).
Note! The XLOGP3-AA atom typing and assignment of terminal groups / correction factors depends on the chemical preparation of the molecule. In particular, aromaticity plays a big role in the assignments, and incorrect preparation can lead to deviations in the log P estimates.