The partitioning of compounds between
aqueous and other phases is important for predicting toxicity. Although
thousands of octanol–water partition coefficients have been
measured, these represent only a small fraction of the anthropogenic
compounds present in the environment. The octanol phase is often taken
to be a mimic of the inner parts of phospholipid membranes. However,
the core of such membranes is typically more hydrophobic than octanol,
and other partition coefficients with other compounds may give complementary
information. Although a number of (cheap) empirical methods exist
to compute octanol–water (log
k
OW
) and hexadecane–water (log
k
HW
) partition coefficients, it would be interesting to know whether
physics-based models can predict these crucial values more accurately.
Here, we have computed log
k
OW
and log
k
HW
for 133 compounds from seven different pollutant
categories as well as a control group using the solvation model based
on electronic density (SMD) protocol based on Hartree–Fock
(HF) or density functional theory (DFT) and the COSMO-RS method. For
comparison, XlogP3 (log
k
OW
) values were
retrieved from the PubChem database, and KowWin log
k
OW
values were determined as well. For 24 of these compounds,
log
k
OW
was computed using potential of
mean force (PMF) calculations based on classical molecular dynamics
simulations. A comparison of the accuracy of the methods shows that
COSMO-RS, KowWin, and XlogP3 all have a root-mean-square deviation
(rmsd) from the experimental data of ≈0.4 log units, whereas
the SMD protocol has an rmsd of 1.0 log units using HF and 0.9 using
DFT. PMF calculations yield the poorest accuracy (rmsd = 1.1 log units).
Thirty-six out of 133 calculations are for compounds without known
log
k
OW
, and for these, we provide what
we consider a robust prediction, in the sense that there are few outliers,
by averaging over the methods. The results supplied may be instrumental
when developing new methods in computational ecotoxicity. The log
k
HW
values are found to be strongly correlated
to log
k
OW
for most compounds.