What Controls Partitioning of the Nucleic Acid Bases between Chloroform and Water?

The free energies of solvation for six nucleic acid bases in water and chloroform are predicted using the SM5.4/A quantum mechanical self-consistent-field solvation model. We obtain a mean unsigned deviation from experiment of 0.2 log10 units in the partition coefficients, lending extra credibility to the predicted solvation free energies. Predictions are then made for an additional six unnatural nucleic acid bases for which no experimental data are available. Functional group contributions to the solvent−solvent partitioning phenomenon are examined, and the validity of fragment-based partitioning models is assessed.