Octanol/water distribution coefficients of the C1 through C7 perfluoro-n-alkyl sulfonates: Comparison of the IEFPCM-UFF, CPCM, and SMD solvation models

The octanol/water distribution coefficients (log Dow) of the C1 through C7 perfluoro-n-alkyl sulfonates (PFSAs) were calculated using the M062X/6311++G(d,p) and MP2/6-311++G(d,p)//M062X/6311++G(d,p) levels of theory and the IEFPCM-UFF, CPCM, and SMD solvation models. At both levels of theory with all solvation models, absolute log Dow calculated for the straight chain C1 through C7 PFSAs display a substantial negative bias against available experimental data and expected trends by several log units. However, the SMD solvation model achieves accurate relative log Dow accuracy, yielding fragmental contributions of a -CF2group towards the log Dow of 0.51±0.02 to 0.54±0.01 units (-3.0±0.1 to -3.1±0.1 kJ mol), in good agreement with the experimental value of 0.61 units (-3.4±0.1 kJ mol). In contrast, the IEFPCM-UFF and CPCM solvation models exhibit either invariant log Dow with increasing perfluoro-n-alkyl chain length (CPCM) or a modestly decreasing trend (IEFPCM-UFF).