Octanol/water distribution coefficients of the C~1~ through C~7~ perfluoro-n-alkyl sulfonates: Comparison of the IEFPCM-UFF, CPCM, and SMD solvation models

Sierra Rayne,Kaya Forest

doi:10.1038/npre.2010.5103.1

Abstract

AbstractThe octanol/water distribution coefficients (log D~ow~) of the C~1~ through C~7~ perfluoro-n-alkyl sulfonates (PFSAs) were calculated using the M062X/6-311++G(d,p) and MP2/6-311++G(d,p)//M062X/6-311++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 D~ow~ calculated for the straight chain C~1~ through C~7~ 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 D~ow~ accuracy, yielding fragmental contributions of a -CF~2~- group towards the log D~ow~ 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 D~ow~ with increasing perfluoro-n-alkyl chain length (CPCM) or a modestly decreasing trend (IEFPCM-UFF).

Highlights

Perfluoroalkyl sulfonic acids (PFSAs; Figure 1) are widely used industrial materials that have become an important class of environmental contaminants [1]
Single point calculations were performed at the SMD-MP2/6311++G(d,p)//M062X/6-311++G(d,p) level of theory, yielding theoretical log Dow estimates based on the corresponding single point energies
At both levels of theory with all solvation models, absolute log Dow calculated for the straight chain C1 through C7 perfluoro-n-alkyl sulfonates (PFSAs) display a substantial negative bias by several log units

Summary

Introduction

Perfluoroalkyl sulfonic acids (PFSAs; Figure 1) are widely used industrial materials that have become an important class of environmental contaminants [1]. Solution phase standard state (298.15 K, 1 mol L−1) density functional theory calculations in n-octanol and water model solvents were conducted using the M062X/6311++G(d,p) [8] [9] [10] method in Gaussian 09 [11] on the C1 (trifluoromethyl sulfonate) through C7 (perfluoro-n-heptane sulfonate) straight chain PFSA anions with the IEFPCM-UFF [12], CPCM [13] [14], and SMD [15] solvation models.

Results

Conclusion