Comment on "Using COSMOtherm to Predict Physicochemical Properties of Poly- and Perfluorinated Alkyl Substances (PFASs)"

Authors: Sierra Rayne

In their study, Wang et al. [Environ. Chem. 2011, 8, 389] use the COSMOtherm software program in an attempt to shed some insights into the physicochemical properties of various poly- and perfluorinated compounds. During the conformation dependent pKa investigations on n-perfluorooctanoic acid (PFOA), the authors appear to make a critical error in their analyses. Wang et al. appear to have allowed a transition from an acid form geometry to a very different anionic form geometry, which is not a correct way of calculating free energy changes during acid dissociation. This error explains why these authors obtained widely ranging conformation dependent pKa values (0.9 to 2.9) for PFOA dissociation. As has been previously shown [Rayne and Forest, J. Mol. Struc. THEOCHEM 2010, 949, 60], there are negligible conformation dependent effects on the pKa value of PFOA.

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[v1] 2013-05-23 07:04:36

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