title: Estimated pKa values for the environmentally relevant C1 through C8 perfluorinated sulfonic acid isomers.
abstract: In order to estimate isomer-specific acidity constants (pKa) for the perfluorinated sulfonic acid (PFSA) environmental contaminants, the parameterization method 6 (PM6) pKa prediction method was extensively validated against a wide range of carbon oxyacids and related sulfonic/sulfinic acids. Excellent pKa prediction performance was observed for the carbon oxyacids using the PM6 method, but this approach was found to have a severe positive bias for sulfonic/sulfinic acids. To overcome this obstacle, a correlation was developed between non-adjusted PM6 pKa values and the corresponding experimentally obtained/estimated acidity constants for a range of representative alkyl, aryl and halogen-substituted sulfonic acids. Application of this correction to the PM6 values allows for extension of this computational method to a new acid functional group. When used to estimate isomer-specific pKa values for the C1 through C8 PFSAs, the modified PM6 approach suggests an adjusted pKa range from -5.3 to -9.0, indicating that all members of this class of well-known environmental contaminants will be effectively completely dissociated in aquatic systems.
authors.affiliation: a Chemologica Research , Moose Jaw , Saskatchewan , Canada.
authors.forename: Sierra
authors.initials: S
authors.lastname: Rayne
authors.affiliation: b Department of Environmental Engineering Technology , Saskatchewan Polytechnic , Moose Jaw , Saskatchewan , Canada.
authors.forename: Kaya
authors.initials: K
authors.lastname: Forest
mesh_terms: D004784:Environmental Monitoring / Q000379:methods*; D004785:Environmental Pollutants / Q000032:analysis* / Q000737:chemistry*; D005466:Fluorocarbons / Q000032:analysis* / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D007536:Isomerism; D013451:Sulfonic Acids / Q000032:analysis* / Q000737:chemistry*
chemical_list: D004785:Environmental Pollutants; D005466:Fluorocarbons; D013451:Sulfonic Acids
keywords: Acidity constant; environmental fate; pKa; perfluorinated sulfonic acids