A new class of perfluorinated acid contaminants: Primary and secondary substituted perfluoroalkyl sulfonamides are acidic at environmentally and toxicologically relevant pH values

Abstract

The SPARC software program was validated for nitrogen-hydrogen acidity constant estimation of primary and secondary sulfonamides against a broad suite of substituted derivatives with experimental datasets in water and dimethylsulfoxide solvent systems and across a wide pK_a range. Following validation, amidic proton pK_a values were estimated for all C₁ through C₈ congeners of five major perfluoroalkyl sulfonamide classes: unsubstituted sulfonamides, N-methyl and N-ethyl sulfonamides, sulfonamidoethanols, and sulfonamidoacetates. Branching of the perfluoroalkyl chain is expected to have substantial impacts on amide moiety acidity in these contaminant groups, with intrahomologue variability of up to four pK_a units and increasing pK_a values with both increasing chain branching and greater proximity of the chain branching to the sulfonamide head group. Perfluoroalkyl chain length is not predicted to have a substantial influence on sulfonamide acidity. The predicted pK_a values and variability are anticipated to have substantial impacts on the environmental partitioning and degradation of these compounds, as well as the modes and magnitudes of toxicological effects. Substantial pH dependent isomeric fractionation of perfluoroalkyl sulfonamides is expected both in situ and in vivo, necessitating the incorporation of amide group acidities in multimedia environmental models and pharmacokinetic studies.

Keywords:

• Perfluoroalkyl sulfonamides
• amide acidity
• pK_a values
• environmental fate
• toxicology

Acknowledgments

S.R. thanks the Natural Sciences and Engineering Research Council (NSERC) of Canada for partial financial support of this work at the University of Winnipeg.