Congener-specific numbering systems for the environmentally relevant C4 through C8 perfluorinated homologue groups of alkyl sulfonates, carboxylates, telomer alcohols, olefins, and acids, and their derivatives.
ABSTRACT We introduce a congener-specific numbering system for the C4 through C8 perfluorinated homologue groups of alkyl sulfonates, carboxylates, telomer alcohols, olefins, and acids, and their derivatives. Increasing length of the carbon chain beyond C3 leads to a corresponding rapid increase in the number of potential isomers (C4 = 4, C5 = 8, C6 = 17, C7 = 39, and C8 = 89 congeners). There is a need for clear and unambiguous chemical shorthand to ensure accuracy and consistency in the future perfluorinated alkyl substance (PFA) literature, and to correct previous misconceptions that may have restricted research efforts into developing full-congener PFA analysis. If adopted by the research community, introduction of a numbering system at this relatively early stage of investigations into the congener-specific analysis, environmental behavior, and toxicology of PFAs would not require an arduous and difficult reassignment of historical structures and naming conventions presented in the prior art. Many PFA congeners are chiral, necessitating a consideration of their enantiospecific environmental behavior and toxicology.
SourceAvailable from: M. Merced Montero-Campillo[Show abstract] [Hide abstract]
ABSTRACT: The thermodynamic stability in the gas phase, water and octanol of the neutral and anionic forms of the 89 PFOS isomers is studied at the M06-2X/6-311++G(d,p) level of theory using the SMD solvation model. The structure–stability relationship is explored and compared to previous B3LYP calculations. This study aims to improve the thermodynamic data for these compounds using a functional that is expected to overcome known deficiencies of the B3LYP functional when considering medium-range electron correlation effects. The M06-2X results place emphasis on the substitution patterns at the head and tail ends of the molecule as a factor in stability, while substitution patterns on the middle carbons tend to decrease stability. Analysis of the electron density revealed a subtle balance between weak interactions in these perfluorinated compounds. M06-2X ranks highly-substituted isomers as more stable than B3LYP did, and ranks linear isomers quite low in relative stability compared to B3LYP. It has been shown that the difference in stability for these compounds is mostly enthalpic, with small entropy changes between the two functionals for most compounds.Computational and Theoretical Chemistry 10/2014; 1046:81–92. DOI:10.1016/j.comptc.2014.08.003 · 1.37 Impact Factor
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ABSTRACT: Human perfluorooctanesulfonate (PFOS) body burdens are attributable to both direct PFOS and indirect PFOS precursor (PreFOS) exposure. The relative importance of these two pathways has been estimated, but the relative temporal trajectory of exposure to PFOS and PreFOS has not been examined. Here, two hypothesized biomarkers of PreFOS exposure, PFOS isomer profiles (quantified as percent branched PFOS, %br-PFOS) and chiral 1m-PFOS enantiomer fractions (1m-PFOS EF) were analyzed in archived human serum samples of individual American adults (1974-2010) and pooled samples of Swedish primiparous women (1996-2010). After correcting for potential confounders, significant correlations between %br-PFOS and 1m-PFOS EFs were observed in American samples and in Swedish samples for the 1996-2000 period, supporting the hypothesis that both %br-PFOS and 1m-PFOS EF are biomarkers of PreFOS exposure. Significant trends of increasing %br-PFOS, from 2000 to 2010, and increasingly non-racemic 1m-PFOS EFs, from 1996 to 2000, were detected in Swedish samples. No statistically significant trend for %br-PFOS or 1m-PFOS EF was observed in American samples, but American males had significantly higher %br-PFOS and significantly lower 1m-PFOS EF (i.e. more non-racemic) than females, and a similar significant difference was shown in the older age group, relative to the younger age group. These temporal trends in %br-PFOS and 1m-PFOS EF are not easily explained and the results highlight uncertainties about how humans are exposed to PFOS. Copyright © 2014 Elsevier Ltd. All rights reserved.Environment International 12/2014; DOI:10.1016/j.envint.2014.11.014 · 5.66 Impact Factor