Congener-specific numbering systems for the environmentally relevant C 4 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: Amila O. De silva
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- "The structures of these isomers are n, iso, 5m, 4m, 3m, 2m, 1m, tb, 4,4m 2 , 5,3m 2 , and 5,4m 2 . While less effort has gone into the characterization of ECF PFOA, out of 39 possible PFOA isomers (Rayne et al. 2008b) it appears that n-, iso-, 5m-, 4m-, and 3m-PFOA make up 99.2% in 3M ECF standards with minor contributions (<0.8%) from 2m, tb, 4,4m 2 , 5,3m 2 , and 5,4m 2 (Loveless et al. 2006; Table 2). While other isomers are theoretically possible, these are unlikely to be present at measurable concentrations in the environment since they are virtually undetectable in the commercially manufactured material. "
ABSTRACT: The ubiquitous detection of perfluorinated acids (PFAs) and their precursors (PFA precursors) in the global environment has led to concern over their effects in humans and wildlife. This is exacerbated by evidence of developmental toxicity (Lau et al. 2007; Apelberg et al. 2007; Fei et al. 2008), along with persistence, chain length-dependent bioaccumulation potential (Houde et al. 2006), and long-range transport potential (Wallington et al. 2006; Wania 2007; Armitage et al. 2006, 2009a, b). In the over half-century of global perfluorochemical manufacturing, the two most commonly used synthetic methods have produced products with very different isomeric purities. Despite the fact that both branched and linear PFA and PFA-precursor isomers exist in the environment, quantitative analysis of these chemicals is, for the most part, still conducted by eluting all isomers together and integrating them as a single peak. This practice has continued despite the fact that emerging literature suggests that more accurate and informative data can be generated by isomer-specific analysis.Reviews of environmental contamination and toxicology 01/2010; 208:111-60. DOI:10.1007/978-1-4419-6880-7_2 · 3.63 Impact Factor
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- "Of the 161 possible C 1 through C 8 congeners within each PFA class, only 8 have linear perfluoroalkyl chains.  As we have demonstrated in prior work, various computational approaches yield differing predictions regarding charge magnitudes and distributions on the PFA head groups within a particular class,    resulting in a current degree of ambiguity as to the role of branching on PFA head group charge distributions. Further progress in this area will require a continuing evaluation as authentic branched PFA standards become available for experimental evaluation and calibration of existing computational studies, and well as the possible extension and refinement of current computational methods to these compound classes. "
ABSTRACT: Organic carbon-normalized soil and sediment-water partitioning coefficients (K(oc)) were estimated for all C(1) through C(8) perfluoroalkyl carboxylic (PFCA) and sulfonic (PFSA) acid congeners. The limited experimental K(oc) data set for the straight chain C(7) through C(10) PFCAs and C(8) and C(10) PFSAs was correlated to SPARC and ALOGPS computationally estimated octanol-water partitioning/distribution constants and used to predict K(oc) values for both branched and linear C(1) through C(8) isomers. Branched and linear congeners in this homologue range are generally expected to have K(oc) values > 1, leading to their accumulation in organic matter on sediments and soils, retardation during ground and pore water flow, and the preferential association with dissolved organic matter in aquatic systems. Both increasing perfluoroalkyl chain length and linearity increase K(oc) values with substantial intra- and inter-homologue variation and interhomologue mixing. Variability in K(oc) values among the PFCA and PFSA congeners will likely lead to an enrichment of more linear and longer-chain isomers in organic matter fractions, resulting in aqueous phases fractionated towards shorter-chain branched congeners. The expected magnitude of fractionation will require inclusion in source apportionment models and risk assessments. A comparison of representative established quantitative structure property relationships for estimating K(oc) values from octanol-water partitioning constants suggests that these equilibrium partitioning frameworks may be applicable towards modeling PFCA and PFSA environmental fate processes.Journal of Environmental Science and Health Part A Toxic/Hazardous Substances & Environmental Engineering 11/2009; 44(13):1374-87. DOI:10.1080/10934520903217229 · 1.14 Impact Factor
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- "      software programs using the SMILES molecular formula language   as inputs. References to PFCA and PFSA isomer patterns and congener identifications follow the framework outlined in ref.  . Experimental log D values for the PFCA and PFSA congeners under consideration (Figure 2) were obtained from ref.  . "
ABSTRACT: New experimental data is available in the literature regarding the octanol-water distribution behavior of representative straight chain perfluoroalkyl carboxylate (PFCA) and sulfonate (PFSA) congeners. The current study provides the first investigation into the predictive ability of various software programs for estimating the corresponding octanol-water partitioning (log P) and distribution (log D) constants of PFCAs and PFSAs. Wide predictive variation was found within and between the various methods. Several programs were able to accurately estimate the log P/D fragmental contributions of a -CF~2~- group for PFCAs, as well as the associated Gibbs free energies for partitioning into octanol from water due to the hydrophobic character of the perfluoroalkyl chain (Δ~hydrophobic~G~ow~). Only the SPARC log D method accurately predicted the electrostatic contributions of the carboxylate head group (Δ~electrostatic~G~ow~) towards octanol-water partitioning for PFCAs. Similar log D values and organic carbon normalized sediment-water partitioning coefficients (K~oc~) for PFCAs and PFSAs having equivalent perfluoroalkyl chain lengths suggests potentially equivalent Δ~electrostatic~G~ow~ and Δ~hydrophobic~G~ow~ contributions towards lipophilic partitioning for these two contaminant classes at near neutral pH values, regardless of head group identity. In contrast, there are potentially different Δ~electrostatic~G~ow~ and Δ~hydrophobic~G~ow~ contributions towards proteinophilic partitioning under biologically relevant conditions.Nature Precedings 06/2009; DOI:10.1038/npre.2009.3282.2