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A comparative assessment of octanol-water partitioning and distribution constant estimation methods for perfluoroalkyl carboxylates and sulfonates

Sierra Rayne¹ and Kaya Forest²

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1. Ecologica Research, Penticton, British Columbia, Canada
2. Okanagan College, Penticton, British Columbia, Canada

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Document Type:

Manuscript

Date:

Received 29 May 2009 05:45 UTC; Posted 01 June 2009

Subjects:

Chemistry, Earth & Environment

Tags:

• Perfluorinated acids
• perfluoroalkyl carboxylates
• perfluoroalkyl sulfonates
• octanol-water partioning constant
• log P
• octanol-water distribution constant
• log D
• in silico estimation methods
• Gibbs free energies
• lipophilicity

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 -CF₂- 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_hydrophobicG_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_hydrophobicG_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_hydrophobicG_ow contributions towards proteinophilic partitioning under biologically relevant conditions.

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This document is licensed to the public under the Creative Commons Attribution 3.0 License

How to cite this document:

Rayne, Sierra and Forest, Kaya. A comparative assessment of octanol-water partitioning and distribution constant estimation methods for perfluoroalkyl carboxylates and sulfonates. Available from Nature Precedings <http://dx.doi.org/10.1038/npre.2009.3282.2> (2009)

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Other versions of this document in Nature Precedings

Version number	Document title	Date
v1	Posted 26 May 2009

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