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

Sierra Rayne,Kaya Forest

doi:10.1038/npre.2009.3282.1

Sierra Rayne, Kaya Forest

Open Access

https://doi.org/10.1038/npre.2009.3282.1

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Journal: Nature Precedings	Publication Date: May 26, 2009
Citations: 3	License type: CC BY 3.0

Affiliation: Penticton Regional Hospital, Okanagan College

Abstract

AbstractNew 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, regardless of head group identity. In contrast, there are potentially different Δ~electrostatic~G~ow~ and Δ~hydrophobic~G~ow~ contributions towards proteinophilic partitioning.

Highlights

Perfluoroalkyl carboxylic acids (PFCAs) and sulfonic acids (PFSAs) (Figure 1) are globally distributed halogenated aliphatic contaminants with ionic head groups that behave as surface active compounds in environmental and biological systems.[1,2,3,4,5,6,7,8,9,10,11]
PFCA and perfluorinated alkylsulfonic acid (PFSA) octanol-water partitioning and distribution constants were calculated with the SPARC [31] and ALOGPS 2.1 [32,33,34,35,36,37] software programs using the SMILES molecular formula language [38, 39] as inputs
The ADME/Tox WEB and CLogD log D programs generally underpredict the log D values at the experimentally determined pH range of 6 to 7 [30] by up to 4 units, with average prediction errors within a program ranging from -0.7 to -3.3 units

Summary

Introduction

Perfluoroalkyl carboxylic acids (PFCAs) and sulfonic acids (PFSAs) (Figure 1) are globally distributed halogenated aliphatic contaminants with ionic head groups that behave as surface active compounds in environmental and biological systems.[1,2,3,4,5,6,7,8,9,10,11] Because of their propensity to accumulate in abiotic and biotic matrices and resulting concerns over in vivo toxicity, their persistence towards a number of possible natural and engineered degradation processes, and their ability to achieve widespread environmental ubiquity, there is much current interest in the partitioning behavior of PFCAs and PFSAs.[11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29] Recently, the first experimental octanol-water distribution constants (log D) have been reported [30] for several representative straight chain PFCA and PFSA congeners (Figure 2).

Results

Conclusion