RP-HPLC measurement and quantitative structure–property relationship analysis of the n-octanol–water partitioning coefficients of selected metabolites of polybrominated diphenyl ethers

Yijun Yu; Weihua Yang; Zishen Gao; Michael H. W. Lam; Xiaohua Liu; Liansheng Wang; Hongxia Yu

doi:10.1071/EN08036

RESEARCH ARTICLE

RP-HPLC measurement and quantitative structure–property relationship analysis of the n-octanol–water partitioning coefficients of selected metabolites of polybrominated diphenyl ethers

Yijun Yu ^A , Weihua Yang ^A , Zishen Gao ^A , Michael H. W. Lam ^B ^C , Xiaohua Liu ^A , Liansheng Wang ^A and Hongxia Yu ^A ^C

+ Author Affiliations

- Author Affiliations

^A State Key Laboratory of Pollution Control and Resource Reuse, School of the Environment, Nanjing University, Nanjing 210093, China.

^B Department of Biology and Chemistry, City University of Hong Kong, Hong Kong SAR, China.

^C Corresponding authors. Email: bhmhwlam@cityu.edu.hk; yuhx@nju.edu.cn

Environmental Chemistry 5(5) 332-339 https://doi.org/10.1071/EN08036
Submitted: 27 June 2008 Accepted: 28 August 2008 Published: 31 October 2008

Environmental context. Polybrominated diphenyl ethers (PBDEs) are ubiquitous environmental contaminants and numerous studies have demonstrated a marked increase in the levels of PBDEs in human biological tissues and fluids, especially breast milk. How PBDEs are transported through the environment, taken up by biota, transported across membranes, and metabolised depends strongly on such fundamental properties as lipophilicity (log K_OW). However, very little data on log K_OW exist for PBDEs. In the present paper, the authors determine PBDE metabolites’ log K_OW using reversed-phase high performance liquid chromatography, as recommended by the Organisation for Economic Co-operation and Development and US Environmental Protection Agency, along with quantitative structure–property relationships.

Abstract. n-Octanol–water partitioning coefficient (log K_OW) values of selected hydroxylated and methoxylated polybrominated diphenyl ether metabolites were measured for the first time by reversed-phase high performance liquid chromatography (RP-HPLC) using a C18 stationary phase with a water/methanol mixture as a mobile phase. The retention parameters, log k_w (extrapolated retention indices) and k′ (gradient retention indices) were calibrated to log K_OW by a set of calibration standards. For the PBDE metabolites investigated, extrapolated retention indices from isocratic elution seem to be more reliable and their RP-HPLC-derived log K_OW values were found to range from 4.63 to 7.67. Some commonly available software, including ClogP, KowWin, AclogP, MlogP, AlogP, MilogP, and XlogP, was used to estimate the log K_OW values of the analytes. Significant correlations were obtained between the RP-HPLC-derived log K_OW and the software-computed log K_OW, with squared correlation coefficients (R²) ranging from 0.793 to 0.922, but the difference between them was also significant. Then a quantitative structure–property relationship model based on topological descriptors was established and showed good reliability and predictive power for the estimation of RP-HPLC-derived log K_OW values of PBDE metabolites. It was applied to estimate the log K_OW values of some PBDE metabolites that are commercially available or have appeared in the literature. Lastly, factor analysis was carried out using the theoretical linear salvation/free-energy relationships, which indicated the average polarisability (α) and the most negative atomic partial Mulliken charge in the molecule (q^–) were the most important parameters affecting their partition between n-octanol and water, supporting the factorisation of log K_OW in bulk and electronic terms.

Additional keywords: extrapolated capacity factors, gradient elution, Kier’s shape index, log K_OW, molecular connectivity indices.

Acknowledgements

The present work was jointly funded by the National Natural Science Foundation of China and the Research Grants Council of the Hong Kong Special Administrative Region, China (grant 20518002/N_CityU110/05), and the National Natural Science Foundation of China (grants 20577020 and 20737001).

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