| Abstract
| - The partitioning to lipid-containing solids (cell membranes, natural organic matters) plays an important role in the fate of organic pollutants. We herein studied sorption of a series of aromatic compounds from aqueous solution to gel-phase egg phospholipids. The regression line describing the free-energy relationship between lipid−water distribution coefficient (Kd) and n-octanol-water partition coefficient (KOW) for the high-polar compounds (phenolics, dinitrobenzene, trinitrobenzene) is displaced upward relative to the low-polar compounds (chlorobenzenes, polycyclic aromatic hydrocarbons (PAHs), nitrobenzene, dichlorobenzonitrile), suggesting additive polar extra-interactions besides hydrophobic effects in sorption. Binding of Cu2+ or decreasing pH increases sorption of the three and four-ring PAHs but not the rest compounds. These results led us to propose a specific sorption mechanism, cation-π bonding between PAHs and complexed metal ions or protonated amine groups of phospholipids. The Cu2+-PAH complexation in solution was supported by the observation that PAHs enhance the saturated solubility of CuSO4 in chloroform, and the enhancement correlates with π-donor strength of PAH (pyrene > phenanthrene > naphthalene). The electron coupling between the protonated amine groups of phospholipids and PAHs in chloroform was verified by the electronic deshielding-induced downfield chemical shifts of phenanthrene at low pH in the 1H NMR spectrum.
- Cobinding of copper ion or proton facilitates the partitioning of PAHs to egg phospholipids via cation-π bonding between PAH and the complexed copper ion or protonated amine group of phospholipids.
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