title: The partitioning of PAHs to egg phospholipids facilitated by copper and proton binding via cation-pi interactions.
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 (K(OW)) 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-pi bonding between PAHs and complexed metal ions or protonated amine groups of phospholipids. The Cu(2+)-PAH complexation in solution was supported by the observation that PAHs enhance the saturated solubility of CuSO4 in chloroform, and the enhancement correlates with pi-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.
authors.affiliation: State Key Laboratory of Pollution Control and Resource Reuse, and School of the Environment, Nanjing University, Jiangsu 210093, PR China.
authors.forename: Xiaolei
authors.initials: X
authors.lastname: Qu
authors.forename: Xiaorong
authors.initials: X
authors.lastname: Wang
authors.forename: Dongqiang
authors.initials: D
authors.lastname: Zhu
mesh_terms: D002412:Cations; D003300:Copper / Q000737:chemistry*; D004531:Eggs / Q000032:analysis*; D006863:Hydrogen-Ion Concentration; D009682:Magnetic Resonance Spectroscopy; D010743:Phospholipids / Q000737:chemistry*; D011083:Polycyclic Compounds / Q000302:isolation & purification*; D011522:Protons; D012995:Solubility
chemical_list: D002412:Cations; D010743:Phospholipids; D011083:Polycyclic Compounds; D011522:Protons; D003300:Copper