title: Effects of Alkali Cations and Halide Anions on the Self-Assembly of Phosphatidylcholine in Oils.
abstract: The interactions between ions and phospholipids are closely associated with the structures and functions of cell membrane. Instead of conventional aqueous systems, we systematically investigated the effects of inorganic ions on the self-assembly of lecithin, a zwitterionic phosphatidylcholine, in cyclohexane. Previous studies have shown that addition of inorganic salts with specific divalent and trivalent cations can transform lecithin organosols into organogels. In this study, we focused on the effect of monovalent alkali halides. Fourier transform infrared spectroscopy was used to demonstrate that the binding strength of the alkali cations with the phosphate of lecithin is in the order Li+> Na+> K+. More importantly, the cation-phosphate interaction is affected by the paired halide anions, and the effect follows the series I-> Br-> Cl-. The salts of stronger interactions with lecithin, including LiCl, LiBr, LiI, and NaI, were found to induce cylindrical micelles sufficiently long to form organogels, while others remain organosols. A mechanism based on the charge density of ions and the enthalpy change of the ion exchange between alkali halides and lecithin headgroup is provided to explain the contrasting interactions and the effectiveness of the salts to induce organogelation.
authors: Institute of Polymer Science and Engineering, National Taiwan University , Taipei 10617, Taiwan.
authors: Shih-Ting
authors: ST
authors: Lin
authors: Institute of Polymer Science and Engineering, National Taiwan University , Taipei 10617, Taiwan.
authors: Chen-Shin
authors: CS
authors: Lin
authors: Institute of Polymer Science and Engineering, National Taiwan University , Taipei 10617, Taiwan.
authors: Ya-Ying
authors: YY
authors: Chang
authors: Australian Nuclear Science and Technology Organisation, Lucas Heights, NSW 2234, Australia.
authors: Andrew E
authors: AE
authors: Whitten
authors: Australian Nuclear Science and Technology Organisation, Lucas Heights, NSW 2234, Australia.
authors: Anna
authors: A
authors: Sokolova
authors: Australian Nuclear Science and Technology Organisation, Lucas Heights, NSW 2234, Australia.|National Synchrotron Radiation Research Center, Hsinchu 30076, Taiwan.
authors: Chun-Ming
authors: CM
authors: Wu
authors: Faculty of Physics, Moscow State University , Moscow 119991, Russia.
authors: Viktor A
authors: VA
authors: Ivanov
authors: Faculty of Physics, Moscow State University , Moscow 119991, Russia.
authors: Alexei R
authors: AR
authors: Khokhlov
authors: Institute of Polymer Science and Engineering, National Taiwan University , Taipei 10617, Taiwan.
authors: Shih-Huang
authors: SH
authors: Tung