Lecithin Organogels Induced By Simple Inorganic Salts
July 21-24, 2019
The interactions between ions and phospholipids are closely associated with the structures and functions of cell membrane. Instead of conventional aqueous systems, we investigated the effects of inorganic ions on the self-assembly of lecithin, a zwitterionic phosphatidylcholine, in low polar organic solvents (oils) such as cyclohexane. Salts are insoluble in low polar organic solvents, and hence their effects on reverse self-assembly have rarely been studied. Our previous studies show, however, that salts can indeed be dissolved in organic liquids in the presence of lecithin. More interestingly, salts of multivalent cations like calcium (Ca2+), magnesium (Mg2+), lanthanum (La3+), and cerium (Ce3+) greatly increase the viscosity of lecithin organosols and transform the samples into optically transparent organogels. On the basis of data from small-angle neutron scattering (SANS), the gelation is accompanied by a nanostructural transition from spherical micelles to cylindrical micelles. In addition to the multivalent cations, we recently investigated the effect of alkali halides and found that the alkali halides show different abilities to induce organogels even though they are all monovalent. 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 mediated by the paired halide anions and the effect follows the order I- > Br- > Cl-. The alkali cations of stronger interactions with lecithin, including LiCl, LiBr, LiI and NaI, were found to induce cylindrical micelles sufficiently long to form organogels, similar to the effects of the salts of multivalent cations, while others remain organosols. The varying abilities of different salts to induce gelation is shown to correlate with their binding tendencies to the phosphocholine headgroups of lecithin. The two-component gelators such as lecithin/Ca2+ could be attractive for applications due to its negligible cost and nontoxic nature.
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Shih–Huang Tung, "Lecithin Organogels Induced By Simple Inorganic Salts" in "Colloidal, Macromolecular and Biological Gels II", Samiul Amin, Manhattan College, USA Saad Khan, North Carolina State University, USA Srini Raghavan, University of Maryland College Park, USA Eds, ECI Symposium Series, (2019). https://dc.engconfintl.org/cmb_gels_ii/30