Structural changes in lecithin-water systems thermal-turbidimetric studies

Turbidity measurements were made of dilute aqueous dispersions of 1,2-dipalmitoyl-l-lecithin as the temperature was varied. In the range from 24 to 33° a decrease in turbidity is associated with the penetration of water between the layers of lipid in the crystalline structure. At the transition to the liquid crystalline form (39–41°) a sharp decrease in turbidity occurs. In solutions of 0.06 M LiCl, 1 mM CaCl₂, MgCl₂ or 0.05 M PO₄³ an increase in turbidity resulted at the transition temperature, whereas in 0.1 M NaCl, or quarternary ammonium salts the turbidity decreased. The presence of small amounts of dicetylphosphoric acid mixed with the lecithin decreased the turbidity, and at elevated pH levels there was no change at the transition temperature.