Effect of calcium ions on the density of lecithin and its effective molecular volume in lecithin–water dispersions

As the packing structure of lipid molecules in the liposomes will vary in the presence of ions, it is expected that the density of lipid and the effective volume of lipid molecules in the dispersions will also vary, albeit minutely. Density measurements of lipid–water dispersions with the addition of Ca2+ ions were determined accurately. The effect of Ca2+ ions on the molecular packing structure of the liposomes was elucidated from the results obtained. The results for the density of the lecithin in the dispersions with and without the addition of Ca2+ ions are, respectively, 1.0782 and 1.0579 g cm−3 at 25 °C; and 1.0048 and 0.9961 g cm−3 at 50 °C. The average values of the effective molecular volume of lecithin in the dispersions with and without the addition of Ca2+ ions are, respectively, 1.131E−21 and 1.152E−21 cm3 at 25 °C; and 1.213E−21 and 1.224E−21 cm3 at 50 °C.