Liposome formation of egg lecithin and its interaction with iodine

The sonicated dispersion of egg lecithin (phosphatidylcholine) in water forms 1:1 molecular complex with iodine, when its concentration is above 1.6 X 10(-5) M. The thermodynamic and spectrophotometric properties of this complex have been determined. The thermodynamic values are: K (25 degrees C) = 1.6 X 10(3) 1 X mol-1, delta G degrees = -18.4 KJ X mol-1, delta H degrees = -27.4 KJ X mol-1 and delta S degrees = -30.0 J X mol-1 X deg-1. The complex shows two absorption bands: one at 293 nm, which is the charge transfer band and the other at 370 nm, which is the blue shifted visible iodine band at 460 nm in water.