Localization and Interactions of Melatonin in Dry Cholesterol/Lecithin Mixed Reversed Micelles used as Cell Membrane Models

The state of melatonin confined in dry cholesterol/lecithin mixed reversed micelles dispersed in CCl4 was investigated using H-1-NMR and FT-IR spectroscopies as a function of the melatonin to lecithin molar ratio (R-MLT) and of the cholesterol to lecithin molar ratio (R-CHL). An analysis of experimental results leads to the hypothesis that, independent of R-MLT and as a consequence of anisotropic melatonin/lecithin, melatonin/cholesterol and cholesterol/lecithin interactions, melatonin is totally solubilized in reversed micelles. Melatonin is mainly located in and oriented in the nanodomain constituted by the hydrophilic groups of cholesterol and lecithin. A competition of melatonin and cholesterol for the hydrophilic binding sites of the reversed micelles was observed by changing the R-CHL. Some possible biological implications of the specific interactions governing the solubilization process, the preferential location and the peculiar properties of melatonin confined in cholesterol/lecithin mixed reversed micelles are discussed.