The use of NMR parameters for the evaluation of the critical micelle concentration of lecithin in reverse micellar systems

Lecithin/water/benzene reverse micellar systems have been studied by 1H NMR. The dependence of the chemical shift of the water and of the trimethylammonium protons on the phospholipid concentration has been measured at several temperatures and water/phospholipid molar ratios (w0) to evaluate the critical micelle concentration of lecithin. Pre-micellar aggregation, with formation of small aggregates comprised of 2-3 monomers, is suggested by the results. The critical micelle concentration has been found to be practically independent of w0, indicating that the systems can be considered as binary, provided w0 is kept constant while varying the surfactant concentration. Some thermodynamic quantities related to the micellization process have also been evaluated.