Chitosan effect on the mesophase behavior of phosphatidylcholine supramolecular systems

Two distinct supramolecular self assemblies of phosphatidylcholine and chitosan, namely liposomes and their precursory organogel. have been investigated by means of SAXS, Light Scattering and Polarized Optical Microscopy. The main goal was the evaluation of the chitosan effect on the self assemblies phase transition behavior upon heating. A distinct smectic organization was observed for the organogel prepared in the presence of chitosan, if compared to that prepared only with phosphatidylcholine. In addition, the phosphatidylcholine-chitosan organogel showed unchanged optical properties upon heating and after 24 h. indicating increased stability when compared to the organogel prepared without chitosan. For the liposomes containing chitosan, the thermotropic behavior features a lamellar pattern that is preserved under heating, until at least 81 degrees C. A phase transition temperature has been determined around 64 degrees C, which was clearly higher than that observed for liposomes prepared without chitosan. The bilayer repeat distance typical of the liposomes increases slowly by increasing the temperature and stacking fluctuations of the bilayers are delayed due to enhancement of the membrane rigidity. (C) 2008 Elsevier B.V. All rights reserved