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The evaluation of the radial electron density profile of a drug containing a sterically stabilized liposomal system is described. Using synchrotron small-angle X-ray scattering, we were able to characterize the hydrophilic shell of the polyethylene glycol chains. Using a Gaussian model for describing the electron density profile along the normal of the bilayer, we got an asymmetric distribution of PEGylated lipids in accordance with theoretical considerations. Moreover, we used anomalous X-ray scattering to study the localization of a hydrophobic drug (a kinase inhibitor), which revealed that these molecules are mainly located in the hydrocarbon chain region of the phospholipid bilayer.

The effect of 5 th generation polyamidoamine (PAMAM G5) dendrimers on multilamellar dipalmitoylphosphocholine (DPPC) vesicles was investigated. PAMAM was added in two different concentration to the lipids (10 -3 and 10 -2 dendrimer/lipid molar ratios). The thermal behavior of the evolved systems was characterized by DSC; while the structure and the morphology were investigated with small-and wide-angel X-ray scattering (SWAXS), freeze-fracture electron microscopy (FFTEM) and phosphorus-31 nuclear magnetic resonance ( 31 P-NMR) spectroscopy, respectively. IR spectroscopy was used to study the molecular interactions between PAMAM and DPPC. The obtained results show that the dendrimers added in 10 -3 molar ratio to the lipids generate minor perturbations in the multilamellar structure and thermal character of liposomes, while added in 10 -2 molar ratio dendrimers cause major disturbance in the vesicular system. The terminal amino groups of the dendrimers are in strong interaction with the phosphate headgroups and through this binding dendrimers disrupt the regular multilamellar structure of DPPC. Besides highly swollen, fragmented bilayers, small vesicles are formed.