Biophysical properties of cationic lipophosphoramidates: Vesicle morphology, bilayer hydration and dynamics

Cationic lipids are used to deliver genetic material to living cells. Their proper biophysical characterization is needed in order to design and control this process. In the present work we characterize some properties of recently synthetized cationic lipophosphoramidates. The studied compounds share the same structure of their hydrophobic backbone, but differ in their hydrophilic cationic headgroup, which is formed by a trimethylammonium, a trimethylarsonium or a dicationic moiety. Dynamic light scattering and cryo-transmission electron microscopy proves that the studied lipophosphoramidates create stable unilamellar vesicles. Fluorescence of polarity probe, Laurdan, analyzed using time-dependent fluorescence shift method (TDFS) and generalized polarization (GP) gives important information about the phase, hydration and dynamics of the lipophosphoramidate bilayers. While all of the compounds produced lipid bilayers that were sufficiently fluid for their potential application in gene therapy, their polarity/hydration and mobility was lower than for the standard cationic lipid - DOTAP. Mixing cationic lipophosphoramidates with DOPC helps to reduce this difference. The structure of the cationic headgroup has an important and complex influence on bilayer hydration and mobility. Both TDFS and GP methods are suitable for the characterization of cationic amphiphiles and can be used for screening of the newly synthesized compounds.