An assessment by fluorescence spectroscopy of the stability of polyanions/positively charged liposome systems in the presence of polycations

The interactions between cationic non-phospholipid liposomes and pyrene-labeled hydrophobically modified sodium poly-2-(acrylamido)-2-methylpropane sulfonates (HM-PAMPS) have been examined by fluorescence spectroscopy and dynamic light scattering. Evidence from changes in the relative intensity of pyrene excimer and monomer emissions indicates that the polyanions bind to cationic liposomes and that, for systems in aqueous 0.2 M NaCl, the binding is only mildly affected by the charge density of the liposomes. The reversibility of the polyanion binding to the liposomes was assessed by addition of the polycation (N-isopropylacrylamide)–N-dimethylethyl(2-acrylamidoethyl)ammonium bromide copolymer (PNIPAM–DMEAB). Based on the level of pyrene fluorescence recovery upon addition of the polycation to complexes between PAMPS and liposomes containing a quencher of fluorescence in their bilayer, we demonstrate reversibility of the binding of sodium poly-2-[acrylamido-2-methylsulfonate–N-(1-pyrenylmethyl)]acrylamide (PAMPS–Py1). In contrast, under the same conditions, a HM-PAMPS sample carrying along its backbone 5 mol% of n-octadecyl groups is not desorbed from the surface of the liposome.