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-lab eled hydrophobically modified sodium poly-2(acrylamido)-2-methylpropane sul fonates (HM-PAMPS) have been examined by fluorescence spectroscopy and dyna mic light scattering. Evidence from changes in the relative intensity of py rene excimer and monomer emissions indicates that the polyanions bind to ca tionic Liposomes and that, for systems in aqueous 0.2 M NaCl, the binding i s only mildly affected by the charge density of the liposomes. The reversib ility of the polyanion binding to the liposomes was assessed by addition of the polycation (N-isopropylacrylamide)-N-dimethylethyl( ethyl)ammonium bro mide copolymer (PNIPAM-DMEAB). Based on the level of pyrene fluorescence re covery upon addition of the polycation to complexes between PAMPS and lipos omes containing a quencher of fluorescence in their bilayer, we demonstrate reversibility of the binding of sodium poly-2-[acrylamido-2-methylsulfonat e-N-(1-pyrenylmethyl)]acrylamide (PAMPS-Py1). In contrast, under the same c onditions, a HM-PAMPS sample carrying along its backbone 5 mol% of n-octade cyl groups is not desorbed from the surface of the liposome. (C) 2001 Elsev ier Science Ltd. All rights reserved.