An Assessment by Fluorescence Spectroscopy of the Interaction of Polyanions Bearing Octadecyl Groups with Positively Charged Liposomes

Abstract

The interactions between positively-charged-liposomes (liposomes) and pyrene-labeled hydrophobically-modified sodium poly-2-(acrylamido)-2-methylpropane sulfonates (PAMPSs) 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 PAMPS carrying 5 mol% pyrenylbutyl-n-octadecyl group binds to the liposomes and that, for systems in 0.2 M aqueous NaCl, the binding is only mildly affected by the charge density of the liposomes. The reversibility of binding of the PAMPSs to the liposomes was assessed by addition of the polycations, (N-isopropylacrylamide)-N-dimethylethyl(2- acrylamido-ethyl)ammonium bromide copolymers. Based on the level of pyrene fluorescence recovery upon addition of the polycations to the complexes between the PAMPSs and liposome carrying a quencher of pyrene fluorescence in its bilayer, we demonstrate that a pyrene-labeled PAMPS without hydrophobic groups desorbs from the surface of the liposoems. In contrast, under the same condition, a pyrene-labeled PAMPS carrying 5 mol% n-octadecyl group is not desorbed from the surface of the liposomes.