Complexation of Polycations to Anionic Liposomes:  Composition and Structure of the Interfacial Complexes

Abstract

Poly(N-ethyl-4-vinylpyridinium bromide) (a polycation with a degree of polymerization of 1100) was adsorbed onto liposomes composed of egg lecithin with a 0.05-0.20 molar fraction (nu) of anionic headgroups provided by cardiolipin (a doubly anionic lipid). According to electrophoretic mobility data, this led to total charge neutralization of the liposomes, whereupon the liposomes adopted a positive charge as additional polymer continued to adsorb. Although the liposomes aggregated at the charge-neutralization point, they disassembled into individual liposomes after becoming positively charged. The degree of polymer adsorption was shown to reach a limit. Thus, by measuring the free polymer content in a liposome suspension, it was possible to determine the polymer concentration at which the liposome surface became saturated with polymer. Beyond this point, an electrostatic/steric barrier at the surface suppressed further adsorption. Dynamic light scattering studies of liposomes with and without adsorbed polymer allowed calculation of the polymer film thickness which ranged from 22 to 35 nm as the molar fraction of cardiolipin (nu) increased from 0.05 to 0.20. The greater the content on the anionic lipid in the bilayer, the thicker the polymer film. The maximum number of polymer molecules adsorbed onto the liposomes was estimated: 1-2 molecules for nu = 0.05; 3 molecules for nu = 0.1; 4- molecules for nu = 0.15; and 6 molecules for nu = 0.2. The polymer appears to lie on the liposome surface, rather than embedding into the bilayer, because addition of NaCl easily dislodges the polymer from the liposome into the bulk water.

The Influence of the Chain Length of Polycations on their Complexation with Anionic Liposomes

“…[20].F irst, the z-average translational diffusion coefficients (D z )a ts everall iposomea nd complex concentrations (C part )w ere measured. Next, the plots of D z versus C part for the free liposomes and fives aturated liposome/ PVPQ complexes werec reated, and the D z values were extrapolated to zero particlec oncentration to determine D z(0) .F inally,t he resulting D z(0) values were used to calculate the hydrodynamic radii (R h )b yu sing the Stokes-Einstein equation.…”

“…[24] According to the IR data, the degree of alkylation was 92-95 %. PVPQs with DP = 20, 40, 100, 270, and 440 were thus prepared (PVPQ 20 ,P VPQ 40 ,P VPQ 100 ,P VPQ 270 ,a nd PVPQ 440 ). Throughout this article, the concentration of polymers presented as concentration of monomer units (base-mol L À1 ).…”

Regulation of acid phosphatase in reverse micellar system by lipids additives: Structural aspects

“…A number of model membrane systems, mainly based on liposomes or lipid monoand multilayers, has been proposed for studying biomembrane transport, receptor functioning and protein-lipid interactions [1][2][3][4][5]. Lipid composition plays a key role in protein association with membrane, regulation of protein conformation and enzymatic activity.…”

Interaction between like-charged polyelectrolyte-colloid complexes in electrolyte solutions: A Monte Carlo simulation study in the Debye–Hückel approximation

“…Understanding complexation of linear polyelectrolyte chains with oppositely charged particles has high potential for applications in nanoscience and bio-technology [2][3][4][5][6][7]. In a number of technological processes and biological systems, linear polyelectrolytes associate with a range of different nanoscopic particles or supramolecular assemblies, including inorganic particles, protein assemblies, micelles and liposomes, forming in aqueous media charged colloidal suspensions.…”