Effect of anionic-lipid-molecule geometry on the structure and properties of liposome-polycation complexes

Abstract

The influence of anionic amphiphilic compounds that have different geometric shapes and become incorporated into bilayers on the polycation-mixed liposome interaction and the structure and properties of the resulting complexes is analyzed. Phosphatidylserine, cardiolipin, and sodium dodecyl phosphate are used as anionic lipids, and poly(N-ethyl-4-vinylpyridinium bromide) and polylysine are used as polycations. Polycation adsorption on the surfaces of all examined types of liposomes is accompanied by the neutralization of their charge, an increase in the size of particles of the systems, and quenching of fluorescence labels. Liposomes whose membranes contain incorporated cylindrical phosphatidylserine molecules retain their integrity during contact with polycations. The resulting complexes quantitatively dissociate into initial components during an increase in the salt concentration in the surrounding solution. In the case of liposomes with asymmetric anionic lipids, that is, cardiolipin and sodium dodecyl phosphate, the conditions of retaining the membrane integrity and reversible complexation are fulfilled only at relatively low molar fractions of both lipids. The obtained data witness the decisive effect of the geometry of anionic lipid molecules on the stability of complexes formed from mixed liposomes and polycations.