ИСТИНА

We considered data on the electrokinetic measurements of the suspension of liposomes of a varied lipid composition upon polylysine adsorption on them. Experimental data is usually presented by Smoluchovsky relation as zeta-potential values. The quantitative analysis of the data is supposed to find principal characteristics of adsorbed polymer layer — lateral distribution and geometry of lipid-polymer clusters and their effect on the position of slipping plane and electric potential distribution close to membrane surface. Previously, we developed a theoretical model in assumption of irreversible adsorption of polylysines at the membranes composed from negatively charged lipid (cardiolipine, CL). This model allowed us to approximate the data using two parameters — thickness h of polylysine layer at the membrane surface and fraction,  of the area occupied by polymer. In this report, we present an improved model that takes into account a number of features of the system previously unaccounted for. In particular, experimental data demonstrate dependence of the point of zero zeta potential on the liposome composition and polymer chain length, which can not be explained in the framework of the previous model. In the present work we assume that during adsorption of polylysine molecules the slipping plane shifts relative to the surface of the membrane. In order to find the zeta potential, we solve the problem of the distribution of the electric potential inside the polymer adsorbed on the charged surface of the membrane, and also take into account the counterion penetration of the polymer layer and adsorption of counterions on the membrane. This allows us to explain the shift of the point of the zero potential with a change in the position of the slipping plane corresponding to the zero zeta potential. Furthermore, theoretical and experimental curves show the same dependence on total amount of CL in the suspension. It was shown that the longer macromolecules create the thicker layer at the membrane surface. It was also shown that increase in the amount of the charged lipid in the liposome composition results in the nonlinear increase of the polymer coverage . Liposome becomes completely covered with the polymer at a relatively small fraction of the charged lipid in the liposome, which is in a good agreement with atomic force microscopy data.