Abstract
Influence of sodium salts of selected chaotropic anions from the Hofmeister series (NaCl, NaBr, NaNO3, NaI) on the surface charge density of phosphatidylcholine membranes was studied. Small unilamellar lipid vesicles were used as a model system in the investigations. The theoretical and experimental approach to the interactions between inorganic anions and phosphatidylcholine membranes is presented. Experimental membrane surface charge densities data were determined as a function of pH of the aqueous electrolytes using microelectrophoresis method. The quantitative description of the interactions between zwitterionic phosphatidylcholine membrane and monovalent anions is presented. The equilibria constants of the binding of solution ions onto phospholipid surface were calculated. Knowledge of these parameters was essential to determine the theoretical membrane surface charge density values. The theoretical data were compared to the experimental ones in order to verify the mathematical model. Both approaches indicate that the anion-phosphatidylcholine membrane interaction increases with the size of the anion. The adsorption of chaotropic anions to membranes was found to follow the Hofmeister series I− > NO3− > Br− > Cl−.
Highlights
Lipids are essential biomolecules in the function and structure of living matter
The major aim of the present paper is to investigate the effect of a range of anions on the electric properties of egg phosphatidylcholine liposomal membranes, using the microelectrophoresis method, for the determination of surface charge density
Depicted in the Figure are the curves of the dependence of PC membranes surface charge densities on pH of the electrolyte solutions
Summary
Lipids are essential biomolecules in the function and structure of living matter. These molecules have amphiphilic properties and are building blocks of cells as well as model membranes. Since natural membranes represent complicated assemblies of molecules, their study is extremely involved. To facilitate this task, the properties of natural membranes are often studied using liposomes. The most widely used lipid in liposome work is phosphatidylcholine (PC), a zwitterionic phospholipid, which at physiological values of pH, possesses one positive and one negative charge [1]. Despite the widespread view that zwitterionic phospholipids do not interact strongly with the ions (especially compared to charged ones, e.g., phosphatidylserine), the phenomenon has been intensively studied. Numerous experimental studies, including those on 1 H-NMR [2],
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