Equilibria in DPPC-Diosgenin and DPPC-Diosgenin Acetate Bilayer Lipid Membranes: Interfacial Tension and Microelectrophoretic Studies

Interactions between components of model lipid membranes (spherical lipid bilayers and liposomes) are investigated here. Parameters characterizing equilibria in the 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC)-diosgenin (Dio) and 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC)-diosgenin acetate (DAc) membrane systems have been determined. The interfacial tension measurement of spherical lipid bilayers was based on the Young-Laplace's equation using a homemade computer-controlled device. We assume a 1:1 complex in the DPPC-Dio and DPPC-DAc membrane systems. The parameters A3-1, the surface concentration of lipid membranes formed from these complexes, gamma 3, the interfacial tension of such membranes, and, K, the constant stability of these complexes were calculated. Microelectrophoresis was used for examinations of the surface charge density of lipid membranes. The values were obtained here from electrophoretic mobility data applying Smoluchowsky's equation. The effect of pH (pH ranged of 2 to 10) on the electrolyte solution and the compositions of the membranes was analyzed. The obtained results indicate that the modification of DPPC membranes with both Dio and DAc causes changes in surface charge density values and shifts of the isoelectric point.