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

Abstract

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 A 3 − 1 , the surface concentration of lipid membranes formed from these complexes, γ 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.

The Equilibria in Lipid–Lipoic Acid Systems: Monolayers, Microelectrophoretic and Interfacial Tension Studies

“…The zeta potential depends on the molecular composition of the biological membrane and plays an essential role in understanding membrane-binding mechanisms and cellular uptake, such as drug delivery. This parameter is an essential property of a cell and is useful for comparing the surface properties between two cell types [35,36]. Changes in the zeta potential of a living cell can commonly occur, including alongside diseases in cells since the membrane zeta potential is influenced by many different factors, such as membrane composition.…”

“…We also considered the case in which the components of a two-component lipid membrane, e.g., PC or PS (component 1), and lipoic acid (component 2) do not form a new chemical compound. The interactions between the membrane components can then be described by a system of equations [35,37]:…”

“…Working conditions and experimental procedure: The interfacial tension measurements were based on Young's and Laplace's equation presented in the previous paper [35].…”

“…The apparatus and method of measurement were both described in detail previously [35]. The measurement cell was built from two glass elements separated by a mount holding (1.5 mm diameter) a circular Teflon cap that was axially pierced, leaving a small orifice.…”

“…The measurement cell was built from two glass elements separated by a mount holding (1.5 mm diameter) a circular Teflon cap that was axially pierced, leaving a small orifice. The Mueller-Rudin method [35,37] was used to form the bilayers at the flat end of the Teflon cap. Both glass elements were filled with 0.1 M KCl.…”