Effect of surface curvature on stability, thermodynamic behavior, and osmotic activity of dipalmitoylphosphatidylcholine single lamellar vesicles

Abstract

The size and surface curvature dependence of the properties and stability of single lamellar vesicles have been investigated by using a variety of physicochemical techniques. Dipalmitoylphosphatidylcholine single lamellar vesicles of sizes ranging between 200 and 900 A in diameter have been prepared by the French press method and characterized with respect to their size distribution, stability, and thermotropic behavior by negative stain electron microscopy, molecular sieve chromatography, nuclear magnetic resonance spectroscopy, and differential scanning calorimetry. Vesicles with a diameter smaller than 400 A are unstable below their transition temperature and fuse spontaneously to form larger single lamellar vesicles. Correlation analysis of experimentally obtained size distributions and calorimetric phase transitions profiles allowed estimation of the size dependence of the transition temperature. The phase transition temperature depends on the vesicle size in a sigmoidal fashion. Throughout the entire 200-700 A diamter range, the phase transition parameters are sensitive to size; however, the size dependence is especially pronounced around 400 A in diameter. The anomalous size dependence of the transition temperature for vesicles smaller than 400 A in diameter has been attributed to a decrease in the effective bilayer curvature due to packing rearrangements of the lipid molecules. Changes in the fractional degree of self-quenching of trapped 6-carboxyfluorescein induced by osmotic stress indicate that large single lamellar vesicles are not spherical under isoosmotic conditions. These vesicles are relatively flexible and can sustain almost a 2-fold increase in their internal aqueous volume without any leakage of the internal content.

Alteration in the Temperature-Dependent Content Release Property of Thermosensitive Liposomes in Plasma

“…When the diameter of the liposomes is below 70 nm, the surface curvature affects the properties of the lipid bilayers such as the T m , enthalpy, and entropy. 33) However, at these sizes, there is no effect of curvature on these properties.…”

Sphingomyelin Inhibits the Lecithin-Cholesterol Acyltransferase Reaction with Reconstituted High Density Lipoproteins by Decreasing Enzyme Binding

“…The properties of phospholipid bilayers in liposomes depend upon liposome composition and curvature (39). Differences in the physical properties of liposomes arise from variations in phospholipid molecular packing with curvature of the liposome (39,40). It is possible that the highly curved surface of the proteoliposomes decreases the hydrogen bonding of SPM molecules to other surface components and facilitates diffusion and binding to the active site, whereas the planar surface of the rHDL discs maximizes the intermolecular interactions of SPM.…”

Effects of divalent cations, temperature, osmotic pressure gradient, and vesicle curvature on phosphatidylserine vesicle fusion

“…Cullis and coworkers proposed that such an inverted micelle structure at the region of contact of two opposing membranes could become an intermediate state for membrane fusion [35,36]. Hui et al [15], Schullery et al [31] and Lichtenberg et al [19] have worked on the fusion of neutral phospholipid membranes and proposed that the phase defect sites, which may arise from different phase behavior of mixed lipid components or which may result from nonuniform phase configurations at a low temperature, may be the sites to induce membrane fusion and stated that such configurations are not necessary for the formation of inverted micelles. Recently, Portis, et al [28], and Ekerdt and Papahadjopoulos [14] have proposed the importance of a transmembrane-Ca 2 + complex as the site of direct interaction between the two opposed membranes.…”