Influence of salt on the structure of DMPG studied by SAXS and optical microscopy

Abstract

Aqueous dispersions of 50 mM dimyristoylphosphatidylglycerol (DMPG) in the presence of increasing salt concentrations (2-500 mM NaCl) were studied by small angle X-ray scattering (SAXS) and optical microscopy between 15 and 35 degrees C. SAXS data show the presence of a broad peak around q approximately 0.12 A(-1) at all temperatures and conditions, arising from the electron density contrasts within the bilayer. Up to 100 mM NaCl, this broad peak is the main feature observed in the gel and fluid phases. At higher ionic strength (250-500 mM NaCl), an incipient lamellar repeat distance around d=90-100 A is detected superimposed to the bilayer form factor. The data with high salt were fit and showed that the emergent Bragg peak is due to loose multilamellar structures, with the local order vanishing after approximately 4d. Optical microscopy revealed that up to 20 mM NaCl, DMPG is arranged in submicroscopic vesicles. Giant (loose) multilamellar vesicles (MLVs) start to appear with 50 mM NaCl, although most lipids are arranged in small vesicles. As the ionic strength increases, more and denser MLVs are seen, up to 500 mM NaCl, when MLVs are the prevailing structure. The DLVO theory could account for the experimentally found interbilayer distances.

Nanoliposomal Buparvaquone Immunomodulates Leishmania infantum-Infected Macrophages and Is Highly Effective in a Murine Model

“…It provides structural information regarding membrane thickness and the electron density profile (EDP). Our analysis demonstrated that in the absence of BPQ, the SAXS curves corresponded to unilamellar vesicles, with an absence of sharp peaks at large (or middle) q values (16,17). Our data also demonstrated that the membrane thickness value was slightly larger than other values reported in the literature, such as 43 Å for the POPC phospholipid (18) or the 34 Ϯ 4 Å for the cationic lipid DODAB (17).…”

“…Under this assumption, the scattering curve can be described by an infinite plane (in the x and y directions) with a nonhomogeneous cross section, along the z-axis, representing the membrane thickness (16,17). The scattering intensity can be calculated as follows:…”

“…In the present study, P t (q) was calculated based on a three-step model (16,17). In this case, each leaflet let of the bilayer is composed of three distinct regions: the polar head group, the paraffinic chains, and the innermost methyl group or the CH 3 region.…”

Microscopic methods in analysis of submicron phospholipid dispersions

“…The presented image indicates that the analysis of dispersion systems by means of an optical microscope can be used to preliminarily defi ne particle size and sample homogeneity rather than to evaluate the morphology and internal structure of individual lipid particles. In the literature (26,27), however, one can fi nd information about liposome visualization carried out by means of the light microscopy method, but it applies to large particles (above 500 nm) with complex structure only, e.g. giant unilamellar vesicles (GUV) or multilamellar vesicles (MLV).…”

Rheological characterization of thermal phase behavior of anionic lipid DMPG dispersions

“…Rheo-SAXS measurements under shear flow of γ = 10 s -1 were performed only for the systems with DMPG concentration of 50 mM. SAXS patterns in the gel and fluid phases show an isotropic ring suggesting that DMPG forms spherical vesicles as expected [3,7,17]. Broad peak is a characteristic of single bilayer membranes [3,18].…”