Restoring structural parameters of lipid mixtures from small-angle X-ray scattering data

Small-angle X-ray scattering (SAXS) is widely utilized to study soluble macromolecules, including those embedded into lipid carriers and delivery systems such as surfactant micelles, phospholipid vesicles and bilayered nanodiscs. To adequately describe the scattering from such systems, one needs to account for both the form factor (overall structure) and long-range-order Bragg reflections emerging from the organization of bilayers, which is a non-trivial task. Presently existing methods separate the analysis of lipid mixtures into distinct procedures using form-factor fitting and the fitting of the Bragg peak regions. This article describes a general approach for the computation and analysis of SAXS data from lipid mixtures over the entire angular range of an experiment. The approach allows one to restore the electron density of a lipid bilayer and simultaneously recover the corresponding size distribution and multilamellar organization of the vesicles. The method is implemented in a computer program, LIPMIX, and its performance is demonstrated on an aqueous solution of layered lipid vesicles undergoing an extrusion process. The approach is expected to be useful for the analysis of various types of lipid-based systems, e.g. for the characterization of interactions between target drug molecules and potential carrier/delivery systems.

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Restoring silicasol structural parameters using gradient and simulation annealing optimization schemes from small-angle X-ray scattering data

Journal of Molecular Liquids ◽

10.1016/j.molliq.2019.03.070 ◽

2019 ◽

Vol 283 ◽

pp. 221-224 ◽

Cited By ~ 3

Author(s):

A.E. Kryukova ◽

P.V. Konarev ◽

V.V. Volkov ◽

V.E. Asadchikov

Keyword(s):

Small Angle ◽

Structural Parameters ◽

Scattering Data ◽

X Ray ◽

X Ray Scattering ◽

Optimization Schemes ◽

Ray Scattering

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Small angle X-ray scattering study of porosity variation in a styrene-divinylbenzene copolymer

Collection of Czechoslovak Chemical Communications ◽

10.1135/cccc19811675 ◽

1981 ◽

Vol 46 (7) ◽

pp. 1675-1681 ◽

Cited By ~ 13

Author(s):

Josef Baldrian ◽

Božena N. Kolarz ◽

Henrik Galina

Keyword(s):

Small Angle ◽

Structural Parameters ◽

Two Phase ◽

X Ray ◽

Porosity Variation ◽

Swelling Agent ◽

X Ray Scattering ◽

Styrene Divinylbenzene ◽

Ray Scattering

Porosity variations induced by swelling agent exchange were studied in a styrene-divinylbenzene copolymer. Standard methods were used in the characterization of copolymer porosity in the dry state and the results were compared with related structural parameters derived from small angle X-ray scattering (SAXS) measurements as developed for the characterization of two-phase systems. The SAXS method was also used for porosity determination in swollen samples. The differences in the porosity of dry samples were found to be an effect of the drying process, while in the swollen state the sample swells and deswells isotropically.

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Osmotic shrinkage of sterically stabilized liposomes as revealed by time-resolved small-angle X-ray scattering

Journal of Applied Crystallography ◽

10.1107/s1600576713030513 ◽

2014 ◽

Vol 47 (1) ◽

pp. 35-40 ◽

Cited By ~ 10

Author(s):

Zoltán Varga ◽

András Wacha ◽

Attila Bóta

Keyword(s):

Form Factor ◽

Small Angle ◽

Freeze Fracture ◽

Initial Step ◽

Time Resolved ◽

X Ray ◽

X Ray Scattering ◽

Sterically Stabilized Liposomes ◽

Liposome Size ◽

Ray Scattering

Time-resolved synchrotron small-angle X-ray scattering (SAXS) was used to study the structural changes during the osmotic shrinkage of a pharmacologically relevant liposomal drug delivery system. Sterically stabilized liposomes (SSLs) with a diameter of 100 nm and composed of hydrogenated soy phosphocholine, cholesterol and distearoyl-phosphoethanolamine-PEG 2000 prepared in a salt-free buffer were mixed with a buffered 0.3 MNaCl solution using a stopped flow apparatus. The changes in the liposome size and the bilayer structure were followed by using SAXS with a time resolution of 20 ms. A linear decrease in liposome size is observed during the first ∼4 s of the osmotic shrinkage, which reveals a water permeability value of 0.215 (15) µm s−1. The change in the size of the liposomes upon the osmotic shrinkage is also confirmed by dynamic light scattering. After this initial step, broad correlation peaks appear on the SAXS curves in theqrange of the bilayer form factor, which indicates the formation of bi- or oligolamellar structures. Freeze-fracture combined with transmission electron microscopy revealed that lens-shaped liposomes are formed during the shrinkage, which account for the appearance of the quasi-Bragg peaks superimposed on the bilayer form factor. On the basis of these observations, it is proposed that the osmotic shrinkage of SSLs is a two-step process: in the initial step, the liposome shrinks in size, while the area/lipid adapts to the decreased surface area, which is then followed by the deformation of the spherical liposomes into lens-shaped vesicles.

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