Method of separated form factors for polydisperse vesicles

Abstract

Use of the Schulz or Gamma distribution in the description of particle sizes facilitates calculation of analytic polydisperse form factors using Laplace transforms, L[f(u)]. Here, the Laplace transform approach is combined with the separated form factor (SFF) approximation [Kiselev et al. (2002). Appl. Phys. A, 74, S1654-S1656] to obtain expressions for form factors, P(q), for polydisperse spherical vesicles with various forms of membrane scattering length density (SLD) profile. The SFF approximation is tested against exact form factors that have been numerically integrated over the size distribution, and is shown to represent the vesicle form factor accurately for typical vesicle sizes and membrane thicknesses. Finally, various model SLD profiles are used with the SFF approximation to fit experimental small-angle neutron scattering (SANS) curves from extruded unilamellar vesicles.

Membrane Fusogenic Activity of the Alzheimer's Peptide Aβ(1–42) Demonstrated by Small-Angle Neutron Scattering

“…As a result of the fit, we obtained for the partially deuterated vesicle a thickness of the head group t h = 10.9 ± 0.2 Å, a hydrophobic thickness 2t c = 29 Å, and a bilayer thickness D = 50.8 Å. These values, in contrast to what has been obtained recently, 21 are in excellent agreement with the values obtained with complementary techniques 29 and reported as a reference in Table 3. The surface area of a lipid molecule (A mol = 64.2 Å 2 ) also confirms the literature data for phospholipids of the same head group, while it is not surprising that we obtained a degree of hydration (n w = 12.7) slightly higher than the value published for pure POPC (n w = 9.3), due to the presence of the anionic lipid POPS.…”

“…The scattering amplitude F b for the membrane is obtained by substituting the profile of the bilayer into Eq. (7) and, as reported in the literature, 21 gives:…”

“…The polydisperse form factor P z (q) is then determined by integrating the monodisperse form factor P(q) = |F(q)| 2 over the Schultz distribution G(R) and can be expressed in terms of a Laplace transformation of the monodisperse form factor. The evaluation of the Laplace transform in the case of the SFF approximation is described in detail elsewhere 21 and results to:…”

pHLIP Peptide Interaction with a Membrane Monitored by SAXS

“…31,34 In the case of unilamellar vesicles, the mean radius, size polydispersity, average membrane thickness, and internal membrane structure can be derived by means of the separated form factor model. 35,36 Here, we have used SAXS over an extended size scale to monitor changes in the unilamellar vesicle form factor and membrane nanostructure.…”

Influence of cholesterol on the structure of stratum corneum lipid model membrane

“…Small-angle neutron scattering (SANS) is not an unusual technique in the studies on various phospholipid systems [10,11]; it has, however, rarely been employed in the skin characterization. The very small-angle neutron scattering has been successfully applied to study the water sorption [12] and to calculate some structural features of SC [13].…”