Figure 1 - uploaded by Yuri O. Volkov
Content may be subject to copyright.
Source publication
The dependence of the structure of a phospholipid layer (DSPC and SOPC)
adsorbed on a hydrosol substrate on the concentration of NaOH in a solution of
5-nm silica particles has been studied by X-ray reflectrometry with the use of
synchrotron radiation. Profiles of the electron density (polarizability) have
been reconstructed from the experimental d...
Citations
... The probe radiation was prepared by a single-reflection crystal monochromator Si(111), tuned to the Kα1 line of copper (photon energy E ≈ 8048 eV, wavelength (1) and at the X19C beamline of the NSLS synchrotron (2). The data taken from [23,24]. Insert: kinematics of X-ray scattering at the air -liquid interface. ...
... Kinetics of the spontaneous ordering of phospholipid multilayers on the surface of silica sol was discussed in our works [23,24]. We used model lipids 1,2-distearoyl-sn-glycero-3-phosphocholine (DSPC) and 1-stearoyl-2-oleoylsn-glycero-3phosphocholine (SOPC) deposited on the surface of silica sols FM-16 (16% wt. ...
... When the DSPC film has been kept in thermodynamic equilibrium for about 24 hours, a regular set of diffraction peaks with a period ∆qz = 2π/d appears on the angular dependence of (2). The data taken from [23,24]. the reflection factor (curve 1 in Fig. 4a), where the characteristic thickness d of a structural element in the multilayer corresponds to the thickness of DSPC bilayer in the crystalline phase L ≈ 68Å known in literature. ...
The authors present a review of the systematic studies of the structure of macroscopically planar thin films at the air-liquid interface (water, alkali solution and silica hydrosol). A common feature of the considered works is the application of a model-independent approach to the analysis of X-ray reflectometry data, which does not require a priori assumptions about the structure of the object under study. It is shown that the experimental results obtained with the laboratory source in some cases are qualitatively on par with the results of those obtained with the use of synchrotron radiation source. The reproducibility of the effect of spontaneous ordering in films of amphiphilic organic molecules (phospholipids) at the surface of the colloidal solution of silica nanoparticles is demonstrated. The possibility of influencing the kinetics of the in situ formation of a phospholipid film by enriching the liquid substrate with alkali metal ions is also discussed.
The structure of an adsorption octadecanamide film at the planar toluene–water interface is studied by X-ray reflectometry using synchrotron radiation with photon energy of 15 keV. The electron density (polarizability) profiles, according to which the interface structure is determined by the pH level in the water subphase, are reconstructed from experimental data with the help of a model-independent approach. For a high pH ≈ 11, the adsorption film is a crystalline octadecanamide monolayer with a thickness of about 26 Å, in which aliphatic tails of surfactant are extended along the normal to the surface. For low pH ≈ 2, the thickness of the surface structure consisting of the crystalline monolayer directly on the toluene–water interface and a thick layer of deposited octadecanamide micelles reaches about 500 Å. In our opinion, the condensation of nonionogenic surfactant micelles for which the surface concentration of the surfactant increases significantly is caused by a change in the polarization direction upon a decrease in the pH level in the electric double layer at the interface between the water subphase and the octadecanamide monolayer. The shape of the reconstructed electron density profiles also indicates the existence of a plane of the closest approach of surfactant micelles to the interface at a distance of about 70 Å from it.
We present a brief review of application of a model-independent analysis of X-ray refleetometry data to our recent investigations of thin films of phospholipids DSPC and DMPS on a surfaces of water and colloidal silica hydrosol. Comparison of the results against analytical models of phospholipid membranes known in literature allowed us to extract more extensive information on the samples in question. The effect of spontaneous ordering of lipid films on a surface of colloidal silica is discussed. We also demonstrate the possibilities to influence the structure of prepared membranes by enriching the substrate with alkali ions.
The structure of the adsorbed layer of alkali ions on the surface of colloidal silica solutions with a particle size of 27 nm has been studied by reflectometry and diffuse scattering of synchrotron radiation with a photon energy of about 71 keV. Electron density profiles in the direction perpendicular to the surface have been reconstructed from experimental data and spectra of the correlation function of heights in the surface plane have been obtained. The revealed deviation of the integral and frequency characteristics of the roughness spectra of the silica sol surface from predictions of the capillary-wave theory is of a fundamental character. This deviation is due to the contribution from roughnesses with low spatial frequencies ν < 10⁻⁴ nm–1 and to the interference of diffuse scattering from different layer interfaces of the surface structure.
The molecular structure of dimyristoyl phosphatidylserine (DMPS) monolayers on a water substrate in different phase states has been investigated under normal conditions by X-ray reflectometry with a photon energy of ~ 8 keV. According to the experimental data, the transition from a two-dimensional expanded liquid state to a solid gel state (liquid crystal) accompanied by the ordering of the hydrocarbon tails of the DMPS molecule occurs in the monolayer as the surface pressure rises. The monolayer thickness is (20 +/- 3) Angstrom and (28 +/- 2) Angstrom in the liquid and solid phases, respectively, with the deflection angle of the molecular tail axis from the normal to the surface in the gel phase being (26 +/- 8) deg. At least a twofold decrease in the degree of hydration of the polar lipid groups also occurs under two-dimensional monolayer compression. The reflectometry data have been analyzed using two approaches: under the assumption about the presence of two layers with different electron densities in the monolayer and without any assumptions about the transverse surface structure. Both approaches demonstrate satisfactory agreement between themselves in describing the experimental results.
The possibility of laboratory X-ray reflectometry study of the structure of dimyristoyl phosphatidylserine (DMPS) phospholipid monolayers on the water surface in various phase states has been demonstrated.
The ordering of a multilayer consisting of DSPC bilayers on a silica sol substrate is studied within the model-independent approach to the reconstruction of profiles of the electron density from X-ray reflectometry data. It is found that the electroporation of bilayers in the field of anion silica nanoparticles significantly accelerates the process of their saturation with Na+ and H2O, which explains both a relatively small time of formation of the structure of the multilayer of 10^5 - 7x10^5 s and ~13 % excess of the electron density in it.
