# Synchrotron and Free electron laser Radiation: generation and application (SFR-2016)

4-7 July 2016
Budker INP
Asia/Novosibirsk timezone
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# Contribution Oral

Budker INP - Conference Hall
SR for medicine and biology application

# Structural parameters of macroscopically flat lipid multilayers on a silica sol substrates

## Speakers

• Mr. Yuriy VOLKOV

## Co-authors

• Dr. Igor KOZHEVNIKOV (Shubnikov Institute of Crystallography, FSRC “Crystallography and Photonics” RAS)
• Mr. Boris ROSHCHIN (Shubnikov Institute of Crystallography, FSRC “Crystallography and Photonics” RAS)
• Dr. Viktor ASADCHIKOV (Shubnikov Institute of Crystallography, FSRC “Crystallography and Photonics” RAS)

## Content

A phospholipid bilayer on liquid substrate can be used as the simplest model of a cell membrane [1]. Previously, the method of preparation of macroscopically flat regular lipid multilayers with the use of colloidal silica hydrosols as substrates has been proposed [2]. Due to the specific boundary conditions at air/sol interface, polar lipid molecules exhibit a spontaneous ordering effect.

In this report we present the investigations of influence of hydrosol compound (i.e. size of silica nanoparticles, pH level and concentration of alkali ions) on the structural parameters of phospholipid layers by the X-ray reflectometry method with the use of synchrotron radiation. Model phosphatidylcholine lipids DSPC, DPPC and SOPC have been used as samples. Experiments have been carried at X19C beamline (radiation energy E = 15 keV) of NSLS facility, Brookhaven. Depth-graded distributions of electron density have been extracted from the measured reflectivity curves by the model-independent reconstruction algorithm [3].

According to the obtained results, overall thickness of lipid film is consistent with the Debye length for the substrate sol and thus can be varied from the monolayer (d ~ 35 Å) to the stack of bilayers (d ~ 450 Å) at pH $approx$ 11.5 and 9 respectively. Separate mono- and bilayers exhibit high degree of structural perfection, with calculated lipid area $A = 45 pm 2$ and $49 pm 3$ Å$^2$ being in agreement with the theoretical values for 2-dimensional phospholipid crystal. Enrichment of the substrate with Na$^+$ and Cs$^+$ leads to the absorption of alkali ions into the lipid membrane, with the surface concentration of ions up to $2 times 10^{19}$ m$^{-2}$.

[1] D. M. Small, "The Physical Chemistry of Lipids", Plenum Press, NY (1986).

[2] A. M. Tikhonov, JETP Letters, 2010, 92:394.

[3] I. V. Kozhevnikov, Nucl. Instr. Meth. Phys. Res. A, 2003, 508:519.