Composition of supported model membranes determined by neutron reflection

Area of Science:

• Materials Science
• Biophysics
• Surface Chemistry

Background:

• Supported lipid bilayers are crucial model systems for cell membranes.
• Controlling the composition and structure of supported bilayers is essential for their applications.
• Phospholipid-surfactant mixtures offer a route to forming stable supported bilayers.

Purpose of the Study:

• To investigate the formation of supported bilayers using dipalmitoyl phosphatidylcholine (DPPC) and beta-D-dodecyl maltoside.
• To determine the composition of these bilayers during formation and surfactant removal.
• To examine the effect of cholesterol coadsorption on DPPC bilayer structure.

Main Methods:

• Neutron reflection was employed to monitor the adsorption of mixed phospholipid-surfactant micelles onto hydrophilic silica surfaces.
• Chain-deuterated lipids and surfactants (d(62)-DPPC and d(25)-beta-D-dodecyl maltoside) enabled precise compositional analysis.
• Sequential dilution techniques were used to control the enrichment of the adsorbed layer in phospholipid.

Main Results:

• Supported bilayers were successfully formed, with thicknesses of 51 +/- 3 Å after complete surfactant removal.
• These DPPC bilayers demonstrated stability upon heating to 37°C.
• Cholesterol coadsorption resulted in its localization below the headgroup region, increasing bilayer thickness to 58 +/- 2 Å at 26 mol%.

Conclusions:

• The coadsorption method allows for the formation of stable, surfactant-free DPPC supported bilayers.
• Neutron reflection with deuterated components is effective for characterizing bilayer composition and structure.
• Cholesterol incorporation modifies DPPC bilayer thickness and structure, providing insights into lipid-cholesterol interactions.