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DOE OSTI · 1774548

Structure of supported DPPC/cholesterol bilayers studied via X-ray reflectivity

Vega, Michael·Lurio, Laurence·Lal, Jyotsana·Karapetrova, Evguenia A.·Gaillard, Elizabeth R.
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Abstract

The electron density profile of bilayers of DPPC/cholesterol mixtures supported on semiconductor grade silicon substrates were studied with the objective of determining how the proximity of a solid interface modifies the phase diagram of mixed bilayers. The bilayers were studiedin situimmersed in waterviasynchrotron X-ray reflectivity (XRR). Measurements were performed as a function of temperature through the main phase transition and cholesterol mole fractions up to 40%. Analysis of XRR yields the bilayer thickness, roughness and leaflet asymmetry. We find that the structure of the pure DPPC bilayers in the gel phase is in agreement with previous X-ray measurements of supported bilayers depositedviavesicle fusion and multilamellar vesicles but show more clearly defined features than measurements made on films formed using Langmuir-Blodget Langmuir-Shaffer (LB) deposition. Examination of bilayer thicknessvs.temperature shows that the melting temperature for supported bilayers is shifted upwards by approximately 4 degrees C relative to multilamellar vesicles and that the melting temperature decreases with increasing cholesterol content up to 20%. For pure DPPC bilayers the leaflets melt in two stages with the distal leaflet melting first. For cholesterol concentrations of 10% and 20% there is no clear indication of separate melting. Finally. for 33% and 40% cholesterol content no clear transition is seen in the bilayer thickness, but an abrupt change in roughness indicates possible microdomain formation in the 40% cholesterol sample.

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Vega, Michael, Lurio, Laurence, Lal, Jyotsana, Karapetrova, Evguenia A., Gaillard, Elizabeth R.. 2020-08-06. Structure of supported DPPC/cholesterol bilayers studied via X-ray reflectivity. https://doi.org/10.1039/d0cp01834a

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