Modelling of lipid monolayer structure from Grazing Incidence X-ray Off Specular Scattering data

VARGAS FONDACARO JUAN M; OLIVEIRA, RAFAEL GUSTAVO

Congreso; LI Reunión Anual de la Sociedad Argentina de Biofísica; 2023

Lipid monolayers within a range of lateral pressures (from gaseous phase till collapse) were probed using Grazing Incidence X-ray Off-Specular Scattering, performed in Synchrotrons; from these measurements reflectivity vs. scattering vector profiles (analogous to X-ray specular reflectivity) were obtained and then fitted from reciprocal into real space via a two layer model between air and water. The two layers represent the lipid polar headgroup on one side, and the acyl chain region on the other. This last step allowed us to derive an approximate electron density profile for the aforementioned lipid monolayer and in turn infer structural data perpendicular to the monolayer. Both a constant electron density in the hydrophobic tails and a fixed thickness of the headgroup were consistent with the data. The roughness of the different interfaces was also fixed to 0.25-0.3 nm. The minimal variables that changed upon compression were the thickness of the hydrophobic tails and the electron density of the headgroup. The final objective is to compare the X-ray electron density profile with the global thickness of the monolayer obtained by other methods. This consists of calculations based on reflectivity and refractive index determination from Brewster angle microscopy, performed in our own laboratory.