Azelaic acid in model membranes: A thermodynamical and structural study

Summary We report a thermodynamical and structural investigation on the effect of a dicarboxylic acid, the azelaic acid, on a synthetic phosophatidylcholine in excess water condition. The results indicate that the drug interacts with the lipid headgroup region, near to the hydrocarbon chains: in particular, at higher concentrations investigated, an interdigitated ?gel phase?, with rigid chains, stiff and perpendicular to the lamellar planes, is induced. The experimental electron density profiles, obtained for samples containing low and high quantity of azelaic acid, support the proposed interaction. Moreover, step electron density models, used to confirm the selected sign combination of the observed structure factors, show the best agreement with the experimental data when the chain terminal methyl groups are frozen in fixed position. Work presented at the second USSR-Italy Bilateral Meeting on Liquid Crystals held in Moscow, September 15–21, 1988.