Experimental and Theoretical Study of Emodin Interaction with Phospholipid Bilayer and Linoleic Acid

H-1 NMR technique, optical spectrophotometry and molecular dynamics simulations have been applied to study the effect of the lipid composition on emodin interaction with the lipid bilayer. The special attention was paid on the presence of the unsaturated fatty acid linoleic acid in the lipid bilayer. Emodin (1,3,8-trihydroxy-6-methylanthraquinone) is a natural anthraquinone which shows a wide spectrum of biological activity including anticancer, anti-inflammatory, antiviral, antibacterial, neuroprotective and others. It is assumed that the location of emodin in the lipid membrane is important for its biological activity. It was demonstrated that in the presence of linoleic acid, the pKa value of the emodin significantly increases. Molecular dynamics simulations show that these changes can be associated with the interaction of emodin and linoleic acid inside the bilayer. Also, it was shown that the order of deprotonation positions in the POPC bilayer differs from the deprotonation order in aqueous solution.