pH and Charge Effects Behind the Interaction of Artepillin C, the Major Component of Green Propolis, With Amphiphilic Aggregates: Optical Absorption and Fluorescence Spectroscopy Studies

Brazilian green propolis is one of the bee products most consumed in the world to prevent diseases, owing antioxidant, antimicrobial, anti-inflammatory and antitumor activities. The major component of Brazilian green propolis is Artepillin C (ArtC), a cinnamic acid derivative with two prenylated groups that improve the affinity of the compound for lipophilic environment. Here, we have employed optical absorption and fluorescence techniques to draw conclusions on how ArtC interacts with amphiphilic aggregates commonly used as model membranes having different charges in the polar head group. Optical absorption spectra were representative of the protonation state of ArtC, dictated by the local pH at the surface of micelles and lipid vesicles. Fluorescence results showed that, in the presence of micelles and vesicles, the polarizability around ArtC was modified, compared to the value in aqueous medium, and the molecule should be located preferentially on the surface region of the model membranes, with an enhanced interaction with the less ordered state of the lipid vesicles.