Interaction of algal polysaccharide with lipid Langmuir monolayers

Algal polysaccharides may assist in the incorporation of metal ions from water and also have applications in health, interacting with biomembranes. In this paper, we have exploited the interactions at the molecular level of an extract of extracellular algal polysaccharide (EPS) with biomembrane models (lipid Langmuir monolayers). From surface pressure–area isotherms and Polarization Modulation Infrared Reflection–Absorption Spectroscopy (PM-IRRAS), we have inferred that EPS interacts with both kinds of lipids: a negatively charged and a positively charged, however with different mechanisms of action. EPS, being negatively charged, interacts with the polar heads of the positively charged lipid monolayer, while for a negatively charged lipid forming the Langmuir film, EPS penetrates into the alkyl chains of lipid in a mechanism driven mainly by hydrophobic interactions. The insights obtained in this paper are relevant because these help to understand the action of EPS in biomembranes and enable future applications of EPS–lipid hybrid Langmuir–Blodgett films for heavy metal ion sensors.