Measuring anion binding at biomembrane interfaces

The quantification of anion binding by molecular receptors within lipid bilayers remains challenging. Here we measure anion binding in lipid bilayers by creating a fluorescent macrocycle featuring a strong sulfate affinity. We find the determinants of anion binding in lipid bilayers to be different from those expected that govern anion binding in solution. Charge-dense anions H2PO4- and Cl- that prevail in dimethyl sulfoxide fail to bind to the macrocycle in lipids. In stark contrast, ClO4- and I- that hardly bind in dimethyl sulfoxide show surprisingly significant affinities for the macrocycle in lipids. We reveal a lipid bilayer anion binding principle that depends on anion polarisability and bilayer penetration depth of complexes leading to unexpected advantages of charge-diffuse anions. These insights enhance our understanding of how biological systems select anions and guide the design of functional molecular systems operating at biomembrane interfaces. Quantification of anion binding by molecular receptors within lipid bilayers is challenging. Here, the authors synthesise a high-affinity macrocyclic anion receptor which provides insights into determinants of anion binding within lipid bilayers.

Automated summary

This study investigates the quantification of anion binding within lipid bilayers using a fluorescent macrocycle with strong sulfate affinity. The authors discover that the determinants of anion binding in lipid bilayers differ from those in solution. These findings provide insights into the principles of anion binding within lipid bilayers and have implications for the design of functional molecular systems at biomembrane interfaces.