Interaction of Mixed-Ligand Monolayer-Protected Au144Clusters with Biomimetic Membranes as a Function of the Transmembrane Potential

Understanding the interaction of nanoparticles with cell membranes is a high-priority research area for possible biomedical applications. We describe our findings concerning the interaction of Au144 monolayer-protected clusters (MPCs) with biomimetic membranes and their permeabilizing effect as a function of the transmembrane potential. We synthesized Au144(SCH2CH2Ph)60 and modified the capping monolayer with 8-mercaptooctanoic acid (Au144OctA) or thiolated trichogin (Au144TCG), a channel-forming peptide. The interactions of these MPCs with mercury-supported lipid mono- and bilayers were studied with a combination of electrochemical techniques specifically sensitive to changes in the properties of biomimetic membranes and/or charge-transfer phenomena. Permeabilization effects were evaluated through the influence of MPC uptake on the reduction of cadmium(II) ions. The nature and properties of the Au144 capping molecules play a crucial role in controlling how MPCs interact with membranes. The native MPC causes a small effect, whereas both Au144OctA and Au144TCG interact significantly with the lipid monolayer and show electroactivity. Whereas Au144OctA penetrates the membrane, Au144TCG pierces the membrane with its peptide appendage while remaining outside of it. Both clusters promote Cd2+ reduction but with apparently different mechanisms. Because of the different way that they interact with the membrane, Au144OctA is more effective in Cd2+ reduction when interacting with the lipid bilayer and Au144TCG performs particularly well when piercing the lipid monolayer.