The Influence of Metal Ions on the Dynamics of Supported Phospholipid Langmuir Films

The translational diffusion dynamics of the zwitterionic lipid 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) at a planar phosphorylated support surface containing metal ions (Mg²⁺, Ca²⁺, Ba²⁺, Ni²⁺, Zn²⁺, Cd²⁺, Zr⁴⁺) was investigated using X-ray photoelectron spectroscopy (XPS) and fluorescence recovery after photobleaching (FRAP). Fluorescence recovery curves yielded diffusion constants on the order of 2–5 μm²/s for the chromophore-tagged 12:0 NBD-Lyso-PC. Ionic interactions between the zwitterionic headgroup and metal ions were found to play a secondary role in mediating lipid fluidity. This work provides quantitative insight into the extent to which the fluidity of a supported lipid film is mediated by the ionic interactions between headgroup and surface versus that of the lipid–lipid tailgroup interactions.