Lateral lipid diffusion in phospholipid monolayers coupled to polyelectrolyte films

The lateral diffusion of lipid probes in lipid monolayers on polyelectrolyte support in different solvent environment was studied by a fringe pattern photobleaching experiment that enabled to measure diffusion coefficients D of over six orders of magnitude. In nonpolar solvents, as well as in air, electrostatic binding of ionic and also of zwitterionic lipids is so strong, that D<10−12 cm2 s−1 was observed. In polar solvents (e.g. methanol), the interaction is reduced for zwitterionic lipids, enabling D>10−7 cm2 s−1. In water, the coupling is similarly reduced for zwitterionic, not for ionic lipids. In the case of a weak interaction with the polymer, one encounters a temperature dependence for the monolayer of 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) as expected for a system with a fluid/gel phase transition.