PROTON LATERAL CONDUCTION ALONG LIPID MONOLAYERS IS PRESENT ONLY IN THE LIQUID-EXPANDED STATE

Proton lateral conduction along lipid monolayers was observed by fluorescence spectroscopy. Very fast diffusion was detected at the lipid/water interface as compared to the bulk phase. This property was specific to liquid-expanded film organization. When the film was brought to the gel phase, either mechanically for zwitterionic and acidic lipids or by the effect of divalent cations in the case of acidic lipids, no facilitated conduction was present. This was explained by the destruction, associated with the phase transition, of the hydrogen bond network between interfacial water molecules and polar lipid headgroups.