Time-dependent fluorescence shift (TDFS) of Laurdan embedded in phospholipid bilayers reports on 
hydration and mobility of the phospholipid acylgroups. Exchange of H2O with D2O prolongs the 
lifetime of lipid-water and lipid-water-lipid interactions, which is reflected in a significantly 
slower TDFS kinetics. Combining TDFS measurements in H2O or D2O hydrated bilayers with atomistic 
molecular dynamics (MD) simulations provides a unique tool for characterization of the hydrogen 
bonding at the acylgroup level of lipid bilayers. In this work, we use this approach to study the 
influence of fluoride anions on the properties of cationic bilayers composed of trimethylammonium-
propane (DOTAP). The results obtained for DOTAP are confronted with those for neutral 
phosphatidylcholine (DOPC) bilayers. Both in DOTAP and DOPC H2O/D2O exchange prolongs hydrogen-
bonding lifetime and does not disturb bilayer structure. These results are confirmed by MD 
simulations. TDFS experiments show, however, that for DOTAP this effect is cancelled in the 
presence of fluoride ions. We interpret these results as evidence that strongly hydrated fluoride 
is able to steal water molecules that bridge lipid carbonyls. Consequently, when attracted to DOTAP
bilayer, fluoride disrupts the local hydrogen-bonding network, and the differences in TDFS kinetics
between H2O and D2O hydrated bilayers are no longer observed. A distinct behavior of fluoride is 
also evidenced by MD simulations, which show different lipid-ion binding for Cl. and F-.