Even though there appears to be a small effect of peptide incubation in terms of the osmotic shock (Fig. ) for the fluid-phase PO membranes, the water diffusion is too rapid to be measured with TR-SANS, even without AMPs. This is evident in the lack of any disenable kinetics in the TR-SANS of POPC/PG membranes (open circles, Fig. ). Despite the rapid water exchange kinetics and the membrane being in the fluid phase, lipid flip-flop is shown to be much slower for POPC membrane, compared to DMPC . This indicates, in line with previous studies that the rate of lipid flip-flop is strongly dependent on the length of the lipid tails . The seemingly limited effect of LL-37 on the ion-permeability of POPC/PG membranes again appears to be consistent with flip-flop induced transient pores, which also in this case occur too infrequently to negate the osmotic pressure. It is also worth mentioning that the water equilibration was too rapid to be tracked (data not shown) also for DPPC/PG membranes with dipalmitoyl (saturated, C-16) tails, which have only 2-C shorter acyl tails compared to DSPC/PG membranes.