The autocatalytic process observed in presence of Na + is much more difficult to rationalize in detail based on the present data, since components beyond the detection limit of SEIRA can likely contribute to the mechanism. However, one can assume that the distorted 2:1 EB2:Na + can again play an important role in the positively cooperative incorporation behaviour (modelled using an autocatalytic kinetic scheme) as a the main species within the membrane core. Accordingly, one EB ligand of the distorted 2:1 EB2:Na + sandwich structure will lack the stabilizing benefits of the kinetic chelate effect of the 3-coordinating EB. As such, EB molecules can get more easily abstracted due to an increased number of H-bond interactions with molecules in the head group region or due to the presence of EB:Na + out complexes. This potential quick exchange and, thus, transient spectroscopically non-detectable species (such as free EB) could act as a mediator for incorporation. In this context, it is interesting to note that it was demonstrated previously that Na + ions but not K + ions reside deeply within the lipid head group region. As a consequence, the local K + concentrations sensed by membrane-bound EB molecules is considerably lowered, such that the specific behaviour of EB in presence of Na + may play an important for membrane incorporation.