As the varying band shapes of the amide I/I' suggest differing secondary structure compositions, we aimed to quantify the amounts of β-sheet structures that Aβ adopted with tMLMs and tBLMs. Towards this goal, we determined the peak areas of signals assigned to β-sheets from the global fitting procedure in H2O and D2O (~1694 and ~1634 cm -1 , see Figure ) and calculated their fraction to the whole amide I bands over time plotted in Figure . There it becomes clear that the potential for insertion into the membrane results in a considerably increased fraction of about 65% of β-sheets (blue line; tBLM), which is approx. 3 times larger than what is observed for interfacial adsorption on tMLMs with a β-sheet fraction of < 25 % (red line). The residual 35 % or > 80 % of the amide I for tBLMs and tMLMs, respectively, are due to the sum of unstructured, α-helical and β-turn fragments, which are not straightforward to decompose. The temporal evolutions of the β-sheet fractions only show small variations by ±10 %, which are occurring within the first hour of incubation, and afterwards a constant relative amount of β-sheets is maintained. This shows that the initial contact of Aβ with the membrane interface is decisive for β-sheet formation. One could speculate that the tMLM system may trap the initial intermediates before Aβ inserts into the membrane (as enabled by the tBLMs); we observed such a scenario in a previous work on antimicrobial peptides. Since the β-sheet fractions observed on tBLMs do not begin at ~25 % but already at ~65 % at our time resolution of 2 min per spectrum, such initial intermediates may be formed within the first minute of Aβ-membrane interactions in such a scenario. It is interesting to note that the β-sheet fractions in Figure contain data points determined from experiments in H2O and in D2O. Considering the small errors (colored areas), which originate from individual experiments in H2O and in D2O, implies that the total β-sheet fraction is not affected by H/Deffects. Furthermore, we analyzed experiments with neutral lipids (Figure ) in a similar fashion, shown as dashed lines in Figure . It is surprising to see that the absence of negatively charged lipids only leads to minor changes in the βsheet fractions, i.e. 60 % -70 % and 20% -40 % for tBLMs and tMLMs (dashed lines in Figure ). This again indicates that the ability to insert into membranes can overcompensate effects of increased misfolding due to negative surface charge or H/D-exchange.