Species 8 In case of the molecular species 8, holding a 5,5-diiodo-allyglycine label at the loop position, five lamellar orders could be obtained in the synchrotron experiment (see the Electronic Supplementary Material). The peak-to-peak distance of the electron density curves reveals a headgroup spacing of approximately 33 Å (4.55 keV) and 32 Å (5.80 keV), respectively. The corresponding electron density difference curve is pronounced due to the double signal intensity resulting from the double iodinated label, but differences in resolution at the different X-ray energies may also play a role. The profile shows strong maxima at ±15.4 Å and additional inflection points around ±7.1 Å (Fig. 10d) . The maxima at ±15.4 Å may indicate a transmembrane orientation of the b-hairpin structure 8 nearly spanning the same distance as the terminally labeled sample 7/DLPC/Chol. The electron density difference curve of in-house reference measurements does not show significant rises in the headgroup region, but only at the membranes outside (±21.4 Å ) in the membrane water layer (see above). A rather diffuse and less intense maximum appears spread out over the bilayer hydrophobic core.