Species 5 The center maximum of the density difference curve for the middle-labeled oligomer 5 (both intertwined strands) indicates that a significant fraction of the iodine labels are buried deeply in the hydrophobic core of the lipid bilayer (Fig. 10b, d) . In both data sets, in-house and synchrotron, the membrane thickness (peak-to-peak distance) is approximately 32 Å (see the Electronic Supplementary Material). The distribution of the central maximum of the difference curve appears relatively broad, especially for the in-house experiment (Fig. 10c) .