The electron density profiles derived from the in-house measurements of compounds 7 and 2 (Fig. 10c) show reasonable lower contrast between labeled and unlabeled samples, which is much closer to the expectation. Four small bumps in the electron density difference curve appear at z = ±17.0 and ±7.0 Å (Fig. 10d ), corresponding to possible inter-iodine distances of approximately Dz = 34, 14, 10, or 24 Å . Compared to b-structures of gramicidin A that are likewise assumed for peptide 7 or the unlabeled analog 2 with a periodicity of 5.6 or 6.3, the investigated b-hairpin with a strand length of 12 residues would give a peptide length of 28.8 or 20.8 Å , respectively (Fahsel et al. 2002) . This would not directly match a transmembrane orientation without assuming additional effects from distortions, tilt (Fig. 11iv) , or a coexisting population (Fig. 11v) . The rather flat difference curve of the in-house data for species 7 appears less conclusive than difference curves with more clearly identifiable maxima.