In this study GID yielded quantitative values for the lipid chain correlation length n and the average lipid chain spacing a via analysis of the lipid chain correlation peak. Reflectivity studies provided additional information about the variation in the lipid spacing d and bilayer thickness d PP (Fig. 7b) . This rather general approach of monitoring the collective lipid response to peptide interaction was combined with multiple site-directed iodine labeling, extending previous studies (Küsel et al. 2007; ) through a larger variety of constructs, labels, and label positions. While a good approach in principle, this part of the presented work showed results that were less consistent and thus less conclusive due to experimental difficulties. Future improvements could include the use of the I-K a edge at 33.17 keV rather than the low energy L edges or the application of a more dedicated setup for this spectral range. Despite some of these problems, the data seem to point to a membranespanning orientation of the designed b-helical peptide hairpins.