A stretching of the lipid bilayer in the z direction caused by hydrophobic mismatch (Killian and Nyholm 2006) may alone result in pronounced lateral effects on annular lipids. Huang and coworkers observed a stretching of a DLPC lipid bilayer upon incorporation of gramicidin A that likewise adopts b-helical structures, similar to the D,L-alternating peptides applied in the presented approach (Harroun et al. 1999) . In previous studies of the homodimeric species 1, comparable effects were indicated by a thickening of the lipid bilayers of 1.4 Å (DMPC = 1,2-dimyristoyl-sn-glycero-3-phosphocholine) and 4.0 Å (DLPC), respectively (Küsel et al. 2007 ). Finally, the reflectivity experiments of the designed peptide hairpin structures 2, 5, 7, 8, and 9 unambiguously prove a positive mismatch situation, also for the hairpin structures, as presented in Table 2 . Such mismatching promotes stretching of the lipid chains and reduction in gauche conformations in the lipid acyl chains. The mismatch situation as well as the described lateral effects may be directly coupled or, alternatively, may independently contribute to the observed changes in a and n upon peptide insertion, as addressed in the following section.