However, the particular molecular properties of different species may be the decisive parameters that determine whether a peptide/lipid interaction is attractive or repulsive. For the presented peptide species 1-6 these parameters are (1) the unique b-helical secondary structure caused by the D,L-alternation and bulkiness of the peptide side chains, (2) the exclusiveness of the side-chain composition with almost entirely aromatic amino acid residues, and (3) the presence of flanking interfacial anchoring moieties. Our findings are also in line with literature studies that report higher order parameters for hydrocarbon chains of lipids adjacent to peptide channels composed of aromatic amino Fig. 6 Schematic representation of the conclusions drawn from GID results, suggesting a positive hydrophobic mismatch and, most likely, an enhanced highly ordered packing of the annular lipid shell. These effects may be attributed to the specific properties of the peptide species, i.e., their sequences, side-chain orientations, and secondary structures Eur Biophys J (2011) 40:417-436 427 acids (Chiu et al. 1999 ). This should be particularly pronounced in the case of tryptophan-containing peptides, such as species 1-9, as tryptophan is known as an amino acid with high preference for lateral interaction (Adamian and Liang 2001; Ridder et al. 2005) . The planarity and hydrophobicity/amphipathicity of the aromatic side chains have already been shown to provide potential for a perfect alignment and interaction with the lipid bilayer core via intercalation between the lipid chains (Hite et al. 2008; Palsdottir and Hunte 2004) . Hydrophobic interaction might further direct lipid chains to approach closer contact to incorporated peptide species via lowering entropic costs for acyl chain deformation. This lipid/peptide interaction might play a predominant role for b-helical peptide species due to the fact that all peptide side chains are pinpointing radiantly outside the helix . Proper vertical alignment for the reconstituted peptide in the bilayer was concluded already in a previous reflectivity study exhibiting up to six lamellar orders nearly independent of the applied peptide concentration (Küsel et al. 2007 ).