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The differences between the hydrophobic moments calculated using the consensus scale are not large. The observed results are interpreted using a comparison of hydrophobic moments calculated for α-helices and β-sheets. The analogs with d-amino acids in two different positions of the sequence, k 9a 10-KLAL and l 11k 12-KLAL, form only β-sheet structures at all surface pressures. The secondary structures are essentially orientated parallel to the air/water interface. We start by a quantitative analysis of the conformational space of a single LK14 in bulk water. In their energy wells, these amino acids confer stability to a proteins transmembrane helix. This finding offers a simple explanation for why tryptophan and tyrosine are usually found near the membrane-water interface of membrane proteins. The main disadvantage of measuring surface tension is that the broken hydrogen bonds and neutralized charged groups remain at the solution-air interface. Here, we study the aggregation behavior of the model peptide LK14 (with amino acid sequence LKKLLKLLKKLLKL) in bulk water and at the air/water interface. In other words, there are energy wells near the edge of the membrane for these particular amino acids. This transition could be observed in the compression isotherm as well as during the adsorption at the air/water interface from the subphase as a function of time. The most widely used hydrophobicity scale was developed by measuring surface tension values for the 20 amino acids found naturally in NaCl solution. For the peptide films the shape and position of the amide I and amide II bands indicate that the KLAL adopts at large areas per molecule an α-helical secondary structure, whereas at higher surface pressures or smaller areas it converts into a β-sheet structure. The linear sequence KLAL (KLALKLALKALKAALKLA-NH 2) and its corresponding d, l-isomers k 9a 10-KLAL (KLALKLALkaLKAALKLA-NH 2) and l 11k 12-KLAL (KLALKLALKAlkAALKLA-NH 2) are model compounds for potentially amphipathic α-helical peptides which are able to bind to membranes and to increase the membrane permeability in a structure- and target-dependent manner (Dathe and Wieprecht, 1999) We first studied the secondary structure of KLAL and its analogs bound to the air/water using infrared reflection absorption spectroscopy. The SC3p hydrophobin of Schizophyllum commune is a small hydrophobic protein (100-101 amino acids with eight cysteine residues) that self-assembles at a water/air interface and coats aerial hyphae with an SDS-insoluble protein membrane, at the outer side highly hydrophobic and with a typical rodlet pattern.