Monolayer Formation and Molecular Orientation of Various Helical Peptides at the Air/Water Interface

Ten kinds of helical peptides were synthesized to study interaction between helices in the peptide monolayer formed at the air/water interface. Five of those have a repeating sequence of Ala-Aib and different end groups, other two a repeating sequence of Lys(Z)-Aib, and the rest a repeating sequence of Leu-Aib. All of the peptides take helical conformation in ethanol as confirmed by CD spectroscopy. The surface pressure-area isotherms of the peptide monolayers showed an inflection at the surface area corresponding to the cross section along the helix axis, where the monolayers are considered to collapse. The monolayers were transferred onto substrates and subjected to IR transmission and reflection absorption spectroscopy. By comparison of amide I and II absorbances, the peptides seemed to lie on the substrates. It was concluded that the peptides in the monolayer orient their helical axis parallel to the air/water interface.