Crystalline cyclic peptide nanotubes at interfaces

The assembly, orientation and structural features of nanoscale tubes compos ed of cyclic peptides, formed at the air-water interface, were detected by grazing incidence X-ray diffraction (GIXD). The peptide cyclo-[(L-Phe-D-N-M eALa-)(4)] (1) exhibits two-dimensional crystallinity in which the plane of the peptide ring is parallel to the water interface. The peptide cyclo-[(L -Trp-D-Leu)(3)-L-Ser-D-Leu] (2) forms predominantly planar aggregates compo sed of several tubes, lying with their long axes parallel to the air-water interface. Tn contrast, the peptide cyclo-[(L-Trp-D-leu)(4)] (3) exhibits a very low tendency to form ordered two-dimensional arrays of nanotubes. Fil ms of peptides 2 and 3 as well as their mixtures with the phospholipid DPPA were transferred onto a solid support and visualized by scanning force mic roscopy (SFM).