Reversible Photoisomerization of Self-Organized Cylindrical Peptide Assemblies at Air−Water and Solid Interfaces

Abstract

A new photoswitchable peptide system composed of two flat, ring-shaped cyclic octapeptides with the sequence cyclo-[(l-Phe-d-MeN-Ala)3-l-Cys-d-MeN-Ala] tethered via an azobenzene moiety was investigated at the air−water interface, on mica, germanium, and quartz glass supports. Surprisingly, both the E- and Z-forms of the peptide system form very stable layers at the air−water interface. The surface pressure−area isotherms of each isomer are readily distinguished by plateau regions at 12.5 mN/m (E-isomer) and 14.0 mN/m (Z-isomer). Scanning force microscopy (SFM) was employed to scrutinize the structure of transferred Langmuir−Blodgett (LB) films on mica. The SFM and film balance measurements as well as the results from ATR-FT-IR spectroscopy indicate that the peptide cylinders are oriented predominantly perpendicular to the surface normal. SFM images demonstrate that at higher surface pressure a second peptide layer atop the first one is formed. The proposed model was further supported by temperature-depen...