Characterization of Peptide-Guided Polymer Assembly at the Air/Water Interface

An organo-soluble, peptide−polymer conjugate that combines poly(n-butyl acrylate) with a β-sheet-forming peptide is spread at the water surface to investigate peptide-guided self-assembly in a two-dimensional environment. Single layers of the conjugate are studied to gain information on the packing, orientation, and structure of the conjugate molecules using standard monolayer techniques: isotherms, grazing incidence X-ray diffraction (GIXD), and infrared reflection absorption spectroscopy (IRRAS). At all conditions studied, the stabilizing β-sheet network consists of antiparallel β-sheets oriented parallel to the air/water interface. The incorporation of temporary switch defects in the peptide segment enables β-sheet assembly to be triggered at different packing densities. Stable monolayers, with low compressibilities similar to peptide monolayers, form when β-sheet assembly occurs in monolayers that contain closely packed conjugate molecules. Langmuir−Schaefer transfer of the switched monolayer seeded with 1/1000 part stearic acid results in a transferred monolayer containing ordered domains with 7 nm wide stripes, a width in agreement with the end-to-end distance of the conjugate molecule. In this interfacial system, high packing densities and a hydrophobic seed molecule play an important role in β-sheet network and structure formation. Both effects likely direct the highly ordered β-sheet structure because of β-strand prealignment. Insights gained from self-assembly in this system can be applied to peptide aggregation mechanisms in more complex interfacial environments.