Self-Assembly of α-Helix Peptide/Crown Ether Conjugate upon Complexation with Ammonium-Terminated Alkanethiolate

Hydrophobic helical crowned peptides were synthesized and investigated on formation of an oriented thin layer of the helix peptides. The helix peptides in ethanol were incubated with a self-assembled monolayer (SAM) of ammonium-terminated alkanethiolate on a gold surface. The thickness of the peptide thin layer formed on the gold surface was determined by the surface plasmon resonance method. Complexation of the crowned peptide with the ammonium-terminated alkanethiolate facilitated formation of a peptide monolayer or multilayers on gold depending on the peptide concentration. The orientation of the helix peptide on the gold surface was investigated by FT-IR reflection−absorption spectroscopy. The tilt angle of the helix axis from the normal of the gold surface was estimated to be 28°, when the crowned peptide complexed with the SAM of N -(ε-aminocaproyl)aminoethyl disulfide. This degree of orientation is more vertical to the surface than that of the complexed peptide with a SAM of 2-aminoethanethiol hydrochloride. Since the helix peptide without the crown ether unit was oriented in parallel to the surface, the crown ether/ammonium complexation should promote the vertical orientation of the helix peptides on the gold surface.