Molecular assembly formation of cyclic hexa-beta-peptide composed of acetylated glycosamino acids.

A novel cyclic hexamer of acetylated beta-glycosamino acid was synthesized and its conformation and molecular assembly formation was investigated. Variable temperature NMR study indicated that the cyclic hexapeptide took a C(3) symmetric conformation at room temperature, but at elevated temperatures a C(6) symmetric one, which was not due to averaging of the C(3) symmetric conformation, appeared. Computational geometry optimization showed that the C(6) symmetric conformation was a highly planar structure with amide groups orienting perpendicular to the ring plane. The cyclic hexa-beta-peptide formed rod-shaped crystals from an N,N-dimethyl formamide solution at elevated temperature. The optical microscopy observation with a sensitive tint plate under cross-nicol configuration and electron diffraction analysis of the crystals revealed that the cyclic hexa-beta-peptides were stacked one after the other to form a regular nanotube structure.