Cyclic peptide-polymer complexes and their self-assembly.

The efficient synthesis of novel chiral cyclic peptides cyclo[NHCHX-CH=CHCH(2)CO(NHCH(2)CH=CHCH(2)CO)(2)] designed to develop hydrogen-bonding interactions with suitable polymers is described. Complexation of a carboxylic acid derivatized cyclic peptide 2 (X = CH(2)OCOCH(2)CH(2)CO(2)H) capable of self-assembling as "endless" tubes, with poly(vinyl alcohol) (PVA) led to a vast weak-interaction network, in which the cyclopeptide developed extensive hydrogen-bonding interactions with the hydroxyl groups of PVA through not only the carboxylic acid, but also its ester carbonyl and amide groups. In aqueous solution, the peptide/PVA complexes self-assemble into long-grain ricelike aggregates compatible with the stacking of cyclic peptides through intercycle hydrogen bonds. Upon casting on silicon wafer, the anisotropic aggregates can coalesce to form filaments tens of micrometers long. The study demonstrates that complexing functionalized cyclic peptides with polymers through hydrogen bonding is a useful approach for using polymers to mediate the self-assembly and self-organization of cyclic peptides.