Synthesis and characterization of amphiphilic o-phenylene ethynylene oligomers

Abstract

We have previously reported the synthesis of short o-phenylene ethynylene oligomers with polar triethylene glycol side chains which adopt a helical conformation in solution with three residues per turn. Two new oligomers have been synthesized, a hexamer and a nonamer, incorporating a repeated triad motif of polar–nonpolar–polar sidechains in order to create a hydrophobic stripe in the folded conformation which we report here for the first time. Helical folding in solution was observed and, unlike the previously-reported oligomers, these new oligomers are ordered solids at room temperature. Although these oligomers were designed to assemble into helical bundle-like structures, no evidence for a quaternary-like structure was found. The difference in polarity between alkyl and triethylene glycol side chains is likely not strong enough to induce self-association of folded helices, especially since the molecules are not water soluble where the driving force for association of the nonpolar stripe would be larger. We expect that more polar side chains, granting water solubility, represent an important target for future research.