Solution effects on the self-association of a water-soluble peptoid.

A desire to replicate the structural and functional complexity of proteins with structured, sequence-specific oligomers motivates study of the structural features of water-soluble peptoids (N-substituted glycine oligomers). Understanding the molecular-level details of peptoid self-assembly in water is essential to advance peptoids' application as novel materials. Peptoid 1, an amphiphilic, putatively helical peptoid previously studied in our laboratory, shows evidence of self-association in aqueous solution. In this work, we evaluate how changes to aqueous solution conditions influence the self-association of 1. We report that changes to pH influence the fluorescence and CD spectroscopic features as well as the peptoid's interaction with a solvatochromic fluorophore and its apparent size as estimated by size exclusion chromatography. Addition of guanidine hydrochloride and ammonium sulfate also modulate spectroscopic features of the peptoid, its interaction with a solvatochromic fluorophore, and its elution in size exclusion chromatography. These data suggest that the ordering of the self-assembly changes in response to pH and with solvent additives and is more ordered at higher pH and in the presence of guanidine hydrochloride. The deeper understanding of the self-association of 1 afforded by these studies informs the design of new stimuli-responsive peptoids with stable tertiary or quaternary structures.