Vibrational Spectroscopic Evidence for the Associated-Anion Promotion of the Helical Structure of N-Acylglycine Oligomers

Abstract

Vibrational spectroscopic evidence for conformational change of the anions of N-acylglycine oligomers (trimers, tetramers, and pentamers) in aqueous solution is reported. The infrared absorption spectra of sample solutions diluted below the critical micelle concentration (cmc) can be explained by the coexistence of several conformations containing the polyglycine I-like extended form and the polyglycine II-like helix. However, above the cmc the infrared bands arising from the polyglycine II-like helix are intensified. This result is due to preferential stabilization of the helical structure, promoted by intermolecular association of the anions. The helical structure is also stable in the hydrophobic environment of micelles.