Helicity induction in charged poly(phenylacetylene)s bearing various acidic functional groups in water and its mechanism

We investigated the helicity induction in a series of stereoregular cis-transoidal poly(phenylacetylene)s bearing various acidic functional groups, such as a phosphonic acid and its monoethyl ester (poly-1-H and poly-2-H, respectively), a carboxylic acid (poly-3-H), and a sulfonic acid (poly-4-H) as the pendants with optically active small molecules with opposite charges, such as amino acids and amines in water. Poly-1-H, poly-2-H, and poly-4-H have a more acidic phosphonic or a sulfonic group than the carboxy group of poly-3-H as the pendant, and they could form complexes with the 19 common free L-amino acids as well as optically active amines. The complexes showed characteristic induced circular dichroisms (ICDs) in the polymer backbone regions, due to the prevailing one-handed helix formations on the polymers. On the other hand, poly-3-H, which was insoluble in water, but became soluble as the sodium salt (poly-3-Na), exhibited ICDs in the presence of only several common free L-amino acids and optically active amines. The interactions of these polyelectrolytes with selected optically active amino acids and amines in water depending on the pH were studied in detail by means of CD spectroscopy together with the potentiometric pH titrations, and the mechanism of the helicity induction in the polyelectrolytes was discussed.