Helicity induction and chiral amplification in a poly(phenylacetylene) bearing N,N-diisopropylaminomethyl groups with chiral acids in water

A water-soluble, hydrochloride of a stereoregular poly(phenylacetylene) bearing an N,N-diisopropylaminomethyl group (poly-1-HCl) as the pendant was found to form a predominantly one-handed helix upon complexation with various chiral acids including aromatic and aliphatic carboxylic acids, phosphoric and sulfonic acids, and amino acids through noncovalent bonding interactions in water. The complexes exhibited an induced circular dichroism (ICD) in the U-V-vis region of the polymer backbone. The Cotton effect signs were the same when chiral carboxylic acids with the same absolute configurations were used. In sharp contrast to the helix induction in the neutral poly-1 with chiral acids in organic solvents, the charged poly-1-HCl is highly sensitive to the chirality of the acids and can detect a small enantiomeric imbalance in the chiral acids in water.