A Traceless Chiral Shift Reagent Based on Nonbonding Interactions with Single-Handed Helical Poly(quinoxaline-2,3-diyl)

A single-handed poly(quinoxaline-2,3-diyl) (PQX) has been found to serve as a new type of chiral shift reagent (CSR) for determining the enantiomeric ratio by NMR spectroscopy. Even though there is no specific binding site in the PQX, its nonbonding interaction with chiral analytes leads to a significant shift of the NMR chemical shift, allowing quantification of the enantiomeric ratio. The new type of CSR has the advantages of a wide scope of analytes including ethers, haloalkanes, and alkanes, easy tunability of the degree of chemical shifts by measurement temperature, and erasability of proton signals of CSR because of the short spin-spin (T₂) relaxation of the macromolecular scaffold.