Positive Synergy
between the Helical Poly(phenylacetylene)
Backbones and the Helical L‑Proline Oligopeptide
Pendants for Enhanced Enantioseparation Properties
A series of optically active helical poly(phenylacetylene)s
(PPA-Pro1, PPA-Pro3, PPA-Pro6, PPA-Pro9, and PPA-Pro12) bearing different chain
lengths of L-proline oligopeptide in the side chains
were obtained
by polymerizing the corresponding novel phenylacetylene monomers.
The monomer adopted a trans-rich helix structure
when the L-proline oligopeptide chain length was
longer, according to the optical activities and 2D-NMR analysis. The
helical structure could be maintained and significantly influenced
the polymers’ helical conformation by introducing the L-proline oligopeptide to the pendants. By the way, the
morphology of PPA-Pro3 was observed
by atomic force microscope (AFM) on highly oriented pyrolytic graphite
(HOPG), and the information on the helix direction, pitch, and chain
arrangement was obtained. Also, the chiral separation properties of
these polymer-based chiral stationary phases (CSPs) were investigated
using high-performance liquid chromatography (HPLC). The poly(phenylacetylene)s
showed enhanced enantioseparation properties toward various racemates
depending on the longer chain length of the L-proline
oligopeptide in the pendants and the positive synergy between the
helical backbone and helical side chains. Particularly, PPA-Pro9 showed comparable or even superior enantioseparation
properties for racemates 2 and 9 to four commercial columns (Daicel
Chiralpak or Chiralcel AD, AS, OD, and OT), indicating that these
poly(phenylacetylene)-based CSPs have potential practical values.
This work presented here provides inspiration for the further development
of CSPs based on a new paradigm.