Switchable enantioseparation based on macromolecular memory of a helical polyacetylene in the solid state

Abstract

In the chromatographic separation of enantiomers the order of elution is determined by the strength of diasteromeric interactions between the components of the mixture and a chiral stationary phase. For analytical purposes, it is ideal to have the minor component elute first, whereas in the preparative mode a faster elution of the major component is desirable. Here we describe a stationary phase constructed from a polyacetylene that bears 2,2'-bisphenol-derived side chains in which chirality can be switched in the solid state prior to use. Both the macromolecular helicity of the polymer backbone and the axial chirality of the side chains can be switched in the solid state by interaction with a chiral alcohol, but importantly are maintained after removal of the chiral alcohol because of a memory effect. The chiral stationary phase thus prepared was used to separate the enantiomers of trans-stilbene oxide with the enantiomer elution order determined by the preseparation treatment.

Macromolecular Helicity Induction and Memory in a Poly(biphenylylacetylene) Bearing an Ester Group and Its Application to a Chiral Stationary Phase for High-performance Liquid Chromatography

“…7 The stereoregularity of the obtained polymer was confirmed to be almost completely cis-transoidal by 1 H NMR analysis ( Figure S1). 8,9 The number-average molecular weight and its distribution, determined by size-exclusion chromatography, were 9.4 © 10 5 and 1.7, respectively.…”

“…7 Moreover, mirror-imaged VCD signals were also observed in the C=O stretching band region of the ester groups in the pendants. These results indicate that the ester groups introduced at the 4¤-position of the biphenyl pendants are arranged in a preferred-handed helical array along the main-chain helicity.…”

“…5,6 We recently reported that poly([2,2¤-bis(methoxymethoxy)-4¤-dodecyloxy-4-biphenylyl]acetylene) (poly(DOBA)) forms a preferred-handed helical conformation together with an excess of one of the axially twisted conformations in the biphenyl pendants, which occurs through the noncovalent interaction with an optically active alcohol ((R)-or (S)-1) both in solution and in the solid state. 7 The induced main-chain helicity and axial chirality can be maintained (or memorized) even after the removal of the chiral alcohol (Scheme 1). By using this unusual feature of poly(DOBA), we succeeded in developing a switchable CSP in which the elution order of the enantiomers could be switched at will on the basis of reversible switching and the subsequent memory of macromolecular helicity in poly(DOBA) by sequential treatment with (R)-and (S)-1 in the solid state.…”

Synthesis of Optically Active Poly(diphenylacetylene)s Using Polymer Reactions and an Evaluation of Their Chiral Recognition Abilities as Chiral Stationary Phases for HPLC

“…Optically active poly(phenylacetylene)s with a preferred-handed helicity have been prepared [16] and some of these systems have been reported to exhibit good chiral recognition abilities as CSPs for HPLC because of their preferred-handed helical conformation [17][18][19][20][21][22][23][24][25][26]. However, very few optically active poly(diphenylacetylene)s have been prepared to date, which has limited research towards evaluating the scope and efficiency of the chiral recognition abilities of these materials [27][28][29][30][31][32][33][34][35].…”

Supramolecular Chirality in Dynamic Coordination Chemistry

“…such as small organic molecules [13][14][15][16][17][18][19], polymers [20][21][22][23], metamaterials [24], and assemblies [25][26][27][28], have been developed for chirality induction and switching in response to external stimuli, more sophisticated systems are required to mimic natural systems.…”