Three-State Switchable Chiral Stationary Phase Based on Helicity Control of an Optically Active Poly(phenylacetylene) Derivative by Using Metal Cations in the Solid State

Abstract

An unprecedented three-state switchable chiral stationary phase (CSP) for high-performance liquid chromatography (HPLC) was developed by using a helical poly(phenylacetylene) bearing a chiral (R)-α-methoxyphenylacetic acid residue as the pendant (poly-1). The left-and right-handed helical conformations were induced in poly-1-based CSP upon coordination with a catalytic amount of soluble sodium and cesium tetrakis[3,5-bis(trifluoromethyl)phenyl]borate salts (MBArF), respectively, which are soluble in the HPLC conditions [hexane−2-propanol (95:5, v/v)]. The switch between the two different helical states of poly-1 can be easily done by rinsing the poly-1-based CSP with MeOH and the subsequent addition of the proper MBArF salt. By using this dynamic helical CSP, we demonstrated how changes on the orientation of secondary structure of a chiral polymer can alter and even invert the elution order of the enantiomers. This study was done without adding chiral additives or changing the mobile phase which could produce changes on the retention times making more difficult to extract the role of the secondary structure during the chiral recognition process. Figure 1. Schematic illustration of macromolecular helicity modulation in poly-1 through conformational switching of the MPA pendants using metal cations in solution. ASSOCIATED CONTENT Supporting Information The Supporting Information is available free of charge on the ACS Publications website at DOI: XXXXXXXXXX. Materials and methods and supporting data (PDF)

Helicity Induction and Its Static Memory of Poly(biphenylylacetylene)s Bearing Pyridine N‐Oxide Groups and Their Use as Asymmetric Organocatalysts

“…INTRODUCTION Inspired by the sophisticated functions of biological helical polymers and their assemblies, a rich variety of artificial helical polymers has been prepared over the past decades [1][2][3][4][5][6][7][8] in order to develop advanced chiral materials for the resolution of enantiomers by chromatography, [9][10][11][12][13][14][15][16][17] sensing of chiral molecules, [18][19][20][21] and circularly polarized luminescence. [22][23][24][25][26][27] The application of optically active helical polymers for asymmetric catalysis has also attracted growing interest, because a onehanded helical chirality can significantly contribute to the enantioselectivity due to a one-handed helical arrangement of the catalytically active, chiral/achiral units along the one-handed helical polymer backbone.…”

Chiral Conflict as a Method to Create Stimuli‐Responsive Materials Based on Dynamic Helical Polymers

“…[33][34][35][36][37] On the other hand, poly-(R)-2 stabil-izes an M helix in the presence of both types of ions (Figure 4b). [38,39] Owing to the active chiral conflict in the copolymer, it was expected that the different interactions of the comonomers with the ions could either enhance acertain helical sense;for example, m-(R)-2 inverts its helical sense from P 2 to M 2 ,while m-(R)-1 keeps its M 1 helical structure;that is,anexcess of M helicity (Figure 4c), or generate another axially racemic copolymer mirror image of the original one,f or example, m-(R)-1 goes from M 1 to P 1 and m-(R)-2 from P 2 to M 2 ;that is,f rom axially racemic 1 to axially racemic 2 (Figure 4c), through the mechanisms shown in Figure 1.…”

“…[39][40][41][42][43][44][45] Their molecular weights were estimated by GPC (THF as eluent with polystyrene standards as calibrants;s ee the Supporting Information for details) to be between M n = 7832 and 20 325 with M n /M w values around 1.58-1.68. [39][40][41][42][43][44][45] Their molecular weights were estimated by GPC (THF as eluent with polystyrene standards as calibrants;s ee the Supporting Information for details) to be between M n = 7832 and 20 325 with M n /M w values around 1.58-1.68.…”

“…Thus,h omopolymers poly-(R)-1 and poly-(R)-2 and the copolymer series poly-[(R)-1 x -co-(R)-2 1Àx ]( x = 0.1-0.9) were prepared by using aR h I catalyst, [{Rh(nbd)Cl} 2 (nbd = 2,5norbonadiene)].A ll the copolymers showed by NMR (vinyl protons, d = 5.7-5.8 ppm) and Raman (1580, 1343, 1006 cm À1 ) to possess a cis polyene backbone. [39][40][41][42][43][44][45] Their molecular weights were estimated by GPC (THF as eluent with polystyrene standards as calibrants;s ee the Supporting Information for details) to be between M n = 7832 and 20 325…”

Chiral Conflict as a Method to Create Stimuli‐Responsive Materials Based on Dynamic Helical Polymers

“…Thus, homopolymers poly‐( R )‐ 1 and poly‐( R )‐ 2 and the copolymer series poly‐[( R )‐ 1 x ‐ co ‐( R )‐ 2 1− x ] ( x =0.1–0.9) were prepared by using a Rh I catalyst, [{Rh(nbd)Cl} 2 (nbd=2,5‐norbonadiene)]. All the copolymers showed by NMR (vinyl protons, δ =5.7–5.8 ppm) and Raman (1580, 1343, 1006 cm −1 ) to possess a cis polyene backbone . Their molecular weights were estimated by GPC (THF as eluent with polystyrene standards as calibrants; see the Supporting Information for details) to be between M n =7832 and 20 325 with M n / M w values around 1.58–1.68.…”