Optically Active Porous Materials Constructed by Chirally Helical Substituted Polyacetylene through a High Internal Phase Emulsion Approach and the Application in Enantioselective Crystallization

Abstract

This article reports the first optically active macroporous materials constructed by helical substituted polyacetylene and prepared by a high internal phase emulsion (HIPE) technique. The macroporous (∼3 μm) materials were fabricated simply through polymerization of the continuous phase in HIPEs. The porous structures of the resulting materials can be adjusted by varying the fraction of the dispersed phase. The obtained materials were characterized by regular pore morphology, high porosity, and low density. Circular dichroism and UV−vis absorption spectra demonstrated that the substituted polyacetylene forming the materials adopted chirally helical conformations, which endowed the materials with considerable optical activity. The optically active porous materials were used as chiral inducers and efficiently induced enantioselective crystallization of threonine and alanine racemates. L-Threonine and L-alanine were preferably induced to form crystals from the respective racemic solutions. The prepared materials open a new type of functional chiral materials with potential applications in asymmetric catalysis, chiral resolution, etc. C hiral porous materials have recently constituted an active research area in materials science. 1 They combine two important concepts, "chirality" and "porosity", in one entity. This distinctive feature renders the materials with intriguing properties, e.g., optical activity, low density, and high specific surface area. They have found significant applications in asymmetric catalysis, 2 enantioselective release, 3 chiral resolution, 4 etc. Unfortunately, chiral porous materials reported to date were primarily limited to inorganics (silica 5 and metals 6 ) and organic−inorganic hybrids. 7 For chiral porous architectures solely constructed by organic polymers (chiral POPs), there have been only a few reports in the literature. 8−12 In particular notably, the chirality of such chiral POPs exclusively originated from configurational chirality (chiral small molecular units). Therefore, it still remains as a big challenge to construct chiral POPs by using synthetic helical polymers, in which the chirality is primarily contributed by conformational chirality (chiral helical structures).In the present study, we prepared chiral POPs consisting of optically active helical substituted polyacetylenes through a straightforward technique, i.e., the high internal phase emulsion (HIPE) polymerization approach. 13,14 A variety of achiral advanced materials have been fabricated through HIPE and exhibited potential applications such as biomaterials 15 and separation materials. 16 Chiral helical substituted polyacetylenes are remarkably attractive as typical synthetic helical polymers 17−19 that show interesting chiral amplification effects. 20−23 Nowadays new synthetic helical polymers have been continuously established. 24−27 Our group has constructed chiral porous (or hollow) nano-and microscaled particles by helical substituted polyacetylenes. 8,28−30 On the basis of the previous studies, we further e...

Graphene Oxide (GO) as Stabilizer for Preparing Chirally Helical Polyacetylene/GO Hybrid Microspheres via Suspension Polymerization

“…Thus, we swelled the MG‐MPs in CHCl 3 and pressed them into a thin film. The film was characterized by CD and UV–vis spectroscopy in the way reported in our earlier studies . For comparison, we also characterized the film of P‐MPs and aqueous dispersions of GO and MGO.…”

“…In spectrum c, the ID/IG ratio for MG‐MPs decreased to 0.6. The consequence was attributed to the increase of sp 2 carbon atoms ( cis CC in substituted polyacetylene) after the polymerization with M1. To further explore the connection between MGO and polymer, we smashed the MG‐MPs and the thus‐obtained powder was also tested by Raman spectroscopy.…”

“…To further explore the connection between MGO and polymer, we smashed the MG‐MPs and the thus‐obtained powder was also tested by Raman spectroscopy. The spectrum d in Figure B was similar to the typical Raman spectra of polyacetylenes studied in earlier research . The peaks at 1625, 1440, 1311, and 1222 cm −1 separately represent the Raman signals of cis CC, trans CC, cis CC, and trans CC structures.…”

“…Optically active helical polymers have attracted great attention owing to their fascinating helical structures and significant potentials in chiral recognition, chiral separation, and asymmetric catalysis . Optically active spheres combining the advantages of helical polymers and the strength of particulate materials become increasingly interesting as a newly emerging type of advanced materials .…”

Visible chiral discrimination via macroscopic selective assembly

“…Although chirality transfer and chiral recognition from the microscopic to the macroscopic scale have promise for many practical applications, e.g., chiral separation [3][4][5] , optical memories and switches [6][7][8][9] , and functional sensors and actuators [10][11][12][13] , they still remain key challenges in artificial systems 1,2,14 . To scale up chirality, a supramolecular strategy is generally employed to obtain various chiral architectures via assemblies of chiral or achiral molecules through non-covalent interactions [15][16][17] .…”