Visible chiral discrimination via macroscopic selective assembly

Abstract

The transfer of chirality from individual molecules to macroscopic objects, and the recognition of chirality on the macroscopic scale have potential for many practical applications, but they are still key challenges for the chiral research community. Here we present a strategy for visible chiral recognition by macroscopic assembly using polyacrylamide-based gels modified with β-cyclodextrin (βCD-gel) and D-or L-tryptophan (homochiral D-or L-Trp-gel), which differs from most methods reported, e.g., colorimetric or chromogenic methods, fluorescence, gel formation and collapse. The circular dichroism spectra demonstrate that the chirality of Trp molecules is successfully transferred and amplified in the corresponding Trpgels. The chirality of the D-and L-Trp-gels is macroscopically recognized by the βCD-gel selectivity in aqueous NaCl through the amplification of interfacial enantioselective host-guest interactions.

Research Progress on Synthesis and Application of Cyclodextrin Polymers

“…Through analysis and research, several factors were modified simultaneously to obtain an optimized separation method. Zheng et al [ 88 ] used β-CD-gel and d - or l -tryptophan (homotype d -or l -Trp-gel) modified polyacrylamide-based gel for visible chiral recognition. In the NaCl aqueous solution, due to the obvious changes, the β-CD gel successfully distinguished the d - and l -Trp gels macroscopically, and the chirality difference becomes obvious, which will be very conducive to more in-depth research.…”

Control of the macroscopic shape of assemblies formed from microparticles based on host–guest interaction

“…For visual discrimination, dyeing of Ad(y)-SAP microparticles was tested using several dyes. The food pigments, which we had used for poly(acrylamide)-based gels in our previous studies 23,24,[28][29][30] , were not useful in this study because the pigment molecules quickly came out of Ad(y)-SAP microparticles. The results of dyeing test indicated that pararosaniline was a useful dye presumably because of electrostatic interaction between the ammonium in pararosaniline and carboxylate residues in Ad(y)-SAP microparticles ( Figure S3 in Supporting Information).…”

The macroscopic shape of assemblies formed from microparticles based on host–guest interaction dependent on the guest content

“…For visual discrimination, dyeing of Ad(y)-SAP microparticles was tested using several dyes. The food pigments, which we had used for poly(acrylamide)-based gels in our previous studies 23,24,[28][29][30] , were not useful in this study because the pigment molecules quickly came out of Ad(y)-SAP microparticles. The results of dyeing test indicated that pararosaniline was a useful dye presumably because of electrostatic interaction between the ammonium in pararosaniline and carboxylate residues in Ad(y)-SAP microparticles (Figure 1c).…”

“…Recently, macroscopic selfassemblies, which allow ones to see molecular recognition by naked eyes, have been realized using millimeter-scale hydrogel pieces possessing molecular recognition moieties [23][24][25][26][27] . Even if the difference in binding constants of molecular recognition moieties is small, the systems of mixture of gel pieces can exhibit perfect delity by controlling the contents of molecular recognition moieties [28][29][30] . During the study on macroscopic self-assembly based on molecular recognition, we noticed that the shape of assemblies might be dependent on the host-guest pair; For example, the pair of β-cyclodextrin (βCD) and adamantyl (Ad), which shows one of the highest binding constants, led to the formation of linear alternating assemblies, whereas βCD and t-butyl, which possesses a lower binding constant, might form planar checkered assemblies 23 .…”