Isolable Chiral Aggregates of Achiral π‐Conjugated Carboxylic Acids

Abstract

The induced aggregation of achiral building blocks by a chiral species to form chiral aggregates with memorized chirality has been observed for a number of systems. However, chiral memory in isolated aggregates of achiral building blocks remains rare. One possible reason for this discrepancy could be that not much is understood in terms of designing these chiral aggregates. Herein, we report a strategy for creating such isolable chiral aggregates from achiral building blocks that retain chiral memory after the facile physical removal of the chiral templates. This strategy was used for the isolation of chiral homoaggregates of neutral achiral π-conjugated carboxylic acids in pure aqueous solution. Under what we have termed an "interaction-substitution" mechanism, we generated chiral homoaggregates of a variety of π-conjugated carboxylic acids by using carboxymethyl cellulose (CMC) as a mediator in acidic aqueous solutions. These aggregates were subsequently isolated from the CMC templates whilst retaining their memorized supramolecular chirality. Circular dichroism (CD) spectra of the aggregates formed in the acidic CMC solution exhibited bisignated exciton-coupled signals of various signs and intensities that were maintained in the isolated pure homoaggregates of the achiral π-conjugated carboxylic acids. The memory of the supramolecular chirality in the isolated aggregates was ascribed to the substitution of COOH/COOH hydrogen-bonding interaction between the carboxylic acid groups within the aggregates for the hydrogen-bonding interactions between the COOH groups of the building blocks and the chiral templates. We expect that this "interaction-substitution" procedure will open up a new route to isolable pure chiral aggregates from achiral species.

Environmentally‐Friendly Lithium Recycling From a Spent Organic Li‐Ion Battery

“…Moreover, the signals seen in the IR spectra for the sam- ples obtained from batteries containing LiPF 6 do not match with LiPF 6 , POF 3 , [48] or H 3 PO 4 . 31 P NMR spectroscopy performed in D 2 O on the LP30 sample revealed multiple peaks at 1-2 ppm in the phosphate O = P(OR) 3 area and a single minor peak at 20 ppm in the phosphonate O = PR(OR') 2 area. This indicates that LiPF 6 /POF 3 are not present and underwent further evolution to water-stable phosphate/phosphonate derivatives.…”

“…[31] Malonic acid 2 is a natural but toxic compound that can be found in fermented fruits or fruit vinegars, [32] but it is especially abundant in alfalfa, [33] one of the most cultivated forage legumes in the world. For instance, dilithium trans-trans benzenediacrylate 1 could be synthesized through a Doebner modification of the Knoevenagel condensation from malonic acid 2 and terephthalaldehyde 3 (Scheme 1).…”

“…For instance, dilithium trans-trans benzenediacrylate 1 could be synthesized through a Doebner modification of the Knoevenagel condensation from malonic acid 2 and terephthalaldehyde 3 (Scheme 1). [31] Malonic acid 2 is a natural but toxic compound that can be found in fermented fruits or fruit vinegars, [32] but it is especially abundant in alfalfa, [33] one of the most cultivated forage legumes in the world. Terephthalaldehyde 3 can be prepared through a reduction reaction from terephthalic acid, [34] an important monomer for thermoplastic polymers.…”

Photoresponsive chiral nanotubes of achiral amphiphilic azobenzene

“…This exciton type CE is near to the absorption maximum of the aggregate suspension, indicating that the CE was due to the chiral interaction between the chromophores. Since the individual molecular building block is achiral, the strong bisignated CD signal, corresponding to the negative exciton-coupled CD, clearly indicates the presence of a helical arrangement of the transition dipoles that were polarized along the long axis of the azobenzene skeleton within a stack, 21 suggesting breaking of the chiral symmetry. The aggregate suspension had the same CD spectrum after being stored for several months, thus the racemization did not occur after the helical stacks had formed.…”

Structure of sodium carboxymethyl cellulose aqueous solutions: A SANS and rheology study

“…Simulations by Wang and Somasundaran 25 suggest that NaCMC adopts a helical conformation in bulk and in solution while Biermann et al 26 found that, depending on the substitution pattern, the chain may be locally collapsed or highly extended. Although a helical chain conformation is suggested by optical rotary dispersion and circular dichroism data, 27 – 29 light scattering, intrinsic viscosity, potentiometric titration, and dielectric spectroscopy data have been successfully interpreted assuming a locally linear conformation. 11 , 17 , 24 , 30 , 31 …”