Supramolecular Chiral Aggregates Exhibiting Nonlinear CD–ee Dependence

Abstract

chiral auxiliaries, has become a major interest in supramolecular chemistry and material sciences, [2,3] highly significant for asymmetric catalysis, [4] chiral recognition and separation, [5] circularly polarized luminescence (CPL), [6] and photovoltaic device. [7] Unique properties such as chiral amplification, chiral induction and chiral memory, have been well studied for supramolecular aggregates, among which the "majorityrules effect" (MRE) represents an appealing class of chiral amplification phenomenon that is of relevance to the understanding of the origin of homochirality in Nature. [8] The MRE means that a slight excess of one enantiomer results in a strong bias toward the helical sense that is preferred by the major enantiomer (Figure 1a). In that case the optical activity, normally indicated by CD signals, of the helical aggregates generated from enantiomeric mixtures of varying enantiomeric excess (ee) is higher than that expected from a linear relationship. Therefore, the MRE is characterized by a positive nonlinear (S-or Z-shaped) dependence of the CD signal against ee of the chiral building block or of the chiral auxiliary or inducer (Figure 1b). A sister effect that implies chiral amplification in supramolecular aggregates is the "sergeants-and-soldiers" principle, which describes the transfer of chirality from chiral monomers to achiral ones, at the supramolecular level. According to this principle, a small amount of chiral auxiliary (sergeants) dictates the overall chirality of a polymeric system that consists mainly of the achiral compound (soldiers, Figure 1c). [8] The "sergeants-andsoldiers" principle is in general demonstrated by a positive nonlinear curve for the helicity (manifested by CD signals) versus the fraction of chiral sergeants (Figure 1c), similar to the positive nonlinear CD-ee dependence shown for the MRE-operative supramolecular polymeric systems (Figure 1b). In fact, the linear CD-ee dependence is most commonly observed in the supramolecular helical aggregates, while the MRE has only been found in minority of the cases. The negative nonlinear (anti-S or anti-Z shaped) CD-ee dependence is much less explored in the supramolecular helical aggregates (Figure 1b). Very recently, this unconventional dependence has indeed been observed in the induced aggregates of achiral boronic acid-functionalized perylenebisimide dyes by chiral phenyllactate and malate. [9] This phenomenon has immediately been applied for the accurate determination of enantiopurity of malate at the high ee region. [10] Although a linear relationship between the optical activity (normally the CD signal) and the enantiomeric excess (ee) of chiral auxiliaries has been the most commonly observed dependence in dynamic supramolecular helical aggregates, positive nonlinear CD-ee dependence, known as the "majorityrules effect" (MRE), indicative of chiral amplification, has also been well documented and to some extent understood. In sharp contrast, the negative nonlinear CD-ee dependence has been much less reported and i...

Chiral Recognition by Flexible Coordination Polymers of Ag+ with a Cysteine-Based Chiral Thiol Ligand That Bears a Binding Site

“…CD-ee (ee = enatiomeric excess) dependence serves as another support. CD signals of the Ag + - 1 coordination polymer vary in a negative nonlinear way with ee of the chiral thiol ligand 1 in 1:1 (v/v) EtOH/buffer of pH 8.5 (Figures and S10c), which was previously termed as the racemate rules effect. − This means that d - 1 and l - 1 prefer to appear in pairs to bind on the Ag + - 1 polymeric backbone, likely with all d - 1 ligands on one side and all l - 1 ligands on the other side of the backbone. A Ag + - 1 coordination polymer shows the same CD profiles at different ee of 1 (Figure S10), whereas in some of the previous reports that also exhibit negative nonlinear CD-ee dependence, the CD profiles were ee-dependent. ,, Interestingly, when a racemic mixture of glucose was added, the CD-ee dependence turns out to be linear (Figures and S10d).…”

Multiple Transformations among Anion-based A2nL3n Assemblies: Bicapped Trigonal Antiprism A8L12, Tetrahedron A4L6, and Triple Helicate A2L3 (A = Anion)

“…The phenomenon of the increased CD signals caused by structural transformation is reminiscent of that induced by chiral auxiliary in supramolecular polymeric systems (Figures S68 and S69). , …”

Chirality in peptide‐based materials: From chirality effects to potential applications

“…Majority-rule effect (MRE) is an uncommon chiral amplification phenomenon in the peptide-based systems containing multiple chiral centers, of which the major enantiomer determines the helicity bias of aggregates rather than the minority ones. 60 For example, the enantiomer that has a numerical advantage in syndiotactic peptides would force the remaining opposite chiral residues to adapt to the screw sense preferred by the superior one. 61 In comparison, the sergeant-soldier principle is 58 Optimized structures of dimers of LPF (E) and LPFEG (F) in both side and top view.…”