Preorganized Homochiral Pyrrole-Based Receptors That Display Enantioselective Anion Binding

Herein, a new scaffold for anion recognition based on a tripodal tris(pyrrolamide) motif is presented. The receptors were able to bind to a variety of anions with high affinity. Using density functional theory methods, the three-dimensional geometry of the receptor-anion complex was calculated. These calculations show that the receptors bind anions via a preorganized cavity of amide and pyrrole hydrogen bond donor groups. Based on these findings, homochiral tris(pyrrolamide) receptors were prepared, which produced as much as a 1.6-fold greater affinity for (S)-(+)-mandelate over (R)-(-)-mandelate, demonstrating the ability to differentiate between these enantiomeric anions. The interaction of (S)-(+)-mandelate and (R)-(-)-mandelate within the homochiral receptor was examined by solution NMR spectroscopy and density functional theory calculations. These findings indicate that the preorganized positioning of the pyrrole groups and subsequent sterics allows to differentiate between the stereoisomeric anions.

Recognition of Chiral Carboxylates by Synthetic Receptors

Recognition of anionic species plays a fundamental role in many essential chemical, biological, and environmental processes. Numerous monographs and review papers on molecular recognition of anions by synthetic receptors reflect the continuing and growing interest in this area of supramolecular chemistry. However, despite the enormous progress made over the last 20 years in the design of these molecules, the design of receptors for chiral anions is much less developed. Chiral recognition is one of the most subtle types of selectivity, and it requires very precise spatial organization of the receptor framework. At the same time, this phenomenon commonly occurs in many processes present in nature, often being their fundamental step. For these reasons, research directed toward understanding the chiral anion recognition phenomenon may lead to the identification of structural patterns that enable increasingly efficient receptor design. In this review, we present the recent progress made in the area of synthetic receptors for biologically relevant chiral carboxylates.

A chiral spirobifluorene-based bis(salen) zinc(ii) receptor towards highly enantioselective binding of chiral carboxylates

We have designed a new chiral receptor based on two salen zinc(ii) complex units connected with a spirobifluorene framework. The chiral receptor is proven to enantioselectively bind chiral carboxylate guests and the differences between the binding constants of enantiomeric guests were up to more than one order of magnitude.

The Impact of Solvent and the Receptor Structure on Chiral Recognition Using Model Acyclic Bisamides Decorated with Glucosamine Pendant Arms

We investigated the influence of various factors (including solvent mixtures) on chiral recognition of chiral carboxylates, using the titration method under ¹H NMR control. We found that strong binding carboxylates (geometrical matching) is not enough for the satisfactory differentiation of enantiomers. Moreover, solvent mixture studies indicate a significant influence of environment on the formation of diastereomeric complexes and variations among them. Our findings offer insights into the complementarity of chiral recognition processes.

Chiral Recognition of Carboxylate Anions by (R)-BINOL-Based Macrocyclic Receptors

Three (R)-BINOL-based macrocyclic receptors obtained via double-amidation reaction were used for chiral recognition of four anions derived from α-hydroxy and α-amino acids. The structural factors of hosts and guests that affect chiral recognition processes were also investigated, indicating that the proper geometry of both receptor and guest molecules plays a crucial role in effective enantio-discrimination.

A pillar[5]arene-calix[4]pyrrole enantioselective receptor for mandelate anion recognition

A novel pillar[5]arene-calix[4]pyrrole was synthesized as a chiral receptor for mandelate anions with a maximum enantioselectivity of 2.47.

Switching chirality in the assemblies of bio-based amphiphiles solely by varying their alkyl chain length

Chirality inversion in the nanotubes of bio-based amphiphiles could be realized solely by increasing the alkyl chain length.

Enhancing the enantioselective recognition and sensing of chiral anions by halogen bonding

Novel halogen bonding chiral (S)-1,1′-bi-2-naphthol-based receptor molecules significantly enhance enantioselective anion recognition and electrochemical sensing compared to their hydrogen bonding analogues.