Chiral Discrimination through ¹H NMR and Luminescence Spectroscopy: Dynamic Processes and Solid Strip for Chiral Recognition

Abstract

The appropriate choice of the host molecules with well-defined optical activity (S-H/R-H) helps in the differentiation between two secondary ammonium ion-derivative guest molecules with different optical activities (R-G/S-G) based on the fluorescence resonance energy transfer (FRET)-based luminescence responses. Crown ether-based host molecules with opposite chiral configurations (R-H, S-H) have been derived from 1,1'-bi-2-naphthol (BINOL) derivatives that have axially chiral biaryl centers. These chiral crown ethers form host-guest complexes (i.e., [2]pseudorotaxanes) with chiral secondary ammonium ion derivatives (R-G, S-G). NMR spectroscopic studies show that the complexes are in a dynamic equilibrium in solution. Results of the H NMR and fluorescence spectroscopic studies indicate a head-on orientation of the host and guest in the [2]pseudorotaxanes. The difference in the efficiency in the FRET-based responses between anthracene and the BINOL derivatives allow efficient chiral discrimination of the guests. Isothermal titration calorimetry and NMR investigations reveal that inclusion complexes between hosts and guests of the same chirality (R-H⋅R-G, S-H⋅S-G) are more stable relative to those of opposite chirality (R-H⋅S-G, S-H⋅R-G). However, FRET-based energy-transfer efficiency is higher for R-H⋅S-G and S-H⋅R-G complexes. NMR spectroscopic studies show that the relative orientation of the guest in the host cavity is significantly different when the host binds a guest of the same or opposite chirality; furthermore, the latter is more favorable for FRET, thus enabling discrimination between enantiomers. Interestingly, chiral discrimination of guest ions could also be achieved by using silica surfaces modified with chiral host molecules.

Optically active crown ether‐based fluorescent sensor molecules: A mini‐review

“…In the cases of ( R )‐ 18 , ( S )‐ 18 , ( R )‐ 19 , ( S )‐ 19 , ( R,R )‐ 20 , and ( S,S )‐ 20 , association constants ( K ) were given only for the formation of ( R )‐( R ) and ( S )‐( S ) complexes showing large fluorescence spectral changes . In the cases of ( R )‐ 17 and ( S )‐ 17 , the complex stability constants ( K ) were determined by isothermal titration calorimetry …”

“…Gangopadhyay et al reported binaphtho‐crown ethers ( R )‐ 17 and ( S )‐ 17 (Figure ) . Functionalization of 1‐phenylethylamines with an anthracene fluorophore furnished such guest molecules, the enantiomers of PhEtAnt·PF 6 (Figure ), of which differentiation by crown hosts ( R )‐ 17 and ( S )‐ 17 could be examined on the basis of Förster resonance energy transfer (FRET)‐based fluorescence responses.…”

Supramolecular Chiral Discrimination of D-Phenylalanine Amino Acid Based on a Perylene Bisimide Derivative

“…The approach that was used in the present work can be considered as the initial point to use chiral perylene bisimide (PBI) based systems for the detection of specific chiral form. The supramolecular chiral discrimination of a single enantiomer over the other is reported even for other systems (Cooper et al, 2017;Gangopadhyay et al, 2017;Noguchi et al, 2017). We present here the symmetric PBI with D-phenylalanine in the amide position which acts as a chiral sensor only for the D form of the phenylalanine.…”

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

“…Since then, BINOL has been extensively used in chiral recognition [13] and exhibit excellent chiral induction in asymmetric reactions [14]. In recent years many scientists have employed this chiral molecule to create a new group of receptors, which have turned out to be appropriate for effective chiral recognition of anions [15,16,17], cations [18,19] and neutral molecules [20,21].…”