Enantioselective Recognition of Neutral Molecules in Water by a Pair of Chiral Biomimetic Macrocyclic Receptors

Enantioselective recognition in water remains an ongoing challenge in supramolecular chemistry but is routine in nature.Herein,we report the first enantiopure pair of biomimetic macrocyclic receptors with hydrogen bonding donors in their deep hydrophobic cavities.The chiral naphthotubes can be efficiently synthesized through a chirality-directed macrocyclization strategy and are able to discriminate the enantiomers of neutral chiral molecules in water.Density functional theory calculations reveal that the“three-point contact”model effectively explains their enantioselectivity.The differential noncovalent interactions inside the hydrophobic cavity are responsible for the enantioselective recognition.Moreover,these chiral naphthotubes are both fluorescent and circular dichroism(CD)-active.In CD spectroscopy,they have been demonstrated to have the ability to detect nonchromophoric,achiral molecules in water.And,the use of fluorescence spectroscopy has aided in the determination of the enantiomeric excess(ee)values of chiral molecules.The results and conclusions obtained with these chiral biomimetic receptors can be used to better understand enantioselective recognition in biological systems.

Enantioselective recognition based on aggregation-induced emission

Chirality is one of the most important features of the nature.The recognition of enantiomers plays significant roles in the field of life science,pharmaceutical analysis and food chemistry.Among various recognition methods,fluorescence spectrometry has attracted much attention of researchers thanks to its high sensitivity and easy operation.Compared with traditional fluorescent probes,chiral molecules with aggregation-induced emission(AIE)have drawn increasing interests due to their huge potential in high-efficiency chemo/biosensors and solid emitters.Chiral AIE luminogens(AIEgens)can not only discriminate two enantiomers with excellent enantioselectivity,but also show general applicability for many chiral analytes,such as chiral acids,amino acids,amines,alcohols.In this review,we mainly summarized the recent development of chiral probes with AIE properties,including chiral tetraphenylethylene(TPE)derivatives,α-cyanostilbene derivatives,Schiff base derivatives and other AIEgens.Their synthetic routes,recognition capabilities and possible working mechanisms were well discussed.It is envisioned that the present review can give some significant guidance for design and synthesis of chiral AIEgens with good enantioselectivity and inspire more readers to join the research of chiral AIE.

Visualization of enantioselective recognition and separation of chiral acids by aggregation-induced emission chiral diamine

Enantioselective recognition and separation are the most important issues in the fields of chemistry,pharmacy,agrochemical,and food science.Here,we developed two optically active diamines showing aggregation-induced emission(AIE)that can discriminate 5 kinds of chiral acids with high enantioselectivity.Especially,a very high fluorescence intensity ratio(IL/ID)of 281 for(±)-Dibenzoyl-D/L-tartaric acid was obtained through the collection of fluorescence change after interaction with chiral AIE-active diamine.By virtue of AIE property and intermolecular acidbase interaction,enantioselective separation was facilely realized by simple filtration of the precipitates formed by chiral AIE luminogen(AIEgen)and one enantiomer in the racemic solution.The chiral HPLC data indicated that the precipitates of AIEgen/chiral acid possessed 82%L-analyte(the enantiomeric excess value was assessed to be 64%ee).Therefore,this method can serve as a simple,convenient,and low-cost tool for chiral detection and separation.

Synthesis of a pair of novel receptors and their properties of enantioselective recognition for amino acid zwitterions

A pair of artificial enantiotopic receptors la and lb composed of (S,S) or (R,R) chiral bicyclic guanidinium, azacrown ether and (t-butyldiphenylsilyloxy) methyl group for amino acid zwitterions have been synthesized. The liquid-liquid competition experiments and 1 H NMR studies indicate that the receptor 1a with (S, S) configuration and 1b with (R,R) configuration selectively recognize L- and D-aromatic amino acids & respectively.

Synthesis and Enantioselective Discrimination of Chiral Fluorescence Receptors Bearing Amino Acid Units

Two chiral fluorescence receptors （1, 2） were synthesized, and their structures were characterized by IR, ^1H NMR, ^13C NMR, mass spectra and elemental analysis. The chiral recognition of receptors was studied by ^1H NMR and fluorescence spectra. The results demonstrate that receptors and dibenzoyl tartrate anion formed a 1 ： 1 complex. The receptor 1 exhibited a good enantioselective recognition ability toward the enantiomers of dibenzoyl tartrate anion.