New Chiral Calixarene Derivatives: Syntheses and Their Chiral Recognition Toward Amino Acids by UV-Vis Spectroscopy

Three novel types of chiral calixarene derivatives 5, 8, and 10 were designed and synthesized by introducing chiral units to parent calixarenes. Their chiralities were confirmed by rotational analysis. Chiral recognition properties of these host compounds towards L- and D-threonine were studied by UV-Vis spectroscopy. The results indicated that calixarene derivatives 5 and 8 exhibited good chiral recognition capabilities toward L- or D-threonine. Although calixarene derivative 10 had no evident chiral recognition ability, the supramolecules of calixarene derivative 10 with L- or D-threonine showed a hypochromic effect or hyperchromic effect respectively. Therefore, calixarene derivative 10 might serve as a good chiral UV-indicator.

Chiral Recognition of Binaphthyl Derivatives with L-Undecyl Leucine Surfactants in the Presence of Sodium and Lysine Counterions

This study investigates the effect of counterions on the chiral recognition of 1,1'-Binaphthyl-2,2'-diamine (BNA) and 1,1'-Binaphthyl-2,2'-diyl hydrogenphosphate (BNP) enantiomers when using an amino acid-based surfactant undecanoyl L-leucine (und-Leu) as the chiral pseudostationary phase in capillary electrophoresis. The effects of using two different counterions (sodium and lysine) on the chiral recognition of binaphthyl derivatives were compared at varying pH conditions. The enantiomeric separation of BNA and BNP enantiomers via capillary electrophoresis, using und-Leu as the chiral recognition medium, significantly improved the enantiomeric resolution in capillary electrophoresis at pH 7 when using Lysine counterions as compared to using sodium as the counterion. More specifically, at a surfactant concentration of 45 mM, at pH 7, a significant increase in chiral selectivity was observed when lysine was used as the counterion compared to sodium. The enantiomeric resolution of BNA and BNP increased by 6-fold and 1.1-fold, respectively, in capillary electrophoresis experiments when lysine was utilized as the counterion compared to using sodium. Furthermore, the retention factor of BNA and BNP enantiomers also increased approximately 3.5-fold and 4-fold, respectively, in the presence of lysine counterions as compared to using sodium counterions. When running buffer in capillary electrophoresis was increased to pH 11, the resolution and retention factors were nearly identical when comparing the effects of the sodium and lysine counterions. This signifies the important role of lysine’s positive net charge on chiral recognition. This study provides insight into the potential advantages of using cationic, pH-dependent counterions such as lysine to significantly improve the chiral recognition of binaphthyl derivatives when using chiral anionic surfactants as the pseudostationary phase in capillary electrophoresis.

Chiral Recognition of Dansyl Derivatives with an Amino Acid-Based Molecular Micelle: A Molecular Dynamics Investigation

In this study, the chiral separation mechanisms of Dansyl amino acids, including Dansyl-Leucine (Dans-Leu), Dansyl-Norleucine (Dans-Nor), Dansyl-Tryptophan (Dans-Trp) and Dansyl-Phenylalanine (Dans-Phe) binding to poly-sodium N-undecanoyl-(L)-Leucylvalinate, poly (SULV), were investigated using molecular dynamics simulations. Micellar electrokinetic chromatography (MEKC) has previously shown that when separating the enantiomers of these aforementioned Dansyl amino acids, the L-enantiomers bind stronger to poly (SULV) than the D-enantiomers. This study aims to investigate the molecular interactions that govern chiral recognition in these systems using computational methods. This study reveals that the computationally-calculated binding free energy values for Dansyl enantiomers binding to poly (SULV) are in agreement with the enantiomeric order produced in experimental MEKC studies. The L-enantiomers of Dans-Leu, Dans-Nor, Dans-Trp, and Dans-Phe binding to their preferred binding pockets in poly (SULV) yielded binding free energy values of -21.8938, -22.1763, -21.3329 and -13.3349 kJ·mol-1, respectively. The D-enantiomers of Dans-Leu, Dans-Nor, Dans-Trp, and Dans-Phe binding to their preferred binding pockets in poly (SULV) yielded binding free energy values of -14.5811, -15.9457, -13.6408, and -12.0959 kJ·mol-1, respectively. Furthermore, hydrogen bonding analyses were used to investigate and elucidate the molecular interactions that govern chiral recognition in these molecular systems.

Synergistic regulation of intermolecular interactions to control chiral structures for chiral recognition

Understanding the regulatory mechanism of self-assembly processes is a necessity to modulate nanostructures and their properties. Herein, we have studied the mechanism of self-assembly in the C3 symmetric 1,3,5-benzentricarboxylic amino acid methyl ester enantiomers(TPE) in a mixed solvent system consisting of methanol and water. The resultant chiral structure was used for chiral recognition. The formation of chiral structures from the synergistic effect of multiple noncovalent interaction forces was confirmed by various techniques. Molecular dynamics simulations were used to characterize the time evolution of TPE structure and properties in solution. The theoretical results were consistent with the experimental results. Furthermore, the chiral structure assembled by the building blocks of TPE molecules was highly stereoselective for diamine compounds.

Preparation and Chiral Recognition of New Chiral Stationary Phases Derived from Cellulose Microspheres

A new way to prepare cellulose-type chiral stationary phases （CSPs） has been established in the present work.Cellulose microspheres with a volume-average diameter of 11.5 m were prepared by an emulsion-solidification method.Three new CSPs were obtained by crosslinking the cellulose microspheres with terephthaloyl chloride （TPC）,and then modifying the crosslinked microspheres with 4-methylbenzoyl chloride,3,5-dimethylbenzoyl chloride and 3,5-dichlorobenzoyl chloride,respectively.The microspheres and the CSPs were characterized by FT-IR,element analysis and scanning electronic microscopy （SEM）.The chiral recognition ability of the CSPs was evaluated with high-performance liquid chromatography （HPLC）.The chromatographic results demonstrate that the CSP prepared from 3,5-dichlorobenzoyl chloride possesses better chiral recognition ability compared with two other CSPs.

Paper-based fluorescent devices for multifunctional assays:Biomarkers detection,inhibitors screening and chiral recognition

The development of a single analytical platform with different functions is highly desirable but remains a challenge at present.Here,a paper-based device based on fluorescent carbon dots(CDs)functionalized paper/MnO_(2)nanosheets(MnO_(2)NS)hybrid devices(PCD/NS)was proposed for single-device multi-function applications.MnO_(2)NS functioned as a fluorescence quencher of CDs and recognizer of H_(2)O_(2)released from the oxidase catalyzed system.Fluorescence recovery would occur after the decomposition of MnO_(2)NS induced by H_(2)O_(2),by which a simple and effective strategy could be developed for fluorescence monitoring multiplex biological events.Xanthine(XA)sensing,xanthine oxidase(XOD)inhibitors screening analysis and chiral recognition of glucose enantiomers were performed on PCD/NS to investigate the multifunctional application of the paper-based device.By means of PCD/NS,XA could be determined in the range of 0.1–40μmol/L with a low detection of limit of 0.06μmol/L.The IC_(50)value of allopurinol,the model inhibitor of XOD,was sensitively detected to be 7.4μmol/L.Glucose enantiomers were also recognized in terms of the specific fluorescence response to d-glucose.This work firstly presented a paper-based device capable of biomarkers detection,inhibitors screening and chiral recognition,which enlightened a promising strategy for the construction of multifunctional devices and hold the great potential application in clinical diagnosis and drug discovery.

Chiral Recognition and Photoreaction of β-Amino Acids with Iridium(III)Complexes

β-Amino acids(AAs),homologs ofα-AAs,are important building blocks of biological materials.Herein,chiral recognitions ofβ-AAs with Ir(III)complexes are reported,in favor of formation of the thermodynamically stableΛ-[Ir(pq)_(2)(D-β-AAs)]andΔ-[Ir(pq)_(2)(L-β-AAs)](pq is 2-phenylquinoline)diastereomers.The photoreactions of[Ir(pq)_(2)(β-AA)]complexes are observed in an EtOH solution in the presence of O_(2) at room temperature.The primaryβ-AAs complexes,such as rac-[Ir(pq)_(2)(β-ala)](β-ala isβ-alanine),Δ-[Ir(pq)_(2)(D-β-ma)]andΛ-[Ir(pq)_(2)(D-β-ma)](β-ma isβ-methylalanine),Δ-[Ir(pq)_(2)(D-β-pa)]andΛ-[Ir(pq)_(2)(D-β-pa)](β-pa isβ-phenylalanine),and rac-[Ir(pq)_(2)(β-dma)](β-dma is 3,3-dimethyl-β-alanine),are interligand C—N cross-coupling in situ between pq andβ-AAs ligands.The secondaryβ-AA complexesΔ-[Ir(pq)_(2)(L-β-pro)]andΛ-[Ir(pq)_(2)(L-β-pro)](β-pro isβ-proline,2-(pyrrolidin-2-yl)acetic acid)are dehydrogenatively oxidized into imino acid complexesΔ-[Ir(pq)_(2)(L-β-pro-2H^(β)’)]andΛ-[Ir(pq)_(2)(L-β-pro-2H^(β)’)](L-β-pro-2H^(β)’=2-(3,4-dihydro-2H-pyrrol-2-yl)acetic acid),respectively.Moreover,the dehydrogenative reaction inΔ-[Ir(pq)_(2)(L-β-pro)]diastereomer is regioselective depending on the reaction temperature,affordingΔ-[Ir(pq)_(2)(L-β-pro-2H^(β)’)]andΔ-[Ir(pq)_(2)(L-β-pro-2H^(β))](β-pro-2H^(β)=2-(3,4-dihydro-2H-pyrrol-5-yl)acetic acid)at low temperature.The chiral recognitions and photoreactions of Ir(III)-β-AAs complexes are much different from the previous observations in Ir(III)-α-AAs complexes.

Preparation and Chiral Recognition of Thermosensitive Poly（N-isopropylacrylamide） Microgels Containing Modified L-Phenylalanine Groups

Thermosensitive poly[N-isopropylacrylamide（NIPAM）-co-N-acryloyl-L-phenylalanine ethyl ester （NALPE）] microgels were prepared by the free radical polymerization of NIPAM and chiral monomer, NALPE. Such microgels exhibited spherical shape and favorable monodispersity. Increasing the content of NALPE units would en- hance the average diameter, but decrease the thermosensitivity and volume-phase transition temperatures of the mi- crogels. Compared with PNIPAM microgels, the microgels containing NALPE units performed chiral recognozable capacities for D-phenylalanine and D-tartaric acid, and the enantioselectivity and adsorption capacity of the microgels improved with increasing the temperature and/or the content of NALPE units.

Synthesis and Chiral Recognition of a New Type of Chiral Calix[4]arene Derivatives

Two new chiral calixarenes bearing chiral pendants, which were from by-product of the antibiotic industry, were synthesized and characterized by 1H NMR, MS-FAB and elemental analysis. Studies of 1H NMR of the two calixarene derivatives indicate that they exist in cone conformation in solution. Results of chiral recognition of the two chiral ligands 2a and 2b towards the tartaric acid derivative 3 show that ligand 2a exhibited good chiral recognition abilities compared to ligand 2b.

Study of chiral recognition mechanism of O,O-diethyl (p-methylbenzenesulfonamindo)-aryl(alkyl)-methylphosphonates by HPLC with a series of CSPs

Five chiral stationary phases (CSPs) were used to separate the enantiomers of a series of O,O-diethyl (p-methyl-benzenesulfonamindo)-aryl(alkyl)-methylphosphonates. A chiral recognition mechanism was presented to explain the resolution of these compounds. Results show that CSP with strong π-acceptor 3,5-dinitrobenzoyl group and high steric hindrance has the best resolution ability in chiral separation of O,O-diethyl (p-methylbenzenesulfonamindo)-aryl(alkyl)-methylphosphonates. When a CSP has just a strong π-acceptor 3,5-dinitrobenzoyl or high steric hindrance it does not have good chiral resolution ability. The chiral recognition is more difficult when the CSP has more than one asymmetric center.

Chirality pairing recognition,a unique reaction forming spiral alkaloids from amino acids stereoselectively in one-pot

A novel chirality pairing recognition was found between D-and L-amino acid derivatives.Novel spiral alkaloids formed in the recognition reaction.Possible mechanism was proposed for the stereoselective and chemoselective reactions.

Heteroepitaxial growth of Au@Pd core–shell nanocrystals with intrinsic chiral surfaces for enantiomeric recognition

Noble metal surfaces with intrinsic chirality serve as an ideal candidate for investigating enantioselective chemistry due to their superior chemical durability and high catalytic activity.Recently,significant advance has been made in synthesizing metal nanocrystals with intrinsic chirality.Nonetheless,the majority reports are limited to gold.Herein,through a heteroepitaxial growth strategy,the synthesis of metal nanocrystals with intrinsic chirality to palladium was extended for the first time and their application in enantioselective recognition was demonstrated.The heteroepitaxial growth strategy allows for transferring the chirality of homochiral Au nanocrystals to Au@Pd core–shell nanocrystals.By employing the chiral Au@Pd nanocrystals as enantiomeric recognizing elements,a series of electrochemical sensors for chiral discrimination were developed.Under optimal conditions,the peak potential between D-dihydroxyphenylalanine(D-DOPA)and L-dihydroxyphenylalanine(L-DOPA)is about 80 m V,and the peak current of D-DOPA is 2 times as much as that of L-DOPA,which enables the determination of the enantiomeric excess(EE,%)of L-DOPA.Overall,this report not only introduces a heteroepitaxial growth strategy to synthesize metal nanocrystals with intrinsic chirality,but also demonstrates the superior capability of integrating intrinsic chirality and catalytic properties into metal nanocrystals for chiral recognition.

An Inherent Chiral Calix[4]arene Bearing Chiral Groups without Forming Sub-ring

The NMR spectra revealed that the calixarene frame of 1, 3-disubstituted calix[4]arenes beating optically active groups is asymmetric, even without the formation of a sub-ring. This inherent chirality arises from the interaction of the two chiral groups, which hinder the substituents＇ free rotation. Thus, these chiral calix[4]arenes display good chiral recognition ability.

Molecular Dynamic Study for Chiral Discrimination of α-Phenylethylamine by Modified Cyclodextrin in Gas Chromatography

A molecular dynamic method in conjunction with a statistic test has been utilized to model chiral recognition of a-phenylethylamine on heptakis (2.6-di-O-butyl-3-O-butyryl)-β- cyclodextrin in gas chromatography. The modelling data correlated with the chromatographic elution order and indicated that the preferred site of α-phenylethylamine is the interior of cavity.

Chiral amino acid recognition in water:A BINOL-based fluorescent probe

A novel BINOL-based fluorescence probe(S)-6 featuring a sodium sulfonate fragment at the 2'-position was designed and synthesized via simple synthetic procedures under mild reaction conditions.The watersoluble probe(S)-6 displays excellent enantioselective recognition toward 15 common amino acids,and it can be used for enantiomeric excess determination of amino acids.The fluorescence intensity of(S)-6 treated with amino acids reaches the maximum after standing for only 30 min at room temperature and remains stable in the following 5.5 h,which has great potential in the application of chiral fluorescence analysis due to its timeliness and outstanding fluorescent stability.

Discrimination of Glycine Enantiomers by the Biologically Important Phosphocompounds:A Theoretical Prediction

With the aid of high-level B3LYP and MP2 calculations, three new neutral structures of glycine （iin, ivn and vn, see Fig. 2） were obtained and validated by frequency calculations. The structural and energetic analyses showed that iin, ivn and vn are enantiomers to the previous IIn, IVn and Vn （J. Am. Chem. Soc. 1992, 114, 9568.）, respectively. Owing to the presence of these novel conformers, a redistribution of the populations of glycine conformers is resulted in and causes the remarkable decrease of the most stabilized Ip （from 48% to 38%）. It indicated that the simple glycine molecule can show chirality under certain conditions. The interacting modes of glycine enantiomeric pairs （e.g., ivn and IVn） with PG showed large differences （Fig. 4）; in addition, their interaction energies corrected with basis set superposition errors （BSSE） were calculated to be --66.81 and -46.99 kJ tool^-1, respectively. Accordingly, the glycine enantiomers can be potentially applied to the chiral recognition in biological and pharmaceutical areas.

Homochiral design of titanium-organic cage for circularly polarized luminescence-based molecular detection

Post-assembly modification strategy is used as an effective approach to improve the functional applications of metal-organic cages. The active vertex of the racemic tetrahedral Ti4L6(L = embonate) cages traps four chiral diamine chelated dinuclear silver ions, obtaining homochiral cages which exhibit helical perovskite stacks. Such a surface modification engineering enables the structural precise cages presenting homochirality and circularly polarized luminescence(CPL) response, further achieving enantioselective recognition toward chiral Camphorquinone molecules and displaying enhanced temperature-dependent effects of CPL output.

Chiral nanocomposite of sulfobutyl ether-b-cyclodextrin embedded in carbon nanofibers for enantioselective electrochemical discrimination of amlodipine, metoprolol and clenbuterol enantiomers

A highly sensitive and selective electrochemical chiral sensor was developed based on the competitive supramolecular interaction of carbon nanofibers(CNFs)embedded sulfobutyl ether-b-cyclodextrin(SBEb-CD)with optically active cationic drugs at glassy carbon electrode(GCE).The difference in intermolecular hydrogen bonding/stability constant/enantioselectivity coefficient and Gibbs free energy of anionic host SBE-b-CD with enantiomers of amlodipine(R-/S-AML),clenbuterol(R-/S-CBL)and metoprolol(R-/S-MET)as a guest paved the way for efficient discrimination.The proposed sensing platform(CNFs-SBE-b-CD/GCE)could recognize the aforementioned enantiomers based on the discernible difference of peak potential(S/R-AML(△Ep=135 mV),R/S-MET(△Ep=99 mV)and R/S-CBL(△Ep=111 mV).The binding mechanisms and thermodynamic study of the enantiospecific behavior have been investigated using the host-guest chemistry approach inside the nanocavity and results suggest that S-AML,RMET,and R-CBL show stronger stability constants than their antipodes.Formation of the diastereomeric complex was taken as a measure of enantioselectivity and experimental results indicated that anionic SBE-b-CD is a better chiral ligand than neutral cyclodextrins.The fabricated sensor could be a useful lowcost electrochemical tool for molecular recognition of a variety of cationic species not only of drugs but also from other sources.

Preparation and Enantioseparation Property of Chiral Stationary Phases Based on Cellulose Tris(3,5-dimethylbenzoate)——A New Way to Prepare Polysaccharide-coating Type Chiral Stationary Phases

A new method to prepare polysaccharide-coating type chiral stationary phases （CSPs） was developed in this work. As a typical example, naked silica gel was coated by cellulose, which was then derivatized with 3,5-dimethylbenzoyl chloride to afford cellulose tris（3,5-dimethylbenzoate）-silica gel （CTDBS） complex. The silanols on CTDBS were end-capped with 3- aminopropyltriethoxysilane to obtain CSP 1. The amino groups on CSP 1 were further end-capped with 3,5-dimethylbenzoyl chloride to give CSP 2. The silanols on CTDBS were end-capped with methyltrimethoxysilane to yield CSP 3. CSPs 1-3 were characterized by FTIR, solid-state 13C-NMR and elemental analysis. The enantioseparation abilities of CSPs 1-3 were evaluated with structurally various chiral analytes. The enantioseparation results demonstrated that the end-capping moieties on CSPs 1 and 2 significantly affected enantioseparation. In addition, the effect of the structures of chiral analytes and end- capping moieties on the retention factors and the resolutions was discussed.