Recognition Of Enantiomers Research Articles

Push or Pull for a Better Selectivity? A Study on the Electronic Effects of Substituents of the Pyridine Ring on the Enantiomeric Recognition of Chiral Pyridino-18-Crown-6 Ethers

Seven dimethyl-substituted optically active pyridino-18-crown-6 ethers containing various substituents at position 4 of the pyridine ring were studied with regards to the electron-donating and -withdrawing effects of substituents on enantiomeric recognition. In order to compile this set of compounds, we prepared four novel pyridino-18-crown-6 ethers, including an intermediate of a new synthetic route for a formerly reported crown ether. The discriminating ability of these pyridino-crown ethers with C2-symmetry toward the enantiomers of protonated primary amines was examined by isothermal titration calorimetry.

Spectro-chemometric determination of panthenol enantiomeric excess in pharmaceutical products

Abstract Antibiotic, soothing and healing properties of panthenol are exploited in various pharmaceutical and cosmetic products. Only D-panthenol is biologically active while its L-form might counteract the biological effectiveness of the D-enantiomer. Hydrating and moisturizing effects are exhibited by both enantiomers. Therefore, it is necessary to develop a rapid and cheap method for the determination of panthenol enantiomeric excess in pharmaceutical preparations. In this study, b-cyclodextrin was used as a chiral selector for the recognition of panthenol enantiomers. Inclusion complexes formed by b-cyclodextrin and the analyte showed small differences in NIR and UV/VIS spectra compared by chemometric assessment. Based on the figure of merit and model characteristics, PLS calibration model in the selected range of NIR spectra is preferred. UV/VIS spectrometry has the disadvantage of complicated sample preparation compared to NIR spectrometry. Results reached by both proposed methods were in good agreement. Statistical investigation of the results (by Student t-test and Fisher F-test) confirmed that the proposed methods are comparable and applicable to chiral analysis of panthenol pharmaceutical preparations.

Dehydroabietic acid-based chiral ionic liquids: Their synthesis and potential enantiomeric recognition ability

Abstract Several new chiral imidazolinium ionic liquids (CILs) have been synthesized by using optically pure dehydroabietic acid (DA) as the chiral precursor. Their enantiomeric recognition abilities were measured using rac-mandelic acid n-Bu4N salt as the substrate by NMR spectroscopy. Based on the structure-interaction relationships, the bulky anion and the side chain linking the DA group to the imidazole ring have crucial effects on CIL recognition. The 1H NMR measurements indicated that [MimMeDA]NTf2 exhibits good and versatile molecular recognition ability. The new DA-based CILs reported here may be interesting chiral media for enantioselective reactions and useful in enantiomeric separations.

Recent advances in chiral carbonized polymer dots: From synthesis and properties to applications

Abstract The outstanding properties of carbon dots (CDs), including biocompatibility, low toxicity, photoluminescence, and easy synthesis and modification, make them strong competitors to traditional semiconductor quantum dots. Chirality exists widely in nature and plays important roles in life sciences and materials sciences. The application of chirality to CDs generates a new class of potentially valuable CDs materials, chiral CDs, that may be useful in areas such as enantiomeric recognition and separation, chiral catalysis, bioimaging, and biomedicine. In the strict sense, chiral CDs synthesized by a “bottom-up” method should be classified as carbonized polymer dots (CPDs), and we therefore propose that such chiral CDs be termed chiral CPDs (Ch-CPDs). Here, we provide the first comprehensive review of recent achievements in Ch-CPDs synthesis methodology, properties, and applications, and discuss the challenges to be overcome in their future development.

Fluorescent and Colorimetric Dual-signal Enantiomers Recognition via Enzyme Catalysis: The Case of Glucose Enantiomers Using Nitrogen-doped Silicon Quantum Dots/Silver Probe Coupled with β-D-Glucose Oxidase.

Chiral enantiomer recognition is important but facing tough challenges in the direct quantitative determination for complex samples. In this work, via chosing nitrogen-doped silicon quantum dots (N-SiQD) as optical nanoprobe and constructing N-SiQD/silver (N-SiQD/Ag NPs) complex, β-D-GOx as model enzyme and glucose enantiomers as analytes, a fluorescent and colorimetric dual-signal chiral sensing strategy was proposed herein for chiral recognition based on specific enzyme-catalyzed reaction. N-SiQD can exhibit intense fluorescence, while it can be quenched by Ag NPs owing to the formation of N-SiQD/Ag NPs. In the presence of glucose isomer, D-glucose is catalytically hydrolyzed by β-D-GOx to form H2O2 owing to the specific enzyme catalyzed reaction between D-glucose and β-D-GOx, and H2O2 can etch Ag NPs from the N-SiQD/Ag NPs probe to change the solution color from brown to colorless and restore the N-SiQD fluorescence; while these phenomena cannot be caused by L-glucose, a dual-signal sensing method was thus constructed for recognizing glucose enantiomers. It is believed that the chiral enantiomers recognition strategy via enzyme catalysis has great application for selective and quantificational detection of enantiomers in the complex sample system.

Ionic Current Rectification Triggered Photoelectrochemical Chiral Sensing Platform for Recognition of Amino Acid Enantiomers on Self-Standing Nanochannel Arrays.

Chirality is an intrinsic and essential property of nature, and the enantiomeric discrimination of chiral molecules can provide important information leading to a better understanding of chiral recognition in biological systems and furthering the development of useful molecular devices in biochemical and pharmaceutical studies. Therefore, the exploration of new detection techniques with high accuracy and reliability for high-throughput enantioselective detection is still highly desirable. Herein, a chiral enantiomers selective recognition platform based on self-standing titanium dioxide nanochannel arrays (TiO2 NCAs) is proposed to implement the ionic current rectification triggered photoelectrochemical (PEC) detection, which provides a novel sensing platform to discriminate chiral amino acid through synchronous output dual response signals of ionic current and photocurrent. The utilization of nanochannel arrays guaranteed the high-throughput detection, and the dual signal model avoided a "false positive" detection. In addition, based on the fabricated detection platform, various chiral substances can be facilely detected through integrating different chiral regulation units, which shed light on the construction of reliable chiral sensors for practical applications in a biological environment.

Chiral recognition and quantitative analysis of tyrosine enantiomers using L-cysteine capped CdTe quantum dots: Circular dichroism, fluorescence, and theoretical calculation studies

In this work, L-cysteine-capped CdTe quantum dots (L-Cys/CdTe QDs) were used as novel chiral probes for in enantioselective recognition and quantitative determination of tyrosine (Tyr) enantiomers using both fluorescence and circular dichroism (CD) spectroscopies. Different quenching percentages in fluorescence of L-Cys/CdTe QDs in the presence of similar concentrations of Tyr enantiomers were clearly observed. Quantum mechanical (QM) calculations were also used to confirm such different interactions of L- and D-Tyr enantiomers with L-Cys/CdTe QDs. However, the CD spectroscopy exhibited higher capability and sensitivity, compared to fluorescence spectroscopy, to distinguish between these enantiomers. While, Tyr enantiomers provided no sensible CD signals at micromolar concentration levels, they exhibited remarkable and opposite CD spectra at these concentration levels in the presence of L-Cys/CdTe QDs. Under the optimized conditions, the CD signals of L- and D-Tyr enantiomers showed good linear relationships with the concentrations of both enantiomers over the range of 10–80 µM with limit of detections (LODs) of 1.5 and 1.6 µM, respectively. This method was also successfully applied to enantiomeric excess determination of Tyr at the total concentration of 50 μM with a LOD of 1.2%.

Synthesis, Molecular Recognition Study and Liquid Membrane-Based Applications of Highly Lipophilic Enantiopure Acridino-Crown Ethers.

New highly lipophilic enantiopure crown ethers containing a heterocyclic unit have been synthesized. Phase transport, UV-Vis- and fluorescence spectrophotometric investigations as well as electrochemical studies on the complexation of the new macrocycles with several amine and amino acid derivatives were also carried out. Achiral amines were used for studying the structural preference of the new macrocycles. Among the studied structural features of the guest molecules, the intermolecular π-π interaction showed the most significant effect on complexation, which made the aralkylamine-type compounds the most preferable guest molecules. The studied liquid membrane-based applications and photophysical investigations showed appreciable enantiomeric recognition toward some aralkylamine model compounds with homochiral preferences. New crown ether derivatives (R,R)-2 and (S,S)-2 were successfully applied as enantioselective carrier and sensor molecules.

Chiral carbon dots-based nanosensors for Sn(II) detection and lysine enantiomers recognition

Chirality has a great influence on chemical, biological, and material science. Chiral recognition is fundamental and crucial in chemistry, biology and pharmaceutics. Compared to the extensive attention on achiral carbon dots (CDs), quite a few studies on chiral CDs have been carried out, among which the effects of chiral CDs on recognizing enantiomers have rarely been explored yet. Herein, chiral CDs are utilized as a simple and efficient dual-sensor for Sn2+ detection and Lysine enantiomers recognition for the first time, with the detection limit of 0.057 μM and 3.44 μM, respectively. Furthermore, the strengths of robust stability, high sensitivity and good cytocompatibility enable CDs to successfully monitor the fluctuations of Sn2+ and l-Lys in live cells by virtue of confocal laser scanning microscope. The work highlights the potential of chiral CDs for enantiomeric recognition and ion detection.

Nafion-stabilized black phosphorus nanosheets-maltosyl-β-cyclodextrin as a chiral sensor for tryptophan enantiomers.

In this work, we have fabricated nafion (NF) stabilized black phosphorus nanosheets (BPNSs) and 6-O-α-maltosyl-β-cyclodextrin (G2-β-CD) composite (BPNSs-G2-β-CD) as novel electrochemical sensoring platform for chiral recognition of tryptophan (Trp) enantiomers. BPNSs-G2-β-CD composite modified glassy carbon electrode (BPNSs-G2-β-CD/GCE) was further coated with NF which served as a protective film to immobilize BPNSs-G2-β-CD on the electrode surface to achieve high stability. Under the optimum conditions, the oxidation peak current ratio of L-Trp to D-Trp (IL/ID) and the difference between the peak potential (ΔEp=ED - EL) were observed to be 1.49 and 20mV at NF/BPNSs-G2-β-CD/GCE by square wave voltammetry (SWV). In addition, a linear calibration curve could be obtained for peak current versus Trp enantiomers in the concentration range 0.01-1.00mM with detection limits of 1.07μM and 1.71μM for L-Trp and D-Trp (signal-to-noise ratio of 3, S/N=3), respectively. The chiral recognition mechanism was also proposed, and the intermolecular hydrogen bonding interactions as well as the hydrophobic-cavity-triggered embedding effect dominated the effective chiral recognition. Moreover, the proposed NF/BPNSs-G2-β-CD/GCE showed excellent stability, good reproducibility and anti-interference capability. Therefore, the designed chiral sensor is expected to be practically applied for the sensitive recognition of Trp enantiomers in real samples.

Electrochemical recognition of tryptophan enantiomers based on the self-assembly of polyethyleneimine and chiral peptides

Electrochemical chiral interface based on achiral polyethyleneimine (PEI) and chiral peptide (D-BGAc) was constructed using self-assembly technology and used for electrochemical recognition of tryptophan (Trp) enantiomers via differential pulse voltammetry (DPV). Under optimized experimental conditions, the oxidation peak current ratio of D-Trp to L-Trp (ID/IL) was observed to be 3.4 using PEI/D-BGAc/GCE (glass carbon electrode). More interestingly, the PEI/D-BGAc chiral interface exhibited chiral recognition of D- and L-Trp via contact angle measurements. In addition, there was a good linear relationship between the peak current and Trp enantiomer concentration in the range of 0.002–0.15 mM. Finally, the PEI/D-BGAc/GCE system can be used to quickly determine the ratio of isomers in Trp racemic solution, which is of great significance for the chiral recognition in racemic mixtures of chiral compounds. Meanwhile, the PEI/D-BGAc/GCE showed good stability and reproducibility.

Zinc oxide/Vancomycin-based Electrochemical Chiral Sensor for the Recognition of Penicillamine Enantiomers

Zinc oxide/Vancomycin-based Electrochemical Chiral Sensor for the Recognition of Penicillamine Enantiomers

Scalable Enantiomeric Separation of Dialkyl‐Arylphosphine Oxides Based on Host–Guest Complexation with TADDOL‐Derivatives, and their Recovery

Several dialkyl‐arylphosphine oxides were prepared, and the enantioseparation of the corresponding racemates was elaborated with host–guest complexation using TADDOL‐derivatives. The crystallization conditions were optimized and two separate crystallization methods, one in organic solvent, and the other in water, were found to yield five examples of phosphine oxides with enantiomeric excess values higher than 94 %. A gram scale resolution was performed, and both enantiomers of the methyl‐phenyl‐propyl‐phosphine oxide were separated with (R,R)‐ or (S,S)‐spiro‐TADDOL. The intermolecular interactions responsible for the enantiomeric recognition between the chiral host and guest molecules were investigated by single‐crystal X‐ray diffractional structural determinations. The similarities in the structural patterns of a few diastereomeric crystals were checked by powder X‐ray diffraction, as well. Organic solvent nanofiltration (OSN) was used as a scalable technique for the decomposition of the corresponding phosphine oxide–spiro‐TADDOL molecular complexes, and for the recovery of the phosphine oxide enantiomers and resolving agents.

One-pot synthesis of an anionic cyclodextrin-stabilized bifunctional gold nanoparticles for visual chiral sensing and catalytic reduction

A facile one-pot synthetic method for preparing gold nanoparticles by employing sugammadex (SUG), a carboxylic acid functionalized γ-cyclodextrin derivative, as reducing-cum-stabilizing agent herein was reported for the first time. The SUG protected gold nanoparticles (SUG-AuNPs) can work as a colorimetric sensor for visual chiral recognition of α-amino acids enantiomers, especially for lysine (Lys) and asparagine (Asn) enantiomers. The chiral recognition assay was successfully applied to determining the enantiometric excess of L-Lys and L-Asn ranging from −100 % to 100 % respectively. Moreover, the prepared SUG-AuNPs was found to exhibit efficient catalytic activity towards the reduction of toxic 4-nitrophenol by NaBH4 and the efficiency of the system was further demonstrated through the reduction of other typical nitroaromatics under mild condition. The as-synthesized SUG-AuNPs shows good performance for both chiral sensing and reduction activity and thus may facilitate the practical application in the area of both chiral discrimination and catalysis.

Circular Dichroism in the Second Harmonic Field Evidenced by Asymmetric Au Coated GaAs Nanowires.

Optical circular dichroism (CD) is an important phenomenon in nanophotonics, that addresses top level applications such as circular polarized photon generation in optics, enantiomeric recognition in biophotonics and so on. Chiral nanostructures can lead to high CD, but the fabrication process usually requires a large effort, and extrinsic chiral samples can be produced by simpler techniques. Glancing angle deposition of gold on GaAs nanowires can (NWs) induces a symmetry breaking that leads to an optical CD response that mimics chiral behavior. The GaAs NWs have been fabricated by a self-catalyzed, bottom-up approach, leading to large surfaces and high-quality samples at a relatively low cost. Here, we investigate the second harmonic generation circular dichroism (SHG-CD) signal on GaAs nanowires partially covered with Au. SHG is a nonlinear process of even order, and thus extremely sensitive to symmetry breaking. Therefore, the visibility of the signal is very high when the fabricated samples present resonances at first and second harmonic frequencies (i.e., 800 and 400 nm, in our case).

Visible Enantiomer Discrimination via Diphenylalanine-Based Chiral Supramolecular Self-Assembly on Multiple Platforms.

The development of enantioselective recognition is of great significance in medical science and pharmaceutical industry, which associates with the molecular recognition phenomenon widely observed in biological systems. In particular, the facile and straight achievement of visual enantioselective recognition has been drawing increasing consideration, but it is still a challenge. Herein, a heterochiral diphenylalanine-based gelator (LFDF) is synthesized, presenting left-handed nanofibers during self-assembly in ethanol, which accomplishes the phenylalaninol enantiomer recognition on multiple platforms. When adding l- or d-phenylalaninol into LFDF supramolecular solution followed by ultrasonic treatment, precipitate and gel are formed, respectively. Meanwhile, LFDF supramolecular gel completely collapses in a minute after dropping l-phenylalaninol, while the gel almost remains when d-type is employed. Moreover, a fluorescent supramolecular xerogel (ThT-LFDF) is fabricated by combining the LFDF gelator with thioflavine T (ThT), which could detect l-phenylalaninol accompanying with fluorescence quenching while d-type with barely decreasing. And the ThT-LFDF xerogel system shows a good sensitivity (reaches to ppm) for the detection of l-phenylalaninol. It is found that the chirality of the assembled nanofibers, as well as amino and carboxyl of phenylalaninol, plays a critical role on the discrimination process. The multiple and visible enantioselective recognition of phenylalaninol through chiral supramolecular self-assemblies shows potential applications in the fields of medical science and pharmaceutical industry.

Chiral Fluorescent Silicon Nanoparticles for Aminopropanol Enantiomer: Fluorescence Discrimination and Mechanism Identification.

As an important chiral molecule for the preparation of levofloxacin, the optical purity of L-aminopropanol has a crucial effect on the pharmacology and pharmacodynamics of levofloxacin. Therefore, it is of great significance to discriminate D-aminopropanol and L-aminopropanol. In this paper, an effective aminopropanol enantiomer recognition method was established on the basis of the chiral fluorescent silicon nanoparticles (SiNPs) probe. The chiral fluorescent SiNPs were fabricated via a one-step aqueous solution synthesis strategy, which avoided multiple steps, pressurizing operation, and time-consuming postmodified procedures. Significantly, D-aminopropanol could significantly enhance the fluorescence of the chiral SiNPs, while L-aminopropanol could not affect the fluorescence of the chiral SiNPs. This could have occurred because of the stronger interaction between the chiral SiNPs and D-aminopropanol than that of L-aminopropanol. Thus, the rapid and selective recognition of the aminopropanol enantiomer was ideally realized. The mechanism of the chiral SiNPs recognizing aminopropanol was simulated by density functional theory quantum mechanical calculations. Interestingly, this was also proved by the separation of aminopropanol enantiomer using this chiral SiNPs-modified silica column in normal phase liquid chromatography. To the best of our knowledge, this is the first time that the chiral fluorescent SiNPs were synthesized and used to detect the aminopropanol enantiomer successfully. This work will inspire additional syntheses of chiral silicon nanomaterials and other nanomaterials with excellent properties and will enable application of chiral nanomaterials to other fields.

A Chiral Voltammetric Sensor Based on a Paste Electrode Modified by Cyanuric Acid for the Recognition and Determination of Tyrosine Enantiomers

An enantioselective voltammetric sensor based on graphitized carbon black (Carboblack C) paste electrode modified by cyanuric acid (CA) was developed for the selective recognition and determination of tyrosine (Tyr) enantiomers. The sensor preferably recognizes D-Tyr because of steric differences between the Tyr enantiomers and nanocavities of CA supramolecules. Using cyclic voltammetry, electrochemical impedance spectroscopy, scanning electron microscopy, and polarimetry, the conditions for modifying Carboblack C with cyanuric acid were optimized and the electrochemical characteristics of the sensor and the conditions for recording voltammograms were studied. The performance of the sensor was estimated under the conditions of differential pulse voltammetry. The proposed sensor was used to recognize and determine the L- and D-enantiomers of tyrosine in a mixture and in samples of urine and human blood plasma. Using molecular dynamics simulation, the features of the interaction of tyrosine enantiomers with CA supramolecules are considered.

Electrospinning chiral fluorescent nanofibers from helical polyacetylene: preparation and enantioselective recognition ability.

Chirality is ubiquitous in nature and closely related to the pharmacological effects of chiral drugs. Therefore, chiral recognition of molecular enantiomers becomes an important research theme. Fluorescence detection is highly sensitive and fast but has achieved only limited success in enantiomeric detection due to the lack of powerful chiral fluorescence detection materials. In this paper, a novel chiral fluorescent probe material, i.e. a chiral fluorescent nanofiber membrane, is prepared from chiral helical substituted polyacetylene by the electrospinning technique. The SEM images demonstrate the success in fabricating continuous, uniform nanofibers with a diameter of about 100 nm. Circular dichroism spectra show that the nanofibers exhibit fascinating optical activity. One of the enantiomeric chiral fluorescent membranes has chiral fluorescence recognition effects towards alanine and chiral phenylethylamine, while the other enantiomeric membrane does not. The prepared chiral fluorescent nano-materials are expected to find various applications in chirality-related fields due to their advantages such as chirality, fluorescence, and a high specific surface area. The established preparation approach also promises a potent and versatile platform for developing advanced nanofiber materials from conjugated polymers.

Harnessing the enantiomeric recognition ability of hydrophobic polymers of intrinsic microporosity (PIM-1) toward amino acids by converting them into hydrophilic polymer dots

In this work, we synthesized novel polymer dots (Pdots) from polymers of intrinsic microporosity (PIM-1) containing a racemic mixture of R- and S-chiral centers as the hydrophobic conjugated polymer chains.