Recognition Of Amino Acid Enantiomers Research Articles

Magneto-electrochemical method for chiral recognition of amino acid enantiomers.

Chiral recognition of enantiomers with identical mirror-symmetric molecular structures is important for the analysis of biomolecules, and it conventionally relies on stereoselective interactions in chiral chemical environments. Here, we develop a magneto-electrochemical method for the enhanced detection of chiral amino acids (AAs), that combines the advantages of the high sensitivity of electrochemiluminescent (ECL) biosensors and chirality-induced effects under a magnetic field. The ECL difference between L- and D-enantiomers can be amplified over 35-fold under a field of 3.5 kG, and the chiral discrimination can be achieved in dilute AA solutions down to the nM level. The field-dependent ECL and chronocoulometry measurements suggest that chiral AAs can lock the spins on their radicals and thus enlarge the ECL change under applied magnetic fields (magneto-ECL, MECL), which explains the field-enhanced chiral discrimination of AA enantiomers. Finally, a detailed protocol is demonstrated for the identification of unknown AA solutions, in which the species, chirality and concentration of AAs can be determined simultaneously from the 2D plots of the ECL and MECL results. This work benefits the development of field-assisted detection methods and represents a promising and universal strategy for the comprehensive analysis of chiral biomolecules.

One-step hydrothermal preparation of chiral carbon quantum dots and enantioselective sensing of glutamine enantiomeric isomers.

A novel method for chiral identification of glutamine enantiomers based on chiral carbon quantum dots (cCQDs) fluorescent probes. cCQDs were prepared using a one-step hydrothermal method with L-tryptophan as the carbon source and chiral source, producing spherical nanoparticles exhibiting a blue colour luminescence. The fluorescence intensity (F) of cCQDs was enhanced or quenched following the addition of chiral enantiomeric glutamine (L/D-Gln), and therefore cCQDs, as a fluorescence probe, could be used for enantioselective sensing of the L/D-Gln. The fluorescence enhancement value (∆FE ) exhibited good linearity with L-Gln concentration in the range 0.23-10.00 mM, and the limit of detection was 0.14 mM. The fluorescence quenching value (∆FQ ) showed a good linear relationship with D-Gln concentration in the range 0.29-10.00 mM, and the detection limit was 0.18 mM. The mechanism of fluorescence enhancement/quenching was explored by molecular modelling and the type of quenching. The method was applied to the determination of L-Gln content in real samples, and the recovery rate was satisfactory. This study provided a novel approach for the synthesis of cCQDs and the recognition of amino acid enantiomers.

Construction of a Chiral Fluorescent Probe for Tryptophan Enantiomers/Ascorbic Acid Identification.

Chiral recognition of amino acid enantiomers is critical in enhancing drug efficacy, detecting disease markers, and understanding physiological processes. Enantioselective fluorescent identification has gained attention among researchers due to its nontoxicity, easy synthesis, and biocompatibility. In this work, chiral fluorescent carbon dots (CCDs) were produced through a hydrothermal reaction followed by chiral modification. The fluorescent probe, Fe3+-CCDs (F-CCDs), was constructed by complexing Fe3+ with CCDs to differentiate between the enantiomers of tryptophan (Trp) and determine ascorbic acid (AA) through an "on-off-on" response. It is worth noting that l-Trp can greatly enhance the fluorescence of F-CCDs with a blue shift, whereas d-Trp does not have any effect on the fluorescence of F-CCDs. F-CCDs showed a low limit of detection (LOD) for l-Trp and l-AA, with an LOD of 3.98 and 6.28 μM, respectively. The chiral recognition mechanism of tryptophan enantiomers using F-CCDs was proposed based on the interaction force between the enantiomers and F-CCDs, as confirmed by UV-vis absorption spectroscopy and density functional theory calculations. The determination of l-AA by F-CCDs was also confirmed through the binding of l-AA to Fe3+ to release CCDs, as seen in UV-vis absorption spectra and time-resolved fluorescence decays. In addition, AND and OR gates were constructed based on the different responses of CCDs to Fe3+ and Fe3+-CCDs to l-Trp/d-Trp, demonstrating the significance of molecular-level logic gates in drug detection and clinical diagnosis.

Specific chiral recognition of amino acid enantiomers promoted by an enzymatic bioreactor in MOFs

A general enzyme-driven indirect fluorescence sensing model based on mesoporous MOFs was proposed to realize specific detection of chiral AAs.

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.

Novel potential and current type chiral amino acids biosensor based on L/D-handed double helix carbon nanotubes@polypyrrole@Au nanoparticles@L/D-cysteine

Novel chiral amino acids biosensor based on both potential difference and current ratio simultaneously was first established by employing left/right-handed double helix carbon nanotubes (L/D-DHCNT) with chiral structure as substrate material, and by self-assembly anchoring L/D-cysteine (L/D-Cys) on the surface of the left/right-handed double helix carbon nanotubes@Polypyrrole@Au nanoparticles nanocomposites (L/D-DHCNT@PPy@AuNPs). In this work, L/D-DHCNT@PPy@AuNPs@L/D-Cys was successfully constructed via a facile and environment-friendly process. Interestingly, in order to obtain highly dispersed AuNPs deposited on L/D-DHCNT, polypyrrole polymerized from pyrrole acts as a locating agent. Owing to the combination of unique performance of the L/D-Cys and L/D-DHCNT with chiral structure, and PPy and AuNPs with outstanding conductivity, an extremely efficient electrochemical chiral biosensing system was constructed that exhibited enhanced conductivity, sensitivity and chiral recognition capacity for tyrosine (Tyr), tryptophan (Trp) and glutamic acids (Glu) enantiomers. Utilizing both the potential difference and current ratio signal to commendably realize the electrochemical recognition and quantitative determination of amino acid enantiomers in their racemic solution. In addition, achieving the detection of Tyr in tablet samples by fabricated ultra-efficient electrochemical chiral biosensing system. Therefore, L/D-DHCNT@PPy@AuNPs@L/D-Cys as novel and ultrasensitive chiral biosensing system possesses the capability of chiral recognition of amino acid enantiomers, and it opens up the potential application of L/D-DHCNT@PPy@AuNPs@L/D-Cys in the field of chiral biosensors.

Chiral recognition of amino acid enantiomers using high-definition differential ion mobility mass spectrometry

Enantiomeric analysis of small molecules is important in many research fields, including in drug development. Here, chiral recognition of amino acid enantiomers using differential ion mobility spectrometry (DMS) mass spectrometry (MS) is demonstrated. Diastereomeric proton bound complexes were formed between enantiomers of amino acids (tryptophan and phenylalanine) and N-tert-butoxycarbonyl-O-benzyl-l-serine (BBS) by electrospray ionization for analysis by DMS-MS and collision-induced dissociation (CID). If the DMS resolution is sufficiently high, ionic diastereomers (as opposed to enantiomers) can in principle be separated without the use of a chiral gas. Peaks corresponding to the L- and D-enantiomers for both tryptophan and phenylalanine in the DMS-MS spectra were resolved by increasing the ratio of He in the carrier gas from 100% N2 to 50:50 He:N2%. In contrast, CID spectra of the corresponding diastereomeric dimer complex ions were nearly identical, indicating that chiral recognition by CID was not possible under these conditions. For mixtures of L- and D-tryptophan, a linear calibration curve can be obtained by plotting the enantiomeric excess measured by DMS-MS vs. the known values in solution (slope of 1.000, intercept of −0.010 and R2 of 0.997). That is, enantiopurity can be quantified using a separation process that occurs in milliseconds. Thus, DMS-MS analysis of proton bound diastereomeric dimers is a powerful approach for the rapid enantiomeric analysis of relatively small molecules.

Enantioselective Recognition of Proline Enantiomers Using Sulfhydryl-modified Self-assembled Gold Electrodes

ABSTRACTPenicillamine, cysteine, and N-isobutyryl-cysteine enantiomers self-assembled gold electrodes were used for the enantioselective recognition of proline in the presence of copper(II). High stereoselectivity for proline was obtained for the D-form of the sulfhydryl compounds, particularly on the D-penicillamine-modified gold electrode. Cyclic voltammetry and electrochemical impedance spectroscopy were used to confirm the chiral discrimination of proline enantiomers on the D-penicillamine modified gold electrode in the presence of copper(II). The largest electrochemical response was obtained for D-proline for the recognition of its enantiomers, whereas small responses were obtained for the L- and D-forms of phenylalanine, tyrosine, serine, and glutamic acid. The influences of incubation time and pH for chiral ligand exchange were evaluated. This study complements and enhances applications for the recognition of amino acid enantiomers based on ligand exchange by electrochemical analysis.

Application of Chiral Ionic Liquid-Modified Gold Nanoparticles in the Chiral Recognition of Amino Acid Enantiomers.

Two chiral ionic liquids (ILs), namely 1-ethyl-3-methylimidazole l-tartrate (EMIML-Tar) and 1-ethyl-3-methylimidazole l-lactate (EMIML-Lac), were used to modify gold nanoparticles (AuNPs) for chiral recognition of amino acid enantiomers. Transmission electron microscopy, infrared spectroscopy, ultraviolet-visible spectroscopy, and capillary electrophoresis were used for the characterization of chiral IL-modified AuNPs. Meanwhile, the performance of l-tartaric acid and l-lactic acid as modifiers was investigated to make a comparison. The chiral recognition mechanism is further discussed.

Chiral Recognition of Amino Acid Enantiomers by a Crown Ether: Chiroptical IR-VCD Response and Computational Study

We report on a combined experimental and computational study of the chiral recognition of the amino acid serine in protonated form (L/D-SerH(+)), by the crown ether (all-S)-(18-crown-6)-2,3,11,12-tetracarboxylic acid (S-18c6H4). Infrared and vibrational circular dichroism spectroscopies (IR-VCD) are employed to characterize the chiroptical response of the complexes formed by S-18c6H4 with the L-SerH(+) and D-SerH(+) enantiomers in dried thin films obtained from aqueous solutions. The study focuses on vibrational modes directly related to the intermolecular hydrogen bonds between the crown ether derivative and serine, responsible for crown-serine binding, namely, the C═O and C-O stretching modes, and on the C-O-H bending mode, which yield intense IR and VCD signals in the range of wavenumbers 900-2000 cm(-1). The experimental spectra are analyzed in combination with a computational structural survey and optimization at different levels of density functional theory. The conformational landscape of the complexes is found to be primarily governed by a bowl-like structure of the crown ether host and a tripodal coordination of the protonated R-NH3(+) group of serine with the oxygen atoms of the central ether ring. Additionally, one or two of the carboxylic side groups of the crown ether interact with the -COH and -COOH groups of serine. Chiral selectivity is probed by recording the IR and VCD spectra of dried thin films obtained from aqueous solutions with equimolar concentrations of the two serine enantiomers and the macrocycle. The results demonstrate a marked chiral recognition of L-SerH(+) relative to D-SerH(+) by the S-18c6H4 substrate, which arises from the favorable host-guest coordination through H-bonds at optimum distances and collinear orientations, also involving a limited distortion of the crown ether backbone.

Pincer ligands based on α-amino acids: V. New generation chiral receptors for the recognition of amino acid enantiomers in aqueous environment

Selective recognition of enantiomers of amino acids valine, methionine, phenylalanine, serine, and tyrosine by a binuclear copper complex with an azomethine obtained from 2,6-diformyl-4-methylphenol and L-valine was studied by means of spectrophotometry. The binding constants of individual enentiomers were estimated for valine, phenylalanine, methionine, serine, and tyrosine, and the enantioselectivity factors were evaluated. The isomers of serine and tyrosine (with respect to the first stage) were recognized with a considerable enantioselectivity (1.34 and 5.46 respectively), whereas the binding constants of valine and phenylalanine enantiomers are virtually indistinguishable.

The role of achiral sorbent matrix in chiral recognition of amino acid enantiomers in ligand-exchange chromatography

As an alternative to the known “three-point interaction” model describing recognition of optical isomers by a chiral resolving agent, a new concept has been developed stating that two interaction points between the resolving agent and the enantiomers are also sufficient for achieving chiral recognition of the latter, provided that the diastereomeric adducts formed by the resolving agent with the enantiomers additionally interact with a non-chiral chromatographic sorbent. This concept is based on the results of ligand-exchange chromatography of α-amino acid enantiomers with copper(II) complexes of chiral bifunctional ligands as the resolving agents in chromatographic systems.

Chiral recognition of amino acid enantiomers applying association models of amino acid derivatives forming intermolecular hydrogen bonds

Chelate-like association of amino acid derivatives made up by intermolecular NH··OC hydrogen bonds can function as chiroselective complexation for resolution of D- and L-amino acid derivatives.