Chiral Differentiation Research Articles

An enzymatic reaction-based SERS saliva analysis microporous array chip for chiral differentiation and high-throughput detection of D-amino acids.

ARaman-active boronate modified surface-enhanced Raman scattering (SERS) microporous array chip based on the enzymatic reaction was constructed for reliable, sensitive, and quantitative monitoring of D-Proline (D-Pro) and D-Alanine (D-Ala) in saliva. Initially, 3-mercaptophenylboronic acid (3-MPBA) was bonded to Au-coated Si nanocrown arrays (Au/SiNCA) via Au-S bonding. Following this, H2O2 obtained from D-amino acid oxidase (DAAO)-specific catalyzed D-amino acids (D-AAs) further reduced 3-MPBA to 3-hydroxythiophenol (3-HTP) with a new Raman peak at 882cm-1. Meanwhile, the original characteristic peak at 998cm-1 remained unchanged. Therefore, the I882/I998 ratio increased with increasing content ofD-AAs in the sample to be tested, allowing D-AAs to be quantitatively detected. TheAu/SiNCA with large-area periodic crown structure prepared provided numerous, uniform "hot spots," and the microporous array chip with 16 detection units was employed as the platform for SERS analysis, realizing high-throughput, high sensitivity, high specificity and high-reliability quantitative detection of D-AAs (D-Pro and D-Ala). The limits of detection (LOD) were down to 10.1µM and 13.7µM throughout the linear range of 20-500µM. The good results of the saliva detection suggested that this SERS sensor could rapidly differentiate between early-stage gastric cancer patients and healthy individuals.

Integrating a Copper-Histidine Brace in a Mimetic Nanozyme Streamlines the Tyrosinase Recognition Moiety to Achieve Chiral Differentiation.

Designing artificial mimetic enzymes with high activity/selectivity to replace chiral bioenzymes is of great interest in the development of chiral materials consisting of molecules, enantiomers, that exist in two forms as mirror images of one another but cannot be superimposed. In this study, the chiral catalytic structural unit was streamlined from tyrosinase to integrate a mimetic nanozyme. The chiral amino acid l-histidine, as the chiral binding/recognition site, and the active metal site Cu were coupled (Cu@l-His) to create a copper-histidine brace with enantioselective catalytic ability to tyrosinol enantiomers. Results of kinetic parameters and activation energies confirmed the excellent peroxidase-like activity with a preference of Cu@l-His to l-tyrosinol. Such a preference could be attributed to the structurally oriented copper-histidine brace with a stronger affinity and catalytic activity to l-tyrosinol. By accurately evaluating chiral recognition units derived from bioenzymes, stable and superior chiral mimetic nanoenzymes could be constructed in a more straightforward and simplified manner, and they could also be extended to the reconstruction of diverse chiral enzymes.

Electrochemical chiral sensor developed using nanofibrous polyaniline chiral Structures: Detection and differentiation of D- and L-tryptophan

In this work, a simple strategy for electrochemical detection and differentiation of D- and L- forms of tryptophan is demonstrated using nanofibrous structures of chiral polyaniline (CP). Basically, CP with desired chirality is prepared using a chiral acid namely, ± camphor sulfonic acid (±CSA) in presence of either a cationic (or) anionic surfactant (CTAB / SDS) through a simple oxidative polymerization process. Structure, morphology and phase purity of the resultant CP materials are characterized by field emission scanning electron microscopy, Fourier transform infrared spectroscopy, Raman spectroscopy and X-ray diffraction studies. Moreover, the chiral properties of these conducting polymers are evaluated using circular dichroism (CD) spectroscopic studies. From these analyses it is found that CP exhibited twisted nanofibrous morphology and possesses the chirality whereas the non-chiral polyaniline (PANI), prepared in the absence of chiral acid, displayed the formation of a simple fibrous structures without any twists or chirality. Interestingly, such CP materials are found to be electrochemically selective for the detection and differentiation of D- and L- forms of tryptophan (Trp). Among the different chiral materials, CP-CT(−) prepared using CTAB displayed a much better sensing characteristics with higher IL/ID ratio, wider concentration range of detection and lower detection limit of 0.98 µM for l-Trp and 1.2 µM for d-Trp respectively. On the other hand, non-chiral PANI does not display any sensing behavior towards the differentiation of amino acid, Trp. Further, chronoamperometric studies reveal the selectivity of this chiral sensor for the detection of Trp among the other potentially interfering analytes. Although the difference in the measured peak current value is smaller, a significant difference of 70 mV peak potential is observed for the differentiation of L- and d-Trp. Moreover, the proposed CP-based sensing platform exhibits excellent stability and reproducibility with statistically negligible error values suggesting the potential use of the developed material towards electrochemical chiral detection and differentiation of amino acid, Trp.

Enantioselective Reduction of Noncovalent Complexes of Amino Acids with CuII via Resonant Collision-Induced Dissociation: Collision Energy, Activation Duration Effects, and RRKM Modeling.

Formation of noncovalent complexes is one of the approaches to perform chiral analysis with mass spectrometry. Enantiomeric distinction of amino acids (AAs) based on the relative rate constants of competitive fragmentations of quaternary copper complexes is an efficient method for chiral differentiation. Here, we studied the complex [CuII,(Phe,PhG,Pro-H)]+ (m/z 493) under resonant collision-induced dissociation conditions while varying the activation time. The precursor ion can yield two main fragments through the loss of the non-natural AA phenylglycine (PhG): the expected product ion [CuII,(Phe,Pro-H)]+ (m/z 342) and the reduced product ion [CuI,(Phe,Pro)]+ (m/z 343). Enantioselective reduction describes the difference in relative abundance of these ions, which depends on the chirality of the precursor ion: the formation of the reduced ion m/z 343 is favored in homochiral complexes (DDD) compared to heterochiral complexes (such as LDD). Energy-resolved mass spectrometry data show that reduction, which arises from rearrangement, is favored at a low collision energy (CE) and long activation time (ActT), whereas direct cleavage preferentially occurs at a high CE and short ActT. These results were confirmed with kinetic modeling based on RRKM theory. For this modeling, it was necessary to set a pre-exponential factor as a reference, so that the E0 values obtained are relative values. Interestingly, these simulations showed that the critical energy E0 required to form the reduced ion is comparable in both homochiral and heterochiral complexes. However, the formation of product ion m/z 342 through direct cleavage is associated with a lower E0 in heterochiral complexes. Consequently, enantioselectivity would not be caused by enhanced reduction in homochiral complexes but rather by direct cleavage being favored in heterochiral complexes.

L-2-hydroxyglutaric aciduria - review of literature and case series.

The authors report two sisters with L2HGA from Pakistan born to consanguineous parents. The 15- and 17-year-old girls presented with psychomotor delay, seizures, ataxia, intentional tremors, and dysarthria. Both had normal anthropometric measurements for age. Exaggerated tendon reflexes and bilateral sustained ankle clonus were observed in addition to cerebellar signs. Urine organic acids analysis showed marked excretion of 2-hydroxyglutaric acid, chiral differentiation of 2-hydroxyglutaric acid showed it to be L2HGA. Brain MRI of the 15-year-old showed diffuse subcortical white matter changes evident by T2/FLAIR hyperintense signals bilaterally, particularly in the frontal region in the centripetal distribution with some diffusion restriction along involvement of globus pallidus. The characteristic MRI pattern raised the suspicion of L2HGA. Targeted L2HGDH sequencing identified a homozygous pathogenic variant, c.829C>T (p.Arg227*) in L2HGDH gene in both girls. Both parents were heterozygous carriers of the familial variant. Neuroradiological features of centripetal subcortical leukoencephalopathy with basal ganglia and dentate nuclei involvement are rather specific to L2HGA and should lead to further biochemical investigations to look for L2HGA and L2HGDH gene sequencing.

Probing Fast Enantio-Recognition of Drugs with Multiple Chiral Centers by Electrospray-Tandem Mass Spectrometry and Its Mechanism

Chiral drugs are very complex substances since individual enantiomers may differ in pharmacological and toxic effects, making it necessary to analyze enantiomers separately. In this study, we investigated the chiral differentiation of two ezetimibe enantiomers (i.e., SRS-EZM and RSR-EZM) and their mechanisms in complex with β-cyclodextrins (CDs) and metal ions as the auxiliary ligands. For this purpose, two complementary approaches have been employed: electrospray-tandem mass spectrometry (ESI-MS/MS) with collision induced dissociation (CID) and molecular modeling methods, including density functional theory (DFT) calculations and molecular dynamics (MD) simulations. The results showed a good agreement between experimental and theoretical data. It was demonstrated that SRS-EZM can be easily distinguished from RSR-EZM by applying CID in ESI-MS/MS. SRS-EZM is likely to form a more stable complex with β-CD and metal ions, and thus the [SRS-EZM]-Cu-[β-CD] cluster is more energetically difficult to separate from the SRS-EZM molecule compared with RSR-EZM. Such a difference may be attributed to the interactions between the drug molecule and the metal ion, as well as the cavity shape changes of the β-CDs upon complexation with molecular guests. Therefore, enantiomers in chiral drug can be recognized as ternary complexes of metal-analyte-β-CD by ESI-MS/MS with CID.

Disclosing the distribution regularities for chiral recognition exemplified by R-and RS- of new antifungal: Impact of pH and temperature

The overall investigation of the distribution behavior for the enantiomer (R-98) and racemic (RS-186) antifungal compounds was carried out to the aim of disclosing the possibility of chiral differentiation. To this end, the study on the thermodynamics of the distribution coefficients in the model systems 1-octanol/water and n-hexane/water was performed. The impact of pH on the transferring of the compounds was revealed by using buffer solutions at pH 2.0 and pH 7.4 as an aqueous phase. The transferring mechanisms for different distribution systems were disclosed based on the complex analysis of the enthalpy and entropy contributions to the Gibbs energy and involved in chiral discrimination. A separation factor or enantioselectivity, as well as the differences between the transfer Gibbs free energy, enthalpy and entropy (excess thermodynamic functions) were determined and discussed. The maximal value of the separation factor in the 1-octanol/buffer pH 7.4 system was shown. The impact of the hydrogen binding potential of the substances on the enantioselectivity was detected.

Chiral Nanoparticles Force Neural Stem Cell Differentiation to Alleviate Alzheimer's Disease.

The differentiation of neural stem cells via nanomaterials has attracted attention and has become a potential tool. However, the chirality effect in neural stem cell differentiation has not been investigated. Here, this study shows that chiral nanoparticles (NPs) with strong chirality can efficiently accelerate the differentiation of mouse neural stem cells (NSCs) into neurons under near‐infrared (NIR) light illumination. L‐type NPs are 1.95 times greater than D‐type NPs in promoting NSCs differentiation due to their 1.47‐fold endocytosis efficiency. Whole gene expression map analysis reveals that circularly polarized light illumination and chiral NPs irradiation significantly upregulate Map2, Yap1, and Taz genes, resulting in mechanical force, cytoskeleton protein action, and accelerated NSCs differentiation. In vivo experiments show that successful differentiation can further alleviate symptoms in Alzheimer's disease mice. Moreover, the clearance of L‐type NPs on amyloid and hyperphosphorylated p‐tau protein reachs 68.24% and 66.43%, respectively, under the synergy of NIR irradiation. The findings suggest that strong chiral nanomaterials may have advantages in guiding cell development and can be used in biomedicine.

Asymmetric Synthesis of Sakuranetin-Relevant Flavanones for the Identification of New Chiral Antifungal Leads

Discovery and efficient synthesis of new promising leads have a central role in agrochemical science. Reported herein is the sakuranetin-directed synergistic exploration of an asymmetric synthesis and an antifungal evaluation of chiral flavanones. A new palladium catalytic system with CarOx-type ligands was successfully identified for the highly enantioselective addition of arylboronic acids to chromones. This enabled the facile and programmable construction of a constellation of chiral flavanones (up to 98% yield and 97% ee), in which (R)-pinostrobin was efficiently constructed without laborious protecting/deprotecting operations. Its good performance in asymmetric induction and functional tolerance expanded the chemical space of pharmaceutically important flavanones. The chiral differentiation of flavanones based on antifungal activity and a concise structure-activity relationship model was disclosed and summarized. This synergistic project culminated with acquisition of the naturally unprecedented flavanones with better antifungal potentials than sakuranetin, in which the R-enantiomer of flavanone 54 (EC50 = 0.8 μM) demonstrated better performance than boscalid against Rhizoctonia solani. The novel scaffold and predicted new target compared with the commercial fungicides in the FRAC reinforce the value of further exploration.

Understanding of chiral site-dependent enantioselective identification on a plasmon-free semiconductor based SERS substrate.

Chiral differentiation is an important topic in diverse fields ranging from pharmaceutics to chiral synthesis. The improvement of sensitivity and the elucidation of the mechanism of chiral recognition are still the two main challenges. Herein, a plasmon-free semiconductive surface-enhanced Raman spectroscopy (SERS) substrate with sensitive chiral recognition ability is proposed for the discrimination of enantiomers. A homochiral environment is constructed by typical π–π stacking between l-tryptophan (l-Trp) and phenyl rings on well-aligned TiO2 nanotubes (TiO2 NTs). Using 3,4-dihydroxyphenylalanine (DOPA) enantiomers as the targets and the chelating interaction of Fe3+–DOPA for the onsite growth of Prussian blue (PB), the enantioselectivity difference between l-DOPA and d-DOPA on the homochiral substrate can be directly monitored from PB signals in the Raman-silent region. By combining the experimental results with molecular dynamic (MD) simulations, it is found that satisfactory enantioselective identification not only requires a homochiral surface but also largely depends on the chiral center environment-differentiated hydrogen-bond formation availability.

Engineering a cationic supramolecular charge switch for facile amino acids enantiodiscrimination based on extended-gate field effect transistors

Chiral recognition of essential amino acids (EAAs) is a huge challenge that keeps plaguing analytical scientists due to their cryptochirality and limited steric interaction sites. Inspired by the superior enantioselectivity of functional supramolecular cyclodextrins (CDs) and strong signal amplification ability of field effect transistors (FETs), this work firstly reports a cationic supramolecular charge switch for facile enantiodiscrimination of EAAs based on extended-gate organic FET (EG-OFET). The cationic phenylcarbamoylated-CD single isomer acts as a charge switch via interacting with different enantiomers and the weak stereo-differentiation intermolecular interaction signals between the cationic perphenylcarbamoylated CDs and EAAs on the EG can be strongly and rapidly amplified through an OFET. Efficient chiral differentiation of six EAAs, including phenylalanine, tryptophan, leucine, isoleucine, lysine and valine, are successfully achieved without any derivation process and the detection limit for d-phenylalanine is down to 10−13 mol/L. We believe that this study provides a new and facile sensing perspective for natural amino acids and may afford deeper understanding of molecular chirality.

Enhanced carboxypeptidase efficacies and differentiation of peptide epimers

Carboxypeptidases enzymatically cleave the peptide bond of C-terminal amino acids. In humans, it is involved in enzymatic synthesis and maturation of proteins and peptides. Carboxypeptidases A and Y have difficulty hydrolyzing the peptide bond of dipeptides and some other amino acid sequences. Early investigations into different N-blocking groups concluded that larger moieties increased substrate susceptibility to peptide bond hydrolysis with carboxypeptidases. This study conclusively demonstrates that 6-aminoquinoline-N-hydroxysuccimidyl carbamate (AQC) as an N-blocking group greatly enhances substrate hydrolysis with carboxypeptidase. AQC addition to the N-terminus of amino acids and peptides also improves chromatographic peak shapes and sensitivities via mass spectrometry detection. These enzymes have been used for amino acid sequence determination prior to the advent of modern proteomics. However, most modern proteomic methods assume that all peptides are comprised of l-amino acids and therefore cannot distinguish L-from d-amino acids within the peptide sequence. The majority of existing methods that allow for chiral differentiation either require synthetic standards or incur racemization in the process. This study highlights the resistance of d-amino acids within peptides to enzymatic hydrolysis by Carboxypeptidase Y. This stereoselectivity may be advantageous when screening for low abundance peptide stereoisomers.

Enantiospecific Molecular Fingerprinting Using Potential-Modulated Surface-Enhanced Raman Scattering to Achieve Label-Free Chiral Differentiation.

Chiral differentiation is critical in diverse fields ranging from pharmaceutics to chiral synthesis. While surface-enhanced Raman scattering (SERS) offers molecule-specific vibrational information with high detection sensitivity, current strategies rely on indirect detection using additional selectors and cannot exploit SERS' key advantages for univocal and generic chiral differentiation. Here, we achieve direct, label-free SERS sensing of biologically important enantiomers by synergizing asymmetric nanoporous gold (NPG) nanoparticles with electrochemical-SERS to generate enantiospecific molecular fingerprints. Experimental and in silico studies reveal that chiral recognition is two pronged. First, the numerous surface atomic defects in NPG provide the necessary localized asymmetric environment to induce enantiospecific molecular adsorptions and interaction affinities. Concurrently, the applied potential drives and orients the enantiomers close to the NPG surface for maximal analyte-surface interactions. Notably, our strategy is versatile and can be readily extended to detect various enantiomers. Furthermore, we can achieve multiplex quantification of enantiomeric ratios with excellent predictive performance. Our combinatorial approach thus offers an important paradigm shift from current approaches to achieve label-free chiral SERS sensing of various enantiomers.

Molecule-specific vibration-based chiral differentiation of Raman spectra using cysteine modified gold nanoparticles: the cases of tyrosine and phenylalanine.

The chirality of amino acids plays a key role in many biochemical processes, with the development of spectroscopic analysis methods for the chiral differentiation of amino acids being significant. Normal Raman spectroscopy is blind to chirality; however, chiral discrimination of tyrosine (Tyr) (or phenylalanine, Phe) enantiomers using Raman spectra can be achieved assisted by the construction of a simple chiral selector (i.e., cysteine (Cys)-modified Au nanoparticles (NPs)). Due to the synergetic effect between Cys and the Au NPs, the characteristic Raman scattering intensities of the Tyr (or Phe) enantiomer with the same chirality of Cys are enantioselectively boosted by over four-fold compared with those of the counter enantiomer of Tyr (or Phe). The large differences in the Raman signals allow for the determination of enantiomeric excess. Interestingly, such enantiomeric discrimination is not revealed by the common chiral analysis method of circular dichroism spectroscopy. Consequently, it is anticipated that Raman spectroscopy based on molecular vibrations will find broad applications in chirality-related detection with high sensitivity and species specificity.

Computational investigation on the chiral differentiation of D- and L-penicillamine by β-cyclodextrin

The identification of chiral penicillamine (Pen) is of great significance for clinical medication safety. The host-guest systems formed by enantiomers and macromolecule can be applied to differentiate the chiral drugs and enable the drug delayed release. We hereby performed the dispersion corrected density functional theory (DFT-D) calculation on the complex formed by β-cyclodextrin(β-CD) and D/L-penicillamine (D/L-Pen). The diverse encapsulation configurations with different interaction energy show that both D-Pen and L-Pen tend to longitudinally embedded into the narrow aperture of β-CD with the front part of the sulfur group and the methyl group, and the interaction energy between L-Pen and β-CD is 5.47 kJ/mol(M062XD3) lower than that between D-Pen and β-CD. Based on the computed vibration frequency of host, guest, and the most stable complex, it is found that the featured peaks attributed to the vibration of the carboxyl group of guest and the skeleton vibration of complex are the most significant spectral standard to distinguish the β-CD-D/L-Pen and β-CD. Moreover, the peaks resulted from the skeleton vibration in terahertz spectra can be also used to distinguish the complex of β-CD with chiral Pen. Through the topological analysis and the Independent Gradient Model (IGM) analysis, the O-H…O hydrogen bond in β-CD-D-Pen is stronger than that in β-CD-L-Pen, and the van der Waals interactions such as C-H…O,C-H…N,C-H…S, O…S and C-H…C-H have the most contributions to the intermolecular interaction in β-CD-D/L-Pen. It is also noted that the H(–OH) in D-Pen and S in L-Pen contribute the most to the intermolecular interaction with β-CD in comparison with other atoms in Pen.

Controlled Synthesis of Au Chiral Propellers from Seeded Growth of Au Nanoplates for Chiral Differentiation of Biomolecules

Chiral plasmonic nanocrystals are promising materials for applications in enantioselective catalysis, DNA detection, and medical diagnosis. Herein, we demonstrate a simple and versatile strategy th...

In situ antioxidation-assisted matrix solid-phase dispersion microextraction and discrimination of chiral flavonoids from citrus fruit via ion mobility quadrupole time-of-flight high-resolution mass spectrometry

A simple and sensitive in situ antioxidation process assisted with a matrix solid-phase dispersion method for extracting chiral flavonoids in citrus fruit was established, and samples were further analyzed using ion mobility quadrupole time-of-flight high-resolution mass spectrometry. The collision cross-sections of the target compounds were studied using single-field and stepped-field methods. The optimal conditions were obtained using 30 mg of C18 as a dispersant, methanol as an elution solvent and 0.6 mM 1,1-diphenyl-2-picrylhydrazyl (DPPH) as a radical solution. Additionally, the method showed satisfactory limits of detection (3.70–6.52 ng/mL) and good recoveries (96.78–104.67%) for four flavonoids in citrus fruit. The IC50 values of DPPH radical-scavenging activities ranged from 817.8 to 981.55 μg/mL for tested samples. The method was a good alternative for the microextraction and determination of antioxidant capacity and chiral differentiation of narirutin, naringin, hesperidin and neohesperidin in citrus fruit.

Chiral differentiation of l- and d-penicillamine by β-cyclodextrin: Investigated by IRMPD spectroscopy and theoretical simulations.

The chirality of penicillamine (Peni) results in different clinic applications. Host-guest complex based drug delivery system that differentiates the two enantiomers and provides delayed release is of significance in medication. We hereby used β-CD to encapsulate d- and l-Peni. IRMPD spectra show different characteristic vibrations to distinguish the two enantiomers. Besides common peaks found at 3000-3100cm-1 and 3520cm-1, featured peaks are found around 2900cm-1 and 3400cm-1. It is found that the featured vibrations of [β-CD+l-Peni+H]+ are more red-shifted than those of [β-CD+d-Peni+H]+. Through DFT calculations on the complex configurations sampled from molecular dynamics simulations, d-Peni is found embedded inside β-CD with a lower free energy of 11.5kJmol-1 in the lowest configuration than that of the lowest [β-CD+l-Peni+H]+ configuration, in which l-Peni is found lying upon the β-CD. The featured vibrational peaks are attributed to the specific NH⋯O, OH⋯O intermolecular hydrogen bonds. The red-shifted characteristic peaks of [β-CD+l-Peni+H]+ in IRMPD spectra owe to the stronger NH⋯O hydrogen bonds.

Gold nanoparticles coated with a tetramethylammonium lactobionate ionic liquid for enhanced chiral differentiation in open tubular capillary electrochromatography: application to enantioseparation of β-blockers.

A new bilayer chiral stationary phase for use in open tubular capillary electrochromatography (OT-CEC) system is described. Gold nanoparticles were modified with L-cysteine, with a tetramethylammonium lactobionate ionic liquid that acts as the chiral selector. The gold nanoparticle-coated column provides good enantioseparation and favorable reproducibility. Compared with an uncoated separation system, the column developed displays improved separation of the racemic β-blockers propranolol, esmolol, bisoprolol and sotalol (resolutions of enotiomers are 6.29, 6.11, 6.12 and 6.02, respectively). The materials and coatings were characterized by scanning electron microscopy and transmission electron microscopy. The main driving forces (CEC and electro-osmotic flow) were studied to evaluate the variation of the immobilized columns. The effects of buffer pH value, concentration of chiral selector, type of organic modifier and applied voltage were optimized. Satisfactory relative standard deviations were achieved in run-to-run, day-to-day and column-to-column experiments. Graphical abstractSchematic preparation of a capillary column with bilayer chiral selectors coated gold nanoparticles. This novel OT-CEC system was applied for separation of four basic racemic β-blockers.

Chiral differentiation of limonene in chiral nematic liquid crystals.

Chirality is of great importance in physical and biological systems. It helps differentiate chemical reactions and physical processes. It was reported that the diffusion of mesogenic chiral guests in chiral nematic liquid crystal hosts profoundly depends on the chirality of the guest and host molecules. When the guest and host molecules have the same handedness, the diffusion is much faster than that when the guest and host molecules have the opposite handedness. In this paper, we report the discovery that chiral differentiation also exists in the diffusion of limonene, which is non-mesogenic in chiral nematic liquid crystals. The diffusion of l-limonene (right-handed) in chiral nematic liquid crystals with a right handed helical structure is faster than that of d-limonene (left-handed). This result might be important in understanding the effects of chirality on physical processes that take place in biological systems. In addition, this effect could be utilized for enantiomer separation in the pharmaceutical industry.