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Chiral Analysis || Quantitative Chiral Analysis by Molecular Rotational Spectroscopy
摘要： This chapter presents early results from the emerging field of quantitative chiral analysis by molecular rotational spectroscopy. The focus is on the development of measurement techniques to solve the challenging analytical chemistry problem of determining the ratios of all stereoisomers for a chiral molecule. This analysis becomes particularly challenging as the number of chiral centers in the molecule increases. Furthermore, this area of spectroscopy has the goal of creating measurement techniques that can be used directly on complex chemical mixtures to perform chiral analysis without the need of chemical separation by chromatography. Examples of chemical samples that fall into this category include natural products like essential oils from plants that are a rich mixture of volatile species and reaction flask samples where stereospecific chemical reactions are performed and which contain unreacted reagents, desired and undesired reaction products, and solvents in the mixture.
关键词： stereoisomers,chiral tag,diastereomers,molecular rotational spectroscopy,chirality,enantiomers,three-wave mixing,analytical chemistry,quantitative chiral analysis
更新于2025-09-23 15:23:52
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Effect of doping by enantiomers with the different absolute configuration and phase sequence on mesomorphic, helical and electro-optical properties of highly tilted chiral anticlinic mixture
摘要： The main objective of the present work is to contribute to better understanding of the effect of the absolute configuration and phase sequences of dopants on the self-assembling and physicochemical properties as well as on the electro-optical parameters of a specific liquid crystalline mixture with a broad temperature range of the antiferroelectric phase. In order to establish this effect, the mesomorphic behaviour, helical pitch length and its handedness, spontaneous polarization and tilt angle, as well as electro-optical performance for all design mixture, are determined. The results show a broad temperature range of the antiferroelectric phase and very low melting points in all mixtures. Mixtures doped with (R) enantiomers exhibit longer helical pitch lengths, lower values of spontaneous polarization and rotational viscosity, comparable values of a tilt angle but also longer switch off times in comparison to similar mixtures doped with (S) enantiomers. The doping by the enantiomers exhibiting isotropic-ferroelectric-antiferroelectric phase sequence reveals the most significant impact on properties of the base mixture. The knowledge gained will very advantageous while designing new multicomponent liquid crystalline mixtures exhibiting the chiral tilted smectic mesophases for application in surface stabilized modes with passive and active matrix drive for utilization in photonics and optoelectronics.
关键词： rotational viscosity,multicomponent mixtures,antiferroelectric liquid crystals,spontaneous polarization,helical pitch,tilt angle,(S) and (R) enantiomers
更新于2025-09-23 15:21:01
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Chiral effects in low-cost plasmonic arrays of elliptic nanoholes
摘要： In this work we present an approach to induce chiral effects in well-known plasmonic nanohole arrays with triangular unit cell. Arrays with circular nanoholes in metals can exhibit interesting light-matter interaction mechanisms such as surface plasmon polaritons and extraordinary optical transmission. Moving from circular to elliptical shape and tilting the ellipse away from the lattice symmetry lines, a symmetry breaking induces a different absorption of the circularly polarized light of opposite handedness, i.e. circular dichroism. We numerically investigate circular dichroism at normal incidence in elliptic nanoholes in Au in the spectral range 400–1000 nm. We focus on its dependence on the elliptic nanohole tilt, and further proceed with the ellipse radii optimization. The optimized circular dichroism reaches 84%, and we report on the near field absorption distribution at the wavelengths of this maximum value.
关键词： Nanohole arrays,Enantiomers,Plasmonics,Chirality
更新于2025-09-23 15:19:57
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Metamaterials and chiral sensing: a review of fundamentals and applications
摘要： Chirality, a property of broken mirror symmetry, prevails in nature. Chiral molecules show different biochemical behaviors to their mirror molecules. For left or right circularly polarized lights, the fundamental chiral states of electromagnetic fields interact differently with chiral matter, and this effect has been used as a powerful tool for the detection of chiral molecules. This optical sensing, also termed chiral sensing, is not only easy to implement but also non-invasive to the analytes. However, the measurements made by the optical sensing of chiral molecules are challenging, as chiroptical signals are extremely weak. Recent years have seen active research efforts into metamaterial and plasmonic platforms for manipulating local fields to enhance chiroptical signals. This metamaterial approach offers new possibilities of chiral sensing with high sensitivity. Here, we review the recent advances in chiral sensing using metamaterial and plasmonic platforms. In addition, we explain the underlying principles behind the enhancement of chiroptical signals and highlight practically efficient chiral sensing platforms. We also provide perspectives that shed light on design considerations for chiral sensing metamaterials and discuss the possibility of other types of chiral sensing based on resonant metamaterials.
关键词： chiral sensing,chiral molecules,optical rotatory dispersion (ORD),chiroptical spectroscopy,circular dichroism (CD),enantiomers,plasmonics,metamaterials,optical spectroscopy
更新于2025-09-19 17:15:36
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Electroactive Au@Ag NP Assemblies Driven Signal Amplification for Ultrasensitive Chiral Recognition of D-/L-Trp
摘要： A novel ingenious and ultrasensitive chiral electrochemical transducer is proposed for the tryptophan (Trp) isomers detection by using electroactive Au@Ag NPs as electrochemical tags. Moreover, the large binding constant of D-Trp on NPs and strong interaction between D-Trp and Cu2+ cause electroactive Au@Ag NP to assembly on the electrode, generating strong differential pulse voltammetry (DPV) signals from the oxidation of Ag0 to Ag+. In sharp contrast to D-Trp, L-Trp leads to the assembly of Au@Ag NP oligomers on electrode, resulting in a weak DPV signal. The distinct DPV responses enable the developed electrochemical chiral transducer for the sensitive and accurate quantification of D-/L-Trp. The limit of detection (LOD) is 1.21 pM for D-Trp. This established electrochemical chiral sensor also achieves the specific determination of enantiomeric excess. In comparison to other reported approaches, this proposed electrochemical chiral sensor excels by its sensitivity, simplicity and good availability of electroactive Au@Ag NP assemblies. Target-induced colorimetric assays can be converted into electrochemical assays for the dual signal amplification in the field of ultrasensitive enantioselective chiral discrimination.
关键词： Au@Ag NPs,Chiral recognition,Trp enantiomers,Electroactive,Assemblies
更新于2025-09-19 17:15:36
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Chirality-dependent growth of self-assembled diphenylalanine microtubes
摘要： The difference in crystal structure and growth kinetics of microtubes formed from L- and D- enantiomers of diphenylalanine dipeptide is investigated both experimentally and theoretically by computer simulation. The microtubes of L- and D- enantiomers grown simultaneously and under identical experimental conditions possess different crystallographic space groups, have essential difference in sizes and demonstrate different growth kinetics. Computer simulation by molecular mechanics methods revealed a fundamental difference in the interaction between structural units of microtubes of different chiralities. A model describing chirality-dependent growth of microtubes is proposed.
关键词： Growth kinetics,Enantiomers,Dipeptide,Computer modeling,Nanotubes,Self-assembly
更新于2025-09-16 10:30:52
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A highly efficient chiral sensing platform for tryptophan isomers based on a coordination self-assembly
摘要： Construction of convenient and effective method for enantiomer identification is of vital significance for biochemistry and medical science. Herein, we design an effective sensor for chiral recognition of tryptophan (Trp) enantiomers, and self-assembly of Cu2+-modified β-cyclodextrin on poly-L-arginine/multi-walled carbon nanotubes (Cu-β-CD/PLA/MWCNTs) is studied. Meanwhile, Cu2+ acts as a cap to prevent the release of the high energy water and compel Trp enantiomer into the smaller opening of β-cyclodextrin. Recognition of L-Trp is accomplished by the formation of hydrogen bonds between the amino of L-Trp and the the high energy water confined in cavity of Cu-β-CD. Compared with D-Trp, the sensor exhibits favorable chiral recognition toward L-Trp with a separation coefficient of 3.37. And the chiral sensor presents admirable enantiomers determination with excellent sensitivity, providing a good linear correlation in the range of 1×10-6 M~5.5×10-5 M, and the detection limit can reach 3.3×10-7 M (S/N=3). Besides, the proposed sensor has been able to predict the percentage of D-Trp in the racemic mixture, suggesting its potential applications in the enantiomer recognition field.
关键词： Chiral recognition,Cu-β-cyclodextrin,Tryptophan enantiomers,self-assembly
更新于2025-09-09 09:28:46
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Chiral Nanoparticle‐Induced Enantioselective Amplification of Molecular Optical Activity
摘要： Chiral Nanoparticle-Induced Enantioselective Amplification of Molecular Optical Activity. Enantiodifferentiation is of fundamental importance in chiral chemistry and substantially requires high optical activity (OA) of enantiomers; but the enantiomeric OA is typically weak due to subwavelength molecular dimension, leading to a lack of sensitive enantiodifferentiation. A new approach is devised to evidently amplify the enantiomeric OA by anchoring axially chiral molecules containing the binaphthyl chromophore on silver chiral nanoparticles (AgCNPs) with a sub-5 nm helical pitch (P). Compared to the OA of dissolved enantiomers, that of (R)- and (S)- enantiomers can be enantioselectively amplified on right-handed and left-handed AgCNPs, respectively, in as high as one order of magnitude. The enantioselective amplification is probably ascribed to the enantiospecific adsorption-induced change in the dihedral angle of the binaphthyl chromophore, resulting from chirality transfer from chiral footprints of the AgCNPs to the binaphthyl chromophore through the Ag–S bicontacts. The enantioselective amplification tends not to occur as long as P > 5 nm or on achiral Ag nanoparticles, due to a lack of the chirality transfer. This work imposes the significant application of enantiodifferentiation, which is on practical demand for producing single-enantiomer pharmaceutics and pesticides with no fatal adverse effect, on the emerging chiral metamaterials composed of metallic CNPs.
关键词： glancing angle deposition,chiral nanoparticles,optical activity,enantiomers,circular dichroism
更新于2025-09-09 09:28:46
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Catalytic deracemization of chiral allenes by sensitized excitation with visible light
摘要： Chiral compounds exist as enantiomers that are non-superimposable mirror images of each other. Owing to the importance of enantiomerically pure chiral compounds—for example, as active pharmaceutical ingredients—separation of racemates (1:1 mixtures of enantiomers) is extensively performed. Frequently, however, only a single enantiomeric form of a chiral compound is required, which raises the question of how a racemate can be selectively converted into a single enantiomer. Such a deracemization process is entropically disfavoured and cannot be performed by a conventional catalyst in solution. Here we show that it is possible to photochemically deracemize chiral compounds with high enantioselectivity using irradiation with visible light (wavelength of 420 nanometres) in the presence of catalytic quantities (2.5 mole per cent) of a chiral sensitizer. We converted an array of 17 chiral racemic allenes into the respective single enantiomers with 89 to 97 per cent enantiomeric excess. The sensitizer is postulated to operate by triplet energy transfer to the allene, with different energy-transfer efficiencies for the two enantiomers. It thus serves as a unidirectional catalyst that converts one enantiomer but not the other, and the decrease in entropy is compensated by light energy. Photochemical deracemization enables the direct formation of enantiopure materials from a racemic mixture of the same compound, providing a novel approach to the challenge of creating asymmetry.
关键词： chiral sensitizer,triplet energy transfer,deracemization,chiral compounds,visible light,enantiomers,photochemical
更新于2025-09-04 15:30:14