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The existence of an object, non-superimposable on its mirror image, constitutes the phenomenon of chirality. This phenomenon is often treated as a curiosity without broader practical consequences. This paper aims to show the significant implications of chirality for chemistry and biology. Chirality is inherent to all living organisms and is essential for their function. For instance, biomolecules are composed of chiral building blocks (amino acids, monosaccharides), which are chiral and occur predominantly with one sense of handedness (homochirality of life). The explanation of the evolution of the homochirality of life therefore helps answer one of the important questions connected with the origin of life.. The paper concludes with a section devoted to current Czech stereochemical terminology. An experimental procedure describing the isolation of carvone enantiomers from natural sources is also included. [ABSTRACT FROM AUTHOR]

Diverse chiral structures observed in nature find applications across various domains, including engineering, chemistry, and medicine. Particularly notable is the optical activity inherent in chiral structures, which has emerged prominently in the field of optics. This phenomenon has led to a wide range of applications, encompassing optical components, catalysts, sensors, and therapeutic interventions. This review summarizes the imitations and applications of naturally occurring chiral structures. Methods for replicating chiral architectures found in nature have evolved with specific research goals. This review primarily focuses on a top-down approach and provides a summary of recent research advancements. In the latter part of this review, we will engage in discussions regarding the diverse array of applications resulting from imitating chiral structures, from the optical activity in photonic crystals to applications spanning light-emitting devices. Furthermore, we will delve into the applications of biorecognition and therapeutic methodologies, comprehensively examining and deliberating upon the multifaceted utility of chiral structures. [ABSTRACT FROM AUTHOR]

Enantiomers are chiral isomers in which the isomer's structure itself and its mirror image cannot be superimposed on each other. Enantiomer selective sensing is critical as enantiomers exhibit distinct functionalities to their mirror image. Discriminating between enantiomers by optical methods has been widely used as these techniques provide nondestructive characterization, however, they are constrained by the intrinsically small chirality of the molecules. Here, a method to effectively discriminate chiral analytes in the nonlinear regime is demonstrated, which is facilitated by an upconverting chiral plasmonic metamaterial. The different handedness of the chiral molecules interacts with the chiral metamaterial platform, which leads to a change in the circular dichroism of the chiral metamaterial in the near‐infrared region. The contrast of the circular dichroism is identified by the upconverted signal in the visible region. [ABSTRACT FROM AUTHOR]

A new concept for the regioselective synthesis of [3 : 2 : 1] hexakis‐adducts of fullerene C60 was developed. Based on sequential tether‐directed remote functionalizations, chiral [3 : 2] pentakis‐adducts with an incomplete octahedral addition pattern were synthesized via stepwise cyclopropanation of C60 with suitable macrocyclic tri‐ and bifunctional cyclomalonate tethers. The four resulting stereoisomers were isolated using chiral HPLC. The corresponding pairs of enantiomers show mirror image behavior in their CD‐spectra. The pentakis‐adducts served as suitable building blocks for the spatially controlled synthesis of mixed hexakis‐adducts. Implementation of functional group‐bearing monomalonates afforded octahedral [3 : 2 : 1] hexakis‐adducts suitable for the construction of larger molecular and supramolecular fullerene architectures in excellent yield. [ABSTRACT FROM AUTHOR]

Chirality is a special phenomenon exhibited by two compounds with non-superimposing mirror images of each other. Chiral enantiomers have the same composition and similar structures, but usually exhibit different physiological behaviors or different pharmacological activities. Therefore, the identification of chiral enantiomers has always been the major topics in the field of asymmetric chemistry and biology. However, traditional chiral recognition methods (such as chromatography) have many disadvantages of complicated operation and high cost. Electrochemiluminescence (ECL), as a classic electrochemical test method, has the advantages of simple operation, high sensitivity, real-time detection, and no background interference, which has a great application prospect in chiral recognition compared with traditional methods. Unfortunately, few researchers have systematically sorted out the field of electrochemiluminescence chiral recognition. In order to provide some help for researchers in different industries to quickly and systematically understand electrochemiluminescence chiral recognition, and better guide researchers in related fields to conduct more in-depth research in the field, we summarize the review of ECL chiral recognition from the following aspects, i.e., the historical development of chiral recognition, the mechanism of ECL chiral recognition, different ECL-active materials for chiral recognition, and some challenges and outlooks in ECL chiral recognition. [Display omitted] • Different recognition mechanisms are introduced with different materials. • Detailed review for the historical development of chiral recognition. • Review about the works of combining ECL with other analytical techniques for identification of chiral enantiomers. [ABSTRACT FROM AUTHOR]

Diclazuril has been widely used in poultry feed for prevention and treatment of coccidiosis, and its chiral separation is rarely reported. Herein, semi‐preparative separation method of diclazuril enantiomers has been developed through normal‐phase high‐performance liquid chromatography. Effects of chiral stationary phases, alcoholic modifiers, and column temperature on separation of diclazuril were discussed in detail. Both the single‐urea‐bound 4‐chlorophenylcarbamoylated β‐cyclodextrin and amylose tris(3,5‐dimethylphenylcarbamate)‐coated chiral stationary phases showed strong ability in separation of diclazuril by using n‐hexane–trifluoroacetic acid–ethanol. Then, semi‐preparative separation of diclazuril was carried out through stacked injection, and the "enantiomeric excess" purities of two fractions were over 98%. Next, the electronic circular dichroism profiles of these two fractions in ethanol solution displayed the mirror image of each other in the range 360–200 nm. Moreover, effects of acidic/basic additive, time, and temperature on racemization of diclazuril enantiomers in ethanol solution have been studied in detail through normal‐phase high‐performance liquid chromatography. Racemization of diclazuril enantiomers was remarkably accelerated through adding triethylamine at high temperature. We envision that this systematic investigation of diclazuril at an enantiomeric level would provide valuable information in future studies involving enantioselective bioactive, metabolic, and toxicological activities. [ABSTRACT FROM AUTHOR]

Chirality governs many chemical and biological processes, since most active substances are chiral. Enantiomers are mirror images of the same molecule that can exhibit significant differences in terms of biochemical activity, toxicity, and transport mechanisms in the human body. Thus, developing effective methods to achieve chiral recognition is of great significance and has been a hot topic in chemo/biological studies. In recent years, electrochemical methods have received considerable attention in this field since they can offer several advantages over chromatographic or spectroscopic methods. In this review, a comprehensive and critical description of the trends in electrochemical chiral recognition over the last five years is presented. In addition, some unconventional electrochemical methods for the transduction of chirality at different length scales are described and discussed. [Display omitted] [ABSTRACT FROM AUTHOR]

A novel method to generate RNA binding D -peptide has been developed. To achieve the screening method, phage display was applied to “Mirrored” RNA ( L -enantiomer of RNA). We have selected pre-miR21 as an initial screening target to demonstrate the method. The mirrored pre-miR-21 binding peptide sequences were successfully obtained, and were chemically synthesized using D -amino acids. D -peptide is expected to have favorable properties as a drug candidate such as protease resistance and low immunogenicity. As a result of binding evaluation of the D -peptide to pre-miR-21, the EC 50 value was 440 nM. In addition, the D -peptide possessed inhibition activity to miR-21 processing. [ABSTRACT FROM AUTHOR]

Precise supersymmetric partner potentials can be generated for exactly solvable problems of the stationary Schrödinger equation. Construction of isospectral potential is not always possible for exactly solvable systems. This is a restriction, as most problems are not exactly solvable. Employment of mirror-image property can help to construct an exact isospectral partner of that potential. These potentials have chemical relevance to enantiomers. In this paper, we present a formulation as modelling to explore the form of SUSY pair of these potentials. Through polynomial fit, we correlate all possible basic SUSY partners and optimise it to best fit polynomial to present a typical energy value of N = 50. [ABSTRACT FROM AUTHOR]

Abstract: Literacy in a script with mirrored symbols boosts the ability to discriminate mirror images, i.e., enantiomorphy. In the present study we evaluated the impact of four factors on enantiomorphic abilities: (i) the degree of literacy of the participants; (ii) the familiarity of the material; (iii) the strength of the association between familiar objects and manipulation, i.e., graspability; and (iv) the involvement of vision-for-action in the task. Three groups of adults – unschooled illiterates, unschooled ex-illiterates, and schooled literates – participated in two experiments. In Experiment 1, participants performed a vision-for-perception task, i.e., an orientation-based same–different comparison task, on pictures of familiar objects and geometric shapes. Graspability of familiar objects and unfamiliarity of the stimuli facilitated orientation discrimination, but did not help illiterate participants to overcome their difficulties with enantiomorphy. Compared to a baseline, illiterate adults had the strongest performance drop for mirror images, whereas for plane rotations the performance drop was similar across groups. In Experiment 2, participants performed a vision-for-action task; they were asked to decide which hand they would use to grasp a familiar object according to its current position (e.g., indicating left-hand usage to grasp a cup with the handle on the left side, and right-hand usage for its mirror image). Illiterates were as skillful as literates to perform this task. The present study thus provided three important findings. First, once triggered by literacy, enantiomorphy generalizes to any visual object category, as part of vision-for-perception, i.e., in visual recognition and identification processes. Second, the impact of literacy is much stronger on enantiomorphy than on the processing of other orientation contrasts. Third, in vision-for-action tasks, illiterates are as sensitive as literates to enantiomorphic-related information. [Copyright &y& Elsevier]

This paper reviews publications of laboratory experiments using pairs of enantiomers in homeopathy. Many molecules in nature have geometry which enables them to exist as nonsuperimposable mirror images or enantiomers. Modulation of toxicity of such molecules provides possibility for therapeutics, since they target multiple points in biochemical pathways. It was hypothesized that toxicity of a chemical agent could be counteracted by a homeopathic preparation of the enantiomer of the chemical agent (patents applied for: PCT/AU2003/000219-PCT/AU2008/001611). A diverse body of data, including controlled laboratory studies, supports the conclusion that toxicity of optical isomers may be inhibited by homeopathic enantiomer preparations. These data were obtained with minimal or no pretesting to determine optimal test solutions. Inhibition of the excitotoxic neurotransmitter Lglutamic acid with homeopathic preparations of D-glutamic acid indicates the latter may be of use for amelioration of symptoms of disturbances of mood. Similarly, homeopathic preparation of (+)-nicotine may be of use for inhibition of effects of nicotine in tobacco. [ABSTRACT FROM AUTHOR]

Abstract: We introduce the mixed product of three vectors spanning four molecular locations as a descriptor of optical isomerism. This descriptor is very efficient as it does not require molecular superposition, and is very robust in discriminating between a given isomer and its mirror image. In particular, conformational isomers that are mirror images of each other, as well as optical isomers have opposite sign of the descriptor value. For efficient database searches, the optical isomerism descriptor can be used to complement an available ultrafast shape recognition (USR) method based solely on distances, which is not able to distinguish enantiomers. By an extensive comparison of the USR-based similarity score with an approach based on Gaussian molecular volume overlap, the accuracy and completeness of the former are discussed. [ABSTRACT FROM AUTHOR]

Proteins and peptides in mammals are based exclusively on L-amino acids. Recent investigations show that D-amino acids exhibit physiological effects in vivo, despite of their very small quantities. We have investigated the hepatoprotective effects of the L- and D-enantiomers of α-melanocortin peptide (α-MSH). The results showed that peptideenantiomerism is related to the protective effects of melanocortin peptides in vivo. L-α- MSH exhibited potent hepatoprotective effect in the experimental model of acetaminophen induced hepatotoxicity in male CBA mice, while its D-mirror image was inefficient. Furthermore, the antibody to the L-peptide did not recognize the D-structure. The results indicate that the opposite peptide configuration may be used to modulate its function and metabolism in vivo and in vitro. [ABSTRACT FROM AUTHOR]

The article focuses on mechanisms for Chiral recognition. Due to their natural symmetry, chiral compounds show different properties in biochemical systems, but they are not distinguishable in inanimate environments. Two molecules that are mirror images of each other are called an enantiomeric pair, and they show same properties in all isotropic conditions. However, because biochemical systems are not isotropic, the pharmacological effects of two enantiomers of a chiral drug may be different. Due to this, there is a need for chiral recognition mechanism. In the "Three-point interaction model" for chiral recognition, molecular recognition can be done on the basis of differential binding of two enantiomers to a chiral three-point site on the selector. The enantiometer can match a maximum of only two sites, irrespective of how its mirror image rotates. Chiral selection can be done by evaluating the possible interactions, and then designing a selector that would interact differently with an enantiomeric form than with its mirror image. Chiral recognition mechanism is based on the measurement of the binding energy of the two chiral-selector-enantiomer complexes.

Peptides comprising D-amino acids have been shown to be resistant to proteolysis. This makes them potential candidates as probes of cellular interactions, notably protein-biomolecule interactions. However, the empirical conversion of the amino acids that constitute a peptide from L-forms to D-forms will result in abrogation of the normal interactions made by the L-amino acids due to side-chain orientation changes that are associated with the changes in chirality. These interactions can be preserved by reversing the sequence of the D-peptide. We present a web server (http://dstabilize.bii.a-star.edu.sg/) that allows users to convert between L-proteins and D-proteins and for sequence reversal of D-peptides, along with the capability of performing other empirical geometric transforms. This resource allows the user to generate structures of interest easily for subsequent in silico processing. • Convert between L- and D-forms of peptides/protein structures • Apply custom geometrical transforms to structures of peptides/proteins • Generate retro-inverso forms of peptides • Webserver is available at http://dstabilize.bii.a-star.edu.sg/ The importance of D-amino acid-containing peptides as therapeutics is increasingly being recognized. In this work, Malik et al. present a webserver allowing users to easily interconvert between L- and D-forms of peptides/protein structures, apply custom geometrical transforms, and generate retro-inverso forms of peptides for in silico investigations. [ABSTRACT FROM AUTHOR]

We present surface enhanced Raman optical activity (SEROA), as well as Raman, SERS and ROA, spectra of d- and l-ribose. By employing a gel forming polyacrylic acid to control colloid aggregation and associated birefringent artefacts we observe the first definitive proof of SEROA through measurement of mirror image bands for the two enantiomers. [ABSTRACT FROM AUTHOR]

We present the second harmonic generation — circular dichroism response from G-shaped gold nanostructures for P-polarized incoming light. By eliminating the contributions of anisotropy to the signal, an absolute measure of the second harmonic generation — circular dichroism is presented. The system of planar nanostructures is an excellent model for studying the correlation between optical properties and chiral morphology at the nanoscale. Samples with both enantiomorphs of the chiral pattern were prepared and, demonstrating the unambiguous presence of chirality, the second harmonic generation — circular dichroism response from two such samples was fitted simultaneously with a single set of fitting parameters. [ABSTRACT FROM AUTHOR]

Chiron approach was used to acquire optically pure (R)- and (S)-1-(2,6-dimethylphenoxy)propan-2-ol, immediate precursors of (S)- and (R)-mexiletines, respectively. Two different routes were followed from a D-mannitol-derived optically pure common precursor to get the enantiomeric alcohols separately. Comparison of their specific rotation values with the corresponding literature values as well as exact mirror-image relationship between their CD curves proved their high enantiopurity. These alcohols were then transformed to the corresponding amine-drugs in an efficient one-step process instead of two steps described in the literature. Image 1 • Chiron approach conveyed stereochemistry from D-mannitol to alcohol enantiomers. • Different routes from a chiral intermediate gave enantiomeric alcohols separately. • First report of one-step conversion of alcohols to corresponding mexiletines. • CD curves of alcohol and amine enantiomers showed exact mirror image relationship. [ABSTRACT FROM AUTHOR]

Spin, not shape, underlies a surprising new method for sorting biomolecules from their opposite-handed counterparts. [ABSTRACT FROM AUTHOR]

The article presents a study which reveals anions and cations play significant roles in chemical reactions as reagents, intermediates and products. According to the study, anions and cations can be chiral molecules, with two non-identical mirror images called enantiomers. Moreover, it shows that chiral anion can help produce a chiral reaction product consisting almost exclusively of one enantiomer. This result is important given the growing demand from academic, agrochemical and pharmaceutical laboratories for enantiopure molecules.

The understanding of chirality is central to molecular sciences. Scientists define chirality as exhibited by systems that exist in two distinct enantiomeric states that are interconverted by the parity operation or space inversion, but not by time reversal combined with any proper spatial rotation. Conservation of parity symmetry manifests itself in enantiomers having exactly the same chemical and physical properties in an achiral medium. According to the standard model, the neutral weak electron-nucleon current leads to parity violation and breakdown of mirror image symmetry or parity nonconservation (PNC) in chiral molecules, thus causing a small energy difference PNC between enantiomers resulting in small differences in spectroscopic properties.