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Dual-Band Terahertz Chiral Metamaterial with Giant Optical Activity and Negative Refractive Index Based on Cross-Wire Strucure

Dual-Band Terahertz Chiral Metamaterial with Giant Optical Activity and Negative Refractive Index Based on Cross-Wire Strucure

rotation angle between the polarization planes of the transmitted and incident waves and can be expressed as θ = [arg(T ++ ) − arg(T −− )]/2. Various enantiomeric forms bi-layer planar chiral structure have been proposed and investigated widely, such as twist rosettes [7], twist cross wires [3, 11, 13], U shape SRRs [14], conjugate swastikas [15, 16], and other novel bi-layer structures [17–24], which could exhibit negative refractive index and optical activity in a single frequency band or dual-band. More recently, negative refractive index of 3 dimensional compact helix structures also has been investigated in microwave frequency [25–27], however, which is hard to fabricate and integrate into present systems, especially in teraherz (THz) and optical region. THz is a unique frequency range which has attracted significant attention due to its potential applications in sensing, biomedical imaging, and wireless communication, among others [5, 28]. Because of the lack of natural materials for manipulating the THz wave, the development of MMs with unusual optical properties for this frequency region is especially important [29, 30].
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Ibuprofen Maltodextrin Interaction: Study of Enantiomeric Recognition and Complex Characterization

Ibuprofen Maltodextrin Interaction: Study of Enantiomeric Recognition and Complex Characterization

NMR based methods, such as 1 H-NMR, have been used to evaluate enantiomeric recognition and to deter- mine the enantiomeric excess of chiral compounds. The development of new types of chiral selectors with higher efficiencies is of primary importance in the development of a versatile and accurate method for the resolution of enantiomeric forms in chiral drugs. In particular, the NMR techniques could provide considerable information about theoretical models of the enantioseparation of en- antiomeric IBP with cyclic and linear oligosaccharides, which may be applied for the chiral recognition process in capillary electrophoresis and chromatographic separa-
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Layered chiral metallic meta materials

Layered chiral metallic meta materials

Fig. 3: Optical manifestations of planar chirality in the diffraction regime. Polarization azimuth rotation ( ¦, c) and change in ellipticity ( „, …) of light wave diffracted from left (c, …) and right (¦, „) handed gammadion arrays plotted as functions of the incident angle. The incident angle β is measured between the direction of the incident beam and normal to the sample, as presented on fig.2. The two enantiomeric forms correspond to α = −45 0 (left-handed) and α = +45 0

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Structural diversity-driven synthesis of cycloalkane-based heterocycles and 1,3-bifunctional compounds

Structural diversity-driven synthesis of cycloalkane-based heterocycles and 1,3-bifunctional compounds

Since monoterpenes are excellent starting materials for the synthesis of enantiomeric alicyclic compounds, our aim was to synthetize new α-pinane-based optically active 1,3- amino alcohols and 1,3-diamines and to apply them as catalysts in the enantioselective addition of diethylzinc to various aldehydes. The major advantage of the chosen α-pinene over other monoterpenes is that both enantiomeric forms are commercially available in bulk. Moreover, due to the highly constrained bicyclic pinane skeleton, a high degree of chiral information transfer can be expected in asymmetric transformations. Besides the synthesis of optically pure 1,3-amino alcohols, an additional aim was to develop a simple and short procedure for the synthesis of alicyclic N-substituted 1,3-amino alcohols, since the prepara- tion of such compounds with increased diversity usually requires a time-consuming multistep process.
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Optical properties of planar chiral meta materials

Optical properties of planar chiral meta materials

Arrays of both clockwise and anticlockwise gammadions, but of otherwise identical design specifications, were fabricated to provide the two enantiomeric forms of the structure, while the 442 symmetry group was chosen because of the absence of any optical birefringence in this structure for light at normal incidence.

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Enantiomeric separation in pharmaceutical analysis: A chromatographic approach

Enantiomeric separation in pharmaceutical analysis: A chromatographic approach

Stereochemical analysis has become an increasingly important problem in the pharmaceutical field, since numerous pharmacologically active agents are chiral and their two enantiomeric forms usually exhibit different physiological properties. Numerous examples exist where the two enantiomeric forms manifest different pharmacological actions, potencies, biodistribution and disposition kinetics, or host toxicities. For instance, most of the β-blocking activity of β-blockers such as propranolol and metoprolol is attributed to the (S)-enantiomer[1]. Furthermore, stereoselective differences have also been observed in the metabolism and pharmacokinetics of the two enantiomers of the above mentioned compounds. Traditional methods for determining the enantiomeric composition of chiral compounds, such as optical rotation measurement or fractional recrystallization of diastereomeric salts, are usually difficult, insensitive, inaccurate, and limited in applicability. Hence modern chromatography, because of its reproducibility, accuracy, selectivity, sensitivity, and speed, has become the technique of choice for the analysis of enantiomers. Since most of the recent developments and applications in enantiomeric resolution have been performed using liquid chromatography because of its wider applicability, particularly in the pharmaceutical field. There are three different approaches under which chromatographic resolution of enantiomers can be achieved[2].
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Enantioseparation of Palonosetron Hydrochloride and Its Related Enantiomeric Impurities by Computer Simulation and Validation

Enantioseparation of Palonosetron Hydrochloride and Its Related Enantiomeric Impurities by Computer Simulation and Validation

using high concentration cyclodextrin (β-CD) as chiral selector [6] or micellar electrokinetic chromatography (MEKC) using sodium cholate as chiral surfactant [7]. The capillary electrophoresis technique is not routinely used in the pharmaceutical industries for the impurities profiling. The only available method for the separation of PALO enantiomers is CZE or MEKC [6,7]. It is impor- tant to note that in the both cases all isomers were sepa- rated in the presence of small amount of PALO (3aS, 2S), the active ingredient. The quantification of other isomers in the presence of high concentration of PALO (3aS, 2S) was not studied in this method. The resolutions (Rs) re- ported by CZE method [6] between PALO (3aR, 2R), PALO (3aS, 2S) and PALO (3aS, 2S), PALO (3aR, 2S) were 1.58 and 1.27, respectively. In MEKC method the resolutions were comparable with CZE method. There- fore, in the presence of the high amount of the active ingredient, PALO (3aS, 2S) the separation of other iso- mers is questionable. Moreover, these methods were not fully validated. So far, to our knowledge no chiral liquid chromatographic method on enantiomeric separation of four enantiomers of PALO is reported in the literature. One chiral LC method for the separation of PALO enan- tiomers has been reported by Radhakrishnanand et al. [8]. The major drawback of this method is that it has been used to separate only PALO (3aS, 2S) from its enanti- omer (3aR, 2R). The interactions of other two enanti- omers PALO (3aS, 2R), and PALO (3aR, 2S) have not been considered. It was observed that under the same experimental conditions as reported in the literature [8] PALO (3aS, 2R) isomer was eluted with PALO (3aR, 2R) isomer. So it is not a suitable method for quantifying the enantiomers in the real samples. Moreover, in the valida- tion study the force degradation was conducted only in the presence of UV and heat. But the researchers didn’t provide any information about the degradations of PALO under acid, base, or peroxide. In this regard, it should be mentioned that there is not a single method available in the literature, which has considered the process chiral impurities with four isomers of PALO for separation.
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HPLC method for determination of enantiomeric purity of a novel respiratory fluoroquinolone: WCK 1152

HPLC method for determination of enantiomeric purity of a novel respiratory fluoroquinolone: WCK 1152

A sensitive, simple, specifi c, precise, accurate and rugged method for determination of enantiomeric purity of S-(-)-1- cyclopropyl-6-fl uoro-1,4-dihydro-8-methoxy-7-{4-amino-3,3-dimethylpiperidin-1-yl}-4-oxo-quinoline-3-carboxylic acid hydrochloride monohydrate, WCK 1152, a new drug substance has been developed. The method is based on prederivatization of analyte to diastereomer followed by RP-HPLC using endcapped C-18 stationary phase. Column was maintained at 30°C. The UV/Vis detector was operated at 290 nm. Flow rate of the mobile phase was 1.25 ml/min. The method offers excellent separation of two enantiomers with resolution more than 4 and tailing factor less than 1.5. The method was validated for the quantifi cation of R-(+)-enantiomer impurity, WCK 1153 in the bulk drug. Calibration curves showed excellent linearity over the concentration range of 0.1 to 1.5 mg/ml for WCK 1152 and 0.01 to 0.15 mg/ml for WCK 1153. Precision of the method was 1.13%. Limit of detection and limit of quantitation of the method for WCK 1152 were 0.0006 mg/ml and 0.0018 mg/ml and for WCK 1153 were 0.0007 mg/ml and 0.0021 mg/ml, respectively. Average recovery of the WCK 1153 in WCK 1152 was 94.4%. This method was employed in determining enantiomeric purity of clinical trial batches of WCK 1152.
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Stereocomplex micelle from nonlinear enantiomeric copolymers efficiently transports antineoplastic drug

Stereocomplex micelle from nonlinear enantiomeric copolymers efficiently transports antineoplastic drug

43.6, 45.9, and 52.7 wt.%, respectively. It indicated that the stable stereocomplex crystallization of enantiomeric PLA in micellar core induced higher DLC and DLE of SCM/ DOX [16]. The morphologies and sizes of the DOX- loaded micelles were characterized by TEM and DLS. As shown in Figure 2A, 2B, and 2C, the TEM micrographs showed that PDM/DOX, PLM/DOX, and SCM/DOX took clear spherical morphologies with the respective average sizes of approximately 100, 90, and 75 nm, re- spectively. In contrast, the DLS measurements showed that the mean diameters of laden micelles were 115 ± 4.6, 105 ± 4.4, and 90 ± 4.2 nm, respectively (Figure 2D, 2E, and 2F). The SCM/DOX exhibited the smallest size. This might be related to the formation of stereocomplex, which strongly improved the stability of copolymer [17,24]. Moreover, the polydispersity indices (PDIs) of D h s were
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Determination of enantiomeric composition of ofloxacin in tablets by chemometric techniques applied to overlapped chromatograms

Determination of enantiomeric composition of ofloxacin in tablets by chemometric techniques applied to overlapped chromatograms

Many trials were done to get enantiomeric separation of ofloxacin isomers with good chromatographic resolution using a (R, R) –Whelk- O-2 chiral column under normal phase and reversed phase conditions using several mobile phase systems with different chromatographic conditions varying the type of the solvent, organic modifier and buffer at different pH, percentage and flow rate. Baseline resolution was hardly achieved but with low enantioseparation factors (not more than 1.18) and the run time was too late (more than 40 min).

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Development and validation of chiral separation of some enantiomeric drugs by HPLC and LC-MS.

Development and validation of chiral separation of some enantiomeric drugs by HPLC and LC-MS.

stability indicating method for the enantioselective estimation of omeprazole enantiomers in the enteric coated formulations by high performance liquid chromatography. Omeprazole is widely prescribed in the form of enteric coated formulations, due to the rapid degradation of the drug in the acidic condition of the stomach. In the current article, they are reporting the development and complete validation of a stability indicating chiral high performance liquid chromatography (HPLC) method for the enantioselective analysis of omeprazole in the enteric-coated formulations. A precise and sensitive enantiomeric separation of omeprazole was obtained on Chiralcel OD-H analytical column (250 mm × 4.6 mm, 5 µm particle size) using normal phase chromatography. The analysis was performed under UV detection at 301 nm wavelength. During method development, the addition of methanol to the mobile phase helped in getting the sharp peaks. The developed method showed linear response over a wide concentration range of 0.39-800 µg/ml and the regression coefficients value (r 2 ) was obtained more than 0.999 for (S)- and (R)-
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Enantioselective Conversion of Racemic Felodipine to S( ) Felodipine by Aspergillus niger and Lipase AP6 Enzyme

Enantioselective Conversion of Racemic Felodipine to S( ) Felodipine by Aspergillus niger and Lipase AP6 Enzyme

Production of the chiral molecule is one of the rapidly progressing fields of modern science. Importance of this field is growing continuously due to various therapeutic benefits of single enantiomer over racemate [4]. Besides the chemical methods, bio- catalytic methods were also proved to be effective towards the generation of single ac- tive enantiomer from its racemate and the use of biocatalysts had been growing rapidly for the past few years [2]. Microorganisms have been shown the capacity for perform- ing a wide range of metabolic biotransformations such as enantiomeric inversion and biocatalytic deracemization processes leading to enantiomerically pure compounds [5] [6].
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Membrane Interactivity of Anesthetic Adjuvant Dexmedetomidine Discriminable from Clonidine and Enantiomeric Levomedetomidine

Membrane Interactivity of Anesthetic Adjuvant Dexmedetomidine Discriminable from Clonidine and Enantiomeric Levomedetomidine

Our main findings are: (1) dexmedetomidine interacts with biomimetic membranes consisting of phospholipids and cholesterol more potently than clonidine and levomedeto[r]

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Soft self-assembly of Weyl materials for light and sound

Soft self-assembly of Weyl materials for light and sound

our analysis, such threefold degeneracies will be split into Weyl points by inducing an asymmetry in the enantiomeric gyroid net- works and applying an appropriate strain in both the dis[r]

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Enantioselective Aldol Reactions and Michael Additions Using Proline Derivatives as Organocatalysts

Enantioselective Aldol Reactions and Michael Additions Using Proline Derivatives as Organocatalysts

With the new derivatives 1 - 6 in hand, we began to evaluate their catalytic behavior in the classical aldol reac- tion between acetone and 4-nitrobenzaldehyde [21], and the results are displayed in Table 1. As can be seen, the reaction proceeded smoothly at room temperature under solvent free conditions and was almost total only beyond several dozen hours, except for catalyst 2 (entry 2). If the chemical yields were acceptable (catalysts 2 and 3), the enantiomeric excesses were very low except for catalyst 2. Indeed in that case, a very interesting enantiose- lectivity of the aldol product was obtained. Regarding the results, we observed the following facts: firstly, the catalyst 2 having proline moieties exhibited higher catalytic efficiencies compared to 1 (entries 1, 2); then, we could notice a strong mismatch effect related to the absolute stereochemistry of the cyclohexane moiety (entries 2, 3). After these initial investigations, catalyst 2, giving the best result, was selected to carry out the optimiza- tion of the reaction conditions. We first investigated the solvent effect with or without some additives and the results are displayed in Table 1. While no reaction occurred in aprotic polar solvents (entries 4, 5), apolar sol- vents (entries 6, 7) induced a significant decrease in catalytic efficiency. Moreover, a catalytic amount of TfOH (entry 9) induced a decrease both rate and yield without significantly affecting the enantiomeric excess. On the other hand, catalytic quantities of AcOH (entry 8) induced an increase of the yield, but involved a slightly de- creasing of the enantiomeric excess. With water as additive (entries 10, 11) no significant variations were ob- served in the reaction rate and enantioselectivity. The reactions, carried out at lower temperatures, have shown as expected a positive effect on the catalytic efficiency and thus the best results were obtained at −20˚C but re- quiring prolonged reaction time (entries 12, 15). Regarding the loading of the catalyst, the reactions carried out with only 10 mol% of 2 (entries 13 - 15) provided the aldol product with almost the same enantioselectivity but with an expected decreasing of the reaction rate. In order to exclude a quite possible retro-aldol process that could lead to partial racemization, the enantiomeric excess of the reaction was measured several times through- out the reaction, showing no significant variation in value.
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Organocatalyzed transformations of alpha,beta-unsaturated carbonyl compounds through iminium ion intermediates

Organocatalyzed transformations of alpha,beta-unsaturated carbonyl compounds through iminium ion intermediates

The role of protic (nucleophilic) solvents in increasing the enantiomeric excess values of the products is due to rapid hydrolysis of the iminium ion adducts (4) before they can undergo retro Diels–Alder reaction (Step 2). This leads to the kinetic product. The presence of a protic solvent (such as methanol) in the reaction mixture increases the reaction rate by accelerating iminium ion formation through hydrogen bonding activation. Interestingly, a Diels–Alder reaction conducted in methanol proceeds slower than a reaction conducted in a methanol/water mix- ture (19 : 1). The basis of rate acceleration by addition of water to methanol is not obvious but was revealed by monitoring reaction progress. Scheme 2• shows
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Atropisomeric determination of chiral hydroxylated metabolites of polychlorinated biphenyls using HPLC-MS

Atropisomeric determination of chiral hydroxylated metabolites of polychlorinated biphenyls using HPLC-MS

Conclusion: This HPLC-MS method was developed to detect chiral OH-PCBs and further successfully applied to measure OH-PCB atropisomer levels and enantiomeric fractions (EFs) in rat liver[r]

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Enantiomeric Separation of S Epichlorohydrin and R Epichlorohydrin by Capillary Gas Chromatography with FID Detector

Enantiomeric Separation of S Epichlorohydrin and R Epichlorohydrin by Capillary Gas Chromatography with FID Detector

The aim of this study was to develop a simple and derivatization free method for the Quantification of S-Epichlorohydrin in R-Epichlorohydrin by using a gas chromato- graphy coupled with flame ionization detector (FID). Enantiopure epichlorohydrin was a valuable epoxide key starting material for preparing optically active Rivarox- aban. The enantiomeric separations of S-Epichlorohydrin and R-Epichlorohydrin were achieved on Gamaa-Dex-225 (30 meters × 0.25 mm I.D, 0.25 µm) column with a total run time of 30 min. Nitrogen was used as a carrier gas with constant pressure 25.0 psi. The critical experimental parameters such as, column selection, flow rate, injection volume and diluent were studied and optimized. Excellent correlation coef- fient between peak responses and concentrations was >0.9998. The recoveries of S-Epichlorohydrin spiked in R-Epichlorohydrin were in the range from 98.2% to 102.8%. Limit of quantitation for S-Epichlorohydrin was sufficiently lower than lim- its specified by ICH. The method has validated as per International Conference on Harmonization (ICH) guidelines. A precise, accurate, linear and robust Gas Chro- matography method was developed for the quantification of S-Epichlorohydrin in R-Epichlorohydrin for Rivaroxaban.
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Mirror image dependence : targeting enantiomeric G quadruplex DNA using triplex metallohelices

Mirror image dependence : targeting enantiomeric G quadruplex DNA using triplex metallohelices

antiparallel G4 DNA, Δ-enantiomer stabilizing G4 DNA while Λ- enantiomer even destabilizing G4 DNA. Δ-3 binding to D-G4 is driven by a favorable enthalpy contribution to compensate the associated unfavorable entropy penalty. To our knowledge, this is the first example to show mirror-image dependence for enantiomeric compounds binding to D- and L-DNA. This will advance current understanding of chiral ligand-DNA recognition and promote DNA-based chiral drug design.

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Metathesis Catalysed by the Platinum Group Metals112-118

Metathesis Catalysed by the Platinum Group Metals112-118

carbene initiators ( 4 M ).. I Enantiomeric cyclic compounds prepared by ring-closing metathesis using benzylidene o r vinylidene ruthenium complexes.. peptidomimetics) obtained [r]

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