Special Issue "Chiral Separations"

A special issue of Symmetry (ISSN 2073-8994).

Deadline for manuscript submissions: closed (30 June 2017)

Special Issue Editor

Guest Editor
Prof. Dr. Maria Elizabeth Tiritan

CESPU-IUCS, Rua Central de Gandra, 1317, 4585-116 Gandra PRD, Portugal
Website | E-Mail
Interests: separation science; chiral environmental analyses; enantioselective in biodegradation; determination of enantiomeric purity and asymmetric synthesis

Special Issue Information

Dear Colleagues,

The importance of chiral separation has been known since Louis Pasteur verified that (-)-tartaric acid was not being metabolized, or was being metabolized much slower than (+)-tartaric acid by Penicillium glaucum in the wine-fermentation process. A few years later, Emile Fischer observed the consequence of the enzymes in selective metabolism by microorganisms, after analyzing the crude extracts of yeast and a preparation obtained from almonds, he found out that only one of the isomers of the monosaccharide methylglucoside was present in each solution. By the same time, in 1886, the Italian chemist Arnaldo Piutti found that D-asparagine was responsible for the sweet taste while L-asparagine was tasteless. Nowadays, the influence of chirality in biological systems is an established fact that should always be kept in mind in the design of new drugs, pesticides, food additives and even fragrances. The biological response of each enantiomer must always be evaluated before its commercialization. Given the verified importance of chirality in the biological systems, the separation of enantiomers is of crucial importance in analytical (quality control) and in the preparative methods to obtain pure enantiomers. Accordingly, the aim of this Special Issue, “Chiral Separations”, is to reunite the different tools regarding separation of enantiomers in preparative and analytical mode.  It is important to present not only the results from well establish methodologies such as chiral chromatography but to highlight innovations within chiral separations. Contributions which address innovations in selective liquid–liquid extraction, membrane separation, crystallization, kinetic or dynamic kinetic resolution, chromatography, and capillary electrophoresis are cordially invited.

Prof. Dr. Maria Elizabeth Tiritan
Guest Editor

Manuscript Submission Information

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Keywords

  • Chiral chromatography
  • Enantioselective liquid–liquid extraction
  • Chiral Capillary Electrophoresis
  • Kinetic resolution
  • Crystallization
  • Enantiomeric purity

Published Papers (5 papers)

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Research

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Open AccessFeature PaperArticle Occurrence of Chiral Bioactive Compounds in the Aquatic Environment: A Review
Symmetry 2017, 9(10), 215; doi:10.3390/sym9100215
Received: 30 August 2017 / Revised: 30 September 2017 / Accepted: 30 September 2017 / Published: 3 October 2017
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Abstract
In recent decades, the presence of micropollutants in the environment has been extensively studied due to their high frequency of occurrence, persistence and possible adverse effects to exposed organisms. Concerning chiral micropollutants in the environment, enantiomers are frequently ignored and enantiomeric composition often
[...] Read more.
In recent decades, the presence of micropollutants in the environment has been extensively studied due to their high frequency of occurrence, persistence and possible adverse effects to exposed organisms. Concerning chiral micropollutants in the environment, enantiomers are frequently ignored and enantiomeric composition often neglected. However, enantioselective toxicity is well recognized, highlighting the need to include enantioselectivity in environmental risk assessment. Additionally, the information about enantiomeric fraction (EF) is crucial since it gives insights about: (i) environmental fate (i.e., occurrence, distribution, removal processes and (bio)degradation); (ii) illicit discharges; (iii) consumption pattern (e.g., illicit drugs, pharmaceuticals used as recreational drugs, illicit use of pesticides); and (iv) enantioselective toxicological effects. Thus, the purpose of this paper is to provide a comprehensive review about the enantioselective occurrence of chiral bioactive compounds in aquatic environmental matrices. These include pharmaceuticals, illicit drugs, pesticides, polychlorinated biphenyls (PCBs) and polycyclic musks (PCMs). Most frequently analytical methods used for separation of enantiomers were liquid chromatography and gas chromatography methodologies using both indirect (enantiomerically pure derivatizing reagents) and direct methods (chiral stationary phases). The occurrence of these chiral micropollutants in the environment is reviewed and future challenges are outlined. Full article
(This article belongs to the Special Issue Chiral Separations)
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Open AccessArticle Enantiomeric Separation of Tramadol and Its Metabolites: Method Validation and Application to Environmental Samples
Symmetry 2017, 9(9), 170; doi:10.3390/sym9090170
Received: 30 July 2017 / Revised: 12 August 2017 / Accepted: 19 August 2017 / Published: 24 August 2017
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Abstract
The accurate assessment of racemic pharmaceuticals requires enantioselective analytical methods. This study presents the development and validation of an enantioselective liquid chromatography with a fluorescence detection method for the concomitant quantification of the enantiomers of tramadol and their metabolites, N-desmethyltramadol and O
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The accurate assessment of racemic pharmaceuticals requires enantioselective analytical methods. This study presents the development and validation of an enantioselective liquid chromatography with a fluorescence detection method for the concomitant quantification of the enantiomers of tramadol and their metabolites, N-desmethyltramadol and O-desmethyltramadol, in wastewater samples. Optimized conditions were achieved using a Lux Cellulose-4 column 150 × 4.6 mm, 3 µm isocratic elution, and 0.1% diethylamine in hexane and ethanol (96:4, v/v) at 0.7 mL min−1. The samples were extracted using 150 mg Oasis® mixed-mode cation exchange (MCX) cartridges. The method was validated using a synthetic effluent of a laboratory-scale aerobic granular sludge sequencing batch reactor. The method demonstrated to be selective, accurate, and linear (r2 > 0.99) over the range of 56 ng L−1 to 392 ng L−1. The detection and the quantification limits of each enantiomer were 8 ng L−1 and 28 ng L−1 for tramadol and N-desmethyltramadol, and 20 ng L−1 and 56 ng L−1 for O-desmethyltramadol. The feasibility of the method was demonstrated in a screening study in influent and effluent samples from a wastewater treatment plant. The results demonstrated the occurrence of tramadol enantiomers up to 325.1 ng L−1 and 357.9 ng L−1, in the effluent and influent samples, respectively. Both metabolites were detected in influents and effluents. Full article
(This article belongs to the Special Issue Chiral Separations)
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Review

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Open AccessReview Chiral Separation in Preparative Scale: A Brief Overview of Membranes as Tools for Enantiomeric Separation
Symmetry 2017, 9(10), 206; doi:10.3390/sym9100206
Received: 28 August 2017 / Revised: 19 September 2017 / Accepted: 26 September 2017 / Published: 30 September 2017
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Abstract
Given the importance of chirality in the biological response, regulators, industries and researchers require chiral compounds in their enantiomeric pure form. Therefore, the approach to separate enantiomers in preparative scale needs to be fast, easy to operate, low cost and allow obtaining the
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Given the importance of chirality in the biological response, regulators, industries and researchers require chiral compounds in their enantiomeric pure form. Therefore, the approach to separate enantiomers in preparative scale needs to be fast, easy to operate, low cost and allow obtaining the enantiomers at high level of optical purity. A variety of methodologies to separate enantiomers in preparative scale is described, but most of them are expensive or with restricted applicability. However, the use of membranes have been pointed out as a promising methodology for scale-up enantiomeric separation due to the low energy consumption, continuous operability, variety of materials and supports, simplicity, eco-friendly and the possibility to be integrated into other separation processes. Different types of membranes (solid and liquid) have been developed and may provide applicability in multi-milligram and industrial scales. In this brief overview, the different types and chemical nature of membranes are described, showing their advantages and drawbacks. Recent applications of enantiomeric separations of pharmaceuticals, amines and amino acids were reported. Full article
(This article belongs to the Special Issue Chiral Separations)
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Open AccessReview Chiral Analysis of Pesticides and Drugs of Environmental Concern: Biodegradation and Enantiomeric Fraction
Symmetry 2017, 9(9), 196; doi:10.3390/sym9090196
Received: 30 August 2017 / Revised: 9 September 2017 / Accepted: 11 September 2017 / Published: 16 September 2017
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Abstract
The importance of stereochemistry for medicinal chemistry and pharmacology is well recognized and the dissimilar behavior of enantiomers is fully documented. Regarding the environment, the significance is equivalent since enantiomers of chiral organic pollutants can also differ in biodegradation processes and fate, as
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The importance of stereochemistry for medicinal chemistry and pharmacology is well recognized and the dissimilar behavior of enantiomers is fully documented. Regarding the environment, the significance is equivalent since enantiomers of chiral organic pollutants can also differ in biodegradation processes and fate, as well as in ecotoxicity. This review comprises designed biodegradation studies of several chiral drugs and pesticides followed by enantioselective analytical methodologies to accurately measure the enantiomeric fraction (EF). The enantioselective monitoring of microcosms and laboratory-scale experiments with different environmental matrices is herein reported. Thus, this review focuses on the importance of evaluating the EF variation during biodegradation studies of chiral pharmaceuticals, drugs of abuse, and agrochemicals and has implications for the understanding of the environmental fate of chiral pollutants. Full article
(This article belongs to the Special Issue Chiral Separations)
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Open AccessFeature PaperReview Chiral Stationary Phases for Liquid Chromatography Based on Chitin- and Chitosan-Derived Marine Polysaccharides
Symmetry 2017, 9(9), 190; doi:10.3390/sym9090190
Received: 1 August 2017 / Revised: 6 September 2017 / Accepted: 6 September 2017 / Published: 11 September 2017
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Abstract
The development of chiral stationary phases (CSPs) for liquid chromatography (LC) revolutionized the enantioseparation and, nowadays, different types of CSPs are commercially available. Polysaccharide-based CSPs are one of the most versatile and widely used for both analytical and preparative applications and they are
[...] Read more.
The development of chiral stationary phases (CSPs) for liquid chromatography (LC) revolutionized the enantioseparation and, nowadays, different types of CSPs are commercially available. Polysaccharide-based CSPs are one of the most versatile and widely used for both analytical and preparative applications and they are able to resolve several classes of racemates. Phenylcarbamates of amylose and cellulose derivatives are the most successful; however, polysaccharide-based CSPs comprising marine-derived polysaccharides are also described revealing high chiral recognition abilities and wider range of mobile phases. A literature survey covering the report on chitin and chitosan based CSPs is presented. The chemical structure of the chiral selectors, their development and applications in chiral LC are emphasized. Full article
(This article belongs to the Special Issue Chiral Separations)
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