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Liquid Chromatography
Published in Ernő Pungor, A Practical Guide to Instrumental Analysis, 2020
Enantiomers have identical physical and chemical properties in an isotropic environment except that they rate the plane of polarized light in opposite directions. Racemic mixture which contains equal amounts of enantiomers are not able to rotate the plane of polarized light. Separation of enantiomers is one of the most difficult tasks, because no difference exists between the two enantiomers such as melting point, boiling point, refractive index, spectroscopic properties, and so on. Separation of enantiomers can be divided into two main types: socalled direct and indirect ones. In direct separation either stationary phase or mobile phase (adsorption of optically active additive from mobile phase) must be unisotropic (chiral). Indirect separation is based on the reaction of racemic mixture with a chiral reagent to form a pair of diastereomers. Diastereomers have different physicochemical properties and can be separated with chromatography.
PFAS Isomers
Published in David M. Kempisty, Yun Xing, LeeAnn Racz, Perfluoroalkyl Substances in the Environment, 2018
Yun Xing, Gabriel Cantu, David M. Kempisty
Many PFOS isomers, including the environmentally relevant monomethyl-branched isomers 1m-, 3m-, 4m-, and 5m-PFOS, have chiral centers, each of which corresponds to two stereoisomers (enantiomers). Enantiomeric analysis measures the enantiomer fraction (EF) (i.e., the relative abundance of the two enantiomers). Unless production of a specific enantiomer is sought, the relative abundance of each enantiomer is equal in commercially produced chemicals, and the chiral signature is said to be racemic (EF = 0.5). Consequently, observations of chiral signatures that deviate significantly from racemic in environmental or biological matrices are strong evidence of biodegradation or metabolism of a precursor material, and hence indicative of indirect exposure.
Applications of Green Chemistry Principles in the Pharmaceutical Industry
Published in Vera M. Kolb, Green Organic Chemistry and Its Interdisciplinary Applications, 2017
Meyer et al. (2009) consider six general consequences of using racemic compounds as drugs: (1) enantiomers have equal pharmacological activity; (2) one enantiomer is biologically active, whereas the other is inactive and innocuous; (3) one enantiomer is biologically active, whereas the other is toxic; (4) the two enantiomers have unequal degrees of the same activity; (5) the two enantiomers exhibit different types of pharmacological activities; and (6) the two enantiomers vary in degrees of pharmacological action and tissue specificity.
Supervisory system for automated simulated moving bed (SMB) liquid chromatography (LC)
Published in Instrumentation Science & Technology, 2023
R. C. de Holanda, F. C. Cunha, A. R. Secchi, A. G. Barreto
Racemic mixtures are solutions composed of two molecules with the same formula, one being the mirror image of the other. Therefore they cannot be overlapped. These molecules are known as enantiomers.[1] Different racemic mixtures are produced daily in many branches of the economy, from food processing to the pharmaceutical industry.[2] One example is praziquantel (PZQ), a drug prescribed to treat Schistosomiasis disease. Only the (R)-PZQ has proven pharmacological activity against the disease, while the (S)-PZQ provides a significant bitterness to the drug, causing vomiting.[3] In the recent decades, many investments in research and development have been made targeting the creation of new technologies capable of producing a drug with high purity of (R)-PZQ to increase the production efficiency.[4]
Detection of chiral enantiomers via an optical fibre sensor
Published in Journal of Modern Optics, 2021
Maoyan Wang, Hailong Li, Guangzhe Zou, Yu Liu, Mengxia Yu, Guiping Li, Xiaochuan Zhang, Jun Xu
Chiral enantiomers generally contain two enantiomers that have identical physical properties (such as refractive index) and opposite handedness (optical activity), yet show different toxicities to biomolecules [10]. A mixture of equal amounts of enantiomers becomes a racemic mixture having no optical activity. The chirality detection is necessary for the enantiomeric purity test of chiral drugs, concentration of solution, and biological processes [9–20]. The chirality of enantiomers is routinely determined by employing the circular dichroism and chromatography techniques [11,12]. The fibre sensing method has advantages of label-free, reliable, and real-time monitoring. Villar et al. reported ultrahigh-sensitivity sensors based on thin-film coated LPFGs with reduced diameter [21]. A thin-film coated long-period fibre grating sensor can be optimized to yield high chirality sensitivity.
Synthesis, characterisation and supercritical fluid chromatography enantioseparation of new liquid crystalline materials
Published in Liquid Crystals, 2020
Magdalena Urbańska, Petra Vaňkátová, Anna Kubíčková, Květa Kalíková
Optical purity of liquid crystals (LCs) has considerable effect on the mesomorphic properties of chiral LCs; even small amounts of the opposite (polluting) enantiomer can affect both the number and types of mesophases formed by chiral LC [1]. Moreover, the optical purity of precursor can change during the synthesis of chiral LCs [2]. Therefore, confirming the enantiomeric ratio in final product via suitable method should be a part of the characterisation process of newly synthesised chiral LCs. To develop an enantioseparation method, it is necessary to have racemic mixtures (or any mixture of both enantiomers) available for the experiments. Recently, new chiral mesogens with chiral moiety based on (S)-(+)-3-octanol were synthesised as part of study of effects of the mesogens structure on its mesomorphic properties [3]. In this article we report synthesis and characterisation of ten new racemic mixtures based on (R,S)-3-octanol, which were used to develop an enantioseparation method that can be subsequently used for the optical purity control of chiral mesogens or assessment of enantiomeric excess in non-racemic mixtures. The reasons behind the design of these compounds are stated below.