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Asymmetric Centers, Functional Groups, and Characterization
Published in Armen S. Casparian, Gergely Sirokman, Ann O. Omollo, Rapid Review of Chemistry for the Life Sciences and Engineering, 2021
Armen S. Casparian, Gergely Sirokman, Ann O. Omollo
The ability of enantiomers to behave differently under chiral conditions enables their separation. The process of separating enantiomers is known as enantiomeric resolution. A racemic mixture may require separation if one enantiomer diminishes the activity of the other, or if one enantiomer is effective in producing the desired therapeutic results while the other has adverse side effects.
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.
Symbols, Terminology, and Nomenclature
Published in W. M. Haynes, David R. Lide, Thomas J. Bruno, CRC Handbook of Chemistry and Physics, 2016
W. M. Haynes, David R. Lide, Thomas J. Bruno
Quadrupole moment - A coefficient of the third term (after monopole and dipole) in the power series expansion of the electric potential of an array of charges. A nucleus of spin greater than 1/2 has a non-vanishing nuclear quadrupole moment which can interact with the electric field gradient of the surrounding electrons. Molecular quadrupole moments have an influence on intermolecular forces. Quality factor (Q) - The ratio of the absolute value of the reactance of an electrical system to the resistance; thus a measure of the energy stored per cycle relative to the energy dissipated. Quantum yield - In photochemistry, the number of moles transformed in a specific process, either physically (e.g., by emission of photons) or chemically, per mole of photons absorbed by the system. [3] Quark - An elementary entity which has not been directly observed but is considered a constituent of protons, neutrons, and other hadrons. Quasar - An extragalactic object emitting electromagnetic radiation at a very high power level and showing a very large red shift, thus indicating that the object is receding at a speed approaching the speed of light. Quasicrystal - A solid having conventional crystalline properties but whose lattice does not display translational periodicity. Quaternary ammonium compounds - Derivatives of ammonium compounds, NH4+ Y-, in which all four of the hydrogens bonded to nitrogen have been replaced with hydrocarbyl groups. Compounds having a carbon-nitrogen double bond (i.e. R2C=N+R2Y-) are more accurately called iminium compounds. [5] Quinones - Compounds having a fully conjugated cyclic dione structure, such as that of benzoquinones, derived from aromatic compounds by conversion of an even number of -CH= groups into -C(=O)- groups with any necessary rearrangement of double bonds. [5] Racemic mixture - A mixture of equal amounts of a pair of enantiomers (optical isomers); such a mixture is not optically active. Rad - A non-SI unit of absorbed dose of radiation, equal to 0.01 Gy. Radiance (L) - The radiant intensity in a given direction from an element of a surface, divided by the area of the orthogonal projection of this element on a plane perpendicular to the given direction. [1] Radiant intensity (I) - The radiant energy flux leaving an element of a source within an element of solid angle, divided by that element of solid angle. [1] Radicals - Molecular entities possessing an unpaired electron, such as CH3, SnH3, Cl. (In these formulas the dot, symbolizing the unpaired electron, should be placed so as to indicate the atom of highest spin density, if this is possible). [5] Raman effect - The inelastic scattering of light by a molecule, in which the incident photon either gives up to, or receives energy from, one of the internal vibrational modes of the molecule. The scattered light thus has either a lower frequency (Stokes radiation) or higher frequency (anti-Stokes radiation) than the incident light. These shifts provide a measure of the normal vibrational frequencies of the molecule. Rankine cycle - A thermodynamic cycle which can be used to calculate the ideal performance of a heat engine that uses a condensable vapor as the working fluid (e.g., a steam engine or a heat pump).
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.