Chiral molecules polysaccharides

The most popular and commonly used chiral stationary phases (CSPs) are polysaccharides, cyclodextrins, macrocyclic glycopeptide antibiotics, Pirkle types, proteins, ligand exchangers, and crown ether based. The art of the chiral resolution on these CSPs has been discussed in detail in Chapters 2-8, respectively. Apart from these CSPs, the chiral resolutions of some racemic compounds have also been reported on other CSPs containing different chiral molecules and polymers. These other types of CSP are based on the use of chiral molecules such as alkaloids, amides, amines, acids, and synthetic polymers. These CSPs have proved to be very useful for the chiral resolutions due to some specific requirements. Moreover, the chiral resolution can be predicted on the CSPs obtained by the molecular imprinted techniques. The chiral resolution on these miscellaneous CSPs using liquid chromatography is discussed in this chapter. 

NMR spectra of chiral molecules aligned in a chiral liquid crystalline solvent. A method for the visualization of enantiomers using natural abundant filtered single and double quantum selective refocusing experiments has been proposed and its application to small chiral molecules demonstrated. A lyotropic liquid crystalline phase of an aqueous solution of polysaccharide xanthan gum has been reported as a scalable weak alignment medium for enantiodiscrimination of water soluble chiral molecules. ... 

D-sugars - and this defines the chiral, side of life. The natural consequence is that more complex large biomolecules - proteins, polysaccharides, and nucleic acids - are homochiral as well. Chiral recognition is therefore a eommon and basic phenomenon in biology. In most cases both enantiomers of a chiral molecule aet differently in living organisms. 

Carbohydrates Chiral Molecules Fischer Projections of Monosaccharides Haworth Structures of Monosaccharides Chemical Properties of Monosaccharides Disaccharides Polysaccharides... 

Chapter 13, Carbohydrates, describes the carbohydrate molecules monosaccharides, disaccharides, and polysaccharides and their formation by photosynthesis. Monosaccharides are classified as aldo or keto pentoses or hexoses. Chiral molecules, moved from Chapter 12 to Chapter 13, are discussed along with Eischer projections and d and l notations. An Explore Your World feature models chiral objects using gumdrops and toothpicks. Carbohydrates used as sweeteners are described and carbohydrates used in blood typing are discussed. The formation of glycosidic bonds in disaccharides and polysaccharides is described. 

The second type of stereoisomerism encompasses all other cases in which the three-dimensional structures of two isomers exhibiting the same connectivity among the atoms are not superimposable. Such stereoisomers are referred to as diastereomers. Diastereomers may arise due to different structural factors. One possibility is the presence of more than one chiral moiety. For example, many natural products contain 2 to 10 asymmetric centers per molecule, and molecules of compound classes such as polysaccharides and proteins contain hundreds. Thus, organisms may build large molecules that exhibit highly stereoselective sites, which are important for many biochemical reactions including the transformation of organic pollutants. 

Complexes between chiral polymers having ionizable groups, and achiral small molecules become, under certain conditions, optically active for the absorption regions of the achiral small molecules. Dyes such as acridine orange and methyl orange have been used as achiral species, since they are in rapport with biopolymers through ionic coupling. This phenomenon has been applied to the detection of the helix chirality in poly-a-amino acids, polynucleotides, or polysaccharides when instrumental limitations prevent direct detection of the helices. 

Resolution is optimized by adjusting the buffer pH and the amount of organic modifiers. The most commonly used buffers are perchlorate, acetate, and phosphate. The protocol of the selection and optimization of the mobile phase for the enantiomeric resolution of drugs on polysaccharide-based CSPs in reversed-phase mode is presented in Scheme 2. Table 4 correlates the effects of separation conditions for neutral, acidic, and basic drugs on polysaccharide-based CSPs. From Table 4, it may be concluded that a simple mixture of water and an organic modifier will produce chiral separation of a neutral molecule because there is no... 

Temperature is also an important parameter for controlling the resolution of enantiomers in HPLC. The enthalpy and entropy control of chiral resolution on antibiotic CSPs is similar to the case of polysaccharide-based CSPs (Chapter 2). Armstrong et al. [1] have studied the effect of temperature on the resolution behavior of proglumide, 5-methyl-5-phenylhydantoin and A-carbamyl-D-pheny-lalanine on the vancomycin column. The experiments were carried out from 0°C to 45°C. These results are given in Table 6 for three chiral compounds. It has been observed that the values of k, a, and Rs for the three studied molecules have decreased with the increase in temperature, indicating the enhancement of chiral resolution at low temperature. In another work, the same workers [22] have also studied the effect of temperature on the resolution of certain amino acid derivatives on the teicoplanin chiral stationary phase. They further observed poor resolution at ambient temperature, whereas the resolution increased at low... 

The chiral recognition mechanisms in NLC and NCE devices are similar to conventional liquid chromatography and capillary electrophoresis with chiral mobile phase additives. It is important to note here that, to date, no chiral stationary phase has been developed in microfluidic devices. As discussed above polysaccharides, cyclodextrins, macrocyclic glycopeptide antibiotics, proteins, crown ethers, ligand exchangers, and Pirkle s type molecules are the most commonly used chiral selectors. These compounds... 

Polysaccharide derivatives used as CSPs interact with chiral analytes in much the same manner as cyclodextrins. These molecules have been shown to exhibit high chiral recognition ability in HPLC [155]. The main advantage of CEC over HPLC is the enhanced efficiency. In chiral separations, slow mass transfer kinetics between the CSP and chiral analytes have somewhat diminished the efficiency advantage of the technique. The goal of using polysaccharide derivatives... 

Chirality is a property resulting from a lack of symmetry of molecules. All carbohydrates, including polysaccharides, have centers of asymmetry and therefore are chiral. Chirality is expressed as a concentration-independent specific rotation, [a]0 ... 

As mentioned above, steroidal assemblies consist of hierarchical structures with supramolecular chirality, leading us to find an analogy on the basis of the concept molecular information and their expression of biopolymers. The information originates from sequential arrangements of a-amino acids. Since it is considered that the steroidal molecules consist of chains of methylene units with various substituents, the concept may be applied to steroidal molecules. Such sequential chains may be considered to hold for other related organic molecules, leading to the idea that chiral methylene chains with various substituents function as universal molecular storage. The methylene chains can be chemically modified to various sequential chains, such as polypetides, polynucleotides, polysaccharides, and ster-... 

Polysaccharides Hydrogen bonds and dipole-dipole interactions with hydroxyl groups of the sugar molecules are assumed to be the main interactions. In some cases, the helical structure of dextrins might be responsible for chiral recognition. Heparin, dextran sulfate, dermatan sulfate, streptomycin sulfate, amylose, chondroitin sulfate C, laminaran, dextrin sulfopropyl, and kanamycin sulfate. Doxylamine, laudanosine, naproxen, oxamniquine, pheniramine, primaquine, timepidium, trimetoquinol, etc. 

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