Chiral separations classification

Centrichromatography, 74 Charge-transfer, 45 Chemisorption, 41, 42 Chiral separations, 261-268 Chiral stationary phases (CSP s), 265-268 Chromatogram, 8 Chromatography classification of, 5 definition of, 4-7 Clathrate, 46... 

Chiral separations of essential oils (FID/MS) Classification of fuels (FID)... 

Today, a more pertinent classification should be proposed in accordance with the great number of chiral selectors reported in LC (about 1500 CSPs have been collected in ChirBase database) and our new knowledge of chiral separation mechanisms. For instance, chromatographic results are clearly suggesting that bimodal and supramolecular systems should be gathered quite separately. 

Chiral Separation of Nonsteroidal Anti-Inflammatory Drugs 13.1.2 Classification of NSAIDs... 

The preceding discussion is somewhat related to Ernst Ruch s extraordinarily fruitful idea to classify chiral objects in two classes shoes and potatoes (Fig. 3.2) If asked to put our left shoes into one box and our right shoes into a second box we could accomplish the task without mental difficulty, in spite of the fact that the right shoes belonging to different people may be quite different in color, shape, and size, and although, probably, there is not a single pair of shoes which are precise mirror images of each other. If asked to solve the same problem with potatoes, we must capitulate. Of course, it is possible that by chance we find an antipodal pair. It is then clear that we must separate them, but for other potatoes different in shape, we have to make new arbitrary decisions each time. Any classification would be very artificial [1-3]. 

The X hgands in (80), (81) can be replaced by another chelate ring to give, for example, [M(en)3] +. Now, four conformers can be constructed for each absolute configuration A(82), or A(83) viz, XXX, XX8, X88, and 888 with A(XXX) energetically equivalent to A 888). This classification is usefid when separate enantiomers are available, but with the racemate, a chirality invariant nomenclature can be... 

Reactions that involve asymmetric synthesis are traditionally classified separately from other dia-stereoselective transformations of chiral substrates, even though there is little fundamental differoice between them. The degree of success realized in both categories depends on the ability of the chemist to distinguish between competing, diastereomeric transition states the critical objective is to maximize AAG - This classification system undoubtedly evolved since the chiral auxiliary used in asymmetric reactions, whether it is introduced as part of a catalyst or is covalently bound to the substrate, is not destined to be an integral structural component of subsequent transformation products, while the reverse situation obviously pertains in the more frequently encountered diastereoselective transformations of chiral substrates. Work that has been reported for asymmetric IMDA reactions is summarized in this section." ... 

Referring to this differentiation in the nature and the polarity of suitable solvents a first classification concerning the adsorbent and thus the phase system can be made. Figure 4.10 describes how the solvent and the nature of the separation problem influence the choice of adsorbent. Separation of enantiomers needs chiral stationary phases (CSP), which will be discussed in Section 4.3.4. 

HPLC provides reliable quantitative precision and accuracy, along with a linear dynamic range (LDR) sufficient to allow for the determination of the API and related substances in the same run using a variety of detectors, and can be performed on fully automated instrumentation. HPLC provides excellent reproducibility and is applicable to a wide array of compound types by judicious choice of HPLC column chemistry. Major modes of HPLC include reversed phase and normal phase for the analysis of small (<2000 Da) organic molecules, ion chromatography for the analysis of ions, size exclusion chromatography for the separation of polymers, and chiral HPLC for the determination of enantiomeric purity. Numerous chemically different columns are available within each broad classification, to further aid method development. 

Most chiral HPLC analyses are performed on CSPs. General classification of CSPs and rules for which columns may be most appropriate for a given separation, based on solute structure, have been described in detail elsewhere. Nominally, CSPs fall into four primary categories (there are additional lesser used approaches) donor-acceptor (Pirkle) type, polymer-based carbohydrates, inclusion complexation type, and protein based. Examples of each CSP type, along with the proposed chiral recognition mechanism, analyte requirement(s), and mode of operation, are given in Table 3. Normal-phase operation indicates that solute elution is promoted by the addition of polar solvent, whereas in reversed-phase operation elution is promoted by a decrease in mobile-phase polarity. 

Fig. C11.2 This table shows all possible prime knots with up to 8 crossings on the projection. For chiral knots, only one of the mirror images is shown. There are many ways to identify certain separate classes of knots for instance, knots 3i, 5i, 7i are called torus knots, because they can be nicely placed on the surface of a doughnut (and there is obviously a torus knot with any odd number of crossings). But the classification of knots relevant for their physics is yet to be developed. The figure is courtesy of R. Scharein the knot images were produced by his software KnotPlot (see http //www.knotplot.com).

Chiral stationary phases that are currently available can be classified into those containing cavities (cellulose derivatives, cyclodextrins, synthetic polymers, crown ethers, and chiral imprinted gels), affinity phases (bovine serum albumin, human serum albumin, a-glycoprotein, enzymes), multiple hydrogen-bond phases, Ti-donor and Ti-acceptor phases, and chiral ligand exchange phases. This classification scheme was used in a review that gave numerous pharmaceutical examples of separation by... 

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