Chiral selectivity parameters determining

The concentration of the chiral selector, for instance, has considerable influence on the mobility and separation of the enantiomers. Optical resolution varies with the chiral selector concentration and reaches a maximum value at a given optimum concentration. Wren and Rowe proposed a model that describes the influence of the selector concentration on selectivity, and which was extended by Vigh s group ° by including the pH as a separation parameter for weak acidic enantiomers. The latter model shows that the chiral selectivity is determined by the complex s relative mobility, the CD concentration, the degree of dissociation... 

Retention of Rohrschneider-McReynolds standards of selected chiral alcohols and ketones was measured to determine the thermodynamic selectivity parameters of stationary phases containing (- -)-61 (M = Pr, Eu, Dy, Er, Yb, n = 3, R = Mef) dissolved in poly(dimethylsiloxane) . Separation of selected racemic alcohols and ketones was achieved and the determined values of thermodynamic enantioselectivity were correlated with the molecular structure of the solutes studied. The decrease of the ionic radius of lanthanides induces greater increase of complexation efficiency for the alcohols than for the ketone coordination complexes. The selectivity of the studied stationary phases follows a common trend which is rationalized in terms of opposing electronic and steric effects of the Lewis acid-base interactions between the selected alcohols, ketones and lanthanide chelates. The retention of over fifty solutes on five stationary phases containing 61 (M = Pr, Eu, Dy, Er, Yb, n = 3, R = Mef) dissolved in polydimethylsiloxane were later measured ". The initial motivation for this work was to explore the utility of a solvation parameter model proposed and developed by Abraham and coworkers for complexing stationary phases containing metal coordination centers. Linear solvation... 

As examples for temperature-dependent enantiomer-selective binding of chiral guests to chiral hosts evaluated by determining thermodynamic parameters (enthalpy, entropy) ... 

The value of these constants depends on the nature of the CS and the enantiomers under study, which will determine the concrete interactions established between the two species - such as hydrogen bonding, n-stacking, or van der Waals interactions -and also on the environment in which the association occurs, which includes the effect of the solvation of the two species by the solvent used as a mobile phase [27], In CCC the separation of analytes is determined by differences in distribution between the two liquid phases. While in HPLC the phase ratio, <, is constant, this is not the case in CCC. Therefore k is not a typical reference retention parameter in CCC as it is in HPLC. The distribution ratio. A , is preferred instead. Therefore, the selectivity factor, ccc, is defined as the ratio of distribution constants for each analyte. However, for a chiral compound in the presence of a CS, two co-existing processes affect distribution of the enantiomers the partition equilibrium between phases and the association with the CS in the stationary phase. Assuming that the CS is confined in this later phase [20, 28] ... 

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